Biallelic Mutations in Citron Kinase Link Mitotic Cytokinesis to Human Primary Microcephaly.

Cell division terminates with cytokinesis and cellular separation. Autosomal-recessive primary microcephaly (MCPH) is a neurodevelopmental disorder characterized by a reduction in brain and head size at birth in addition to non-progressive intellectual disability. MCPH is genetically heterogeneous, and 16 loci are known to be associated with loss-of-function mutations predominantly affecting centrosomal-associated proteins, but the multiple roles of centrosomes in cellular function has left questions about etiology.

Novel STAMBP mutation and additional findings in an Arabic family.

Microcephaly-capillary malformation syndrome (MIC-CAP syndrome) is a newly recognized autosomal recessive congenital neurocutaneous central nervous system disorder characterized by severe microcephaly, early-onset seizures, profound psychomotor disability, and multiple cutaneous capillary lesions. In addition, affected patients have variable dysmorphic facial features and hypoplastic distal phalanges. It is distinctively caused by mutations in a newly characterized gene, STAMBP, encoding the deubiquitinating (DUB) isopeptidase that has a key role in cell surface receptor-mediated endocytosis and sorting.

Dynamic control of excitatory synapse development by a Rac1 GEF/GAP regulatory complex.

The small GTPase Rac1 orchestrates actin-dependent remodeling essential for numerous cellular processes including synapse development. While precise spatiotemporal regulation of Rac1 is necessary for its function, little is known about the mechanisms that enable Rac1 activators (GEFs) and inhibitors (GAPs) to act in concert to regulate Rac1 signaling. Here, we identify a regulatory complex composed of a Rac-GEF (Tiam1) and a Rac-GAP (Bcr) that cooperate to control excitatory synapse development.

The Rac-GAP Bcr is a novel regulator of the Par complex that controls cell polarity.

Cell polarization is essential for many biological processes, including directed cell migration, and loss of polarity contributes to pathological conditions such as cancer. The Par complex (Par3, Par6, and PKCζ) controls cell polarity in part by recruiting the Rac-specific guanine nucleotide exchange factor T-lymphoma invasion and metastasis 1 (Tiam1) to specialized cellular sites, where Tiam1 promotes local Rac1 activation and cytoskeletal remodeling. However, the mechanisms that restrict Par-Tiam1 complex activity to the leading edge to maintain cell polarity during migration remain unclear.

Control of synapse development and plasticity by Rho GTPase regulatory proteins.

Synapses are specialized cell-cell contacts that mediate communication between neurons. Most excitatory synapses in the brain are housed on dendritic spines, small actin-rich protrusions extending from dendrites. During development and in response to environmental stimuli, spines undergo marked changes in shape and number thought to underlie processes like learning and memory.