Functional analysis of RAC1B during neuronal development

Neurite extension requires the concerted action of a number of events including actin polymerization at the growth cone, formation of new adhesive sites to the substrate, and membrane addition, to extend the surface of the elongating neurite. The small GTPase Rac IB, identified from developing chicken retina, is specifically expressed during neural development, and overexpression of Rac IB in embryonic retinal neurons specifically stimulates neurite extension and branching (Albertinazzi et al., 1998). Very little is known about the molecular mechanisms which coordinate Rac IB-mediated neurite extension. In order to study in detail this mechanism in an in vivo system, recombinant embryonic stem cells (ES) for the deletion of mouse Rac IB gene were produced. ES cells from four independent clones that resulted positive for the deletion of mouse Rac IB gene were microinjected in blastocysts, and chimeric mice were generated to be used for the generation of Rac IB-null mice. Recently, p95-APPl was identified as a protein able to interact with Rac IB in a GTP-dependent manner (Di Cesare et al. 2000). P95-APP1 is an ArfGAP of the GIT family, highly expressed in the developing nervous system. Expression of p95- APPl with a mutated or deleted ArfGAP domain in retinal neurons prevented Rac IB-induced neuritogenesis, leading to PIX-mediated accumulation of mutant p95-APPl and associated proteins at large Rab 11-positive endocytic vesicles. Analysis of neurons expressing different p95-derived constructs together with wild-type or mutant Arf6 GTPases revealed the requirement of both p95-APPl and a cycling Arf6 for a normal Rac IB-mediated neuritogenesis. The data obtained in this thesis show a functional connection between the localization of the p95-APPl complex at recycling endosomes and Rac IB-dependent neuritogenesis, and suggest a role of this complex in the regulation of membrane recycling to/from the neuronal surface during neuritogenesis

Generation and Characterization of Rac3 Knockout Mice

Rac proteins are members of the Rho family of GTPases involved in the regulation of actin dynamics. The three highly homologous Rac proteins in mammals are the ubiquitous Rac1, the hematopoiesis-specific Rac2, and the least-characterized Rac3. We show here that Rac3 mRNA is widely and specifically expressed in the developing nervous system, with highest concentration at embryonic day 13 in the dorsal root ganglia and ventral spinal cord. At postnatal day 7 Rac3 appears particularly abundant in populations of projection neurons in several regions of the brain, including the fifth layer of the cortex and the CA1-CA3 region of the hippocampus. We generated mice deleted for the Rac3 gene with the aim of analyzing the function of this GTPase in vivo. Rac3 knockout animals survive embryogenesis and show no obvious developmental defects. Interestingly, specific behavioral differences were detected in the Rac3-deficient animals, since motor coordination and motor learning on the rotarod was superior to that of their wild-type littermates. No obvious histological or immunohistological differences were observed at major sites of Rac3 expression. Our results indicate that, in vivo, Rac3 activity is not strictly required for normal development in utero but may be relevant to later events in the development of a functional nervous system

Accounting change in Italy

The paper highlights the changes which are occurring in accounting regulation and in the accounting profession in Italy. This 'revolution' is analysed both in its 'technical' terms and in the light of the wider socio-economic context of the country. Some anomalies and contradictions affecting Italian accounting are pointed out and discussed. The concrete significance of those changes is ques tioned with reference to the day-to-day practice and social perception of accounting. In conclusion, drawing on this national situation, some methodolog ical remarks are made concerning the difficulties of an evaluatory perspective in the study of international accounting.