A role for tight junction-associated MARVEL proteins in larval sea lamprey (Petromyzon marinus) osmoregulation

Abstract

This study reports on tight junction-associated MARVEL proteins of larval sea lamprey () and their potential role in ammocoete osmoregulation. Two occludin isoforms (designated Ocln and Ocln-a) and a tricellulin (Tric) were identified. Transcripts encoding , and were broadly expressed in larval lamprey, with the greatest abundance of in the gut, liver and kidney, in the gill and skin, and in the kidney. Ocln and Ocln-a resolved as ∼63 kDa and ∼35 kDa MW proteins, respectively, while Tric resolved as a ∼50 kDa protein. Ocln immunolocalized to the gill vasculature and in gill mucous cells while Ocln-a localized to the gill pouch and gill epithelium. Both Ocln and Ocln-a localized in the nephron, the epidermis and the luminal side of the gut. In branchial tissue, Tric exhibited punctate localization, consistent with its presence at regions of tricellular contact. Following ion-poor water (IPW) acclimation of ammocoetes, serum [Na] and [Cl] decreased, but not [Ca], and carcass moisture content increased. In association, Ocln abundance increased in the skin and kidney, but reduced in the gill of IPW-acclimated ammocoetes while Ocln-a abundance reduced in the kidney only. Tric abundance increased in the gill. Region-specific alterations in , and mRNA abundance were also observed in the gut. Data support a role for Ocln, Ocln-a and Tric in the osmoregulatory strategies of a basal vertebrate.

Claudins of sea lamprey (Petromyzon marinus) – organ‐specific expression and transcriptional responses to water of varying ion content

“…Previous reports have shown that IPW acclimation of ammocoetes leads to a reduction in circulating Na + and Cl − levels and causes general body hydration (Kolosov et al ., ), whereas SW acclimation of transformed juveniles increases blood Na + and Cl − levels (Beamish, ; Ferreira‐Martins et al ., ; Reis‐Santos et al ., ). In teleosts, previous studies have indicated that paracellular permeability and mRNA abundance of TJ proteins are altered in gill and skin epithelia on exposure or acclimation to IPW ( e.g ., Chasiotis, Kolosov, Bui, & Kelly, ; Gauberg et al ., ).…”

“…The identity of annotated genes was confirmed using sequence identity comparison and NCBI BLAST. RNA extraction from lamprey tissues and cDNA synthesis (mentioned earlier) were conducted according to previously published protocols (Kolosov et al ., ). PCR products employing gene‐specific primers were sequenced, and their identity was confirmed by comparing with vertebrate homologues available in the NCBI database as well as by comparing with original genomic data in Ensembl Genome Browser.…”

“…In contrast, some Cldns, such as members of the Cldn‐10 subfamily, have been linked to “selectively permeable” TJs and enhanced Na + secretion across branchial epithelia of teleosts (Bui et al ., ; Bui & Kelly, ; Loh et al ., ; Marshall et al ., ). Similarly, in the kidney and gastrointestinal (GI) tract, the spatial expression of cldns/Cldns and other TJ proteins (or transcripts encoding them), such as ocln/Ocln and tric/Tric, as well as alterations in abundance and TJ morphology after changes in environmental ion levels, supports the idea that TJ proteins play a crucial role in fish osmoregulation ( e.g ., Chasiotis & Kelly, ; Clelland et al ., ; Duffy et al ., ; Hu et al ., ; Kolosov et al ., ). Nonetheless, with the exception of one study ( i.e ., Kolosov et al ., ), current understanding of how TJ proteins participate in the osmoregulatory physiology of fishes is based solely on teleost models.…”

“…Similarly, in the kidney and gastrointestinal (GI) tract, the spatial expression of cldns/Cldns and other TJ proteins (or transcripts encoding them), such as ocln/Ocln and tric/Tric, as well as alterations in abundance and TJ morphology after changes in environmental ion levels, supports the idea that TJ proteins play a crucial role in fish osmoregulation ( e.g ., Chasiotis & Kelly, ; Clelland et al ., ; Duffy et al ., ; Hu et al ., ; Kolosov et al ., ). Nonetheless, with the exception of one study ( i.e ., Kolosov et al ., ), current understanding of how TJ proteins participate in the osmoregulatory physiology of fishes is based solely on teleost models. Recently, steps have been taken to consider how TJ proteins might play a role in the osmoregulatory physiology of other fish groups by initiating studies on sea lamprey ( Petromyzon marinus , 1758 L) TJ‐associated MARVEL proteins such as Ocln and Tric (Kolosov et al ., ).…”

“…Nonetheless, with the exception of one study ( i.e ., Kolosov et al ., ), current understanding of how TJ proteins participate in the osmoregulatory physiology of fishes is based solely on teleost models. Recently, steps have been taken to consider how TJ proteins might play a role in the osmoregulatory physiology of other fish groups by initiating studies on sea lamprey ( Petromyzon marinus , 1758 L) TJ‐associated MARVEL proteins such as Ocln and Tric (Kolosov et al ., ). To date, no study has examined how Cldn TJ proteins participate in the regulation of salt and water balance in sea lamprey.…”