Evidence of Alternative Splicing as a Regulatory Mechanism for Kissr2 in Pejerrey Fish

Abstract

Kisspeptin receptors are G-Protein-Coupled Receptors that regulate GnRH synthesis and release in vertebrates. Here, we report the gene structure of two kisspeptin receptors (<i>kissr2</i> and <i>kissr3</i>) in pejerrey fish. Genomic analysis exposed a gene structure with 5 exons and 4 introns for <i>kissr2</i> and 6 exons and 5 introns for <i>kissr3</i>. Two alternative variants for both genes, named <i>kissr2_v1</i> and <i>_v2</i>, and <i>kissr3_v1</i> and <i>v2</i>, were revealed by gene expression analyses of several tissues. For both receptors, these variants were originated by alternative splicing retaining intron 3 and intron 4 for <i>kissr2_v2</i> and <i>kissr3_v2</i>, respectively. In the case of <i>kissr2</i>, the intron retention introduced two stop codons leading to a putatively truncated protein whereas for <i>kissr3</i>, the intron retention produced a reading shift leading to a stop codon in exon 5. Modeling and structural analysis of Kissr2 and Kissr3 spliced variants revealed that truncation of the proteins may lead to non-functional proteins, as the structural elements missing are critical for receptor function. To understand the functional significance of splicing variants, the expression pattern for <i>kissr2</i> was characterized on fish subjected to different diets. Fasting induced an up-regulation of <i>kissr2_v1</i> in the hypothalamus, a brain region implicated in control of reproduction and food intake, with no expression of <i>kissr2_v2</i>. On the other hand, fasting did not elicit differential expression in testes and habenula. These results suggest that alternative splicing may play a role in regulating Kissr2 function in pejerrey.