Generation and Characterization of Rac3 Knockout Mice

Abstract

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.

ACKNOWLEDGMENTS

We thank Andras Nagy for the R1 ES cells and Lorenza Ronfani and the Core Facility for Conditional Mutagenesis at the San Raffaele Scientific Institute for helping with the screening of ES cells and the production of chimeric mice. We thank the following people for helpful discussion and assistance with this work: Ivana Benzoni, Annalisa Bolis, Patrizia D'Adamo, Laura Feltri, Cinzia Ferri, Alessandro Nodari, and Larry Wrabetz.

This work is supported by Telethon-Italy (grant GGP02190 to I.D.C.) and by the Italian Ministry of University and Research (MIUR) within the framework of project FIRB (FIRB RBNE01WY7P). Part of this work was carried out in Alembic, an advanced microscopy laboratory established by the San Raffaele Scientific Institute.