# Bridging the gap between transcriptional activation and cell fate specification in the Drosophila visual system

> **NIH NIH R00** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2021 · $241,529

## Abstract

Cell fate specification occurs through the tightly regulated expression of key transcription factors at precise
levels, times, and places during development. The expression of these determinants is controlled by
enhancers and promoters. This proposal focuses on two cases where the level and timing of gene expression
are especially important for cell fate specification in the Drosophila visual system. A number of mutations have
been shown to cause abnormal gene regulation and cell fate, making a better understanding of these
processes highly relevant to understanding the genetic basis of disease.
Live imaging of stochastic gene activation in the visual system: In Aim 1, I will examine the stochastic
specification of cell fate in the Drosophila retina, where otherwise equivalent R7 photoreceptor precursors have
a particular probability of taking one of two fates important for color vision. This decision is controlled by the
stochastic, cell-intrinsic expression of the transcription factor Spineless. I will examine two possible sources of
spineless stochasticity: variability in transcriptional activation at the level of the promoter, and variation in
chromatin accessibility. In order to quantify the underlying transcriptional dynamics, I will image gene
expression in real time using the MS2 and PP7-based live transcriptional imaging systems. MS2 live imaging
has recently revolutionized the study of gene regulation in the Drosophila embryo by providing a new level of
quantitative measurement. This approach combined with direct tagging by CRISPR/Cas9 of the spineless
locus will allow me to determine the origin of stochasticity in this cell fate decision.
Factors that influence stochastic fate: In Aim 2, I will directly test two models that predict how different
factors influence the probability of spineless expression. To directly test the role of transcriptional initiation vs.
chromatin state, I will modify the spineless basal promoter using CRISPR/Cas9 by replacing it with
characterized promoters that have been shown to initiate expression more or less robustly in the Drosophila
embryo, for instance through recruitment of paused RNA Polymerase II. This will allow me to test the role of
the promoter in stochastic fate decisions. If stochastic outcomes are unaffected by such changes, I will test the
role of local chromatin state via local, targeted changes in chromatin state to evaluate the effect on the
stochastic ratio of fates produced. This approach will be complemented by live imaging of transcription, which
will provide an additional means of assessing the quantitative effects of specific modifications.
Studying the role of transcriptional timing and levels in temporal transitions in neuroblast fate: Aim 3
will examine a series of temporal transitions between five different transcription factors in medulla neuroblasts
that generate neural diversity in the fly brain. Although we know that there is cross regulation among these
temporal transcripti...

## Key facts

- **NIH application ID:** 10104508
- **Project number:** 5R00EY027016-05
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** Michael William Perry
- **Activity code:** R00 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $241,529
- **Award type:** 5
- **Project period:** 2016-09-01 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10104508

## Citation

> US National Institutes of Health, RePORTER application 10104508, Bridging the gap between transcriptional activation and cell fate specification in the Drosophila visual system (5R00EY027016-05). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10104508. Licensed CC0.

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