ABSTRACT
Calcium is essential for a variety of functions in animals, including signal transduction, transmission of nerve impulses, and bone and scale growth. In freshwater adapted teleosts, blood calcium levels are maintained constant (2-4 mM) even at low external calcium concentration (< 0.01 mM). Epithelial cells in skin and gill have been implicated in calcium homeostasis. We have cloned a cDNA from Ictalurus punctatus, the channel catfish, that codes for ictacalcin, a novel member of the S100 family of calcium-binding protein. In-situ hybridization demonstrates ictacalcin mRNA is abundant in epithelial cells of olfactory rosette, barbel, skin and gill but not brain or muscle. The presence of ictacalcin protein in these tissues was confirmed by immuno-blot analysis. Tissue extracts and recombinant ictacalcin bind calcium with attendant changes in electrophoretic mobility indicative of changes in protein conformation. The calcium-binding activity and abundant localization of ictacalcin in epithelial cells of several tissues indicates that this protein plays an important role in catfish calcium homeostasis.
Subject(s)
Calcium-Binding Proteins/genetics , Ictaluridae/genetics , Transcription Factors/genetics , Amino Acid Sequence , Animals , Base Sequence , Calcium/metabolism , Calcium-Binding Proteins/chemistry , Calcium-Binding Proteins/isolation & purification , Chemoreceptor Cells/metabolism , Cloning, Molecular , DNA, Complementary/genetics , Epidermis/metabolism , Gills/metabolism , Ictaluridae/metabolism , In Situ Hybridization , Molecular Sequence Data , Multigene Family , Nerve Tissue Proteins/metabolism , Olfactory Pathways/metabolism , Organ Specificity , Protein Conformation , RNA, Messenger/analysis , Receptors, Cell Surface , Recombinant Fusion Proteins/metabolism , Transcription Factors/chemistry , Transcription Factors/isolation & purificationABSTRACT
A cDNA clone (rpS13) encoding the S13 ribosomal protein (rpS13) has been isolated from the catfish Ictalurus punctatus, and is the first example of an rpS13 isolated from a teleost species. The deduced 151-amino-acid (aa) sequence is 96% identical to the rat and human rpS13, extending the evolutionary conservation of this protein.
Subject(s)
Ictaluridae/genetics , Ribosomal Proteins/genetics , Amino Acid Sequence , Animals , Base Sequence , Cloning, Molecular , DNA, Complementary/genetics , DNA, Complementary/isolation & purification , Humans , Ictaluridae/metabolism , Molecular Sequence Data , Rats , Sequence AnalysisABSTRACT
Expressed sequence tags (ESTs) for the catfish (Ictalurus punctatus) were identified and characterized by shotgun sequencing coupled to Northern analysis. We have identified and characterized a number of cDNA clones from a catfish olfactory mucosal library that show differential tissue expression including several that are enriched in chemosensory tissue. Among the novel cDNA clones studied were an olfactory specific beta-tubulin and a novel member of the S-100 family of calcium-binding proteins that is highly expressed in barbel, olfactory mucosa and gill, but not in brain. Several clones of low abundance mRNAs were also identified, including one manifesting a basic-helix-loop-helix (b-HLH) motif that is typical of many transcription factors. Additional cDNA clones whose mRNAs are differentially expressed, but are of unknown function, were also obtained. These results demonstrate the case with which novel gene products enriched in chemosensory tissues can be identified.
