Gene expression profiles of FABP genes in protochordates, Ciona intestinalis and Branchiostoma belcheri

Abstract

Fatty-acid-binding proteins (FABPs) are small intracellular proteins associated with the transportation of fatty acids. Members of the FABPs share similar amino acid sequences and tertiary structures and form, together with a member of the cellular retinol-binding proteins (CRBPs), the intracellular-lipid-binding protein (iLBP) family. In vertebrates, several types of FABP have been isolated and classified into three subfamilies: 2-4. In invertebrates, several FABP-related proteins have been reported in protostomes and amphioxus; however, little is known about the relationship between their phylogenetic positions and expression patterns. We have performed a genome-wide survey of FABP-related genes in protochordates: amphioxus Branchiostoma belcheri and the ascidian Ciona intestinalis. Comprehensive BLAST searches in NCBI and the Ciona Ghost Database by using amino acid sequences of all FABPs have revealed that the ascidian C. intestinalis and amphioxus B. belcheri contain six and seven FABP-related genes in their haploid genomes, respectively. Expression pattern analyses by whole-mount in situ hybridization in Ciona transparent juveniles and serial-section in situ hybridizations in adult amphioxus have revealed that all genes are mainly expressed in the postpharyngeal digestive tract. In particular, the expression of FABP-related genes of subfamily-2 (liver/ileum type) and subfamily-3 (intestinal type) in the ascidian pyloric gland and amphioxus hepatic cecum provides insight into the evolution of hepatic-related structures of chordates and FABP-related genes.

Comparative Transcriptomic Analysis Reveals the Functionally Segmented Intestine in Tunicate Ascidian

“…It is known that in mice, the pancreas derives from the foregut endoderm, which is formed by a small field of epithelial precursor cells expressed by pancreatic duodenal transcription factor 1 [ 18 ]. A hepatopancreas (also called a pyloric gland), as an accessory organ, is a branching structure developed from the boundary between the stomach and intestine in ascidians [ 48 , 49 ]. In a previous study, the expression of Ciona homologs of pancreatic- and gastric-related exocrine enzyme genes and their transcriptional regulator genes is restricted to the Ciona stomach [ 15 , 19 ].…”

Machinery and Developmental Role of Retinoic Acid Signaling in Echinoderms

“…Previous studies have indicated that several fabp-like genes have RA transportation capacity in protostomes, although their orthology with vertebrate CRABP genes is not supported [29,30]. In deuterostomes, Orito et al [31] classified vertebrate FABPs into three subfamilies and identified the basal gene(s) of each subfamily using urochordate genomic data; however, they did not identify any genes that were orthologous with the crabp and rbp genes, suggesting that CRABPs are components specific to vertebrates [31]. By contrast, based on sea urchin genomic data, one crabp gene, two rbp genes (rbp-1 and rbp-2), and two fabp genes (fabp-1 and fabp-2) were identified [32], although no phylogenetic analysis has been conducted.…”