# Collaboration between actin nucleators - Spire and Cappuccino

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2021 · $315,697

## Abstract

Project Summary/Abstract
 Cell polarity is essential to an array of processes, including transport of nutrients across epithelial layers,
chemotaxis, and development. Thus, defects in polarization can have dire physiological consequences. The
overarching goal of this proposal is to understand the role(s) of actin in polarity establishment in the developing
egg. Cytoplasmic actin meshes are observed in oocytes of mouse, Drosophila, starfish, and C. elegans, which
suggests meshes are a conserved feature that have diverged functionally, in some cases. The Drosophila oocyte
is an ideal system in which to study the actin mesh because the ovaries are large, facilitating cell biological and
biochemical examination in a genetically tractable model organism. The presence of the actin mesh and its
correctly timed removal are critical to polarity establishment. Little is known about the mesh makeup beyond the
two actin nucleators required to build it, Spire and Cappuccino, and a molecular motor that colocalizes with Spire
on vesicles, myosin V. Our knowledge about the mesh is limited by two technical challenges: 1) several stages
of oogenesis do not take place ex vivo and 2) many actin-binding proteins are essential to early oogenesis,
diminishing the power of classical genetics to discover mesh components necessary during mid-oogenesis. We
are developing an intra vital imaging platform to address both issues. Intra vital imaging will facilitate long-term,
direct observation of the mesh and its disappearance within the animal. When combined with Crispr/Cas9-
mediated gene editing and auxin-inducible-degradation, we will be able to observe changes in the mesh upon
removal of specific proteins in a temporally controlled manner. We will use these tools to test the hypothesis that
the mesh slows fluid flows to facilitate formation of a posterior anchoring structure that is necessary for polarity
establishment and fails to form when fluid flows are prematurely accelerated, as is the case if the mesh is
compromised. A comparable actin mesh, also built by Spire, Cappuccino, and myosin V, was recently discovered
in a somatic cell, the dendritic melanocyte. Interestingly, in the mouse oocyte, the mesh moves vesicles towards
each other and the periphery of the cell, whereas, in the melanocyte, the mesh moves vesicles apart, dispersing
them throughout the cell. By combining in vivo experiments with in vitro reconstitution of the mesh, we will
determine how the same set of proteins can drive vesicles in opposite directions in mouse oocytes and
melanocytes and determine how the mesh is built in the Drosophila oocyte. Finally, we will examine the
consequences of the recently-discovered interaction between Spir and myosin V, using complementary
biochemical and genetic approaches. Coordination between an actin nucleator and an actin-based motor has
exciting implications for how the mesh and other structures are built. Upon completion of this work, we will have
established ...

## Key facts

- **NIH application ID:** 10314737
- **Project number:** 2R01GM096133-10A1
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** Margot E Quinlan
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $315,697
- **Award type:** 2
- **Project period:** 2011-09-01 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10314737

## Citation

> US National Institutes of Health, RePORTER application 10314737, Collaboration between actin nucleators - Spire and Cappuccino (2R01GM096133-10A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10314737. Licensed CC0.

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