Rheb is essential for murine development

Ras homolog enriched in brain (Rheb) couples growth factor signaling to activation of the target of rapamycin complex 1 (TORC1). To study its role in mammals, we generated a Rheb knockout mouse. In contrast to mTOR or regulatory-associated protein of mTOR (Raptor) mutants, the inner cell mass of Rheb-/-embryos differentiated normally. Nevertheless, Rheb-/-embryos died around midgestation, most likely due to impaired development of the cardiovascular system. Rheb-/-embryonic fibroblasts showed decreased TORC1 activity, were smaller, and showed impaired proliferation. Rheb heterozygosity extended the life span of tuberous sclerosis complex 1-deficient (Tsc1-/-) embryos, indicating that there is a genetic interaction between the Tsc1 and Rheb genes in mouse.