Abstract
We present the first detailed cytological study of male meiosis in Daphnia (Crustacea: Branchiopoda: Cladocera)—an aquatic microcrustacean with a cyclical parthenogenetic life cycle. Using immunostaining of the testes in Daphnia magna for baseline knowledge, we characterized the different stages of meiotic division and spermiogenesis in relation to the distribution of proteins involved in synapsis, early recombination events and sister chromatid cohesion. We also studied post-translational histone modifications in male spermatocytes, in relation to the dynamic chromatin progression of meiosis. Finally, we applied a DNA fragmentation test to measure sperm quality of D. magna, with respect to levels of inbreeding. As a proxy for fertility, this technique may be used to assess the reproductive health of a sentinel species of aquatic ecosystems. Daphnia proves to be a model species for comparative studies of meiosis that is poised to improve our understanding of the cytological basis of sexual and asexual reproduction.Electronic supplementary materialThe online version of this article (doi:10.1007/s00412-015-0558-1) contains supplementary material, which is available to authorized users.
Highlights
Meiosis is the most fundamental biological process that is shared among sexually reproducing eukaryotes
For each of the antibodies against SMC3, γH2AX, Rad51, H3S10ph, H3K9m3 and αTubulin, a specific band was recognized corresponding to the expected molecular weight based on sequence homology and protein size
The earliest defined molecular event in meiotic recombination occurs with the formation of Double Stranded Breaks (DSBs)
Summary
Meiosis is the most fundamental biological process that is shared among sexually reproducing eukaryotes. Meiosis is a specialized cell division program that consists of two consecutive rounds of cell division, following a single round of DNA replication, thereby forming haploid gametes from diploid germ cells. Failures during this process lead to errors in chromosome segregation, which are a major cause for miscarriages and birth defects in animals. To ensure the correct transmission of chromosomes during both meiotic divisions, chromosome sister chromatids must be held together by the Cohesin Complexes through an event called sister chromatid cohesion (SCC), which must be tightly regulated for chromosomes to properly segregate. Homologous chromosomes must first recognize each other, pair, closely associate by a proteinaceous structure called the synaptonemal
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