Document Type

Honors Capstone Project

Date of Submission

Spring 5-2017

Capstone Advisor

Steve Dorus

Honors Reader

John Belote

Capstone Major

Biology

Capstone College

Arts and Science

Audio/Visual Component

no

Capstone Prize Winner

no

Won Capstone Funding

yes

Honors Categories

Sciences and Engineering

Subject Categories

Biology | Life Sciences

Abstract

Reproductive traits, including phenotypes related to sperm form and function, frequently evolve rapidly under the influence of strong sexual selection. Understanding the genetic basis of this process is of paramount importance to evolutionary biologists and has important implications on our understanding of reproductive outcomes and fertility. The creation of new genes is suspected to contribute to this process as new genes are often expressed in the testis. However, little is currently known about how, and if, these genes acquire novel functions in spermatogenesis. Many novel genes are retrogenes. Retrogenes are formed through reverse transcription of mRNA. A set of retrogenes showing testes specific expression and putative roles in mitochondrial function was selected for genetic manipulation and phenotypic testing. Mitochondrial genes were selected because of their mechanistic role in spermatogenesis and tail elongation. Additionally, there has been a pattern previously identified for prevalent creation of testis specific mitochondrial genes during Drosophila evolution. The RNAi (ribonucleic acid interference) knockdown method, using a bipartite system, was used to construct knockdowns of the genes of interest (GOI). This involved crossing a female line containing a Vasa-Gal4 driver with a male line containing the UAS (upstream activation sequence)-GOI construct. The effect of knocking down the GOI was analyzed via three methods: fertility assays, sperm length measurements, and confocal microscopy. Fertility assays were done to determine whether the GOI plays a role in male fertility. Experimental and control males were mated to females and the number of eggs laid and hatched were counted over a four-day period. Four of the RNAi lines exhibited a significant reduction in fertility relative to controls, suggesting a fertility affect for these retrogenes. Sperm length measurements were significantly different from controls for 2 RNAi lines, supporting a role for these mitochondrial retrogenes in sperm tail elongation. Longer sperm length has been correlated with greater fertilization success in Drosophila. Finally, seminal vesicles were stained using DAPI and confocal images were taken to compare sperm number. Of particular note, for one gene (CG31003) the knockdown males produced very little or no sperm, implying an important role in sperm production. This work demonstrates that novel mitochondrial genes effect spermatogenesis, sperm traits and fertility. Although more analyses need to be done, this substantiates the importance of new genes in reproduction.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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Biology Commons

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