The Most Proximal Oocyte and Future Directions

This summer, we have performed a comparative analysis of oocyte maturation in the nematode species C. elegans and R. sp. SB347. These studies have allowed us to gain insights on how this process differs between the two species. Specifically, this summer, we studied what role the protein FBF plays in oocyte maturation. We observed different patterns of FBF antibody staining within the gonad (see my previous post) and in the most proximal oocytes of the related nematode, R. sp. SB347, confirming results from previous studies (Lin et al. unpublished studies).

While we focused our analysis on the self-fertilizing hermaphrodites of both species, one future direction of the project is to observe oocyte maturation patterns in R. sp. SB347 females. While C. elegans only exists as males and self-fertilizing hermaphrodites, R. sp. SB347 exists as males, self-fertilizing hermaphrodites and females. In addition, the gonads of R. sp. SB347 contain fewer cells than those of C. elegans. However, both species produce similar numbers of progeny. Studying the females will allow us to further distinguish R. sp. SB347 from C. elegans.

In hermaphrodite C. elegans, oocytes undergo maturation prior to fertilization (McCarter et al. 1999). Once stem cells are fated to become oocytes, they enter meiotic prophase, where they prepare for meiotic division at the proximal region of the gonad. Oocyte maturation is the process by which oocytes become fertilization competent. Previous studies on hermaphrodite C. elegans indicate that oocyte maturation depends on the presence of sperm; in the absence of sperm, the oocytes arrest at meiotic prophase and accumulate in the proximal region (Jud et al. 2007). In other words, they fail to proceed to fertilization. This occurs because stem cells continue to divide and generate oocytes while existing oocytes remain in the proximal region. However, in Rhabditella axei, a male/female nematode species more related to R. sp. SB347 than C. elegans, the number of oocytes remains constant, and oocytes proceed to fertilization regardless of the presence of sperm (Jud et al. 2007). Based on these models, we hypothesize that in R. sp. SB347, if sperm presence facilitates fertilization, then we will find oocyte accumulation in the gonads of SB347 unmated females and mated females whose stock of sperm is depleted. Similarly, we expect to find normal maturation and fertilization patterns in mated females. We will test this by observing oocyte maturation in the gonads of mated and unmated female R. sp. SB347 and comparing that with previous data regarding C. elegans and R. axei. Thus, in future studies, we hope to study how the presence of sperm affects oocyte maturation in R. sp. SB347.

Ultimately, studying oocyte maturation allows us to further characterize oogenesis, the process by which stem cells develop into mature oocytes and then into specialized eggs. This process varies between different organisms, and understanding different reproductive strategies will give us more insights on the diversity of the Nematoda phylum.

 

References:

Alberts, Bruce, et al. (2015). Molecular Biology of the Cell (6th ed.). New York: Garland Science.

McCarter, J., Bartlett, B., Dang, T., & Schedl, T. (1999). On the Control of Oocyte Meiotic Maturation and Ovulation in Caenorhabditis elegans. Developmental biology, 205(1), 111-128.

Jud, M., Razelun, J., Bickel, J., Czerwinski, M., & Schisa, J. A. (2007). Conservation of large foci formation in arrested oocytes of Caenorhabditis nematodes. Development genes and evolution, 217(3), 221-226.

 

 

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