The Role of CXCR4 in hippocampal neurogenesis and cerebellar development

SDF-1/CXCR4 signaling plays an important role in a number of processes, including the entry of T cell-tropic HIV into lymphocytes, cancer progression, and homing hematopoietic stem cells. CXCR4 is also expressed in the developmental brain. In the postnatal brain, CXCR4 is expressed in the hippocampus, subventriclar zone, and cerebellum. Several studies have already demonstrated the importance CXCR4 in the cerebellar and hippocampal development in the embryo. However, the function of CXCR4 in the postnatal brain is still poorly understood because the CXCR4 knockout mice is embryonic lethal. In this project, we used Cre/Lox strategy to delete CXCR4 gene in central nervous system. We bred CXCR4 flox mice with SOX1-Cre mice, which are viable and allows us to study the role of CXCR4 during development and in the adult brain. First of all, the most obvious phenotype we detected in the brain is the ectopic cells in the cerebellum. Thus, my first aim is to investigate the phenotypes and genes involved in the cerebellar development in the CXCR4 null mice. To find out the genes involved in this process, we are going to use gene expression microarray to detect the expression profile in P2 cerebellum, and confirm them by in situ hybridization. We will then use Weighted Gene Co-Expression Network Analysis ((WGCNA) to find the network and linkage of these candidate genes. Next, we are going to investigate the histology of cerebellum in the CXCR4 null mice. To do so, we will use a variety staining meothods, such as Golgi staining, Gallyas sliver staining, and Dil tracing, and immunostaining for Calbindin antibody to assess the density of dendrite and axon projection of Purkinje cells. To get a quantitative analysis of cells that commit to a neuronal fate and migrates to their final destination, we are going to conduct a birthdating experiment. BrdU will be given and labeled dividing cells in E15, E17, E19, the brain tissue will be harvested at P30. For the last part of this aim, we will assess animal behavior linked to cerebellar function, such as locomotion activity, rotarod, exercise learning, and mesh grip test. In the second aim of this project, we are going to investigate the adult neurogenesis in the subventricular zone and hippocampus. CXCR4 is expressed in these two regions, where adult neuroegnesis occurs, and it colocalized with BrdU-labeled postive cells in the adult brain. This implies another role CXCR4 in adult brain is regulating neuroegnesis. To avoid the developmental deficit in neuronal migration which may affect adult neuroegensis, we will also cross CXCR4 flox mice with GLAST-CreERT2 mice to generate tamoxifen-inducible knockout mice, so we can delete the CXCR4 gene in the progenitor cells in adult mice. We will then do a series of staining by to detect proliferating, differentiating, and mature neuronal cells. This inducible knockout strategy would allow us to measure the impact of CXCR4 in adult neuroegnesis in a more specific way. In addition CXCR4 has been suggested to be critical for neuronal migration and neurogenesis in the ischemic brain. Thus, we will explore this by using CXCR4 null mice to examine neuronal migration and neurogenesis from the subventricular zone after ischemia surgery in the CXCR4 null mice.

Project ID:PC10202-0650
External Project ID:NSC101-2320-B182-006-MY3