Mutations in genes encoding condensin complex proteins cause microcephaly through decatenation failure at mitosis

Area of Science:

• Genetics
• Cell Biology
• Developmental Biology

Background:

• Chromosome condensation is vital for accurate genome segregation during mitosis.
• Two main condensin complexes in vertebrates regulate chromosome structure and DNA disentanglement.
• Defects in these processes can lead to developmental abnormalities.

Purpose of the Study:

• To investigate the role of condensin complex subunits in microcephaly.
• To identify the molecular mechanisms underlying microcephaly caused by condensin gene mutations.
• To establish condensinopathies as a class of microcephalic disorders.

Main Methods:

• Analysis of biallelic mutations in NCAPD2, NCAPH, and NCAPD3 genes.
• Phenotypic characterization of hypomorphic Ncaph2 mice.
• Examination of neural progenitor cells from patients and mice for DNA bridges and aneuploidy.

Main Results:

• Biallelic mutations in NCAPD2, NCAPH, or NCAPD3 cause microcephaly.
• Hypomorphic Ncaph2 mice exhibit reduced brain size and DNA bridges in neural progenitors.
• Condensin deficiency leads to failed sister chromatid disentanglement, resulting in chromosome segregation errors, micronuclei, and aneuploidy.

Conclusions:

• Condensinopathies are a newly defined group of microcephalic disorders.
• Failure in sister chromatid decatenation is a novel mechanism contributing to microcephaly.
• Mitotic chromosome condensation is crucial for mammalian cerebral cortex development and size.