Cloning and expression profiling of discus fish (symphysodon aequifasciata) prolactin receptor (prlr)
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Date
2009-03
Authors
Hou Keat, Khong
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Abstract
Discus fish (Symphysodon aequifasciata) is a popular ornamental fish that uniquely
exhibits extensive parental care behaviour. Parental discus fish feed their newborns with
bodily-secreted mucus which is essential for the growth and development of free swimming
larvae. Prolactin (PRL) has long been shown to directly influence parental care associated
behaviour in many vertebrate species. We cloned the full-length eDNA of discus fish PRLR
(dfPRLR). dfPRLR consists of 2214 bp, encoding a 632 amino acid mature protein. The
deduced amino acid sequence of dfPRLR composes a putative signal peptide of 23 amino
acids, an extracellular domain of 210 amino acids, a single transmembrane domain of 24
amino acids and an intracellular domain of 375 amino acids. Several characteristics of the
Class I cytokine receptor superfamily were identified in this clone including two pairs of
cysteine residues and a WS motif in the extracellular domain, a single transmembrane
domain, Box I and Box 2 regions in the intracellular domain. The deduced amino acid
sequence of dfPRLR shared 34 to 79% identity among fish and 29 to 36% with vertebrates.
Adult tissue expression results depicted significantly higher expression of dfPRLR in the
osmoregulatory organs including kidney, stomach, gill and intestine followed by an
appreciable level of expression in brain and ovary. Liver, muscle and skin showed low
expression of dfPRLR. Moreover, comparative studies of skin PRLR in parental and nonparental
discus fish showed a significant elevation in PRLR mRNA expression in both male
and female parental fish as compared to non-parental fish. Our findings support the fact that
dfPRLR is involved in osmoregulatory mechanisms and also reproductive functions. The
possible roles of dfPRLR that regulate its parental care behaviour in various epidermal cell
activities such as mucosal cell differentiation, proliferation and production of mucus are
discussed.
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Keywords
Expression profiling , Discus fish (symphysodon aequifasciata)