# Molecular Mechanisms Guiding TRIM28 Contribution to Determination

> **NIH NIH F31** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2024 · $20,816

## Abstract

Project Summary/ Abstract:
Primordial Germ Cells (PGCs) are embryonic precursors to the adult germline, the proper development of which
is tantamount to organismal fitness. During embryonic development PGCs undergo two fate-restriction steps: 1)
specification, in which PGCs express pluripotent genes, a state called latent pluripotency, while undergoing
myriad epigenetic remodeling and 2) determination, in which the pluripotency program is extinguished and PGCs
differentiate according to the sex of the embryo. While molecular studies have carefully dissected PGC
specification, PGC determination remains poorly understood. Although the current state-of-the-art allows in vitro
induction of PGC-Like-Cells (PGCLCs) from pluripotent stem cells (PSCs), these PGCLCs represent specified
PGCs and, thus far, cannot be reliably induced to undergo determination in vitro. This constitutes a significant
roadblock for in vitro gametogenesis, which offers a possibility for clinical relief of infertility in couples where
either partner is unable to produce their own gametes. We hypothesize that specific epigenetic changes drive
PGC determination and license gametogenic capacity. Of particular interest during this process is the regulation
of Transposable Elements (TEs), some of which remain capable of transposition and therefore threaten the
integrity of the germline genome. Conversely, some TEs of the Long Terminal Repeat (LTR) subclass harbor
transcription- and pluripotency- factor binding sites and could function during the time of determination to regulate
expression of the pluripotency network. To understand how regulation of LTR elements contributes to PGC
determination we employ an in vitro mouse model. The central hypothesis of this proposal is that PGC
determination is an epigenetic transition that is reliant on TRIM28, a highly conserved epigenetic scaffolding
protein, for two independent processes: regulation of LTR-class transposable elements and proper nucleolar
function. To test this, we will employ a PGC-specific conditional knockout model of TRIM28, allowing us to
interrogate determination in vivo. In Aim 1, I will use ATAC-seq and CutnTag sequencing to understand how loss
of TRIM28 alters genome accessibility and enhancer dynamics, hypothesizing that misregulation of LTR
elements in the absence of TRIM28 drives a failure to correctly regulate the switch in gene expression networks
as PGCs enter determination. In Aim 2, I use OligoPaint, a DNA-FISH approach, to assess how TRIM28 loss
effects nucleolar heterochromatin and morphology, and use chemical perturbation ex vivo to observe possible
phenocopy with loss of TRIM28. Completion of this work will have broad implications in our understanding of
how the PGC epigenome is rewired during determination to license gametogenesis. Insights from this work can
be leveraged to advance in vitro PGC models towards functional gametogenesis.

## Key facts

- **NIH application ID:** 10899499
- **Project number:** 5F31HD113346-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** Jonathan Adam DiRusso
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $20,816
- **Award type:** 5
- **Project period:** 2023-07-06 → 2025-01-05

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10899499

## Citation

> US National Institutes of Health, RePORTER application 10899499, Molecular Mechanisms Guiding TRIM28 Contribution to Determination (5F31HD113346-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10899499. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*