Extraordinary centromeres: differences in the meiotic chromosomes of two rock lizards speciesDarevskia portschinskiiandDarevskia raddei

Abstract

According to the synthesis of 30 years of multidisciplinary studies, parthenogenetic species of rock lizards of genusDarevskiawere formed as a result of different combination patterns of interspecific hybridization of the four bisexual parental species:Darevskia raddei,D. mixta,D. valentini, andD. portschinskii. In particular,D. portschinskiiandD. raddeiare considered as the parental species for the parthenogenetic speciesD. rostombekowi. Here for the first time, we present the result of comparative immunocytochemical study of primary spermatocyte nuclei spreads from the leptotene to diplotene stages of meiotic prophase I in two species:D. portschinskiiandD. raddei. We observed similar chromosome lengths for both synaptonemal complex (SC) karyotypes as well as a similar number of crossing over sites. However, unexpected differences in the number and distribution of anti-centromere antibody (ACA) foci were detected in the SC structure of bivalents of the two species. In all examinedD. portschinskiispermatocyte nuclei, one immunostained centromere focus was detected per SC bivalent. In contrast, in almost every studiedD. raddeinuclei we identified three to nine SCs with additional immunostained ACA foci per SC bivalent. Thus, the obtained results allow us to identify species-specific karyotype features, previously not been detected using conventional mitotic chromosome analysis. Presumably the additional centromere foci are result of epigenetic chromatin modifications. We assume that this characteristic of theD. raddeikaryotype could represent useful marker for the future studies of parthenogenetic species hybrid karyotypes related toD. raddei.