Genomic organization and differential expression of channel catfish MHC class I genes.
Two clones, designated Icpu-UA/3 and Icpu-UA/26, were isolated from a genomic library prepared from a single homozygous gynogenetic channel catfish. Sequence analysis showed that each clone encoded a gene product containing features conserved among MHC class I molecules. The genomic organization of both clones indicated that each domain, with the exception of the cytoplasmic, was encoded by a separate exon. Moreover, like mammals, catfish cytoplasmic regions were encoded by three exons rather than two as previously described for other teleost MHC class I genes. Analysis of nucleotide sequences upstream of catfish class I genes revealed the presence of several regulatory motifs similar to those seen in mammalian class I genes. These included a TATA box, Enhancer B, Site alpha, ISRE, and GAS elements. To determine the functional significance of these elements, EMSAs and tissue expression assays were performed. EMSAs demonstrated that an Enhancer B element within Icpu-UA/26, and an imperfect Enhancer B element and/or a GC-rich region within Icpu-UA/3 were responsible for formation of specific DNA/protein complexes. Expression studies detected Icpu-UA/26 transcripts in all tissues tested, whereas Icpu-UA/3 encoded messages were seen in a limited number of tissues. These results define the intron/exon organization of catfish MHC class I genes, suggest that Icpu-UA/3 encodes a nonclassical gene, and provide the first functional evidence that upstream sequences, similar to those seen in mammalian class I genes, play important roles in regulating teleost MHC gene expression.
Antao
A B
AB
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Wilson
M
M
Wang
J
J
Bengtén
E
E
Miller
N W
NW
Clem
L W
LW
Chinchar
V G
VG
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000302:isolation & purification; D005786:Gene Expression Regulation; D005805:Genes, MHC Class I; D015698:Genomic Library; D007059:Ictaluridae / Q000235:genetics* / Q000276:immunology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000302:isolation & purification; D012045:Regulatory Sequences, Nucleic Acid; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins