# Lmo2-Lyl1 and the bHLH factor network in pro-T cells

> **NIH NIH R01** · CALIFORNIA INSTITUTE OF TECHNOLOGY · 2022 · $613,350

## Abstract

PROJECT SUMMARY
The progression of T cell precursors from multipotency to commitment occurs after multiple cell cycles in the
thymus. These early, pre-commitment cell cycles are important for expansion of the precursors to generate
enough pro-T cells to survive later selection events. However, the early stages are poorly understood, and in
particular it has not been clear what controls the precise trajectory of the cells' differentiation nor the timing or
irreversibility of commitment when it occurs. Genomic regulatory elements that are active after commitment
tend to be characterized by motifs for basic helix-loop-helix (bHLH) E proteins, E2A or HEB, whereas those
that are active before commitment have other signatures, suggesting that there is a major increase in E protein
activity across this transition. In fact, the expression of E proteins is almost equally high before commitment,
but our recent data show that they are occupied in substantially different roles before commitment, in
complexes with other heterodimerization partners. This proposal is based on recent evidence that the
alternative complex, containing Lmo2 and Lyl1 dimerized with E2A or HEB, may actually be a major controller
of the commitment transition in early T cells. Our recent evidence shows that expression of Lmo2 and Lyl1 is
sufficient to make committed pro-T cells reverse their differentiation in terms of gene expression. Not only
does the Lmo2/Lyl1/E2A complex bind to different genomic sites than E protein dimers, but also the addition of
Lmo2 and Lyl1 to committed pro-T cells is sufficient to remove E proteins from sites that they occupy after
commitment and shift them to sites that are normally active only before commitment. The implication is that
the kinetics of downregulation of Lmo2 and Lyl1 in normal T-cell differentiation could be vital for determining
the timing of commitment and of the maturation of the pro-T cells. Lmo2 and Lyl1 have been considered as T-
lineage proto-oncogenes, but our evidence suggests a potent role in normal development.
This proposal is to determine the mechanism of how this works and to test its significance for the actual
developmental dynamics of normal early T cells. Our preliminary work identifies the signature target genes
affected by Lmo2+Lyl1 and their overlap with genes expressed in normal pro-T cells. We now propose to
define: (1) the distinct molecular mechanisms that control different subsets of these signature genes, based on
genome-wide mapping of the chromatin state changes caused by Lmo2+Lyl1/E protein complex binding as
compared to pure E protein dimer binding; (2) whether endogenous Lmo2/Lyl1/E protein complexes indeed
control differentiation kinetics and commitment of normal pro-T cells, based on acute CRISPR and monitoring
in vitro and in vivo; and (3) the gene regulatory network architecture, involving factors regulated by Lmo2+Lyl1,
through which Lmo2+Lyl1 exert their surprisingly broad impacts on T cell development....

## Key facts

- **NIH application ID:** 10427443
- **Project number:** 5R01AI151704-02
- **Recipient organization:** CALIFORNIA INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** ELLEN V. ROTHENBERG
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $613,350
- **Award type:** 5
- **Project period:** 2021-06-15 → 2026-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10427443

## Citation

> US National Institutes of Health, RePORTER application 10427443, Lmo2-Lyl1 and the bHLH factor network in pro-T cells (5R01AI151704-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10427443. Licensed CC0.

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