Characterization of two forms of cocaine- and amphetamine-regulated transcript (CART) peptide precursors in goldfish: molecular cloning and distribution, modulation of expression by nutritional status, and interactions with leptin.

Abstract

Complementary DNAs encoding two forms of cocaine- and amphetamine-regulated transcript (CART) peptide precursors were identified from goldfish brain and named CART I and CART II. Each cDNA contains a signal peptide sequence, the putative CART-like peptide, and a carboxy-terminal extension peptide. Form I encodes a 117-amino acid pro-CART, whereas form II encodes a 120-amino acid pro-CART. Both forms resemble mammalian CART peptides. Each goldfish CART precursor is encoded by three exons interrupted by two introns within genomic DNA. RT-PCR, slot blot, and Northern blot analysis showed that the mRNAs for form I and II precursors have a widespread distribution. Form I and II are present in the brain, pituitary, eye, gonads, and kidney. Form I is also present in the gill. In the brain, form I is predominant in the olfactory bulb and hypothalamus, and form II is predominant in the optic tectum. Food deprivation for 96 h induced a decrease in form I mRNA levels in the telencephalon-preoptic region, hypothalamus, and olfactory bulb and in form II mRNA expression in the olfactory bulb. An increase in mRNA levels was observed 2 h following a meal in the olfactory bulbs and hypothalamus for form I whereas no postprandial changes in form II mRNA levels were observed. Intracerebroventricular injections of human CART alone induced a significant decrease in food intake. Injections of leptin reinforced the inhibition of feeding behavior and food intake seen in CART-treated fish. Central injection of leptin induced an increase in CART I mRNA in the optic tectum, hypothalamus, and olfactory bulbs but had no effect on CART II mRNA expression in the brain. These results suggest that CART peptides act as leptin-regulated satiety factors in goldfish and that they might have other physiological roles besides feeding, possibly in sensory information processing.