Ontogeny of the GnRH systems in zebrafish brain: In situ hybridization and promoter-reporter expression analyses in intact animals

Ori Palevitch, Katherine Kight, Eytan Abraham, Susan Wray, Yonathan Zohar, Yoav Gothilf*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The ontogeny of two gonadotropin-releasing-hormone (GnRH) systems, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), was investigated in zebrafish (Danio rerio). In situ hybridization (ISH) first detected sGnRH mRNA-expressing cells at 1 day post-fertilization (pf) anterior to the developing olfactory organs. Subsequently, cells were seen along the ventral olfactory organs and the olfactory bulbs, reaching the terminal nerve (TN) ganglion at 5-6 days pf. Some cells were detected passing posteriorly through the ventral telencephalon (10-25 days pf), and by 25-30 days pf, sGnRH cells were found in the hypothalamic/preoptic area. Continuous documentation in live zebrafish was achieved by a promoter-reporter expression system. The expression of enhanced green fluorescent protein (EGFP) driven by the sGnRH promoter allowed the earlier detection of cells and projections and the migration of sGnRH neurons. This expression system revealed that long leading processes, presumably axons, preceded the migration of the sGnRH neuron somata. cGnRH-II mRNA expressing cells were initially detected (1 day pf) by ISH analysis at lateral aspects of the midbrain and later on (starting at 5 days pf) at the midline of the midbrain tegmentum. Detection of red fluorescent protein (DsRed) driven by the cGnRH-II promoter confirmed the midbrain expression domain and identified specific hindbrain and forebrain cGnRH-II-cells that were not identified by ISH. The forebrain DsRed-expressing cells seemed to emerge from the same site as the sGnRH-EGFP-expressing cells, as revealed by co-injection of both constructs. These studies indicate that zebrafish TN and hypothalamic sGnRH cell populations share a common embryonic origin and migratory path, and that midbrain cGnRH-II cells originate within the midbrain.

Original languageEnglish
Pages (from-to)313-322
Number of pages10
JournalCell and Tissue Research
Issue number2
StatePublished - Feb 2007


FundersFunder number
US-Israel Bi-national Agricultural Research and Development
National Institute of Neurological Disorders and StrokeZ01NS002824
United States - Israel Binational Agricultural Research and Development Fund3428-03


    • Danio rerio (Teleostei)
    • Gonadotropin-releasing hormone
    • In situ hybridization
    • Neuronal migration
    • Reporter protein


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