Transgenic expression of the N525S-tuberin variant in Tsc2 mutant (Eker) rats causes dominant embryonic lethality

Abstract

The Tsc2 product, tuberin, negatively regulates the mTOR pathway. We have exploited the Eker (Tsc2-mutant) rat system to analyse various Tsc2 mutations. Here, we focus on the N525S-Tsc2 variant (NSM), which is known to cause distinct symptoms in patients even though normal suppression of mTOR is observed. Unexpectedly, we were repeatedly unable to generate viable rats carrying the NSM transgene. Genotypic analysis revealed that most of the embryos carrying the transgene died around embryonic day after 14.5—similar to the stage of lethality observed for Eker homozygotes. Thus, the NSM transgene appeared to have a dominant lethal effect in our rat model. Further, no significant differences were observed for various signal transduction molecules in transiently expressed NSM cells compared to WT. These results indicate that a non-mTOR pathway, critical for embryogenesis, is being regulated by tuberin, providing a link between tuberin expression and the severity of Tsc2 mutation-related pathogenesis.

Hyperactivation of mTORC1 disrupts cellular homeostasis in cerebellar Purkinje cells

“…However, mTORC1 activity is modulated by many regulatory molecules, the phenotypes observed in Tsc1/2 knockout mice should not be attributed solely to mTORC1 hyperactivation. In fact, human patients with N525S in TSC2 display severe symptoms of tuberous sclerosis without affecting TSC1/2 complex formation or GAP activity toward Rheb, whereas G1556S mutation impairs GAP activity with mild symptoms 13,14 . These clinical cases raise the possibility that activity of mTORC1 signaling does not correlate with symptom severity in some cases of tuberous sclerosis.…”