MOLECULAR ANALYSIS OF THE CITRON KINASE PATHWAY IN HUMAN MICROCEPHALIES AND IN EXPERIMENTAL MODELS

Small GTPases of the Rho family are critical regulators of the actin cytoskeleton and their identification has represented a crucial step to understand the molecular basis of Central Nervous System (CNS) development. The effects of these molecules are mediated by the coordinated action of many effector molecules, including Citron Kinase (CRIK or CIT-K) and CIT-N. In our previous studies we demonstrated that CIT-K and CIT-N are two alternative products of the same gene. During the previous period of financing we have discovered that these molecules are strongly expressed in the CNS, and that their expression is strikingly modulated during embryonic development. Indeed, CIT-K is expressed only by proliferating neuronal precursors, whereas post-mitotic neuroblasts and adult neurons express only CIT-N. To directly investigate the in vivo function of CIT-K, along with its potential involvement in human genetic diseases, we have generated, using the gene targeting technologies, a mouse experimental model completely lacking CIT-K expression (-/-), but still producing normal levels of CIT-N. CIT-K -/- mice are affected by a complex neurological syndrome, characterized by severe ataxia and epilepsy, which brings them to death a few days after birth. Their brains are much smaller than normal controls, and display dramatic malformation of specific structures. These studies have identified CIT-K as the first potential candidate for a heterogeneous group of human inherited diseases characterized by microcephaly. The aims of our future studies will be to: a) identify more candidate genes for this class of genetic syndromes; b) clarify if mutations of CIT-N may cause specific genetic diseases; c) directly investigate if mutations of the human homologue of CIT-K are responsible for human microcephalies.