A Novel Guanylin Family (Guanylin, Uroguanylin, and Renoguanylin) in Eels

Abstract

As the intestine is an essential organ for fish osmoregulation, the intestinal hormone guanylins may perform major functions, especially in euryhaline fish such as eels and salmonids. From the intestine of an eel, we identified cDNAs encoding three distinct guanylin-like peptides. Based on the sequence of mature peptide and sites of production, we named them guanylin, uroguanylin, and renoguanylin. Renoguanylin is a novel peptide that possesses the characteristics of both guanylin and uroguanylin and was abundantly expressed in the kidney. By immunohistochemistry, guanylin was localized exclusively in goblet cells, but not enterochromaffin cells, of the intestine. After transfer of eels from fresh water to seawater, mRNA expression of guanylin and uroguanylin did not change for 3 h, but it increased after 24 h. The increase was profound (2-6-fold) after adaptation to seawater. The expression of uroguanylin was also up-regulated in the kidney of seawater-adapted eels, but that of renoguanylin was not so prominent as other guanylins in both intestine and kidney. Collectively, the novel eel guanylin family appears to have important functions for seawater adaptation, particularly long-term adaptation. Eel guanylin may be secreted from goblet cells into the lumen with mucus in response to increased luminal osmolality and act on the epithelium to regulate water and salt absorption.

A novel role for uroguanylin in the regulation of sodium balance

“…A biological role for uroguanylin in the regulation of body sodium balance may be the mammalian counterpart to the possible contribution of uroguanylin to the processes controlling osmoregulation in euryhaline fish, which can adapt to living in either freshwater or seawater conditions. For example, uroguanylin mRNA levels are upregulated in the intestine and kidney when freshwateradapted eels are exposed to the considerably higher NaCl concentration of seawater (16,17). This finding suggests that uroguanylin may function in fish to regulate body sodium levels in a fashion similar to the physiological role that Lorenz et al (7) suggest for uroguanylin in the mouse, where the expression of uroguanylin mRNAs may also be under the influence of NaCl in the diet (14,15).…”

“…The peptides are aligned using the conserved cysteine residues found in the three classes of peptides. Sequences for Zebrafish and Fugu peptides were derived from their respective genome sequencing projects, and those for eel peptides were taken from Yuge et al (17).…”

Regulation of Ion Transport in Eel Intestine by the Homologous Guanylin Family of Peptides

“…Guanylin was first discovered in mammals as an endogenous ligand for STa receptor (Currie et al, 1992). In the eel intestine, guanylin is produced in the goblet (mucus) cells (Yuge et al, 2003), and acts in a luminocrine fashion . Guanylin is also a potent inhibitory hormone for NaCl/water absorption across the SW eel intestine .…”

Predominant expression and cellular distribution of fish Agr2 in renal collecting system

“…Besides, scattered punctuate immunoreactive signals were visually distinguishable in the larval intestine (Fig. 5B), which might be the developing goblet cells (Yuge et al, 2003).…”