# Uncovering molecular factors driving sexual dimorphism in crossing over in diverse mouse genetic backgrounds

> **NIH NIH K99** · CORNELL UNIVERSITY · 2024 · $109,022

## Abstract

Meiotic recombination results in the formation of DNA crossovers (CO) that are critical for ensuring the correct
segregation of homologous (maternal and paternal) chromosomes at the first meiotic division. Chromosome
segregation errors show striking sexual dimorphism: In humans, 20-80% of eggs versus 2.5-7% of sperm are
aneuploid, likely due in large part to errors in CO formation. Meiotic recombination is initiated by the formation
of DNA double strand breaks (DSB) that are then repaired via various pathways to achieve a tightly regulated
frequency and distribution of COs across the genome. These DSB repair events occur in the context of the
synaptonemal complex (SC), a proteinaceous structure that forms along the chromosome axes, tethering
homolog pairs together. SC length correlates strongly with CO number, and most studies in human and mouse
report females have higher CO rates due to their longer SC length. Paradoxically, meiotic recombination in
females is highly error-prone, implying critical sex differences in CO formation cannot be explained by a
correlation with SC length. I hypothesize that sexual dimorphism in CO rates is the product of key
differences in molecular features of meiotic prophase I, namely the factors that orchestrate meiotic
recombination and chromosome axis assembly. Unlike common laboratory mice (e.g., B6) and humans,
wild-derived PWD male mice have higher CO number despite their shorter SCs, challenging the dogma that
CO rates are inextricably linked to SC length. Thus, I propose to address my hypothesis using mice from
diverse genetic backgrounds to dissect the molecular and genetic factors underlying sexually dimorphic CO
rates. In Aim 1, I will examine dynamic localization of meiotic recombination proteins in male and female PWD
and B6 mice to elucidate how sexually dimorphic CO rates progressively manifest through prophase I. Using
high resolution imaging methods, I will characterize the accumulation of critical DSB repair factors (including
RAD51, RPA2, MSH4, RNF212, and MLH1) to pinpoint sexually dimorphic differences in CO regulation. In
Aim 2, I will evaluate cohesin-mediated chromatin organization in male and female B6 and PWD mice. Using
CUT&Tag to profile REC8 and RAD21L cohesin distributions, I will identify sex differences in cohesin axis
assembly and how they correlate with early DSB repair intermediates. In Aim 3, I will use the recombinant
mouse lines of the Collaborative Cross to map genetic loci associated with sex differences in CO number and
SC length. Collectively, these studies will be the first to examine the molecular and genetic factors that
influence sexually dimorphic CO rate and SC length in diverse mouse genetic backgrounds. Insights gained
from this project will provide critical understanding of why recombination errors are more common in females.
Over the course of this project, I will receive invaluable training in the use of super-resolution microscopy,
computational analysis of genomi...

## Key facts

- **NIH application ID:** 10890160
- **Project number:** 5K99HD112986-02
- **Recipient organization:** CORNELL UNIVERSITY
- **Principal Investigator:** Tegan Sonia-Adeline Horan
- **Activity code:** K99 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $109,022
- **Award type:** 5
- **Project period:** 2023-07-19 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10890160

## Citation

> US National Institutes of Health, RePORTER application 10890160, Uncovering molecular factors driving sexual dimorphism in crossing over in diverse mouse genetic backgrounds (5K99HD112986-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10890160. Licensed CC0.

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