Discovery and Characterization of Novel Sperm Development Patterns in the Nematode Rhabditis Sp. Sb347

• Main Author: McCaig, Caitlin M.
• Format: Others
• Language: English
• Published: W&M ScholarWorks 2017
• Subjects: Biology
• Online Access: https://scholarworks.wm.edu/etd/1499450066; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=1184&context=etd

Studies of gamete production in Caenorhabditis elegans self-fertile hermaphrodites have informed textbook descriptions of nematode reproduction and have significantly contributed to our understanding of fundamental cellular and developmental mechanisms. However, C. elegans is one species within a large phylum of mostly dioecious (male/female) species. Whether the C. elegans pattern of self-fertile hermaphroditism and gamete development is representative of other nematodes remains largely unexplored. In Chapter 1, we describe an alternative pattern of sperm production in the trioecious (male/female/hermaphrodite) nematode Rhabditis sp. SB347 that differs from C. elegans in two striking ways. First, instead of making a one-time switch from sperm to oocyte production, R. sp. SB347 hermaphrodites produce sperm and oocytes simultaneously. Secondly, instead of limiting germ cell proliferation to germline stem cells (GSCs), sperm production in R. sp. SB347 includes an additional population of mitotically dividing cells that are a developmental intermediate between GSCs and fully differentiated spermatocytes. These cells, which are present in males and hermaphrodites but not females, exhibit key characteristics of spermatogonia, the mitotic progenitors of spermatocytes in flies and vertebrates. Specifically, they amplify germ cell numbers, exist outside the stem cell niche, and synchronously develop and proliferate within germ cell clusters (or cysts). Spermatogonia are a feature of sperm production in other trioecious species of the Rhabditis genus, but not in the male/female species Rhabditis axei. The discovery of simultaneous hermaphroditism and spermatogonia in a lab-cultivatable nematode suggests R. sp. SB347 as a richly informative species for comparative studies of gametogenesis. In Chapter 2, we assess whether C. elegans germ cell development genes have been conserved across species, identify homologs in R. sp. SB347, and begin to investigate expression of two homologs, FBF and SPE-44. We suggest that by comparing these homologs’ roles and expression patterns between species, we can better understand differences between these two divergent mechanisms of hermaphroditism and sperm production. Such molecular comparative analyses may also inform our understanding of germ cell evolution. In Chapter 3, we consider what aspects about R. sp. SB347’s unique form of sperm development have not yet been fully explored. We report relevant preliminary data and recommend future directions for addressing these questions.