# Novel signals regulate cell fate patterning

> **NIH NIH R01** · TEXAS A&M UNIVERSITY HEALTH SCIENCE CTR · 2020 · $311,850

## Abstract

Cell fate patterning of the C. elegans vulva is an ideal system for the study of signal transduction mechanisms.
EGF induces six equipotent vulval precursor cells (VPCs) to assume cell fates in a 3˚-3˚-2˚-1˚-2˚-3˚ pattern with
99.8% accuracy. In the “Morphogen Gradient” model for vulval patterning, distance from the EGF source
dictates the fate of each VPC. In the “Sequential Induction” model, the Ras→Raf→MEK→ERK MAP kinase
cascade induces 1˚ fate, elicits DSL ligand production, and thus, via the LIN-12/Notch receptor, induces its two
neighboring VPCs to become 2˚. Because of the absence of key molecular details, these two models were
debated for 16 years. We resolved this debate: to interpret the EGF gradient, presumptive 2˚ cells use
Ras→RalGEF→Ral rather than the canonical Ras→Raf used in 1˚s. Mutating RalGEF or Ral (a cousin of Ras)
does not confer strong patterning defects, suggesting that sequential induction is the dominant patterning
mechanism. These are clinically relevant molecules: Ras is the most mutated oncoprotein. Ras→RalGEF→Ral
is thought to be equally important for oncogenesis as the canonical Ras→Raf.
 Our central hypothesis is that the Ras→RalGEF→Ral story justifies pursuing unexplored areas of VPC
patterning because clinically important signals are found as positive and negative regulators. The objectives of
this proposal are to unveil new facets of the molecular basis for the 1˚/2˚ fate choice and its high reproducibility
in vivo, exploiting the strengths of this system for dissection of signaling mechanisms. Our preliminary results
support the feasibility of three aims, each with a hypothesis focused on distinct molecular mechanisms.
 Aim 1: Our CRISPR-generated activating mutation in endogenous Rap1 (Ras proximal) induced ectopic 1˚
cells. Lack of Rap1 reduces 1˚ cell induction. We will test the hypothesis that Rap1 is the nexus of two
opposed regulatory inputs that promote and repress ERK activation in presumptive 1˚ vs 2˚ cells, respectively.
 Aim 2: We identified a novel Ral effector, GCK-2/MAP4 kinase, that possibly signals via p38 MAP kinase
to promote 2˚ fate. We will test the hypothesis that Ral→GCK-2 triggers a p38 cascade. We will also test
whether Ral→GCK-2 signal regulates CCCH RNA binding proteins to stabilize 3’UTRs of 2˚-promoting genes.
 Aim 3: MIG-15/MAP4K, the sole paralog of GCK-2/MAP4K, paradoxically inhibits 2˚ fate. We will test the
hypothesis that MIG-15 triggers a JNK MAP kinase cascade, which may be the missing signal that represses
the Notch receptor in presumptive 1° cells. MIG-15 defines a novel class of vulval-specific Notch repressors.
We will make use of the results of a screen we have completed for MIG-15-like targets to identify new players.
 For all three aims we will use CRISPR-engineered endogenous fluorescent reporters to deconvolute
specific signals embedded within the vulval signaling network. Successful completion of these aims will define
components and organizational principles of th...

## Key facts

- **NIH application ID:** 9983490
- **Project number:** 5R01GM121625-04
- **Recipient organization:** TEXAS A&M UNIVERSITY HEALTH SCIENCE CTR
- **Principal Investigator:** David Reiner
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $311,850
- **Award type:** 5
- **Project period:** 2017-08-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9983490

## Citation

> US National Institutes of Health, RePORTER application 9983490, Novel signals regulate cell fate patterning (5R01GM121625-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9983490. Licensed CC0.

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