Homologous chromosome dynamics in mouse oocytes

The National Institute of Child Health and Human Development awarded Oklahoma Medical Research Foundation $468,875 on August 1, 2026, under the Child Health and Human Development Extramural Research program (CFDA 93.865) to investigate homologous chromosome dynamics in mouse oocytes.

The research addresses aneuploidy, which occurs in 10 to 30 percent of human gametes and typically results from chromosome segregation errors during meiosis, leading to pregnancy loss or genetic disorders such as Down's Syndrome. The project develops a fluorescence reporter-operator system based on the lac operator-lac repressor paradigm to enable protein targeting to specific genomic regions and elucidate mechanisms regulating chromosome segregation during female meiosis.

Aim 1 employs the system to study telomere-led rapid chromosome motions in developing mouse oocytes at prophase I, testing the hypothesis that dynein and/or kinesin walking on microtubules generates primary forces for these motions, transmitted to telomeres through the nuclear membrane by the LINC complex. The research uses immunocytochemistry in whole-mounted ovaries, mutant mice, and small molecule inhibitors to reconstruct the machinery supporting and regulating these motions. Aim 2 examines homologous chromosome pairing in real time using four-dimensional fluorescence imaging of tagged chromosomal loci at high spatiotemporal resolution in intact mouse ovaries to test existing alternative pairing models.

Performance occurs at Oklahoma City, Oklahoma. The award period runs from August 1, 2026, through July 31, 2028.

Abstract

Aneuploidy, the presence of an abnormal number of chromosomes in a cell, often leads to pregnancy loss or disorders such as down's syndrome. This condition occurs in 10-30% of human gametes and typically results from chromosome segregation errors during meiosis. Proper chromosome segregation is ensured by meiotic events like homologous chromosome pairing, but the mechanisms regulating these events are not fully understood. As a result, there are currently few strategies to predict or prevent aneuploidy during gametogenesis. To address these challenges, we are developing a fluorescence reporter-operator system (fros) based on the LAC operator-LAC repressor (laco-lacr) paradigm, which enables protein targeting to specific genomic regions. Our long-term goal is to elucidate the mechanisms regulating chromosome segregation during female meiosis, ensuring the formation of oocytes with a normal karyotype. In aim 1, we use fros to study telomere-led rapid chromosome motions (rpms) in developing mouse oocytes at prophase i. Building on our preliminary data, we will employ immunocytochemistry in whole-mounted ovaries, along with mutant mice and small molecule inhibitors, to reconstruct the machinery supporting and regulating rpms in oocytes. We will test the hypothesis that dynein and or kinesin walking on microtubules generates the primary forces for rpms, transmitted to telomeres through the nuclear membrane by the linc complex (SUN1/SUN2-KASH5). Our data will reveal how rpms are generated and regulated in mouse oocytes, a process not yet understood, and explain fundamental differences we observed between oocytes and spermatocytes. In aim 2, we propose to examine homologous chromosome pairing in real time using 4D fluorescence imaging of tagged chromosomal loci at high spatio- temporal resolution in intact mouse ovaries. Here, we will test existing alternative models for homologous chromosome pairing. Additionally, we will use fros in mutant oocytes to determine how the linc complex (rpms), synaptonemal complex (SYCP1), and proteins required for recombination (SPO11 and DMC1) affect long-term homologous and non-homologous chromosome interactions. This research will be the first to discern how meiotic chromosome dynamics affect chromosome segregation mechanisms in mammalian oocytes, advancing our understanding of fundamental meiotic processes and the causes of aneuploidy.