# Overcoming Barriers to Pluripotency Reprogramming

> **NIH NIH P01** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2020 · $439,364

## Abstract

Project summary 
 The goal of this proposal is to understand how heterochromatin can physically impede the binding of 
activator proteins and thus impede cellular reprogramming to pluripotency and other fate changes. Of all 
the forms of directed conversion of one cell fate to another, the conversion of somatic cells to pluripotency 
(iPS) is the most robust. Yet all forms of cell type conversion, including to iPS cells, remain inefficient, 
with a stochastic period that precedes a deterministic, developmental path to the terminal state. Various 
screens have identified genes whose impairment results in enhanced cell fate conversion, yet the 
underlying mechanisms are often obscure. We discovered a specific epigenetic impediment, H3K9me3- 
based heterochromatin, whose mechanism of action is by physically blocking the binding of 
reprogramming transcription factors. H3K9me3-heterochromatin blankets genes at the top of a 
developmental hierarchy, explaining how loss of H3K9me3 promotes cell conversion. We now find that 
such domains can explain deficiencies in direct cell reprogramming to other fates, demonstrating the 
generality of the mechanism. Dynamics in H3K9me3 heterochromatin are also involved in X chromosome 
inactivation, which we will investigate with Kathrin Plath. We developed methods to physically isolate 
H3K9me3-heterochromatin from somatic cells, determine its protein composition, and perform functional 
screens, thereby establishing our premise that heterochromatic proteins play selective roles in impairing 
the ability of H3K9me3-embedded genes to be induced by reprogramming transcription factors. Relevant 
proteins overlap with studies of Konrad Hochedlinger. The central theme guiding this proposal, based on 
our latest data, is that there are different heterochromatin complexes blocking different sets of protein 
coding genes, and that by understanding the composition and function of such complexes, we will change 
cell fate far more selectively and efficiently than by targeting all H3Kme3-based heterochromatin. We 
therefore propose: 
 Aim 1. We will identify heterochromatin components and specific genomic complexes that impede the 
action of reprogramming transcription factors and, with K. Plath, that maintain an inactive X chromosome. 
 Aim 2. We will define the function of heterochromatin components and subcomplexes, including those 
involved in RNA processing and others with K. Hochedlinger. 
 Our mechanistic understanding will provide a more rational and selective ability to activate different 
types of heterochromatic genes, and thereby more specifically enhance cellular reprogramming for 
disease models and cell therapeutics in the future.

## Key facts

- **NIH application ID:** 9930460
- **Project number:** 5P01GM099134-09
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** Kenneth Zaret
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $439,364
- **Award type:** 5
- **Project period:** — → —

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9930460

## Citation

> US National Institutes of Health, RePORTER application 9930460, Overcoming Barriers to Pluripotency Reprogramming (5P01GM099134-09). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9930460. Licensed CC0.

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