From trascriptomic analysis to in vivo functional experiments: zebrafish as a model for studying GnRH system

GnRH neurons are a small group of hypothalamic neurons that controls reproductive functions and fertility in mammals. During embryonic life, GnRH neurons arise from the olfacory placode and migrate towards the hypothalamus throughout the nasal mesenchyme and the forebrain. Once they have established in their final location, they extend their axons to the median eminence where GnRH is secreted. Defects in the development of the this neuroendocrine system could lead to rare genetic disorders such as Kallmann Syndrome (KS) and Hypogonadotropic Hypogonadism (HH). To date, the genetic basis of such syndromes is largely still unknown and only few mutated genes have been identified. The study of GnRH neuron develpoment is difficult because GnRH neurons are small in numbers and scattered along the migratory route, making complex their isolation. Here, we have taken advantage from a transgenic rat carrying GFP-labelled GnRH neurons and FACS to isolate GnRH neurons and perform a gene expression analysis to generate a trascriptome profile of GnRH neurons. Specifically, GnRH neurons at three different embryonic stages that represent the beginning, the transition from nose to forebrain and the cease of migration have been isolated. GFP-positive cells have been separated from GFP-negative cells by FACS and gene expression analysis performed using the Affymetrix GeneChip. All arrays have been normalized and data filtered by removing the probes with the smallest variances across the arrays. We have classified the differentially expressed genes into gene ontology pathways by using bioinformatic tools and selected a small number of genes associated to migration and neurite extension pathways. To study the functional relevance of these novel genes we first performed in situ hybridization experiments in zebrafish embryos to study their expression pattern during GnRH neuron development and started gene knock-down experiments with morfolinos.