Cohesin axis maturation and presence of RAD51 during first meiotic prophase in a true bug
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We have analyzed in a true bug, Graphosoma italicum (Pentatomidae, Hemiptera), the temporal and functional relationships between recombination events, synapsis progression, and SMC1α and SMC3 cohesin axis maturation throughout the male first meiotic prophase. The localization of the histone variant histone H3 trimethylated at lysine 9 at chromosome ends has allowed us to determine the association of these heterochromatic domains through prophase I stages. Results highlighted that cohesins provide to be good markers for synapsis progression since the formation, morphology, and development of the SMC1α and SMC3 cohesin axes resemble the synaptonemal complex dynamics and, also, that in this species the initiation of recombination precedes synapsis. In addition, we have carried out an accurate cytological characterization of the diffuse stage, which takes place after pachytene, and also analyzed the presence of the cohesin subunits, SMC1α and SMC3, and the recombinase RAD51 at this stage. The mechanisms underlying the absence of SMC1α and SMC3 axes from the diffuse stage onwards are discussed.
KeywordsSeminiferous Tubule Synaptonemal Complex Diffuse Stage Sister Chromatid Cohesion Cohesin Complex
We would like to express our gratitude to Consejería de Medio Ambiente y Ordenación del Territorio (Comunidad de Madrid; España) for emitting the authorization for animal recollections in natural populations, to Dr. José Luis Barbero for generously supplying us the anti-SMC3 anti-SMC1α antibodies, to Dr. Kim McKim for his generous gift of the anti-H2Av antibody, and to Dr. García de la Verga for the critical reading of the manuscript. This work was supported by grants BFU2006-06655, BFU2005-02431, BFU200800459, and BFU2008-00300-BCM from the Ministerio de Educación y Ciencia Spain.
SMC3 distribution in squashed spermatocytes. 3-D reconstruction of a field of spermatocytes immunolabeled for SMC3 (green) and DAPI-stained (pseudocolored in red). Leptotene (Le), zygotene (Zy), early-, mid-, and late-pachytene (Pearly, Pmid, and Plate), diffuse, and metaphase I (MI) spermatocytes are observed and one spermatid (Sp). Note the presence of a brighter structure in pachytene and diffuse spermatocytes, corresponding to the chromatin of the sex chromosomes (XY). This video corresponds to the reconstructions of the spermatocytes shown in Fig. 1. See text for further details (MOV 710 kb)
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