Genome-Wide Binding Analyses of HOXB1 Revealed a Novel DNA Binding Motif Associated with Gene Repression

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Transcription factors regulate gene expression crucial for animal development and evolution.
• HOXB1 is a member of the HOX family of transcription factors with known roles in development.
• Understanding DNA binding specificities is key to deciphering regulatory functions.

Purpose of the Study:

• To investigate the genome-wide DNA binding properties of mouse HOXB1 during neural differentiation.
• To identify novel binding partners and DNA motifs associated with HOXB1 function.
• To elucidate the regulatory roles of HOXB1, including its interactions with cofactors and repressors.

Main Methods:

• Genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) to map HOXB1 binding sites.
• Analysis of co-occupancy with known HOX cofactors (PBX, MEIS) and the repressor REST.
• Histone mark analysis to correlate HOXB1 binding with active or repressive chromatin states.
• In vitro DNA binding assays and reporter gene assays to characterize the novel HOXB1 binding motif (HB1RE).

Main Results:

• HOXB1 binding is unexpectedly divergent, with limited co-occupancy (7%) by PBX/MEIS but significant co-occupancy (22%) by REST.
• HOXB1/PBX co-binding correlates with active marks and gene activation, while HOXB1/REST co-binding associates with repressive marks and gene repression.
• A novel 15 bp motif, HB1RE, is identified as a direct HOXB1 binding site.
• HB1RE is sufficient for reporter gene expression, which is repressed by HOXB1 overexpression, indicating a repressive role.

Conclusions:

• HOXB1 exhibits diverse DNA binding specificities, interacting with both activators and repressors.
• HOXB1 has evolved an association with the transcriptional repressor REST for gene regulation.
• The novel HB1RE motif plays a role in HOXB1 function, particularly in gene repression.