Biology subjects

Little, J. N.

Publications and source records attributed to Little, J. N..

3 recordsLinked to original sources

bioRxiv2020

Loss of coiled-coil protein Cep55 impairs abscission processes and results in p53-dependent apoptosis in developing cortex

To produce a brain of normal size and structure, embryonic neural stem cell (NSCs) must tightly regulate their cell divisions. Cerebral cortex NSCs undergo a polarized form of cytokinesis whose regulation is poorly understood. Cytokinetic abscission severs the daughter cells and is mediated by the midbody at the apical membrane. Here we elucidate the role of the coiled-coil midbody protein Cep55 in NSC abscission and brain development. A knockout of Cep55 in mice causes microcephaly with reduced NSCs and neurons, but relatively normal body size. Fixed and live analyses show NSCs lacking Cep55 have decreased but not eliminated ESCRT recruitment, and have abnormal abscission and higher rates of failure. P53-mediated apoptosis is greatly increased in the brain, but not other tissues, and p53 knockout partly rescues brain size. Thus, loss of Cep55 causes abscission defects and failures in multiple cell types, but the secondary p53 response and apoptosis is brain-specific.

developmental biology↗

bioRxiv2019

Cytokinetic furrowing and abscission dynamics during brain development revealed by live imaging

McNeely et al. quantitatively analyze polarized cytokinetic furrow ingression and abscission in mouse neuroepithelium by live imaging. The findings show important differences from HeLa cells, and suggest abscission timing and midbody release may be developmentally regulated, to influence daughter cell fate during brain growth. AbstractWhile mechanisms of cytokinesis have been identified in single cell models, the spatial and temporal regulation in developing tissues is less understood. Here we compare cytokinetic furrowing and abscission in mouse neuroepithelial stem cells (NESCs) at different developmental stages and in a cytokinesis mutant, including imaging abscission dynamics in a polarized epithelium for the first time. We find that asymmetric furrows of NESCs ingress at a constant but slow rate, and form the midbody at the apical membrane. Usually, bilateral abscission on each midbody flank releases the midbody remnant extracellularly. Interestingly, midbody remnants are more associated with early proliferative divisions. Unexpectedly, in the microcephalic Kif20b mutant, abscission is accelerated and occurs when the midbody is wider. The daughter cells of mutant NESCs show increased cell cycle exit that is p53-independent. We suggest that abscission mechanisms are developmentally regulated. These results provide significant insight into adaptations of a fundamental cell biological process required for proper brain growth.

developmental biology↗

bioRxiv2018

p53 deletion rescues apoptosis and microcephaly in a Kif20b mouse mutant

Building a cerebral cortex of the proper size involves balancing rates and timing of neural stem cell (NSC) proliferation, neurogenesis, and cell death. The cellular mechanisms connecting genetic mutations to brain malformation phenotypes are still poorly understood. Microcephaly may result when NSC divisions are too slow, produce neurons too early, or undergo apoptosis, but the relative contributions of these cellular mechanisms to various types of microcephaly are not understood. We previously showed that mouse mutants in Kif20b (formerly called Mphosph1, Mpp1, or KRMP1) have small cortices that show elevated apoptosis, and defects in maturation of NSC midbodies, which mediate cytokinetic abscission. Here we test the contribution of intrinsic NSC apoptosis to brain size reduction in this lethal microcephaly model. By making double mutants with the pro-apoptotic genes Bax and Trp53 (p53), we find that apoptosis of cortical NSCs accounts for most of the microcephaly, but that there is a significant apoptosis-independent contribution as well. Remarkably, heterozygous p53 deletion is sufficient to fully rescue survival of the Kif20b mutant into adulthood. In addition, the NSC midbody maturation defects are not rescued by p53 deletion, showing that they are either upstream of p53 activation, or in a parallel pathway. Thus, this work potentially identifies a novel midbody-mediated pathway for p53 activation, and elucidates both NSC apoptosis and abscission mechanisms that could underlie human microcephaly or other brain malformations.

developmental biology↗