Endocrine Abstracts

The G protein-coupled receptor PROKR2 play an important and not fully understood role in GnRH-secreting neurons physiology. Indeed, mutations of PROKR2 in humans are known to cause Congenital Hypogonadotropic Hypogonadism (CHH) although with an important reproductive and olfactory phenotypic heterogeneity. The attempt to mimic PROKR2 human allelic variants in mouse model has so far failed to give insights into the mechanisms involved. The zebrafish (ZF), due to its amenability to genetic manipulation and imaging, has proved to be an ideal model organism for studying the early migration of GnRH neurons and the formation of the GnRH network. Nevertheless, only few data are available in the literature concerning the prokineticin-receptors in ZF. We performed bioinformatics analysis using public databases (Pubmed, ZFIN and ENSEMBLE) and bioinformatics tools (UCSC BLAT alignment, Genomicus) unmasking the presence of two well-conserved loci in the ZF genome, on chr1 and chr13, named prokr1a and prokr1b respectively. In order to correlate their expression with GnRH3 neuronal development we performed whole mount in situ hybridization (WISH) and qRT-PCR experiments. WISH experiments revealed peculiar pattern of expression for prok-receptors. Indeed, prokr1a is mainly expressed in midbrain-hindbrain boundary at 36 and 48 hpf and later in development in liver; while prokr1b presented a strong signal in olfactory placode and hypothalamic GnRH neurons starting from 36 hpf. The qRT-PCR results underline how prokr1b displayed higher expression level compared to prokr1a but, most interesting, the expression level start to increase at 24 hpf until 72 hpf, consistently with the migration pattern of GnRH3 fibers. In conclusion, our results suggest that prokr1b is the potential candidate involved in the GnRH-secreting neurons migration process from olfactory placode to their final hypothalamic destination. These data open the possibility to characterize the role of ZF prokineticin-receptors in physiological and pathological conditions thus giving novel insights into the pathogenesis of human CHH due to mutations in the PROKR2 gene.