Molecular control of zebrafish pancreatic islet specification

The aim of this project is to characterize the molecular and cell biological mechanisms of regeneration of insulin- producing beta-cells. Pancreatic beta-cells produce hormones, the most important of which, insulin, plays a crucial role in glucose homeostasis. Loss or dysfunction of beta-cells leads to diabetes mellitus, an incurable chronic disease with major public health implications. While insulin injection is the major treatment currently used for insulin-dependent diabetes, future therapies aim to re-establish the potential for regulated insulin production in patients through the regeneration of beta-cells. To achieve this goal, it is necessary to improve our understanding of the control of beta-cell differentiation and regeneration. This project utilizes zebrafish embryos, in which beta-cell regeneration can be studied in the living animal using stable transgenic gene expression, as well as by transient modulation of gene function. Early studies showed that reduction of the conserved homeobox-transcription factors Hb9 or Pdx1 using antisense morpholinos leads to a loss of beta-cell precursors. Additional experiments indicated that this beta-cell loss is reversed later in development by cellular regeneration. The data showed that beta-cell recovery occurs by two mechanisms that are differentially regulated by hb9 and pdx1 function. Furthermore, knockdown of both hb9 and pdx1 led to irreversible beta-cell loss. In this project, new methods for the fate mapping of endocrine cells will be established and the different types of beta-cell regeneration, as regulated by the functions of Pdx1 and Hb9, will be characterized.