Mutation in PHC1 implicates chromatin remodeling in primary microcephaly pathogenesis.

Area of Science:

• Genetics
• Developmental Biology
• Neuroscience

Background:

• Primary microcephaly (PM) is a severe neurodevelopmental disorder characterized by reduced brain size, particularly the cerebral cortex.
• The underlying genetic causes of PM are diverse, highlighting the complexity of early brain development.

Purpose of the Study:

• To investigate the genetic basis and cellular mechanisms of a novel form of primary microcephaly.
• To identify the specific gene and mutation responsible for PM in a consanguineous family.

Main Methods:

• Autozygosity mapping and exome sequencing were employed to identify the causative genetic variant.
• Functional assays were conducted on patient-derived cells expressing wild-type and mutant PHC1.
• Cellular processes including protein expression, histone modification, cell cycle progression, and DNA damage repair were analyzed.

Main Results:

• A novel mutation in PHC1, a polycomb group gene, was identified as the cause of PM.
• The mutation leads to decreased PHC1 protein, increased Geminin levels, and impaired histone H2A ubiquitination in patient cells.
• Patient cells exhibit cell cycle defects and aberrant DNA damage repair, which are rescued by PHC1 re-expression.

Conclusions:

• The findings reveal that mutations in PHC1 disrupt chromatin remodeling, leading to cellular defects underlying primary microcephaly.
• This study underscores the critical role of PHC1 and histone ubiquitination in neurodevelopment and cell cycle regulation.
• Aberrant DNA damage repair is a newly identified cellular consequence of PHC1 mutations in PM.