Activities of Amphioxus GH-Like Protein in Osmoregulation: Insight into Origin of Vertebrate GH Family.

Mengyang Li,Chengyan Jiang,Yu Zhang,Shicui Zhang

doi:10.1155/2017/9538685

Abstract

GH is known to play an important role in both growth promotion and osmoregulation in vertebrates. We have shown that amphioxus possesses a single GH-like hormone (GHl) gene encoding a functional protein capable of promoting growth. However, if GHl can mediate osmoregulation remains open. Here, we demonstrated clearly that GHl increased not only the survival rate of amphioxus but also the muscle moisture under high salinity. Moreover, GHl induced the expression of both the ion transporter Na+-K+-ATPase (NKA) and Na+-K+-2Cl− cotransporter (NKCC) in the gill as well as the mediator of GH action IGFl in the hepatic caecum, indicating that GHl fulfills this osmoregulatory activity through the same mechanisms of vertebrate GH. These results together suggest that the osmoregulatory activities of GH had emerged in the basal chordate amphioxus. We also proposed a new model depicting the origin of pituitary hormone family in vertebrates.

Highlights

Growth hormone (GH) and prolactin (PRL) are structurally related pituitary polypeptide hormones that belong to a superfamily of helical cytokines
We demonstrated that amphioxus GH-like hormone (GHl), like vertebrate GH, was able to induce the expression of nka and nkcc in the gill in vivo
By contrast, when the same animals were injected with saline plus recombinant protein of amphioxus GHl (rGHl) or rzGH, their muscle moisture was increased to 83.7% and 86.0% as well as 83.5% and 85.1% at 24 and 48 h after injection (Figure 4(b)), individually

Summary

Introduction

Growth hormone (GH) and prolactin (PRL) are structurally related pituitary polypeptide hormones that belong to a superfamily of helical cytokines. Both GH and PRL act by interacting with single transmembrane domain receptors that are structurally related and belong to the type 1 cytokine receptor superfamily [1, 2] These hormones and their receptors are believed to have evolved from common ancestral genes through gene duplication and subsequent divergence early in vertebrate evolution [3, 4]. GH and PRL are both multifunctional and share some overlapping biological properties [4, 5] They are both known to be involved in the regulation of hydromineral balance in fishes [6, 7]. PRL usually maintains plasma homeostasis of fishes in FW by altering salt and water permeability across epithelial cell membranes in the gill, gut, and kidney [22,23,24,25]

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