RNA Polymerase III subunit Polr3a is required for craniofacial cartilage and bone development

Area of Science:

• Genetics
• Developmental Biology
• Molecular Biology

Background:

• RNA Polymerase III (Pol III) is crucial for cell functions like ribosome biogenesis and translation.
• Pathogenic variants in Pol III genes cause craniofacial abnormalities.

Purpose of the Study:

• To investigate the role of Pol III in craniofacial development using polr3a mutant zebrafish.
• To understand the molecular mechanisms underlying craniofacial defects caused by Pol III dysfunction.

Main Methods:

• Generation and analysis of polr3a mutant zebrafish.
• Assessment of neural crest cell proliferation, survival, and apoptosis.
• Measurement of transfer RNA (tRNA) transcription and ribosome biogenesis.
• Single-cell RNA-sequencing (scRNA-seq) for tissue-specific transcriptional analysis.
• Tp53 inhibition experiments.

Main Results:

• Polr3a mutants exhibited craniofacial cartilage and bone hypoplasia without changes in early neural crest cell proliferation or survival.
• Increased cell death was observed in the head, particularly in craniofacial cartilage at larval stages.
• Reduced tRNA transcription and ribosome biogenesis were detected in polr3a mutants.
• scRNA-seq revealed global and cartilage-specific transcriptional changes, including tp53 upregulation.
• Tp53 inhibition did not fully rescue the craniofacial phenotype.

Conclusions:

• Pol III is essential for craniofacial development, impacting cartilage and bone formation.
• Pol III dysfunction leads to reduced tRNA transcription, ribosome biogenesis, and increased cell death in craniofacial tissues.
• While tp53 is upregulated, it is not the sole driver of the craniofacial defects, suggesting complex regulatory networks are involved.