A zebrafish model to investigate beta-cell functional maturation and heterogeneity

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-cells are a small population of highly specialized endocrine cells in the pancreas that produce insulin, a hormone required for survival and key to the proper regulation of energy homeostasis. While there is an increasing appreciation that there exists considerable -cell heterogeneity, our understanding of the basis and significance of this heterogeneity, along with the factors guiding -cell maturation, remain poorly understood. Zebrafish provide an excellent model to elucidate the molecular mechanisms underlying the development and maturation of -cells. From a genetic and physiological perspective, zebrafish are surprisingly similar to humans. Indeed, all organs and cells involved in controlling mammalian metabolism are present in these fish. They are also readily amenable to genetic engineering to generate novel lines of fish to permit sophisticated probing of the function of genes, proteins and cells. A particularly useful aspect of using zebrafish as a model organism is the fact that they develop very rapidly. Moreover, the embryos are remarkably transparent, a characteristic that makes them ideal to study vertebrate development. Therefore, with zebrafish we can visualize the entire process of -cell development, as well as monitor -cell functional maturation, in real time in a living organism. Our overall goal is to delineate the molecular pathways underlying the maturation of insulin-secreting cells, and to investigate -cell heterogeneity from a developmental and physiological perspective. This will be achieved by the following three specific objectives: Objective 1: To delineate -cell functional maturation in zebrafish. We will use a novel zebrafish transgenic line which allows visualization of -cell stimulus-secretion coupling in vivo. Objective 2: To determine whether the different lineages of -cells arising during pancreas development contribute to -cell heterogeneity in the adult zebrafish pancreas. One of our main hypotheses is that -cells are composed of different sub-populations which are specialized either to secrete insulin in response to nutrients or proliferate when tissue damage occurs. To investigate this aspect, we will use a novel zebrafish transgenic line where we can label different -cell populations and follow them through the entire life of the fish to assess their specific genetic profile and function. Objective 3: To delineate the contribution of nutrient sensing to -cell functional maturation. How zebrafish -cells sense nutrients and coordinate responses to stimuli has not been investigated. We will use genetic tools combined with live imaging approaches to probe the key components essential to proper nutrient sensing. Collectively, this unprecedented depth of -cell characterization will provide a deeper understanding of -cell biology and the molecular mechanisms that control -cell development, maturation and function.