# The function and evolution of female-expressed seminal fluid proteins

> **NIH NIH K99** · UNIVERSITY OF CALIFORNIA AT DAVIS · 2024 · $124,913

## Abstract

PROJECT SUMMARY
In all animals with internal fertilization, hundreds of seminal fluid proteins (SFPs) are transferred to females
during mating. These SFPs have canonically been primarily thought of as a set of male proteins that advance
male interests during post-mating processes, including by manipulatively influencing female behavior and
reproductive investment. From this perspective, SFPs are thought to be an important substrate of interlocus
sexual conflict against which females must continually evolve defensive countermeasures, which has been
hypothesized to explain observations that SFPs evolve rapidly. Using single-nucleus RNAseq of the Drosophila
melanogaster female reproductive tract (uterus, oviduct, glands, and sperm storage organs), I discovered that
females express >40% of the 292 known D. melanogaster SFPs. Moreover, multiple female reproductive cell
types specialize in producing SFPs prior to mating. For example, in a cell type in the seminal receptacle, SFP
genes comprise 30% of mRNAs in the average sequenced nucleus (up to 65% of mRNAs in some sequenced
nuclei). This result demands a re-evaluation of SFP biology that integrates the function and possible selection
on the female-contributed protein fraction, which I take on in this proposal by asking: 1) What are the functions
of female-expressed SFPs, i.e. shared reproductive secreted proteins? Do the female- and male-contributed
protein fractions have the same function? And 2) How do shared secreted reproductive proteins evolve? Do
the sex-shared secreted proteins exhibit different evolutionary modalities than the sex-limited SFPs? Do
evolutionary and functional patterns in these genes better support a model of cooperation or sexual
antagonism? Importantly, for the sex-shared proteins, any potential sexual conflict would have to be intra-locus
conflict, with implications for the predicted duration and outcome of the conflict. I address these knowledge
gaps using cutting-edge genome engineering methods, specifically gene knock-out and scarless CRISPR
insertion of transgenic nanobody-epitope tagged proteins, to allow both immunofluorescent visualization and
functional characterization. A second set of experiments uses comparative genomics and transcriptomics in a
phylogenetic framework to determine the history of the proteins, the persistence of their expression by each
sex, their evolutionary rate, and the evidence for either directional or stabilizing selection on the protein
sequences. Because the cell types in D. melanogaster females that specialize in SFP production belong to the
sperm storage organs, the proposed work will additionally test whether convergently evolved gains of sperm
storage in a third female organ, observed among select non-melanogaster Drosophila species, are associated
with gains of SFP expression in additional cell types. In total, the proposed work will provide a missing
perspective on a famous set of genes in a premier genetic model organism. Simultaneo...

## Key facts

- **NIH application ID:** 10950074
- **Project number:** 1K99HD115833-01
- **Recipient organization:** UNIVERSITY OF CALIFORNIA AT DAVIS
- **Principal Investigator:** Rachel C Thayer
- **Activity code:** K99 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $124,913
- **Award type:** 1
- **Project period:** 2024-09-01 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10950074

## Citation

> US National Institutes of Health, RePORTER application 10950074, The function and evolution of female-expressed seminal fluid proteins (1K99HD115833-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10950074. Licensed CC0.

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