Abstract
Centromeres exert an inhibitory effect on meiotic recombination, but the possible contribution of satellite DNA to this “centromere effect” is under debate. In the horse, satellite DNA is present at all centromeres with the exception of the one from chromosome 11. This organization of centromeres allowed us to investigate the role of satellite DNA on recombination suppression in horse spermatocytes at the stage of pachytene. To this aim we analysed the distribution of the MLH1 protein, marker of recombination foci, relative to CENP-A, marker of centromeric function. We demonstrated that the satellite-less centromere of chromosome 11 causes crossover suppression, similarly to satellite-based centromeres. These results suggest that the centromere effect does not depend on satellite DNA. During this analysis, we observed a peculiar phenomenon: while, as expected, the centromere of the majority of meiotic bivalent chromosomes was labelled with a single immunofluorescence centromeric signal, double-spotted or extended signals were also detected. Their number varied from 0 to 7 in different cells. This observation can be explained by positional variation of the centromeric domain on the two homologs and/or misalignment of pericentromeric satellite DNA arrays during homolog pairing confirming the great plasticity of equine centromeres.
Highlights
Centromeres exert an inhibitory effect on meiotic recombination, but the possible contribution of satellite DNA to this “centromere effect” is under debate
In the 13 metacentric bivalents we detected an average number of 24.12 ± 3.04 foci per cell, with 1.86 ± 0.23 foci per chromosome, while in the 18 acrocentric chromosomes the mean frequency of MLH1 foci per cell was 21.18 ± 2.78, with an average of 1.18 ± 0.15 foci per bivalent (Table 1)
We describe the chromosomal distribution of recombination events in male horse meiosis
Summary
Centromeres exert an inhibitory effect on meiotic recombination, but the possible contribution of satellite DNA to this “centromere effect” is under debate. These results suggest that the centromere effect does not depend on satellite DNA During this analysis, we observed a peculiar phenomenon: while, as expected, the centromere of the majority of meiotic bivalent chromosomes was labelled with a single immunofluorescence centromeric signal, double-spotted or extended signals were detected. We observed a peculiar phenomenon: while, as expected, the centromere of the majority of meiotic bivalent chromosomes was labelled with a single immunofluorescence centromeric signal, double-spotted or extended signals were detected Their number varied from 0 to 7 in different cells. In the leptotene phase of prophase I, homologous chromosomes begin to pair through the assembly of the synaptonemal complex (SC), an evolutionarily conserved zipper-like protein structure[2,3] This stage is followed by zygotene, where meiotic recombination is triggered by the formation of SPO11 induced double strand breaks (DSBs)[4].
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