Research paperGenomic structure and promoter functional analysis of GnRH3 gene in large yellow croaker (Larimichthys crocea)

- GnRH3 gene was firstly identified and characterized in L. crocea.
- Special exon-intron organizations of GnRH3 were detected in the different families.
- Promoter of LcGnRH3 can drive EGFP expression in the larval zebrafish brain.

Gonadotropin-releasing hormone III (GnRH3) is considered to be a key neurohormone in fish reproduction control. In the present study, the cDNA and genomic sequences of GnRH3 were cloned and characterized from large yellow croaker Larimichthys crocea. The cDNA encoded a protein of 99 amino acids with four functional motifs. The full-length genome sequence was composed of 3797 nucleotides, including four exons and three introns. Higher identities of amino acid sequences and conserved exon-intron organizations were found between LcGnRH3 and other GnRH3 genes. In addition, some special features of the sequences were detected in partial species. For example, two specific residues (V and A) were found in the family Sciaenidae, and the unique 75-72 bp type of the open reading frame 2 and 3 existed in the family Cyprinidae. Analysis of the 2576 bp promoter fragment of LcGnRH3 showed a number of transcription factor binding sites, such as AP1, CREB, GATA-1, HSF, FOXA2, and FOXL1. Promoter functional analysis using an EGFP reporter fusion in zebrafish larvae presented positive signals in the brain, including the olfactory region, the terminal nerve ganglion, the telencephalon, and the hypothalamus. The expression pattern was generally consistent with the endogenous GnRH3 GFP-expressing transgenic zebrafish lines, but the details were different. These results indicate that the structure and function of LcGnRH3 are generally similar to the other teleost GnRH3 genes, but there exist some distinctions among them.

The GnRH3 gene was isolated from large yellow croaker (Larimichthys crocea). Higher identities of amino acid sequences and conservative exon-intron organizations were found between LcGnRH3 and other GnRH3. Functional analysis of the LcGnRH3 promoter using an EGFP reporter presented that a 2576 bp region had the specific activity in the brain of zebrafish embryos, including the olfactory region, the terminal nerve ganglion, the telencephalon, and the hypothalamus. These results indicated that the structure and function of LcGnRH3 were generally similar to other teleost GnRH3 genes, but there existed some distinctions among them.47