Sara and Danielle to present at Student Seminar Thursday (20.August) at noon
Background for Sara’s talk
The existence of ancient asexual lineages in nature contradicts the current prevailing hypotheses regarding the apparent advantages of sexual over asexual reproduction. Bdelloid rotifers are one such putative ancient asexual group. Interestingly, meiosis-specific genes have been identified in the genomes of multiple bdelloid species, as well as in their facultatively sexual sister taxa, monogonont rotifers. This proposed work will explore functional implications of the presence of these genes through the following specific aims: 1. Complete meiotic gene inventory of monogonont rotifers. 2. Analyze expression patterns of meiotic genes in monogonont and bdelloid cultures. 3. Examine location and timing of meiotic gene expression in monogononts and bdelloids. This work will examine the potential for meiosis in bdelloids as well as the possibility of neo-functionalization of genes not known to be involved in cellular processes outside of meiosis.
Background for Danielle’s talk
Chiasmata play a major role in meiosis by helping to properly join homologous chromosome pairs, which is necessary for recombination and proper segregation. Male Drosophila, however, are unique amongst nearly all other male eukaryotes: they undergo achiasmatic meiosis. During spermatogenesis, the germ cell proceeds through meiosis and divides into four haploid gametes without formation of chiasmata or recombination. A number of genes have been found which play a role in achiasmatic meiosis in Drosophila, two of which arose from gene duplication events (Stromalin in Meiosis (snm) and Australin(aust)). These genes are both male- and meiosis-specific, in contrast to their paralogs (Stromal Antigen (SA) and Borrealin-related (borr)) which are ubiquitously expressed and have important roles in both mitosis and meiosis. To better understand how achiasmatic meiosis evolved in flies, I will trace the origin of the snm and aust gene duplications through degenerate PCR, sequencing and phylogenetic analysis in fly species throughout the Dipteran clade. This will pinpoint when during Dipteran evolution the duplication event(s) which gave rise to these genes occurred, and potentially indicate the origin of achiasmatic meiosis. Currently, partial gene sequences have been amplified from 19 Dipteran species outside of the Drosophila clade. Phylogenetic analysis of these sequences shows that they are orthologs of SA and not snm. This suggests that either snm is Drosophila-specific or that it may be evolving rapidly and thus difficult to amplify by degenerate PCR. Degenerate primers are also being used to amplify borr and aust in Dipterans. Future work will involve using deep sequencing to examine the expression levels of genes involved in chiasmatic meiosis in flies within the Schizophora group. If genes that are involved in chiasmata formation are not expressed, meiosis in that species might be achiasmatic, even if snm, aust, and other genes involved in Drosophila achiasmatic meiosis are not present. The expression of achiasmatic meiosis genes will also be examined to determine whether they are testes-specific in all species with these genes.
Posted on August 17, 2009, in Student Seminar and tagged asexual reproduction, Bdelloid rotifers, Danielle M., Drosophila, meiosis, monogonont rotifers, Sara H., spermatogenesis. Bookmark the permalink. Leave a comment.