Structure, linkage mapping and expression of the heart-type fatty acid-binding protein gene (fabp3) from zebrafish (Danio rerio)

We have determined the cDNA nucleotide sequence, deduced the amino acid sequence and defined the gene structure for the cellular heart-type (H-FABP) or fatty acid-binding protein 3 (FABP3) from zebrafish. The zebrafish FABP3 exhibited the greatest amino acid sequence identity to fish and mammalian heart-type FABPs. 3' RACE and 5' RLM-RACE mapped two alternative polyadenylation sites and three transcription start sites, respectively. Southern blot and hybridization analysis indicated that a single fabp3 gene exists in the zebrafish genome. The zebrafish fabp3 gene consists of four exons interrupted by three introns with identical exon/intron structure and coding capacity with that of orthologous mammalian H-FABP genes. Radiation hybrid mapping assigned the zebrafish fabp3 gene to linkage group 19 of the zebrafish genome. Comparative genomic analysis revealed conserved syntenies of the zebrafish fabp3 gene and the orthologous human and mouse fabp3 genes. Northern blot analysis detected an mRNA transcript of 780 nucleotides. In situ hybridization of the zebrafish fabp3 -specific oligonucleotide probe to tissue sections of adult zebrafish revealed that the fabp3 mRNA was localized in the ovary and liver, but not in the heart, muscle or brain as reported for the mammalian fabp3 gene transcript. RT-PCR, however, detected zebrafish fabp3 mRNA in all the tissues examined. Emulsion autoradiography further revealed that the zebrafish fabp3 mRNA was most abundant in primary growth stage (stage I) oocytes and decreased during the oocyte growth phase. The fabp3 mRNA levels were reduced and restricted to the ooplasm of cortical alveolus stage (stage II) oocytes, and nearly undetectable in stage III and matured oocytes. Inspection of the 5' upstream sequence of the zebrafish fabp3 gene revealed a number of cis elements that may be involved in the expression of the zebrafish fabp3 gene in oocytes and liver.