Transcriptional regulation of crb and mpp5 genes in nuclear space: Coupling nuclear polarization with cell polarization at the level of transcription

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Differential gene expression is essential for normal tissue development and functions. Gene expression is regulated not only by cis- and trans-regulatory elements but also by the organization of the chromatin in the three-dimensional (3D) nuclear space. However, how the transcription of functionally-related genes is coordinated in 3D nuclear space in vivo is not clearly understood. This project will study how the differential transcription of the genes related to cell polarization and patterning are spatially coordinated in the nuclei of zebrafish retinal cells. The resultant polarization and patterning are important in light sensing in retinal cells. The significance of this study is also applicable to other tissues because polarity genes are required to be expressed in a coordinated fashion for proper tissue polarization, integrity, and function. The research will also contribute to the training of early career scientists and STEM workers through a structured mentoring program. The Crumbs and MPP5 genes and zebrafish retina form a unique system to study the roles of 3D nuclear organization in gene expression regulation. The Crumbs gene family has five members, and the MPP5 gene family has two members. Within the gene families, genes are differentially expressed in retinal cells; however, between the two families, some members are coexpressed in the same set of cell types for coordinated functions. The nuclei of zebrafish red, green, and blue cone photoreceptors (RGB cones) are almost twice as large as the nuclei of other retinal cells, offering the possibility of high-resolution 3D gene mapping. In addition, these nuclei are aligned in a mirror-symmetric pentameric pattern to allow defined spatial registration of gene positioning. This research will evaluate how in vivo nuclear positioning of these genes is correlated with their differential expression patterns by in situ hybridization and chromatin tagging. In addition, the roles of the enhancers of crb2b and mpp5b genes in gene positioning will be evaluated by genetic and transgenic approaches.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.