# FOXI3 establishes the ectodermal niche in pharyngeal arches for cranial neural crest cells and their lineages

## TL;DR

The study shows that FOXI3 helps create a supportive environment for cranial neural crest cells in the pharyngeal arches, which is important for facial development.

## Contribution

The study reveals that FOXI3 establishes an ectodermal niche for cranial neural crest cells and their lineages, which was previously unknown.

## Key findings

- FOXI3 is not directly involved in regulating cranial neural crest cells but is crucial for the ectodermal niche.
- FOXI3 deficiency in the ectoderm reduces cytokines like TGF-β1, affecting neural crest cell proliferation.
- FOXI3 regulates genes related to translation and cytokine production in epidermal cells.

## Abstract

Craniofacial development relies on the migration of cranial neural crest cells (CNCCs) to the first and second pharyngeal arches, followed by their differentiation into various cell types during embryogenesis. Although the CNCC migration has been well-studied, the role of the niche in relation to CNCC remains unclear. Variants in FOXI3 have been implicated in craniofacial microsomia (CFM), yet the molecular mechanisms remain unexplored. FOXI3 is expressed in the ectoderm and auricle epidermis, but not in CNCCs or cartilage. Deletion of Foxi3 in the mouse CNCCs did not disrupt mandible and auricular development, further confirming that FOXI3 does not directly regulate CNCCs. However, Foxi3 deficiency in the ectoderm reduced the production of chondrogenesis-related cytokines derived from ectodermal cells, such as TGF-β1. This impairment affected CNCC proliferation through cell communication, subsequently altering the development of the mandible and auricle. These results emphasize the critical role of FOXI3 in establishing the microenvironment supporting CNCC function. Furthermore, FOXI3 directly regulates target genes associated with translation, thereby orchestrating cytokine production in epidermal cells. The validation using auricle sample from a CFM patient carrying FOXI3 mutation further supports our findings. These insights highlight the function of FOXI3 in creating the niche necessary for CNCC development and provide a basis for understanding the molecular mechanisms driving CFM pathogenesis.