PBX1 and PBX3 transcription factors regulate SHH expression in the Frontonasal Ectodermal Zone through complementary...

Area of Science:

• Developmental Biology
• Molecular Genetics
• Craniofacial Development

Background:

• Sonic hedgehog (SHH) signaling is vital for craniofacial morphogenesis.
• Pre-B-cell leukemia homeobox (PBX) transcription factors are implicated in midfacial development.
• The precise interaction between PBXs and SHH in facial development remains unelucidated.

Purpose of the Study:

• To investigate the hypothesis that PBX1 and PBX3 regulate SHH expression in the Frontonasal Ectodermal Zone (FEZ).
• To identify direct interactions between PBX1/3 and the SHH locus.
• To characterize the regulatory role of PBX1/3 in SHH-mediated craniofacial development.

Main Methods:

• Perturbation of PBX1/3 expression in chick embryos using RCAS viruses.
• Epigenomic profiling including ATAC-seq and ChIP-seq on the FEZ.
• Reporter assays (in ovo electroporation and in vitro luciferase) to assess enhancer activity.

Main Results:

• PBX1 and PBX3 exhibit opposing effects on SHH expression domains.
• A novel 400 bp PBX1-enriched element (SFE1) in the SHH intron was identified.
• SFE1 functions as a cis-regulatory element, upregulating SHH when bound by PBX1 and downregulating when bound by PBX3.

Conclusions:

• PBX1 and PBX3 play complementary and direct roles in modulating SHH expression within the FEZ.
• The identified SFE1 element is a key regulatory region controlled by PBX1/3.
• This study elucidates a novel mechanism of SHH regulation critical for craniofacial development.