Pten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects

Abstract

SUMMARYNeuronal precursors, generated throughout life in the subventricular zone, migrate through the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. We found that the PI3K-Akt-mTorc1 pathway is selectively inactivated in migrating neuroblasts in the subventricular zone and rostral migratory stream, and activated when these cells reach the olfactory bulb. Postnatal deletion of Pten caused aberrant activation of the PI3K-Akt-mTorc1 pathway and an enlarged subventricular zone and rostral migratory stream. This expansion was caused by premature termination of migration and differentiation of neuroblasts and was rescued by inhibition of mTorc1. This phenotype is reminiscent of lamination defects caused by Pten deletion in developing brain that were previously described as defective migration. However, live imaging in acute slices showed that Pten deletion did not cause a uniform defect in the mechanics of directional neuroblast migration. Instead, a subpopulation of Pten-null neuroblasts showed minimal movement and altered morphology associated with differentiation, whereas the remainder showed unimpeded directional migration towards the olfactory bulb. Therefore, migration defects of Pten-null neurons might be secondary to ectopic differentiation. KEY WORDS: Pten, Differentiation, Migration, Neuroblast, mTOR/PI3K, MousePten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects RESEARCH ARTICLEPten function in neuroblasts deletion in this study was a decrease in random movement in the absence of a chemotactic signal (Hoeller and Kay, 2007). Thus, even within simple organisms, the precise mechanisms through which PI3K signaling influences migration are not straightforward.Inherited mutations disrupting PI3K-AKT-mTORC1 regulation are associated with human syndromes that include neurological abnormalities, indicating that the pathway is important in normal neural development and/or function (Inoki et al., 2005;Endersby and Baker, 2008). Conditional knockout mice showed that Pten is important in brain for diverse processes, including proper neuronal positioning during development as well as negative regulation of neural stem cell self-renewal and proliferation, and neuronal morphogenesis and size regulation (Backman et al., 2001;Kwon et al., 2001;Marino et al., 2002;Waite and Eickholt, 2010). However, the underlying mechanism of how Pten is involved in neuronal migration is currently unknown.In the present study, we demonstrated that Pten inhibits downstream activation of mTorc1 in normal migrating neuroblasts in the RMS. Postnatal deletion of Pten in this population resulted in ectopic positioning of neurons that failed to reach their final destination, reminiscent of defects in radial glia-guided neuronal migration caused by Pten deletion during development. The phenotype was fully rescued by rapamycin, demonstrating that mTorc1 is required for the Pten-mediated regulation of migration in the RMS. We used live imaging o...

Brain patterning perturbations following PTEN loss

“…Similar observations have been made regarding adult neurogenesis in the hippocampus and sub-ependymal zone (SEZ)/sub-ventricular zone (SVZ) (Bonaguidi et al, 2011; Amiri et al, 2012; Zhu et al, 2012). The observations that PTEN loss accelerates G1/S transition (Sun et al, 1999) and promotes G0 exit into the cell cycle (Groszer et al, 2006) provide an excellent backdrop to consider the effects of PTEN deletion in neural progenitors.…”

Expansion of oligodendrocyte progenitor cells following SIRT1 inactivation in the adult brain

“…To this end, we crossed mice in which exon 4 of the Sirt1 gene is flanked by loxP sites ( Sirt1 lox/lox ) with NestinCreER T2 – IRES – hPLAP transgenic mice 41–44 ( NestinCreER ), which express a tamoxifen-inducible form of Cre (CreER) in adult NSCs and neural progenitors (Fig. 2a).…”

“…NestinCreER T2 – IRES – hPLAP (abbreviated NestinCreER ) mice expressing CreERT2 under the control of the rat Nestin promoter and second intron as a transgene were generated in the S.J.B. laboratory and maintained on a predominantly 129/Sv background 41,42,44 . All mice used for in vivo experiments were male.…”

Detecting PTEN and PI3K Signaling in Brain

“…Representative Pten (A), p-Akt (B) and p-S6 (C) IHC images in the subventricular zone (SVZ) of vehicle- or rapamycin-treated Nestin-creER; Pten flox/flox mice induced to delete Pten by tamoxifen administration at P0, P1[7]. Pten conditional loss in the SVZ causes an expanded SVZ with elevated levels of pAkt and pS6.…”

“…Pten loss in the mouse brain could result in diverse phenotypes such as neuronal hypertrophy and premature differentiation, astrocyte hypertrophy or increased neural stem cell self-renewal and proliferation given different cellular and developmental contexts. [7–14]…”