In addition, the level of PTEN in RGC growth cones is important for axon branching and is tightly regulated by the ubiquitin-proteasome system (Drinjakovic et al., 2010). Rabbit Polyclonal to RAB18 function and augmented oscillatory potentials originating from amacrine cells inPtenmutants. Furthermore, MCC950 sodium deletingPtenor elevating Akt activity in individual amacrine cells is sufficient to disrupt dendritic arborization, indicating thatPtenactivity is required cell autonomously to control neuronal morphology. Moreover, inhibiting endogenous Akt activity attenuates inner plexiform layer formation in vitro. Together, these findings demonstrate that suppression of PI3K/Akt signaling by PTEN is crucial for proper neuronal differentiation and normal retinal network formation. Keywords:Mouse retinal development, PTEN function, retinal specific knockout, PI3K/Akt MCC950 sodium signaling, amacrine cell morphogenesis == INTRODUCTION == The vertebrate retina is a sophisticated neural network organized into three cellular layers interconnected by two synaptic layers (Sanes and Zipursky, 2010). A common progenitor pool gives rise to seven major retinal cell classes, which can be further classified into more than 60 subtypes of neurons based on gene expression profiles ad morphologies (Livesey and Cepko, 2001;Masland, 2001). Determination of retinal cell fates is predominantly dictated by cell-intrinsic determinants, especially the combinations of various transcription factors (Hatakeyama and Kageyama, 2004;Ohsawa and Kageyama, 2008). In addition, contact-mediated and secreted signals also influence retinal progenitor proliferation and fate specification (Jadhav et al., 2006;Kim et al., 2005;Sakagami et al., 2009;Wang et al., 2005;Yang, 2004;Yaron et al., 2006;Zhang and Yang, 2001). Upon establishing cellular identities, the morphogenesis of various neurons appears to follow intrinsic differentiation programs (Kay et al., 2004). Recent studies have revealed that retinal cell soma and dendritic arbor distribution involves self-recognition through cell adhesion molecules (Fuerst et al., 2009;Fuerst et al., 2008;Yamagata and Sanes, 2008), while synaptic connection and pruning involve classic immune molecules (Stevens et al., 2007;Xu et al., 2010). Nonetheless, a comprehensive understanding of retinal network formation, especially its modulation by cell extrinsic signals, is still lacking. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has emerged as an important regulator of growth factor signaling in the nervous system (Iwanami et al., 2009).Ptenencodes a lipid phosphatase that antagonizes the activity of phosphotidylinosital-3-kinase (PI3K), which can be activated by receptor tyrosine kinase (RTK) or G-protein-coupled receptor (GPCR) mediated extracellular signals (Engelman et al., 2006). InactivatingPtenelevates the intracellular level of phosphatidylinositol 3,4,5-triphosphate (PIP3) and consequently triggers activation of PDK1 and mammalian target of rapamycin complex 2 (mTORC2) (Manning and Cantley, 2007). Both PDK1 and mTOR subsequently activate Akt through phosphorylation at distinct sites. Deletion ofPtenin the developing mouse brain leads to over-proliferation of progenitors and enhanced neuronal survival (Backman et al., 2001;Groszer et al., 2001;Kwon et al., 2001).Ptennull neural progenitor cells show reduced growth factor dependency, shortened cell cycles and accelerated G0G1 entry (Groszer et al., 2006).Ptenmutation-induced Akt activation also leads to hypertrophic neuronal somata and more elaborate dendritic arbors of cortical neurons (Jaworski et al., 2005;Kwon et al., 2006). In the adult nervous system, deletion ofPtenenhances neurogenesis through perpetual self-renewal of endogenous stem cells (Gregorian et al., 2009). Inactivation ofPtenalso activates mTOR and promotes axonal regeneration of CNS neurons (Liu et al., 2010;Park et al., 2008). In the developing eye, ablation ofPtenin the retinal pigment epithelium (RPE) causes the loss of adhesion junctions, an epithelial MCC950 sodium to mesenchymal transition, abnormal RPE cell migration, and ultimately the death of adjacent photoreceptor cells (Kim et al., 2008). In the mature retina, activation of the insulin/mTOR pathway has been shown to delay cone photoreceptor death in mouse models of retinitis pigmentosa (Punzo et al., 2009). However, the function of PTEN during development of the neural retina has not been elucidated. In this study, we have abolished PTEN function from the onset of retinal neurogenesis. We provide evidence that PTEN activity differentially influences retinal neuron production and critically regulates retinal synaptic layer formation. We further demonstrate that PTEN acts cell-autonomously to suppress PI3K/Akt activation and control amacrine interneuron morphogenesis. == MATERIALS AND METHODS == == Mice == ThePtenfloxed mouse line was previously described (Groszer et al., 2001). The Chx10-cre transgenic mouse line was generated by Rowan and Cepko (Rowan and Cepko, 2004). Both mouse lines were backcrossed for more than six generations to the.
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