Four functional GnRH receptors in zebrafish: analysis of structure, signaling, synteny and phylogeny
Why this work is in the frame
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Bibliographic record
Abstract
Reproduction in all vertebrates requires the brain hormone gonadotropin-releasing hormone (GnRH) to activate a cascade of events leading to gametogenesis. All vertebrates studied to date have one to three forms of GnRH in specific but different neurons in the brain. In addition, at least one type of GnRH receptor is present in each vertebrate for activation of specific physiological events within a target cell. Humans possess two types of GnRH (GnRH1 and GnRH2) but only one functional GnRH receptor. Zebrafish, Danio rerio, also have two types of GnRH (GnRH2 and GnRH3), although in contrast to humans, zebrafish appear to have four different GnRH receptors in their genome. To characterize the biological significance of multiple GnRH receptors within a single species, we cloned four GnRH receptor cDNAs from zebrafish and compared their structures, expression, and cell physiology. The zebrafish receptors are 7-transmembrane G-protein coupled receptors with amino-acid sequence identities ranging from 45 to 71% among the four receptors. High sequence similarity was observed among the seven helices of zebrafish GnRHRs compared with the human GnRHR, the green monkey type II GnRHR, and the two goldfish GnRHRs. Also, key amino acids for putative ligand binding, disulfide bond formation, N-glycosylation, and G-protein coupling were present in the extracellular and intracellular domains. The four zebrafish receptors were expressed in a variety of tissues including the brain, eye, and gonads. In an inositol phosphate assay, each receptor was functional as shown by its response to physiological doses of native GnRH peptides; two receptors showed selectivity between GnRH2 and GnRH3. Each of the four receptor genes was mapped to distinct chromosomes. Our phylogenetic and syntenic analysis segregated the four zebrafish GnRH receptors into two distinct phylogenetic groups that are separate gene lineages conserved throughout vertebrate evolution. We suggest the maintenance of four functional GnRH receptors in zebrafish compared with only one in humans may depend either on subfunctionalization or neofunctionalization in fish compared with mammalian GnRH receptors. The differences in structure, location, and response to GnRH forms strongly suggests that the four zebrafish GnRH receptors have novel functions in addition to the conventional activation of the pituitary gland in the reproductive axis.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it