Essential Role Of Presenilin Enhancer 2 In Cortical Development

The neocortex of brain is the center for higher order cognitive function,sensory perception and consciousness.The mammalian neocortex is a highly organized six layer structure,which contains various types of neurons and glia.Two major types of neurons compose the cerebral cortex,glutamatergic projection neurons and GABAergic interneurons.The laminar organization of the cortex are formed by sequential birth and orderly migration of neurons in an inside-first and outside-last manner during neurogenesis.The process of neurogenesis is highly regulated,requiring the integration of many cellular processes.Any mistakes in the time or space will results in neurodevelopmental disorder.Lissencephaly and microcephaly are two major groups of human neurodevelopmental disorders that have been intensely studied and featured by reduced cerebral cortex size,also intellectual disability and global growth deficiency.The cause of these disorders is complicated and there must be far more genes than already known to date get involved in regulation brain development.Previous studies have shown that substrate of ?-secretase,PS 1/2,NCT is essential for survival of mature neurons.Moreover,embryos lacking PS1,NCT,Pen2,Aphla exhibit a variety of defects,including defects in heart looping,branchial arch development,midbrain mesenchyme cell loss,and trunk ventral neural tube disorganization.The phenotype resemble a complete absence of all mammalian Notch signaling activity and loss of Hes1,or Hes5.Knockdown of Pen-2 in zebrafish directly led to a reduction of neurons.In addition,ablation PS 1/2 lead to reduced NPC proliferation and premature neurogenesis and finally results in malformation of cortex during embryonic development.These data suggest y-secretase is important for normal neuronal development.However,the phenotype loss of these genes resemble,but are not identical to each other and those of Notch1 indicate they may contain additional functions except serve as substrate of ?-secretase.Especially,presenilins contain both?-secretase-dependent and ?-secretase-dependent activities,including regulation of ?catenin signaling and control of calcium release from the endoplasmic reticulum.Therefore,there is a need to study the function of each substrates,Pen2,NCT,Aph1a,in the process of neurogenesis.In our study,we found that Pen2 is important for correct brain development during the whole process of cortical development.Loss of Pen2 resulted in NPC get out of cell cycle,prematurely differentiate into neurons instead of proliferation,which result in NPC depletion and eventually lead to brain malformation.In addition,dramatically decreased RGPs on one hand produce much neurons,on the other hand produce more BPs,which directly give rise neurons.These data indicate that after ablation of Pen2,overproduced neurons are come from directly differentiation of RGCs and indirectly cell division of BPs.Moreover,we delete Pen2 at latter stage of neurogenesis by Nestincre,which start expression from E11.5,also lead cortical lamination defect.Former studies have proven that Notch signaling,one of the major substrate of y-secretase,play an important role in NPC maintain and correct brain development.Removal of Pen2 results in impaired Notch signaling pathway,which is important for NPC reserve,and a marked up-regulation in pre-neural gene expression,the consequence of which is a shift in the balance between self-renewal and differentiation toward differentiation.We also found that loss of NCT also resulted in NPC prematurely differentiate into neurons instead of proliferation and eventually lead to brain malformation.Moreover,we delete NCT at latter stage of neurogenesis by Nestin-cre also lead to cortical lamination defect,similarly to Pen2.Notch signaling pathway is impaired,as Hes1 and Hes5 expression decreased,whereas Dll1 expression elevated.Impaired Notch signaling lead to up-regulation of pre-neural gene expression.These data indicates that the role of Pen2 and NCT in cortical development is y-secretase dependent.In other words,y-secretase is essential for cortical development at whole process of brain development.