The zebrafish, a teleost model recapitulating the mammalian molecular events during endocrine development and function

In the last decades, the tropical teleost zebrafish (Danio rerio) has proved to be an excellent vertebrate system to model mammalian molecular events occurring during embryonic development, organ formation and adult physiology, either under normal or pathological conditions. Low costs and small dimensions, external fertilization and high fecundity, tissue transparency, rapid development, availability of mutant and transgenic lines, easy manipulability for gene perturbation and pharmacological screening, are some examples of the advantages characterizing this model organism. In the past 15 years, the use of zebrafish in the endocrinology field has been mainly focused on the analysis of endocrine organ development. Our team and other research groups have elucidated the main steps leading to the formation of endocrine glands such as pancreatic islets and thyroid, hypothalamus and pituitary, interrenal gland and gonads. Comparison of the zebrafish endocrine system to that of mammals has demonstrated that the systems are sufficiently similar for zebrafish to be employed as a model for endocrine research. In more recent years, new zebrafish-based tools have been generated to elucidate in vivo the molecular cross-talks occurring among cells, tissues and organs. Signalling pathway reporter lines represent an interesting implementation of classical transgenesis to visualize in vivo, in an intact organism, the anatomical regions that, in a given time interval, are responding to a specific signalling pathway. To generate these transgenic fish lines, signal specific responsive sequences, identified at the genomic level, are multimerized and placed upstream of reporter genes, typically encoding for fluorescent proteins such as GFP or mCherry. At present, a series of pathway reporter lines are already available, among which Bmp, Shh, FGF, Notch, TGFβ, Wnt, hypoxia and glucocorticoid signalling. Our group is currently generating and validating additional lines, among which the cAMP/CREB pathway, while others, such as thyroid hormone and Foxo signalling, are in the planning phase. Preliminary results and envisaged applications will be presented and discussed.