Molecular rescue of Tsc1-ablated cortical tuber mice

Tuberous sclerosis (TSC) is a multi-organic, autosomal-dominant disorder commonly caused by mutations in one of the two tumor suppressor genes TSC1 or TSC2 that encode the proteins hamartin and tuberin, respectively. TSC is characterized by highly differentiated malformations in different organs, including cortical tubers in the brain. They occur in the majority of patients and represent the major clinical burden, as they are commonly assumed to be responsible for the severe epilepsy phenotype [1]. While parallel loss of heterozygosity (LOH) is often found in extracerebral TSC associated malformations, such events are only rarely detected in cortical tubers [2]. Independent studies found that classical second hit events in TSC1 heterozygous patients may explain the formation of cortical tubers, while in direct contrast to these findings another group claims that second hits are rare in cortical tubers [1, 3]. Despite the tremendous ongoing research effort on TSC, the exact pathomechanisms leading to the emergence of cortical tubers remain controversial. A major breakthrough for studying the contribution of TSC1 to brain malformations including cortical tubers was the establishment of Tsc1 knockout mice by the Kwiatkowski group [4]. In our recently published article [5], we started out from respective transgenic mice to study tuber molecular development aspects [4, 6]. The frequently used C57Bl/6 Tsc1fl/fl mouse line was backcrossed into the CD1 genetic background for at least 3 generations to achieve CD1 Tsc1fl/fl mice. By using this mouse strain we increase pup survival after intraventricular in utero electroporation (IUE) dramatically, thus accelerating research on TSC. In utero expression of Cre at embryonic day 14 (E14) and subsequent loss of Tsc1 expression in single cells induced cytopathological alterations in mature mice (>P24) reflecting typical tuber-like features: enlarged neuronal cell bodies, increased mTOR activation (assessed by pS6 immunoreactivity), aberrant dendritic arborization and abnormal positioning of cortical neurons (Figure 1A-1C).