# Identification of an FGF-regulated signaling center in the Groove of Ranvier that controls longitudinal bone growth.

> **NIH NIH R21** · WASHINGTON UNIVERSITY · 2024 · $165,919

## Abstract

ABSTRACT
 Growing bones contain a circumferential anatomical structure called the groove of Ranvier (GOR) that may
contain skeletal stem cells and signaling cells critical to skeletal development. Clinically, the GOR is important
as pediatric fractures involving the GOR (Salter-Harris type II) often affect longitudinal bone growth. However,
the identity and functional properties of cells within the GOR that regulate longitudinal bone growth are not
known. Our preliminary data suggest that Fibroblast Growth Factor Receptors (FGFRs) within the GOR
contribute to a “signaling center” that regulates adjacent growth plate chondrocytes and longitudinal bone growth.
This observation establishes a functional link between cells in the GOR and the growth plate and has implications
for the pathogenesis of pediatric physeal fractures. We refer to these poorly defined cells as the “GOR signaling
center”.
 Conditional inactivation of Fgfr1 and Fgfr2 with the Osx-Cre transgene (Osx-Cre, DCKO mice) results in
decreased longitudinal bone growth in postnatal mice. Through an unknown feedback mechanism, this
inactivation also results in increased Fgf9 expression in the fibrous capsule and perichondrium, which is in close
proximity to the GOR. Experimentally, we showed that expression of FGF9 in the perichondrium can activate
FGFR3 in adjacent proliferating chondrocytes to suppress chondrogenesis.
 By regulating the expression of Osx-Cre, we show that Cre must be active during embryonic development
to elicit this postnatal growth phenotype. Significantly, embryonic, but not postnatal, expression of Osx-Cre
specifically targets the GOR. These data functionally define the region encompassing the GOR as the location
of a critical FGFR1/2 signaling center by showing that inactivation of Fgfr1/2 in an embryonic cell lineage that
gives rise to the GOR, rather than in definitive osteoblasts, is responsible for the dramatic reduction in bone
growth observed in Osx-Cre, DCKO mice.
 In specific aim 1, we will use lineage tracing to differentially label the GOR and single cell mRNA sequencing
to identify cell sub-populations within the GOR that have signaling center and/or skeletal stem cell properties.
Identification of selective markers for these cell sub-populations will be used to reveal their location relative to
the anatomical GOR. In specific aim 2, we will characterize the signaling properties of GOR cells for their ability
to regulate osteogenesis and chondrogenesis. The studies proposed here will identify unique features of GOR
cells as a potential cell signaling center with the unique ability to regulate adjacent growth plate tissue. These
studies will provide mechanistic insight into why a large percentage of pediatric physeal fractures result in growth
arrest despite theoretically preserving the proliferating chondrocytes and their intact blood supply. These studies
will provide new genetic tools to study the GOR in future grant proposals and potential therapeutic ...

## Key facts

- **NIH application ID:** 10851938
- **Project number:** 5R21AR082001-02
- **Recipient organization:** WASHINGTON UNIVERSITY
- **Principal Investigator:** David M Ornitz
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $165,919
- **Award type:** 5
- **Project period:** 2023-06-01 → 2025-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10851938

## Citation

> US National Institutes of Health, RePORTER application 10851938, Identification of an FGF-regulated signaling center in the Groove of Ranvier that controls longitudinal bone growth. (5R21AR082001-02). Retrieved via AI Analytics 2026-06-03 from https://api.ai-analytics.org/grant/nih/10851938. Licensed CC0.

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