Differential expression of duplicated genes for brain-type fatty acid-binding proteins (fabp7a and fabp7b) during early development of the CNS in zebrafish (Danio rerio)

A gene for the zebrafish brain-type fatty acid-binding protein (fabp7b) was identified and its structure defined. The zebrafish fabp7b gene spans 1479 bp and consists of four exons encoding 24, 58, 34 and 16 amino acids, respectively, which is identical to the structure of the fabp7a gene previously described. The complete fabp7b cDNA was isolated by 5′ and 3′ RACE and its nucleotide sequence determined. The deduced amino acid sequence of FABP7B encoded by the zebrafish fabp7b gene shares 82% identity with that of FABP7A encoded by the zebrafish fabp7a gene. A single transcription start site for the fabp7b gene was mapped by 5′ RNA ligase-mediated RACE. Phylogenetic analysis indicated that the duplication of the fabp7 genes occurred in the fish lineage after their divergence from mammals. The zebrafish fabp7b gene was assigned to linkage group 20 by radiation hybrid mapping. Reverse transcription-polymerase chain reaction detected fabp7b transcripts in the same adult tissues as fabp7a transcripts. In the brain, levels of fabp7b transcripts were lower than fabp7a transcripts. Whole-mount in situ hybridization showed that the zebrafish fabp7a transcripts were distributed in the early developing central nervous system. In addition to being expressed in the developing brain and retina, zebrafish fabp7b mRNA was also detected in the swim bladder and pharynx during the embryonic to larval transitory phase.