Molecular Characterization and Expression of Urotensin II and its Receptor in the Flounder (Platichthys flesus): A Hormone System Supporting Body Fluid Homeostasis in Euryhaline Fish

Abstract

Urotensin II (UII) is a potent vasoconstrictor in mammals, but the source of circulating UII remains unclear. Investigations of the caudal neurosecretory system (CNSS), considered the major source of UII in fish, alongside target tissue expression of UII receptor (UT), can provide valuable insights into this highly conserved regulatory system. We report UII gene characterization, expression of the first fish UT, and responses to salinity challenge in flounder. The 12-aa UII peptide shares 73% sequence identity with pig and human UII. Flounder UT receptor shares 56.7% identity with rat. Although the CNSS is the major site of UII expression, RT-PCR revealed expression of UII and UT in all tissues tested. Around 30-40% of large CNSS Dahlgren cells expressed UII, alone or in combination with urotensin I and/or corticotrophin releasing hormone. Immunolocalization of UT in osmoregulatory tissues (gill, kidney) was associated with vascular elements. There were no consistent differences in CNSS UII expression or plasma UII between seawater (SW)- and freshwater (FW)-adapted fish, although gill and kidney UT expression was lower in FW animals. After acute transfer from SW to FW, plasma UII and kidney and gill UT expression were reduced, whereas UT expression in kidney was increased after reverse transfer. UII appears to be more important to combat dehydration and salt-loading in SW than the hemodilution faced in FW. Potentially, altered target tissue sensitivity through changes in UT expression, is an important physiological controlling mechanism, not only relevant for migratory fish but also likely conserved in mammals.

UII and UT in grouper: cloning and effects on the transcription of hormones related to growth control

“…Moreover, the difference is that the ovary instead of the CNSS is the major site of UT expression. This result is quite consistent with the results obtained in flounder with the exception that the site with the highest expression of UT is the midbrain of flounder (Lu et al 2006). The mRNA expression of UII and UT in various fish tissues indicate that this peptide also has tissue-specific autocrine/ -free medium (with 2 mM EGTA) and then challenged with a single dose of UII (1 nM).…”

“…The detection of UII in the pituitary, forebrain, midbrain, and hindbrain in grouper is in accordance with the results obtained in flounder (Lu et al 2006) and frogs (Coulouarn et al 1998). Among the peripheral tissues, the highest expression of UII was observed in the ovary, and this result is different from the results obtained in flounder, which exhibited the highest expression of UII in the rectum, even though the ovary was also found to be an important site of UII expression (Lu et al 2006). However, in eels, UII was only detected in the CNSS using the RT-PCR technique (Nobata et al 2011).…”

“…Consistent with the results of previous studies in teleosts (Le Mevel et al 2008), the CNSS is the major site of UII expression, although UII is also expressed at very high levels in the CNS. The detection of UII in the pituitary, forebrain, midbrain, and hindbrain in grouper is in accordance with the results obtained in flounder (Lu et al 2006) and frogs (Coulouarn et al 1998). Among the peripheral tissues, the highest expression of UII was observed in the ovary, and this result is different from the results obtained in flounder, which exhibited the highest expression of UII in the rectum, even though the ovary was also found to be an important site of UII expression (Lu et al 2006).…”

“…In mammals, both UII and UT are widely expressed in the CNS and various peripheral tissues (Onan et al 2004, Malagon et al 2008. UII has been cloned from many fish species, such as flounder (Lu et al 2006), killifish (Evans et al 2011), and eels (Nobata et al 2011). Although the caudal neurosecretory system (CNSS) is the major site of UII expression, as in mammals, UII is also widely expressed in the CNS, such as in the optic nerve, different parts of the brain, hypothalamus, pituitary, and spinal cord, and in peripheral tissues, including gill, head kidney, kidney, bladder, stomach, intestine, rectum, heart, spleen, liver, and ovary (Lu et al 2006, Evans et al 2011.…”

“…UII has been cloned from many fish species, such as flounder (Lu et al 2006), killifish (Evans et al 2011), and eels (Nobata et al 2011). Although the caudal neurosecretory system (CNSS) is the major site of UII expression, as in mammals, UII is also widely expressed in the CNS, such as in the optic nerve, different parts of the brain, hypothalamus, pituitary, and spinal cord, and in peripheral tissues, including gill, head kidney, kidney, bladder, stomach, intestine, rectum, heart, spleen, liver, and ovary (Lu et al 2006, Evans et al 2011. The mRNA expression of UT has been identified in the CNSS, CNS, and different peripheral tissues of fish (Lu et al 2006, Evans et al 2011.…”