Date Thesis Awarded

5-2017

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Diane C. Shakes

Committee Members

Patty Zwollo

Matthew Wawersik

Dana Lashley

Abstract

Germ cell development and gametogenesis are essential for the continuity of future generations in most eukaryotic organisms, including humans. One well-established system for studying the complex mechanisms of gametogenesis is the nematode species, Caenorhabditis elegans. The fact that C. elegans hermaphrodite germlines undergo different cellular development at the same life stage in a linear progression makes C. elegans a model system for the study of the conversion of uncommitted germ cells into either oocytes or sperm. C. elegans hermaphrodite produces spermatocytes during the final larval stage and then makes a one-time switch over to oogenesis as the worm enters adulthood. Recently our lab made the surprising discovery that hermaphrodites of another nematode species, Rhabditis sp. SB347, evolved an alternative mechanism for achieving self-fertility.

In Chapter one, we describe that the germline in R. sp. SB347 hermaphrodites is capable of producing both sperm and oocytes from the final larval stage throughout adulthood. Along the length of SB347 hermaphrodite germline, we found clusters of distinct “mystery cells” that divide mitotically outside of stem cell. These “mystery cells” serve as spermatocyte progenitors and share features of spermatogonial cells that are key components of sperm production in other organisms, including Drosophila, mice and humans. Our finding is significant for the understanding of germ cell development because it reveals a completely new reproductive characteristic that is not present in C. elegans but in other model organisms.

In Chapter two, we look at further characterization of spermatogonial cells using a key molecular player known as fem-3 binding factor (FBF). Previously described to regulate both mitosis/meiosis switch and oocyte/sperm determination in Caenorhabditis elegans, FBF belongs to PUF (Pumilio and FBF) protein family and shares a conserved role of germline stem cell regulation. We report the presence of FBF in both the distal germline and the spermatogonia, and unexpectedly, in late maturing oocytes. Our results highlight SB347 spermatogonial cells as an intermediate stage of partially committed spermatocyte progenitors that remain features of germline stem cells.

Through this study of the first reported case of spermatogonial cells in the phylum nematode, we hope to extend our knowledge of germline stem cell development to decipher features of stem cell differentiation and provide more insights with broader, medical implications.

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