# Regulation of protamine incorporation and nuclear reorganization during Drosophila spermatogenesis

> **NIH NIH F30** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2022 · $51,752

## Abstract

ABSTRACT
In many species, sperm maturation requires a process of nuclear compaction, which occurs via
dramatic chromatin reorganization from histone to protamine-based architecture. Nuclear
compaction is essential for sperm fertility, functioning to enhance hydrodynamics and genomic
integrity. While several genes have been identified to be involved in this process, it is unknown
how these genes are regulated. Here, we have utilized the Drosophila testis model system to
identify Modulo, the Drosophila homolog of Nucleolin, as a key player in sperm nuclear
reorganization. In somatic cells, modulo has been shown to be involved in chromatin remodeling,
cell proliferation, and morphogenesis. Viable modulo mutant allele that specifically influences
testis-specific isoform has been known to be sterile, but the reason underlying this sterility
remained unknown. We find that modulo mutants display nuclear compaction defects during late
spermatogenesis alongside decreased protamine protein incorporation. Importantly, modulo’s
unique phenotype cannot be explained simply by lack of protamine incorporation: compound
mutant that lacks protamines Prot A/B and Mst77F causes only mild nuclear deformation rather
than complete nuclear decompaction as observed in modulo mutant. Indeed, in addition to
decreased incorporation of main protamines in mutant, we have detected increased expression
of Mst77Y, a lesser-studied protamine gene with numerous duplications on the Y-chromosome.
Thus, we hypothesize that modulo mediates sperm nuclei compaction by coordinating expression
of multiple genes that are specifically involved in nuclear compaction during spermiogenesis. To
test this hypothesis, we will conclusively establish the cytological defects of modulo mutant by
inducing expression of mst77Y in wild-type nuclei and assessing protamine protein expression in
whole testis vs. in spermatid nuclei. Additionally, we will investigate transcription and/or splicing
as modulo’s mechanism for regulating its target genes. Previous literature has identified modulo
to interact with testis-specific transcription factors while protein sequence analysis and gene
ontology have predicted modulo as being involved in splicing. Therefore, we further hypothesize
that modulo regulates its target genes at the RNA level either by functioning during transcription
or splicing. If our hypothesis is true, it would result in the identification of a previously
uncharacterized regulatory network governing nuclear reorganization in late stage
spermatogenesis and have implications for male infertility.

## Key facts

- **NIH application ID:** 10462097
- **Project number:** 1F30HD105324-01A1
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Jun Il Park
- **Activity code:** F30 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $51,752
- **Award type:** 1
- **Project period:** 2022-05-01 → 2023-10-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10462097

## Citation

> US National Institutes of Health, RePORTER application 10462097, Regulation of protamine incorporation and nuclear reorganization during Drosophila spermatogenesis (1F30HD105324-01A1). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10462097. Licensed CC0.

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