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Survey of the leg exocrine glands in termites(Isoptera)

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Revista Brasileira de Entomologia 46(1): 1-6 31.III.2002 Survey of the leg exocrine glands in termites (Isoptera)1 Helena Xavier Soares 2 Ana Maria Costa-Leonardo 2,3 ABSTRACT. A survey of the leg exocrine glands in the termite workers of 16 species of the families Kalotermitidae and Termitidae was carried out through scanning electron microscope. Glandular openings were not found in the legs of Anoplotermes sp., Ruptitermes sp. (Apicotermitinae, Termitidae) or Glyptotermes planus (Kalotermitidae), but they are present, spread over the ventral surface of the first, second and third tarsomeres of other Termitidae such as Armitermes euamignathus, Cornitermes cumulans, Nasutitermes coxipoensis, Rhynchotermes nasutissimus, Syntermes nanus, Embiratermes festivellus (Nasutitermitinae), Amitermes beaumonti, Hoplotermes amplus, Microcerotermes sp., Neocapritermes opacus, Orthognathotermes sp., Spinitermes brevicornutus and Termes sp. (Termitinae). The pores are usually isolated but they can also be grouped inside a round depression. The occurrence of leg exocrine glands in the family Termitidae is reported for the first time. KEYWORDS. Exocrine gland; leg; morphology; scanning electron microscopy; termite. INTRODUCTION MATERIAL AND METHODS The leg exocrine glands of Isoptera were first described by BACCHUS (1979), who investigated 12 species of termite (Rhinotermitidae, Kalotermitidae, Termopsidae and Termitidae) through scanning electron microscope. The author found such glands only in species of Rhinotermitidae (Reticulitermes lucifugus, Heterotermes perfidus, Coptotermes formosanus, Schedorhinotermes putorius and Termitogeton planus). The glandular openings correspond to pore plates with different sizes and shapes. The pore plates were observed on the three leg pairs of the reproductive and sterile castes and were present on the distal tibia and on the ventral surface of the first and second tarsomeres. Later contributions also revealed the presence of glandular openings in Serritermitidae (Serritermes serrifer) and Kalotermitidae (Kalotermes flavicollis). The glandular pores of S. serrifer are located on the ventral surface of the first and second tarsomeres, associated with papilar structures and not arranged in plates (COSTA-LEONARDO 1994). In K. flavicollis, the pores are located on the ventral surface of the first and second tarsomeres and in the lateral part of the third tarsomere and distal tibia (FAUCHEUX 1994). This study presents the first record of leg exocrine glands in 13 species of the family Termitidae. In this research it was used termite workers collected from nests or soil baits at different sites. The following species were analysed: Glyptotermes planus (Kalotermitidae), Armitermes euamignathus, Cornitermes cumulans, Embiratermes festivellus, Nasutitermes coxipoensis, Rhynchotermes nasutissimus, Syntermes nanus (Termitidae, Nasutitermitinae), Armitermes beaumonti, Hoplotermes amplus, Neocapritermes opacus, Microcerotermes sp., Orthognathotermes sp., Spinitermes brevicornutus, Termes sp. (Termitidae, Termitinae), Anoplotermes sp., Ruptitermes sp. (Termitidae, Apicotermitinae). The material was fixed in Karnovsky mixture or 80% alcohol. Ten specimens of each species were cleaned with ultrasonic vibration in a detergent solution, dehydrated in a graded alcohol and acetone series, dried in a critical point Balzers CPD 030 dryer and coated with gold in a Balzers SCD 050 sputterer. The material was examined with a JEOL JSM-P 15 scanning electron microscope. Voucher specimens are deposited in the collection of the Centro de Insetos Sociais (CEIS), Rio Claro, SP, Brazil. RESULTS The pores were present in all pairs of worker legs of the 1. 2. 3. Financial support from CNPq. Departamento de Biologia, Instituto de Biociências, Universidade Estadual Paulista. Caixa Postal 199, 13506-900 Rio Claro - SP, Brazil. Centro de Insetos Sociais, Universidade Estadual Paulista. Rio Claro - SP. E-mail: amcl@rc.unesp.br 2 Soares & Costa-Leonardo Figs. 1-3. 1, Ventral surface of the tarsal segments 1 to 3 of a Termes sp. worker (left hind leg); the arrows indicate the glandular openings; scale: 10 µm. 2, Detail of the isolated pores (i) on the third tarsal segment of a Termes sp. worker (right midleg); scale: 5 µm. 3, Detail of isolated pore (i) on the second tarsomere of Embiratermes festivellus worker (right midleg); scale: 1 µm. cd = cuticular depression; i = isolated pore; pp = pore plate; t1 = first tarsomere; t2 = second tarsomere; t3 = third tarsomere. following Termitidae species: Armitermes euamignathus, Cornitermes cumulans, Nasutitermes coxipoensis, Rynchotermes nasutissimus, Syntermes nanus, Amitermes beaumonti, Hoplotermes amplus, Microcerotermes sp., Neocapritermes opacus, Embiratermes festivellus, Orthognathotermes sp., Spinitermes brevicornutus, and Termes sp. (Figs. 1-9). The pores were predominantly located on the ventral surface of the first, second and third tarsal segments. Several morphological types of glandular openings were identified in the different termite species. According to the results, the glandular openings can be classified into four morphological types (Table I). Revista Brasileira de Entomologia 46 (1), 2002 Pore plate and isolated pore in a cuticular depression – Termes sp. and Amitermes beaumonti presented isolated pores inserted in cuticular depressions and pores grouped into plates. The pore plates were located mainly on the first and second tarsomeres in Termes sp. (Figs. 1, 2), containing each from 2 to 7 pores. All pores were inserted in cuticle depressions and usually in rounded shape. When only one pore was present its diameter ranged from 1.09 to 1.35 µm but when there were two or more pores their diameters ranged from 1.60 to 4.04 µm. The pore diameters of the different tarsomeres were almost constant (0.25 – 0.27 µm). In some specimens, isolated pores were occasionally found in the lateral regions of the first and second tarsal segments, a feature that seems to be exclusive of Termes sp. Survey of the leg exocrine glands in termites 3 Figs. 4, 5. Scanning electron micrography of the leg’s exocrine glands of Spinitermes brevicornutus. 4, Ventral view of the first and second tarsomeres of a worker’s left foreleg showing the glandular openings (arrows); scale: 5 µm. 5, Detail of the glandular openings (arrows) present on the first tarsal segment of a worker’s left foreleg; note the cuticular rugosity of the surface; scale: 5 µm. cd = cuticular depression; i = isolated pores; t1 = first tarsomere; t2 = second tarsomere. Table I. Morphological patterns of the glandular openings in the legs of worker Termitidae. Family Termitidae Subfamily Nasutitermitinae Species Armitermes euamignathus Cornitermes cumulans Embiratermes festivellus Nasutitermes coxipoensis Rhynchotermes nasutissimus Syntermes nanus Amitermes beaumonti Hoplotermes amplus Microcerotermes sp. Neocapritermes opacus Orthognathotermes sp Spinitermes brevicornutus Termes sp. Part of leg Pattern 1st tars. 2nd tars. 3rd tars. tibia + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - C B C D C B A C C B D C A+C + presence of glandular opening; - absence of glandular opening; A pore plate; B isolated pore without cuticular specialization; C isolated pore inserted in a cuticular depression; D isolated pore on a cuticular elevation. Revista Brasileira de Entomologia 46 (1), 2002 4 Soares & Costa-Leonardo Figs. 6-9. 6, Ventral surface of the third tarsomere of Nasutitermes sp. worker (right midleg); the arrows indicate the glandular openings; scale: 5 µm. 7, Detail of isolated pores (i) of the same tarsomere; note the cuticular elevation (ce); scale: 1 µm. 8, Ventral surface of the first to third tarsomeres of Cornitermes cumulans worker (right midleg); the arrows indicate the glandular openings; scale: 10 µm. 9, Detail of the glandular openings (arrows) on the third tarsomere of Neocapritermes opacus (left foreleg); scale: 5 µm. ce = cuticular elevation; i = isolated pores; t1 = first tarsomere; t2 = second tarsomere; t3 = third tarsomere. Revista Brasileira de Entomologia 46 (1), 2002 Survey of the leg exocrine glands in termites 5 Table II. Morphological data of the glandular openings of the legs of nine species of Termitidae. Species Armitermes euamignathus (n= 8) Cornitermes cumulans (n= 7) Nasutitermes coxipoensis (n= 8) Syntermes nanus (n= 6) Microcerotermes sp. (n= 7) Neocapritermes opacus (n= 9) Embiratermes festivellus (n= 9) Orthognathotermes sp. (n= 5) Spinitermes brevicornutus (n= 8) Number of pores 1st tarsomere 2nd tarsomere 3rd tarsomere 11-12 14-15 9-14 9-10 10 10-16 22-32 11-12 12-13 10-13 12 12 10 10-18 20-23 13 11 15-20 9-14 14-24 20-30 17-18 Pore diameter (µm) Depression diameter (µm) 0.15-0.16 0.12 0.14-0.16 0.18 0.23 0.18-0.25 0.10-0.14 0.12 0.15-0.16 0.88-1.02 0.91 0.67-0.68 0.87 n = number of specimens analysed. The glandular openings on the tarsomeres of Amitermes beaumonti showed the same characteristics as those described for Termes sp. The pore plates also predominated on the first and second tarsomeres and contained up to four pores. The other 11 species of Termitidae presented isolated pores spread throughout the ventral surface of the first three tarsal segments (Figs. 3-9). Isolated pore inserted in a cuticular depression - Each pore was individually inserted in a round cuticular depression in Spinitermes brevicornutus, Embiratermes festivellus, Microcerotermes sp., Armitermes euamignathus, Rhynchotermes nasutissimus, and Hoplotermes amplus (Figs. 3-5). Isolated pore in a cuticular elevation – The individual pores were inserted in a cuticular elevation in Nasutitermes coxipoensis and Orthognathotermes sp. (Figs. 6, 7). Orthognathotermes sp. showed many pores in its tarsomeres, however, it was possible to analyze only the third tarsomere, which contained a maximum of 30 pores. Isolated pore without cuticular specialization – The individual pore was not surrounded by a cuticular specialization in Cornitermes cumulans, Neocapritermes opacus and Syntermes nanus (Figs. 8,9). Table II shows the data concerning the number of pores present in the different tarsomeres and their diameter range (0.67 to 1.02 µm). The pores varied in number and diameter according to the species. The number of pores was higher in Spinitermes brevicornutus and Embiratermes festivellus. In general, the pore diameter ranged from 0,10 to 0.23 µm. No sensory structures were found associated with the glandular openings in the species studied. The cuticle that surrounded the pores was smooth, except in Spinitermes brevicornutus legs that presented a certain rugosity (Fig. 5). Glandular openings were not observed in the legs of Anoplotermes sp., Ruptitermes sp. (Termitidae, Apicotermitinae) or Glyptotermes planus (Kalotermitidae). DISCUSSION The present results and the available literature data are summarized in Table III. The location of the exocrine glands seems to be constant in the tarsi of all Nasutitermitinae and Termitinae (Termitidae). An exception is Longipeditermes longipes (Nasutitermitinae), where such gland is not found (BACCHUS 1979). However, the lack of observation of cuticular pores on the tarsomeres of that species by that author may have been due to the dirt on material, as often observed in our specimens. The taxonomic value of the 4 pore patterns (Table I) recognized in the present study is still not clear for Termitidae. Nevertheless, for Rhinotermitidae, FAUCHEUX (1994) and LEBRUN & FAUCHEUX (1994), separated species of Reticulitermes according to differences in the glandular openings of the legs. We believe that there is no pattern in the number and location of the pores in the tarsomeres, but future analyses of a larger number of specimens will be more conclusive. Glandular openings were not found in the specimens of Apicotermitinae studied here, in agreement with data obtained by BACCHUS (1979), who did not observe glands on the legs of Jugositermes tuberculatus (Apicotermitinae). The leg exocrine glands are present only in some Kalotermitidae species. Glandular openings were not observed on the legs of Glyptotermes planus or Cryptotermes brevis (BACCHUS, 1979). FAUCHEUX (1994) observed the presence of cuticular pores on the first, second and third tarsomeres and tibia of all castes of Kalotermes flavicollis. We also found Revista Brasileira de Entomologia 46 (1), 2002 6 Soares & Costa-Leonardo Table III. Summary of the bibliographic data about the exocrine glands on the legs of termites. Family Subfamily Mastotermitidae Termopsidae Kalotermitidae Serritermitidae Mastotermes darwiniensis Zootermopsis nevadensis Cryptotermes brevis Glyptotermes planus Kalotermes flavicollis Serritermes serrifer W a a a a p p Castes S p p R p p Localization of the glandular openings t1, t2, t3, dt t1, t2, t3 Rhinotermitidae Coptotermitinae Coptotermes havilandi p - - t1, t2, dt SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* Coptotermes formosanus Heterotermes perfidus Heterotermes tenuis p p p p - p p p p p - t1, t2, dt t1, t2, dt t1, t2 t1, t2, dt t1, t2, dt Termitogeton planus p p p p p p p p p t1, t2, dt t1, t2, dt t1, t2, dt BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) COSTA-LEONARDO (1994) COSTA-LEONARDO (1994) SOARES & & COSTA -LEONARDO (2002)* SOARES COSTA-LEONARDO (2001)* BACCHUS (1979) BACCHUS (1979) LEBRUN &&FFAUCHEUX AUCHEUX (1994) LEBRUN (1994) FAUCHEUX (1994) FAUCHEUX (1994) LEBRUN &&FFAUCHEUX AUCHEUX (1994) LEBRUN (1994) FAUCHEUX (1993) FAUCHEUX (1993) BACCHUS (1979) BACCHUS (1979) Schedorhinotermes putorius p - - t1, t2, dt BACCHUS (1979) BACCHUS (1979) Jugositermes tuberculatus Ruptitermes sp. Anoplotermes sp. Armitermes euamignathus Cornitermes cumulans Embiratermes festivellus Nasutitermes coxipoensis Longipeditermes longipes Rhynchotermes nasutissimus Syntermes nanus Amitermes beaumonti Hoplotermes amplus Neocapritermes opacus Microcerotermes sp. Orthognathotermes sp. Spinitermes brevicornutus Termes sp. Microtermes thoracalis Macrotermes bellicosus a a a p p p p a p p p p p p p p p a a - - t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 t1, t2, t3 - BACCHUS (1979) BACCHUS (1979) SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* BACCHUS (1979) BACCHUS (1979) SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA-LEONARDO OSTA-LEONARDO (2002)* SOARES (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* S OARES & C OSTA -L EONARDO (2002)* SOARES & COSTA LEONARDO (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* SOARES &&CCOSTA OSTA-LEONARDO (2002)* SOARES LEONARDO (2001)* BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) Heterotermitinae Genus/Species Reticulitermes lucifugus Reticulitermes santonensis Termitogetoninae Rhinotermitinae Termitidae Apicotermitinae Nasutitermitinae Termitinae Macrotermitinae Reference BACCHUS, 1979 BACCHUS, 1979 BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) BACCHUS (1979) SOARES (2001)* SOARES &&CCOSTA-LEONARDO, OSTA-L EONARDO, (2002)* FAUCHEUX (1994) FAUCHEUX (1994) COSTA-LEONARDO (1994) COSTA-LEONARDO (1994) a absence of exocrine gland; p presence of exocrine gland; - caste not analised; * present paper; dt distal tibia; R reproductives; S soldier; t1 first tarsomere; t2 second tarsomere; t3 third tarsomere; W worker and/or pseudo-worker. isolated pores on all tarsomeres of a Kalotermitidae alate, probably of the genus Neotermes (SOARES & COSTA-LEONARDO, unpublished data). According to FAUCHEUX (1994) the presence of isolated glandular pores on the legs of Kalotermes flavicollis (Kalotermitidae) is an ancestral characteristic in relation to the pore plate observed in the species of Reticulitermes (Rhinotermitidae). In the present study, we found isolated pores on the tarsomeres of several Termitidae, a result showing a non-linear evolution of this characteristic. Because of this fact and due to the scarce phylogenetic studies available, further knowledge of these glands in Isoptera is needed to confirm the observations of FAUCHEUX (1994). Acknowledgements. We are grateful to CNPq for financial support. Received in 08.II.2000; accepted in 27.XII.2001 Revista Brasileira de Entomologia 46 (1), 2002 REFERENCES BACCHUS, S. 1979. New exocrine gland on the legs of some Rhinotermitidae (Isoptera). International Journal of Insect Morphology and Embryology 8(2): 135-142. COSTA-LEONARDO , A. M. 1994. The leg exocrine system in Serritermes serrifer (Hagen, 1858), phylogenetic implications (Isoptera: Serritermitidae). Insectes Sociaux 41: 111-114. FAUCHEUX, M. J. 1993. Glandes exocrines tibiales, tarsiennes et abdominales du Termite de Saintonge, Reticulitermes santonensis Feytaud (Isoptera, Rhinotermitidae). Bulletin de la Société des Sciences Naturelles de L’Ouest de la France 15(4): 196-207. FAUCHEUX , M. J. 1994. Les plaques perforées des pattes de trois termites français: Kalotermes flavicollis Fabr., Reticulitermes lucifugus Rossi et R. santonensis Feytaud (Isoptera). Bulletin de la Société des Sciences Naturelles de L’Ouest de la France 16(1): 10-19. LEBRUN , D. & M. J. FAUCHEUX. 1994. Étude morphologique relative a la spéciation dans le genre equilibrium value of MeCpG steps (,+14 deg.) [31,44]. In comparison, methylation has a significantly lower stability cost when happening at major groove positions, such as 211 and 21 base pair from dyad (mutations 9 and 12), where the roll of the nucleosome bound conformation (+10 deg.) is more compatible with the equilibrium geometry of MeCpG steps. The nucleosome destabilizing effect of cytosine methylation increases with the number of methylated cytosines, following the same position dependence as the single methylations. The multiple-methylation case reveals that each major groove meth- PLOS Computational Biology | www.ploscompbiol.org 3 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning ylation destabilizes the nucleosome by around 1 kJ/mol (close to the average estimate of 2 kJ/mol obtained for from individual methylation studies), while each minor groove methylation destabilizes it by up to 5 kJ/mol (average free energy as single mutation is around 6 kJ/mol). This energetic position-dependence is the reverse of what was observed in a recent FRET/SAXS study [30]. The differences can be attributed to the use of different ionic conditions and different sequences: a modified Widom-601 sequence of 157 bp, which already contains multiple CpG steps in mixed orientations, and which could assume different positioning due to the introduction of new CpG steps and by effect of the methylation. The analysis of our trajectories reveals a larger root mean square deviation (RMSD) and fluctuation (RMSF; see Figures S2– S3 in Text S1) for the methylated nucleosomes, but failed to detect any systematic change in DNA geometry or in intermolecular DNA-histone energy related to methylation (Fig. S1B, S1C, S4–S6 in Text S1). The hydrophobic effect should favor orientation of the methyl group out from the solvent but this effect alone is not likely to justify the positional dependent stability changes in Figure 2, as the differential solvation of the methyl groups in the bound and unbound states is only in the order of a fraction of a water molecule (Figure S5 in Text S1). We find however, a reasonable correlation between methylation-induced changes in hydrogen bond and stacking interactions of the bases and the change in nucleosome stability (see Figure S6 in Text S1). This finding suggests that methylation-induced nucleosome destabilization is related to the poorer ability of methylated DNA to fit into the required conformation for DNA in a nucleosome. Changes in the elastic deformation energy between methylated and un-methylated DNA correlate with nucleosomal differential binding free energies To further analyze the idea that methylation-induced nucleosome destabilization is connected to a worse fit of methylated DNA into the required nucleosome-bound conformation, we computed the elastic energy of the nucleosomal DNA using a harmonic deformation method [36,37,44]. This method provides a rough estimate of the energy required to deform a DNA fiber to adopt the super helical conformation in the nucleosome (full details in Suppl. Information Text S1). As shown in Figure 2, there is an evident correlation between the increase that methylation produces in the elastic deformation energy (DDE def.) and the free energy variation (DDG bind.) computed from MD/TI calculations. Clearly, methylation increases the stiffness of the CpG step [31], raising the energy cost required to wrap DNA around the histone octamers. This extra energy cost will be smaller in regions of high positive roll (naked DNA MeCpG steps have a higher roll than CpG steps [31]) than in regions of high negative roll. Thus, simple elastic considerations explain why methylation is better tolerated when the DNA faces the histones through the major groove (where positive roll is required) that when it faces histones through the minor groove (where negative roll is required). Nucleosome methylation can give rise to nucleosome repositioning We have established that methylation affects the wrapping of DNA in nucleosomes, but how does this translate into chromatin structure? As noted above, accumulation of minor groove methylations strongly destabilizes the nucleosome, and could trigger nucleosome unfolding, or notable changes in positioning or phasing of DNA around the histone core. While accumulation of methylations might be well tolerated if placed in favorable positions, accumulation in unfavorable positions would destabilize the nucleosome, which might trigger changes in chromatin structure. Chromatin could in fact react in two different ways in response to significant levels of methylation in unfavorable positions: i) the DNA could either detach from the histone core, leading to nucleosome eviction or nucleosome repositioning, or ii) the DNA could rotate around the histone core, changing its phase to place MeCpG steps in favorable positions. Both effects are anticipated to alter DNA accessibility and impact gene expression regulation. The sub-microsecond time scale of our MD trajectories of methylated DNAs bound to nucleosomes is not large enough to capture these effects, but clear trends are visible in cases of multiple mutations occurring in unfavorable positions, where unmethylated and methylated DNA sequences are out of phase by around 28 degrees (Figure S7 in Text S1). Due to this repositioning, large or small, DNA could move and the nucleosome structure could assume a more compact and distorted conformation, as detected by Lee and Lee [29], or a slightly open conformation as found in Jimenez-Useche et al. [30]. Using the harmonic deformation method, we additionally predicted the change in stability induced by cytosine methylation for millions of different nucleosomal DNA sequences. Consistently with our calculations, we used two extreme scenarios to prepare our DNA sequences (see Fig. 3): i) all positions where the minor grooves contact the histone core are occupied by CpG steps, and ii) all positions where the major grooves contact the histone core are occupied by CpG steps. We then computed the elastic energy required to wrap the DNA around the histone proteins in unmethylated and methylated states, and, as expected, observed that methylation disfavors DNA wrapping (Figure 3A). We have rescaled the elastic energy differences with a factor of 0.23 to match the DDG prediction in figure 2B. In agreement with the rest of our results, our analysis confirms that the effect of methylation is position-dependent. In fact, the overall difference between the two extreme methylation scenarios (all-in-minor vs all-in-major) is larger than 60 kJ/mol, the average difference being around 15 kJ/ mol. We have also computed the elastic energy differences for a million sequences with CpG/MeCpG steps positioned at all possible intermediate locations with respect to the position (figure 3B). The large differences between the extreme cases can induce rotations of DNA around the histone core, shifting its phase to allow the placement of the methylated CpG steps facing the histones through the major groove. It is illustrative to compare the magnitude of CpG methylation penalty with sequence dependent differences. Since there are roughly 1.5e88 possible 147 base pairs long sequence combinations (i.e., (4n+4(n/2))/2, n = 147), it is unfeasible to calculate all the possible sequence effects. However, using our elastic model we can provide a range of values based on a reasonably large number of samples. If we consider all possible nucleosomal sequences in the yeast genome (around 12 Mbp), the energy difference between the best and the worst sequence that could form a nucleosome is 0.7 kj/mol per base (a minimum of 1 kJ/mol and maximum of around 1.7 kJ/mol per base, the first best and the last worst sequences are displayed in Table S3 in Text S1). We repeated the same calculation for one million random sequences and we obtained equivalent results. Placing one CpG step every helical turn gives an average energetic difference between minor groove and major groove methylation of 15 kJ/ mol, which translates into ,0.5 kJ/mol per methyl group, 2 kJ/ mol per base for the largest effects. Considering that not all nucleosome base pair steps are likely to be CpG steps, we can conclude that the balance between the destabilization due to CpG methylation and sequence repositioning will depend on the PLOS Computational Biology | www.ploscompbiol.org 4 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning Figure 3. Methylated and non-methylated DNA elastic deformation energies. (A) Distribution of deformation energies for 147 bplong random DNA sequences with CpG steps positioned every 10 base steps (one helical turn) in minor (red and dark red) and major (light and dark blue) grooves respectively. The energy values were rescaled by the slope of a best-fit straight line of figure 2, which is 0.23, to por la lectura a través de la lectura de la prensa. La educación en los medios las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio adquiere pleno derecho y entidad en la sección sexta titulada «competencias sociales y cívi- técnico de los aparatos. cas» que indica que «los alum- nos deberán ser capaces de juz- gar y tendrán espíritu crítico, lo que supone ser educados en los las programaciones oficiales, ya que, a lo largo de un medios y tener conciencia de su lugar y de su influencia estudio de los textos, los documentalistas del CLEMI en la sociedad». han podido señalar más de una centena de referencias a la educación de los medios en el seno de disciplinas 4. Un entorno positivo como el francés, la historia, la geografía, las lenguas, Si nos atenemos a las cifras, el panorama de la las artes plásticas : trabajos sobre las portadas de educación en medios es muy positivo. Una gran ope- prensa, reflexiones sobre temas mediáticos, análisis de ración de visibilidad como la «Semana de la prensa y publicidad, análisis de imágenes desde todos los ángu- de los medios en la escuela», coordinada por el CLE- los, reflexión sobre las noticias en los países europeos, MI, confirma año tras año, después de 17 convocato- información y opinión rias, el atractivo que ejerce sobre los profesores y los Esta presencia se constata desde la escuela mater- alumnos. Concebida como una gran operación de nal (2 a 6 años) donde, por ejemplo, se le pregunta a complementariedad entre la escuela y los profesiona- los niños más pequeños si saben diferenciar entre un les de los medios, alrededor del aprendizaje ciudada- periódico, un libro, un catálogo, a través de activida- no de la comunicación mediática, este evento moviliza des sensoriales, si saben para qué sirve un cartel, un durante toda una semana un porcentaje elevado de periódico, un cuaderno, un ordenador si son capa- centros escolares que representan un potencial de 4,3 ces de reconocer y distinguir imágenes de origen y de millones de alumnos (cifras de 2006). Basada en el naturaleza distintas. Podríamos continuar con más voluntariado, la semana permite desarrollar activida- ejemplos en todos los niveles de enseñanza y práctica- des más o menos ambiciosas centradas en la introduc- Páginas 43-48 ción de los medios en la vida de la escuela a través de la instalación de kioscos, organización de debates con profesionales y la confección por parte de los alumnos de documentos difundidos en los medios profesionales. Es la ocasión de dar un empujón a la educación en medios y de disfrutarlos. Los medios –un millar en 2006– se asocian de maneras diversas ofreciendo ejemplares de periódicos, acceso a noticias o a imágenes, proponiendo encuentros, permitiendo intervenir a los jóvenes en sus ondas o en sus columnas Esta operación da luz al trabajo de la educación en medios y moviliza a los diferentes participantes en el proyecto. 5. La formación de los docentes La formación es uno de los pilares principales de la educación en los medios. Su función es indispensable ya que no se trata de una disciplina, sino de una enseñanza que se hace sobre la base del voluntariado y del compromiso personal. Se trata de convencer, de mostrar, de interactuar. En primer lugar es necesario incluirla en la formación continua de los docentes, cuyo volumen se ha incrementado desde 1981 con la aparición de una verdadera política de formación continua de personal. Es difícil dar una imagen completa del volumen y del público, pero si nos atenemos a las cifras del CLEMI, hay más de 24.000 profesores que han asistido y se han involucrado durante 2004-05. 5.1. La formación continua En la mayoría de los casos, los profesores reciben su formación en contextos cercanos a su centro de trabajo, o incluso en este mismo. Después de una política centrada en la oferta que hacían los formadores, se valora más positivamente la demanda por parte del profesorado, ya que sólo así será verdaderamente fructífera. Los cursos de formación se repartieron en varias categorías: desde los formatos más tradicionales (cursos, debates, animaciones), hasta actividades de asesoramiento y de acompañamiento, y por supuesto los coloquios que permiten un trabajo en profundidad ya que van acompañados de expertos investigadores y profesionales. Citemos, por ejemplo en 2005, los coloquios del CLEMI-Toulouse sobre el cine documental o el del CLEMI-Dijon sobre «Políticos y medios: ¿connivencia?». Estos coloquios, que forman parte de un trabajo pedagógico regular, reagrupan a los diferentes participantes regionales y nacionales alrededor de grandes temas de la educación en medios y permiten generar nuevos conocimientos de aproximación y una profundización. Páginas 43-48 Hay otro tipo de formación original que se viene desarrollando desde hace menos tiempo, a través de cursos profesionales, como por ejemplo, en el Festival Internacional de Foto-periodismo «Visa para la imagen», en Perpignan. La formación se consolida en el curso, da acceso a las exposiciones, a las conferencias de profesionales y a los grandes debates, pero añade además propuestas pedagógicas y reflexiones didácticas destinadas a los docentes. Estas nuevas modalidades de formación son también consecuencia del agotamiento de la formación tradicional en las regiones. Los contenidos más frecuentes en formación continua conciernen tanto a los temas más clásicos como a los cambios que se están llevando a cabo en las prácticas mediáticas. Así encontramos distintas tendencias para 2004-05: La imagen desde el ángulo de la producción de imágenes animadas, el análisis de la imagen de la información o las imágenes del J.T. La prensa escrita y el periódico escolar. Internet y la información en línea. Medios y educación de los medios. 5.2 La formación inicial La formación inicial está aun en un grado muy ini- cial. El hecho de que la educación en medios no sea una disciplina impide su presencia en los IUFM (Institutos Universitarios de Formación de Maestros) que dan una prioridad absoluta a la didáctica de las disciplinas. En 2003, alrededor de 1.400 cursillistas sobre un total de 30.000 participaron en un momento u otro de un módulo de educación en medios. Estos módulos se ofrecen en función del interés que ese formador encuentra puntualmente y forman parte a menudo de varias disciplinas: documentación, letras, historia-geografía Estamos aún lejos de una política concertada en este dominio. La optativa «Cine-audiovisual» ha entrado desde hace muy poco tiempo en algunos IUFM destinada a obtener un certificado de enseñanza de la opción audiovisual y cine. Internet tiene cabida también en los cursos de formación inicial, recientemente con la aparición de un certificado informático y de Internet para los docentes, dirigido más a constatar competencias personales que a valorar una aptitud para enseñarlos. 6. ¿Y el futuro? El problema del futuro se plantea una vez más por la irrupción de nuevas técnicas y nuevos soportes. La difusión acelerada de lo digital replantea hoy muchas cuestiones relativas a prácticas mediáticas. Muchos Comunicar, 28, 2007 47 Comunicar, 28, 2007 Enrique Martínez-Salanova '2007 para Comunicar 48 trabajos que llevan el rótulo de la educación en medios solicitan una revisión ya que los conceptos cambian. La metodología elaborada en el marco de la educación en medios parece incluso permitir la inclinación de la sociedad de la información hacia una sociedad del conocimiento, como defiende la UNESCO. En Francia, se necesitaría unir las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio técnico de los aparatos. Los avances recientes en el reconocimiento de estos contenidos y las competencias que supondrían podrían permitirlo. Referencias CLEMI/ACADEMIE DE BORDEAUX (Ed.) (2003): Parcours médias au collège: approches disciplinaires et transdisciplinaires. Aquitaine, Sceren-CRDP. GONNET, J. (2001): Education aux médias. Les controverses fécondes. Paris, Hachette Education/CNDP. SAVINO, J.; MARMIESSE, C. et BENSA, F. (2005): L’éducation aux médias de la maternelle au lycée. Direction de l’Enseignement Scolaire. Paris, Ministère de l’Education Nationale, Sceren/CNDP, Témoigner. BEVORT, E. et FREMONT, P. (2001): Médias, violence et education. Paris, CNDP, Actes et rapports pour l’éducation. – www.clemi.org: fiches pédagogiques, rapports et liens avec les pages régionales/académiques. – www.ac-nancy-metz.fr/cinemav/quai.html: Le site «Quai des images» est dédié à l’enseignement du cinéma et de l’audiovisuel. – www.france5.fr/education: la rubrique «Côté profs» a une entrée «education aux médias». – www.educaunet.org: Programme européen d’éducation aux risques liés à Internet. dResedfeleexliobnuetsacón Páginas 43-48
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