Function Of Lgl1 Gene In The Development Of Cerebral Cortex And Hippocampus In Mice

BackgroundThe health of many patients worldwide are affected by the central nervous system diseases,such as autism,epilepsy,schizophrenia,mental retardation,depression etc.Neurological diseases not only seriously affect the quality of life of patients,but also bring tremendous economic burden and pressure to society.It is a major issue affecting the sustainable development of China’s economy and society.Many disease-related genes are expressed in the development of the nervous system and participate in various cellular physiological processes,such as cell proliferation,differentiation,migration and synaptogenesis.Previous studies have shown that the genes associated with autism are only active in the early stage of brain development;the genes associated with epilepsy play an important role in the increase of neuronal progenitor cells and neuronal migration.Therefore,the study of the regulation mechanism of brain development through animal models is essential for revealing the development of central nervous system and the pathogenesis of neurological diseases,which could provide significant reference for the diagnosis and treatment of clinical related diseases.The development of cerebral cortex and hippocampus is a hot topic in the field of neurology.The cerebral cortex and hippocampus contain neural circuitry that is important for cognitive performance in mice,such as cognitive,emotional,sensory,motor coordination,learning and memory.Neurogenesis in the embryonic cerebral cortex and hippocampus requires highly precise coordination among hundreds of genes.Both the exogenous and endogenous factors could participate in the development of cortex by affecting the proliferation and differentiation of neural stem cells,neural migration and localization,and maturation of neurons.The abnormality of any process can cause disorders of brain function and form neurological diseases.During the development of cortex,the proper migration of new-born neurons is crucial for the formation of cortical layered structure and the basis of cortex diverse functions.These process depends on the precise regulation of many genes in time and space.Therefore,the study of the molecular mechanism of cerebral cortex and hippocampus development is particularly important.Lethal giant larvae(Lgl)protein,which is a ubiquitously expressed and evolutionarily conserved cytoskeletal protein,is essential for the cell polarity and has been initially identified to be a tumor suppressor in Drosophila.Accumulating evidence have shown that the Lgl1 gene has a crucial function in the development of central nervous system.The inactivation of Lgl1 may cause the disorder of cytoskeleton,a misregulation of cell proliferation and neoplastic overgrowth.These studies suggest that Lgl1 may play an important role in the realization and maintenance of brain morphogenesis and function.In 2004,Klezovitch et al.used More-Cre to knock out Lgl1 at E5.5 ectoderm and found that newborn mice died within 24 hours after birth,accompanied by severe hydrocephalus.The above studies suggest that Lgl1 gene plays an important role in the development of nervous system.However,knockout of Lgl1 gene mediated by More-Cre leads to postnatal death of mice,which precludes a direct analysis of the role study the development and function of Lgl1 in the nervous system.In addition,the role of Lgl1 in the development of cortical layered structure,hippocampal development and function is unknown.In particular,the development of cortex and hippocampus can not be completed until birth.The specific expression time and pattern of Lgl1 in the cerebral cortex and hippocampus of mice,and how does Lgl1 affect the development of the cerebral cortex and hippocampus remain unclear.Therefore,the study of the molecular mechanism of Lgl1 in the development of cortex and hippocampus is crucial for further study in the development mechanism of nervous system.Scientific QuestionsThe scientific questions in this paper are:(1)The role of Lgl1 in the development of mouse cerebral cortex;(2)Function of Lgl1 in the development of mouse hippocampus;(3)Role of Lgl1 in mouse cognitive behavior performacne.Research Programmes and ResultsThe expression of More-Cre recombinant enzyme in the whole embryo was too early(E5.5),which led to death of knockout mice after birth.In the current study,we employed a Cre recombinase-mediated conditional gene-targeting strategy to circumvent this problem.To this end,Emx1-Cre mice were used to generate dorsal telencephalon-specific Lgl1 conditional knockout(CKO)mice.To investigate Lgl1 functions in the generation of cortical-layer diversity,we studied the cortical patterning of juvenile and adult cortical organization in viable CKO mice.The learning and memory abilities and anxiety-related behavioral levels were tested by behavioral experiments.The animal model was used to explore the effects of Lgl1 on proliferation,differentiation,migration,apoptosis and possible molecular mechanisms of neural stem cells in cortex and hippocampus.In this study,the study of cerebral cortex and hippocampus were focused.Firstly,the expression of Lgl1 in the development of cerebral cortex and hippocampus was determined.Based on these results,the effects of Lgl1 on the proliferation and differentiation of neural progenitor cells and the migration of neurons during the development of cortex and hippocampus were analysed.Furthermore,the organisms of Lgl1 gene in the development of mouse cerebral cortex and hippocampus were further discussed.In this study,the deletion of Lgl1 gene during the development of cerebral cortex resulted in the cerebral cortex malformation in mice,including thinned but layered cortical and subcortical heterotopic band,disruption of adhesion junctions between radial glial cells in cerebral cortex,and disrupted apical-basal process of radial glial cells.In addition,disrupted radial glial fiber-guided cortical neuronal migration leads to the formation of ectopic cell mass.During the development of hippocampus,the deletion of Lgl1 gene can cause increased cell proliferation,abnormal interkinetic nuclear migration,reduced differentiation,increased apoptosis,gradual disruption of adherens junctions,and abnormal neuronal migration.Severe developmental abnormalities in the cortex and hippocampus of Lgl1Emx1 CKO mice also resulted in the impairment in cognitive performance.In the water maze test,the motor coordination ability of Lgl1 conditional knockout mice remained unchanged,but they learned not as efficiently as the WT mice,and their spatial memory ability was severely impaired.In the conditioned fear memory test,the acquisition and consolidation of conditioned memory in knockout mice were lower than that in WT mice.In the elevated crosswater maze and open field behavioral tests,the anxiety-related behavioral level of Lgl1 conditional knockout mice decreased.Taken together,Lgl1 plays a distinct role in neurogenesis of cerebral cortex and hippocampus,and its deficiency impaired cognitive performance.SignificanceHere we showed that the deletion of Lgl1 in the developing cerebral cortex and hippocampus resulted in SBH formation,deformed hippocampus,and impaired cognitive performance in mice.Through this study,we can fully understand the mechanism of Lgl1 regulating the development of nervous system at the molecular and cellular level,which provide theoretical basis for further exploring the development of mammalian nervous system.The Lgl1Emx1 CKO mice represent a new model that may be used not only to better understand the etiology of cerebral malformation but also to investigate future therapeutic strategies for CNS diseases,which can provide certain reference for clinical diagnosis and treatment,and has important theoretical and practical significance.