Regulation of the Morphogenesis and Development by RapGAP9

Abstract

The small GTPase Rap1 is involved in the control of diverse cellular processes including integrin-mediated cell adhesion, cadherin-based cell-cell adhesion, cell polarity formation, and cell migration. Recent reports have demonstrated that the importance of Rap1-specific GTPase-activating proteins (GAPs) in the spatial and temporal regulation of Rap1 activity during cell migration and development in Dictyostelium. Here, I identified another Rap1 GAP-domain containing protein by bioinformatic search of Dictyostelium database (www.dictybase.org). The putative Rap1 GAP domain of RapGAP9 showed high sequence homologies with those of human Rap1GAP and Dictyostelium RapGAP3. To investigate the functions of RapGAP9, I prepared rapGAP9 null cells by homologous recombination and found that rapGAP9 null cells were more flattened and spread than wild-type cells. rapGAP9 null cells displayed a small increase of cell-substratum attachment compared with wild-type cells. The loss of RapGAP9 resulted in an altered morphology of fruiting body with a shorter length of stalk and spore. These data suggest that RapGAP9 is involved in cell adhesion and multicellular development. The localization assay showed that RapGAP9 localized to the cell cortex and preferentially at the leading edge in migrating cells. Upon chemoattractant stimulation, RapGAP9 was translocated transiently and rapidly to the cell cortex from the cytosol. Rap1 is emerging as a major regulator of cytoskeleton reorganization and cell adhesion in Dictyostelium. Identification and characterization of RapGAP9 in this study will provide further insight into the molecular mechanism by which Rap1 regulates cytoskeleton reorganization and morphogenesis in Dictyostelium.