Development of Retinal Bipolar Cells

描述（由申请人提供）：脊椎动物视网膜的细胞结构和连通性在物种中非常保守。这些视网膜的最大区别在于每种不同细胞类型的相对数量。即使在同一物种内，神经元群的大小也存在显著差异。控制调节细胞生产、命运分配和生存过程的多态性基因是个体之间这种差异的主要原因，本研究将寻求确定导致这种差异的基因，并了解它们在调节增殖、命运决定和凋亡过程中的作用。利用A/J和C57BL/6J两种小鼠系衍生的26株重组近交系小鼠，测定四种不同类型视网膜双极细胞的自然变异，并检测细胞类型间共变异的程度。双极细胞数量的变化也将与锥状光感受器数量的数据和杆状光感受器的新数据进行比较。细胞数量的变化将被映射到基因组位点，候选多态性基因将被识别并使用基因敲除策略进行测试。细胞死亡在建立双极细胞数量中的作用及其时间发生将在Bax敲除小鼠中直接评估，而其传入依赖性将在无锥体和锥体突变小鼠中定义。其他细胞类型的形态分化受邻近样型细胞的密度及其传入事件的控制，因此这些变量中的每一个都将被调节以确定它们对双极细胞树突分化的影响。最后，将对这些重组近交系进行视网膜发育转录组分析，并在NerveNetwork上提供给科学界。这将使基因表达变异与基因组位点的直接映射成为可能，从而有助于识别上述双极和光感受器细胞数量变化的候选基因，并检测基因表达的相关性，以识别参与双极或光感受器细胞个体类型产生的调节网络。这些实验将揭示神经细胞数量和形态的决定因素，阐明我们对视网膜发育的理解，以及识别可能导致视网膜疾病的基因多态性。

DESCRIPTION (provided by applicant): The cellular architecture and connectivity of the vertebrate retina is remarkably conserved across species. What distinguishes these retinas most is the relative numbers of each of the different cell types. Even within a species, there is significant variation in the size of neuronal populations. Polymorphic genes controlling the processes regulating cellular production, fate assignment and survival contribute most of this variation between individuals, and the present investigation will seek to identify genes responsible for this variation, and to understand their role in those processes modulating proliferation, fate determination and apoptosis. Twenty-six recombinant inbred strains of mice derived from the A/J and C57BL/6J strains of mice will be used to determine the natural variation in four different types of retinal bipolar cell, and the degree of co-variation between cell types will be examined. The variation in bipolar cell number will also be compared with data for cone photoreceptor number and with new data collected for rod photoreceptors. Variation in cell number will be mapped to genomic loci where candidate polymorphic genes will be identified and tested using gene knock-out strategies. The role of cell death in establishing bipolar cell numbers, and its temporal occurrence, will be assessed directly in Bax knock-out mice, while its afferent-dependency will be defined in coneless and conefull mutant mice. Other cell types have been shown to have their morphological differentiation controlled by the density of neighboring like-type cells as well as by their afferents, and so each of these variables will be modulated to determine their effects upon the differentiation of bipolar cell dendrites. Finally, a developmental transcriptome analysis of the retina will be conducted in these each of these recombinant inbred strains, and made available to the scientific community on-line at NerveNetwork. This will enable the direct mapping of variations in gene expression to genomic loci, thereby aiding in the identification of candidate genes underlying the above variations in bipolar and photoreceptor cell number, and the detection of correlations in gene expression to identify regulatory networks that participate in the production of individual types of bipolar or photoreceptor cells. These experiments will reveal the determinants of nerve cell number and morphology, clarifying our understanding of retinal development, as well as identifying gene polymorphisms that may contribute to retinal disease. PUBLIC HEALTH RELEVANCE: This research program will identify the molecular and genetic determinants controlling the natural variation in nerve cell number, examining the populations of photoreceptors and bipolar cells. It will determine how this variation in afferent and target cell number modulates the dendritic morphology of the bipolar cell. It will, consequently, clarify the developmental events and their underlying mechanisms that produce the functional architecture and connectivity of the retina. These studies will contribute to our understanding of retinal development and degeneration, and will enlighten our approach in developing treatments for retinal disease, particularly where the latter seek to re- establish connectivity following cell replacement therapy.