Kobe University Repository : Kernel タイトル Tit le Defect ive vascular morphogenesis and mid-gestat ion embryonic death in mice lacking

A multitude of guanine nucleotide exchange factors (GEFs) regulate Rapl small GTPases, however, their individual functions remain obscure. Here, we investigate the in vivo function of the Rapl GEF RA-GEF-l. The expression of RA-GEF-l in wild-type mice starts at embryonic day (E) 8.5, and continues thereafter. RA-GEF-r mice appear normal until E7.5, but become grossly abnormal and dead by E9.5. This mid-gestation death appears to be closely associated with severe defects in yolk sac blood vessel formation. RA-GEF-l-lyolk sacs form apparently normal blood islands by E8.5, but the blood islands fail to coalesce into a primary vascular plexus, indicating that vasculogenesis is impaired. Furthermore, RA-GEF-r embryos proper show severe defects in the formation of major blood vessels. These results suggest that deficient Rapl signaling may lead to defective vascular morphogenesis in the yolk sac and embryos proper. Rap 1 belongs to the Ras family of small GTPases, and is implicated in regulation of a variety of cellular phenomena such as proliferation, adhesion, and exocytosis [I]. In particular, many in vitro experiments have shown that Rap 1 is involved in integrin-mediated adhesion [2]. Recent studies employing gene targeting of individual Rapl members also support this notion [3,4]. In response to extracellular stimuli, Rap 1 activity is regulated through the action of specific guanine nucleotide exchange factors (GEFs) including C3G, Epacs, CalDAG-GEFs, RA-GEFs (PDZ-GEFs), and phospholipase CE [1]. Two related GEFs called RA-GEF-I (also called PDZ-GEFI, nRapGEP and CNRasGEF) [1,5,6] and RA-GEF-2 [7] are characterized by possession of both PSD-95/DlgA/ZO-l (PDZ) and RaslRap-associating (RA) domains. Through the interaction with Rapl-GTP, RA-GEF-I co-localizes with Rapl at the Golgi complex, leading to the amplification of the Rapl-mediated signaling [6]. On the other hand, RA-GEF-2 is recruited to the plasma membrane by association with M-Ras-GTP [7].