# Understanding how Connexin43 regulates joint formation in the regenerating zebrafish fin

> **NIH NIH R15** · LEHIGH UNIVERSITY · 2021 · $483,000

## Abstract

Summary
Synovial joints are critical for skeletal form and function, but are susceptible to debilitating diseases such as
osteoarthritis and injury. While much is known about the composition and mechanics of functioning joints,
relatively little is known about how joint-forming cells (JFCs) are specified in a particular location, thereby
permitting the development of joints that provide flexibility. Addressing this gap in knowledge could facilitate the
development of novel therapies for joint disease by targeting molecular pathways influencing cell fate
decisions. The zebrafish regenerating fin is an important model system for addressing fundamental questions
of skeletal development, including the specification and commitment of JFCs. The fin skeleton is made of bony
fin rays, and each fin ray is made of bony segments separated by joints. Thus, the fin is a rich source of joints,
which are produced regularly during typical outgrowth and during regeneration. The osteoblasts and JFCs that
build the fin skeleton are derived from a common skeletal precursor cell (SPC) located in the lateral fin ray
mesenchyme. Recent studies from the Iovine lab provide strong evidence that Connexin43 (Cx43), via gap
junctional intercellular communication (GJIC), influences JFC specification by suppressing expression of evx1.
Evx1 is a transcription factor required for joint formation. The overall objectives for this proposal are to reveal
the nature of Cx43-GJIC, and to reveal the subsequent mechanism of evx1 suppression. The central
hypothesis of this proposal is that Cx43-GJIC influences joint formation by transducing changes in
membrane potential to the SPCs; changes in membrane potential in turn trigger changes in gene
expression that influence evx1 expression, JFC specification, and joint formation. This hypothesis was
formulated on the basis of prior and preliminary data. For example, Cx43-GJIC promotes simplet (smp)
expression in SPCs. Smp is required to bring -catenin to the nucleus. In concert with Lef1 or TCF7
transcription factors, -catenin (directly or indirectly) suppresses evx1 transcription. The Aims of this proposal
are designed to test the central hypothesis. Aim 1 is to test if changes in membrane resting potential are
sufficient to influence gene expression in SPCs. This will be accomplished by driving membrane
hyperpolarization or depolarization in Cx43-expressing cells, and evaluating smp and evx1 expression in
SPCs. Aim 2 is to identify cis-regulatory elements (CREs) that influence evx1 transcription. Putative CREs will
be deleted from a BAC reporter for evx1, and impacts on reporter expression will be assessed to reveal likely
enhancers or silencers acting on evx1. Completion of these Aims will significantly advance our understanding
of signals mediated by GJIC influencing cell specification, and will further provide novel insights into the
spatiotemporal regulation of JFC specification.

## Key facts

- **NIH application ID:** 10291593
- **Project number:** 2R15HD080507-03
- **Recipient organization:** LEHIGH UNIVERSITY
- **Principal Investigator:** Mary Kathryn Iovine
- **Activity code:** R15 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $483,000
- **Award type:** 2
- **Project period:** 2015-08-15 → 2025-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10291593

## Citation

> US National Institutes of Health, RePORTER application 10291593, Understanding how Connexin43 regulates joint formation in the regenerating zebrafish fin (2R15HD080507-03). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10291593. Licensed CC0.

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