Splicing Defects and Cell Death Cause SF3B2-Linked Craniofacial Microsomia

Area of Science:

• Genetics
• Developmental Biology
• Molecular Medicine

Background:

• Craniofacial microsomia (CFM) is a heterogeneous disorder with variable facial hypoplasia.
• Loss-of-function variants in SF3B2 are an emerging genetic cause of CFM.
• The precise mechanisms underlying SF3B2-related CFM are not fully understood.

Purpose of the Study:

• To define the phenotypic spectrum of SF3B2 variants in CFM.
• To elucidate the molecular mechanisms of SF3B2 dysfunction in craniofacial development.

Main Methods:

• Identified novel SF3B2 loss-of-function variants in five new CFM families.
• Generated sf3b2-null mutant zebrafish to study craniofacial development.
• Created SF3B2-variant human induced pluripotent stem cells (hiPSCs) using CRISPR/Cas9.
• Performed RNA sequencing on mutant zebrafish and differentiated hiPSCs.

Main Results:

• SF3B2 variants were identified in five new CFM families.
• sf3b2 mutant zebrafish showed craniofacial cartilage and bone progenitor deficiencies due to apoptosis and reduced proliferation of cranial neural crest cells.
• SF3B2-variant hiPSCs exhibited increased cell death and reduced proliferation during neural crest differentiation.
• RNA sequencing revealed widespread mRNA splicing disruption in sf3b2 mutants, affecting genes like mdm2.
• Tp53 inhibition reduced apoptosis but did not rescue proliferation or craniofacial development in mutants.

Conclusions:

• Widespread mRNA splicing disruption is a key mechanism in SF3B2-related CFM.
• Tp53-dependent apoptosis contributes to the craniofacial defects.
• SF3B2 variants impact cranial neural crest cell development through both splicing defects and cell death pathways.