Citron, a Rho target that affects contractility during cytokinesis

The small GTPase Rho, which regulates cell shape, is thought to contribute to cytokinesis. Recently, Citron was characterized as a Rho target. This la rge protein contains a Ser/Thr kinase domain related to that of ROCK, anoth er Rho effector. Both endogenous Citron and recombinant Citron localize to the cleavage furrow in dividing cells and to the midbody in postmitotic cel ls. Moreover, overexpression of Citron deleted from its C-terminal sequence caused abnormal contractions specifically during cytokinesis, resulting in the formation of multinucleated cells. Cell shape, F-actin, intermediate f ilaments, and microtubules appeared essentially normal in these cells durin g interphase. Thus, Citron is a Rho effector that appears to function durin g cytokinesis, modulating its contractile process. In brain, however, Citro n is highly expressed in a subset of neurons as a brain-specific isoform th at lacks a kinase domain, Citron-N. This protein accumulates in synapses an d associates to the NMDA receptor via interaction with the adaptor protein PSD95, suggesting that the function of Citron is specialized in the neurons . Microsc. Res. Tech. 49:123-126, 2000. (C) 2000 Wiley-Liss, Inc.