Genomic organization and differential expression of channel catfish MHC class I genes

• Published in: Developmental and comparative immunology 2001-09, Vol.25 (7), p.579-595
• Main Authors: Antao, A B, Wilson, M, Wang, J, Bengtén, E, Miller, N W, Clem, L W, Chinchar, V G
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; DNA-Binding Proteins - isolation & purification; Freshwater; Gene Expression Regulation; Genes, MHC Class I; Genomic Library; Icpu-UA/26 gene; Icpu-UA/3 gene; Ictaluridae - genetics; Ictaluridae - immunology; Ictalurus punctatus; Major histocompatibility complex; Molecular Sequence Data; Nuclear Proteins - isolation & purification; Regulatory Sequences, Nucleic Acid; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Tissue Distribution
• ISSN: 0145-305X
• DOI: 10.1016/s0145-305x(01)00017-9

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.