# Role of phosphorylation in regulating morphogen dynamics

> **NIH NIH R03** · CALIFORNIA INSTITUTE OF TECHNOLOGY · 2020 · $83,250

## Abstract

SUMMARY
During embryogenesis, tissues must be correctly patterned in order to properly develop. The fruit fly embryo is
patterned along the dorsal-ventral (DV) axis by the morphogen Dorsal, a transcription factor that forms a nuclear
concentration gradient with high levels present ventrally and little to none present dorsally. Dorsal protein is also
known to be phosphorylated; however, it is unknown where the phosphorylation occurs, and whether it plays an
important role in development. Both Dorsal, and the protein that binds and inhibits it, Cactus, are downstream of
the Toll receptor. The textbook view is that Toll signaling acts only on Cactus, whereas we hypothesize that Toll
signaling may also act to phosphorylate Dorsal. Study of the regulatory relationships of these three factors may
elucidate general signaling mechanisms in which an activated signaling complex phosphorylates both inhibitor
(Cactus protein which retains Dorsal in the cytoplasm) and activator (Dorsal transcription factor that functions in
the nucleus to turn on gene expression upon being freed from Cactus). We propose that this regulatory circuit
acts to shape the developmentally appropriate cellular response required for patterning the DV axis: fast increase
in Dorsal nuclear levels to support zygotic transcription across the DV axis followed by a precipitous drop in
Dorsal nuclear levels at the onset of gastrulation once patterning is complete. To provide support for this
hypothesized alternate role of Toll signaling in the regulation of Dorsal activity through phosphorylation, our
proposal has two experimental aims. The goal of Aim 1 is to determine if phosphorylation of C-terminal serines
alters Dorsal protein function or key, Dorsal-dependent developmental outcomes; whereas the goal of Aim 2 is
to discern the relationship between Toll signaling and Dorsal C-terminal phosphorylation. The overarching goal
of the proposed research is to probe the mechanisms by which signaling pathways regulate transcription factor
dynamics, and how this leads to the proper morphogenesis of tissues. Phosphorylation as a result of Toll
signaling may serve to both increase nuclear residence of Dorsal and degrade Cactus, which frees Dorsal to
enter the nucleus. This dual role would represent a signaling mechanism that functions to amplify a specific
downstream outcome and may allow the cell or embryo to perform a nuanced regulatory computation. The
insights gained here will set the groundwork for additional studies of regulation of signaling and transcription
factor dynamics by phosphorylation. Specifically, the mammalian homolog of Dorsal, NF-kB, is also
phosphorylated, is important for diverse developmental processes such as inflammation during the immune
response, and has been implicated in cancer. Therefore, understanding where Dorsal is phosphorylated and
how this post-translational modification affects its function has the potential for far-reaching insights.

## Key facts

- **NIH application ID:** 9958849
- **Project number:** 1R03HD101961-01
- **Recipient organization:** CALIFORNIA INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Angelike Stathopoulos
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $83,250
- **Award type:** 1
- **Project period:** 2020-03-15 → 2022-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9958849

## Citation

> US National Institutes of Health, RePORTER application 9958849, Role of phosphorylation in regulating morphogen dynamics (1R03HD101961-01). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9958849. Licensed CC0.

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