Molecular cloning, sequencing and tissue expression of vasotocin and isotocin precursor genes from Ostariophysian catfishes: phylogeny and evolutionary considerations in teleosts

Abstract

Basic and neutral neurohypophyseal (NH) nonapeptides have evolved from vasotocin (VT) by a gene duplication at the base of the gnathostome lineage. In teleosts, VT and IT are the basic and neutral peptides, respectively. In the present study, VT and IT precursor genes of Heteropneustes fossilis and Clarias batrachus (Siluriformes, Ostariophysi) were cloned and sequenced. The channel catfish Icatalurus punctatus NH precursor sequences were obtained from EST database. The catfish NH sequences were used along with the available Acanthopterygii and other vertebrate NH precursor sequences to draw phylogenetic inference on the evolutionary history of the teleost NH peptides. Synteny analysis of the NH gene loci in various teleost species was done to complement the phylogenetic analysis. In H. fossilis, the NH transcripts were also sequenced from the ovary. The cloned genes and the deduced precursor proteins showed conserved characteristics of the NH nonapeptide precursors. The genes are expressed in brain and ovary (follicular envelope) of H. fossilis with higher transcript abundance in the brain. The addition of the catfish sequences in the phylogenetic analysis revealed that the VT and IT precursors of the species-rich superorders of teleosts have a distinct phylogenetic history with the Acanthopterygii VT and IT precursors sharing a less evolutionary distance and the Ostariophysi VT and IT having a greater evolutionary distance. The genomic location of VT and IT precursors, and synteny analysis of the NH loci lend support to the phylogenetic inference and suggest a footprint of fish- specific whole genome duplication (3R) and subsequent diploidization in the NH loci. The VT and IT precursor genes are most likely lineage-specific paralogs resulting from differential losses of the 3R NH paralogs in the two superorders. The independent yet consistent retention of VT and IT in the two superorders might be directed by a stringent ligand-receptor selectivity.

Investigation of the Gene Encoding Isotocin and its Expression in Cinnamon Clownfish, Amphiprion melanopus

“…4). This is consistent with a previous finding of the expression of the nonapeptide in the brain and ovaries of an ostariophysian catfish [1]. Detection of the IT-specific transcript in the gonads reflected its expression in the ovaries, as the largest clownfish in the social group, probably a female, was used for RNA isolation.…”

Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish, Clarias batrachus

“…The results of the present study are in agreement with a recent study showing reproduction phase-dependent changes in IST mRNA expression in the brain of C. batrachus (14). IST mRNA expression showed a steady increase from the preparatory through spawning phases followed by a drastic reduction in the post-spawning phase (14). Although changes in IST mRNA expression were observed in the entire telencephalon (14), the present study demonstrates reproduction-phase dependent changes in IST-IR fibre innervation specifically in the NPPa.…”

“…Immunoreactivity showed a drastic reduction during the postspawning phase. The results of the present study are in agreement with a recent study showing reproduction phase-dependent changes in IST mRNA expression in the brain of C. batrachus (14). IST mRNA expression showed a steady increase from the preparatory through spawning phases followed by a drastic reduction in the post-spawning phase (14).…”

“…Changes in IST‐IR fibres in the NPPa also appear to be consistent with the reports in other teleosts. IST levels in the brain of N. melanostomus, measured using high‐performance liquid chromatography showed a peak during the spawning phase and a significant reduction in postspawning phase . In the NPO of female O. latipes , the IST‐IR neurones dominated during the prespawning phase and showed a significant decrease in the postspawning phase .…”

“…While treatment of the superfused pituitary tissue of C. batrachus with IST peptide stimulates LH cells , injection of IST increased the circulating levels of LH by up to 167% in C. auratus . IST mRNA levels in the brain of catfish , IST concentration in the brain of round goby, Neogobius melanostomus , and IST‐immunoreactive (IST‐IR) neurones in the preoptic‐hypothalamic region of medaka, Oryzias latipes , showed reproduction phase‐dependent variation, with a peak during the spawning phase and a significant reduction in the postspawning phase . IST‐synthesising neurones are present in the nucleus preopticus (NPO) and reside in a strategic location close to DA neurones of NPPa .…”