Cohesin axis maturation and presence of RAD51 during first meiotic prophase in a true bug.

We have analyzed in a true bug, Graphosoma italicum (Pentatomidae, Hemiptera), the temporal and functional relationships between recombination events, synapsis progression, and SMC1alpha 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 SMC1alpha 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, SMC1alpha and SMC3, and the recombinase RAD51 at this stage. The mechanisms underlying the absence of SMC1alpha and SMC3 axes from the diffuse stage onwards are discussed.