February 15-18, 2009 Washington State Convention Center Seattle ...

TISSUE DISTRIBUTION OF LEPTIN-LIKE MRNA AND CHANGES IN ITS EXPRESSION
AFTER PROLONGED FASTING AND EXPOSURE TO Edwardsiella ictaluri IN CHANNEL
CATFISH
Yasuhiro Kobayashi, Sylvie Quiniou and Brian C. Peterson
Division of Biological and Physical Sciences
Delta State University
Cleveland MS USA
Leptin is thought to be a key pleiotropic cytokine involved in regulation of food intake and energy homeostasis in fish and
mammals. Studies show that nucleotide and amino acid sequence of leptin are poorly conserved among different fish species
and share very little similarity with the mammalian counterpart. An mRNA transcript that encodes leptin-like peptide has been
identified in channel catfish. However, the function of leptin in channel catfish is unknown.
The objectives of this research were to characterize tissue expression of leptin-like mRNA and changes in its expression after
prolonged fasting and exposure to Edwardsiella ictaluri in channel catfish. Catfish leptin-like gene was sequenced by genome
walking. The coding sequence for catfish leptin-like gene was determined by 5’- and 3’-RACE. Our results showed that the
open reading frame of the catfish leptin-like mRNA was 519 bp and encoded a peptide that was 172 amino acids in length.
Analyses of the secondary structure revealed a series of helixes and coils that were conserved among peptides that belonged
to the leptin superfamily. Putative amino acid sequence of the channel catfish leptin-like peptide shared very low sequence
similarities with leptin of other fish species or the mammalian leptin (24-49 %). Leptin-like mRNA expression was detected
in various tissues including brain, stomach, spleen, heart, liver, and trunk kidney but was especially high in liver and trunk kidney.
Expression of leptin-like mRNA in liver and brain was unaffected (P > 0.1) by prolonged fasting or 15 days of refeeding
after prolonged fasting. Hepatic expression of leptin-like mRNA was elevated (P < 0.05) 24 hours after fish were exposed to
E. ictaluri. In comparison, expression of leptin-like mRNA in trunk kidney and spleen was elevated (P < 0.05) 48 hours after
E. ictaluri exposure. Furthermore, spleen expression of leptin-like mRNA was elevated (P < 0.05) 72 hours post exposure to
E. ictaluri.
Based on our results, catfish leptin-like gene does not seem to assume mammalian leptin functions. Further investigations are
required to clearly define the identity and functions of this transcript.
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