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Hypothalamic-pituitary-gonadal endocrine system in the hagfish
1Sado Marine Biological Station, Faculty of Science, Niigata University , Sado , Japan.
Frontiers in Endocrinology
|January 14, 2014
Summary
Hagfish possess a single pituitary gonadotropin (GTH) and evidence of estradiol feedback, indicating a conserved hypothalamic-pituitary-gonadal system in primitive vertebrates.
Area of Science:
- Comparative endocrinology
- Evolutionary biology
- Reproductive physiology
Background:
- The hypothalamic-pituitary system is crucial for vertebrate reproduction, but its primitive form in jawless fish (agnathans) is poorly understood.
- Hagfish, as the most primitive vertebrates, offer insights into the evolution of reproductive endocrine systems.
- Previous research questioned the neuroendocrine control of reproduction in hagfish due to uncertainty about pituitary tropic hormones.
Purpose of the Study:
- To review recent findings on the hypothalamic-pituitary-gonadal (HPG) endocrine system in hagfish.
- To compare the hagfish HPG system with that of jawed vertebrates (gnathostomes).
- To elucidate the evolutionary origins of vertebrate reproductive neuroendocrine regulation.
Main Methods:
- Immunohistochemical analysis of pituitary gonadotropin (GTH).
- Functional studies assessing GTH correlation with gonadal development.
- Investigation of steroid feedback mechanisms (estradiol).
- Detection of immunoreactive gonadotropin-releasing hormone (GnRH) in the brain.
- Identification and functional assessment of hagfish PQRFamide peptide.
Main Results:
- Hagfish possess a single pituitary GTH, unlike the two found in gnathostomes.
- This hagfish GTH shows seasonal changes and correlates with gonadal developmental stages.
- Evidence suggests an estradiol feedback system operates at the hypothalamic-pituitary level in hagfish.
- Immunoreactive GnRH is present in the hagfish brain, with seasonal variations linked to reproduction.
- A hagfish PQRFamide peptide stimulates GTHβ mRNA expression in the pituitary.
Conclusions:
- Hagfish exhibit a neuroendocrine-pituitary hormone system for reproduction with conserved structural and functional features compared to more evolved vertebrates.
- These findings support the early evolution of the vertebrate HPG axis.
- The hagfish reproductive endocrine system provides a model for understanding the phylogenetic development of vertebrate reproduction.
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