TRANSCRIPTIONAL ACTIVITIES IN THE PITUITARIES OF CHANNEL CATFISH BEFORE AND AFTER INDUCED OVULATION BY INJECTION OF CARP PITUITARY EXTRACT AS REVEALED BY EXPRESSED SEQUENCE TAG ANALYSIS

The Fish Molecular Genetics and Biotechnology Laboratory, Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, AL 36849 USA

Expressed sequence tag (EST) analysis was adopted to address physiological changes after injection of carp pituitary extract for induction of ovulation. ESTs were analyzed from cDNA libraries constructed from mRNAs isolated from channel catfish (Ictalurus punctatus) pituitaries before and after induction of ovulation by injection of carp pituitary extract. One hundred randomly picked clones were analyzed. Of the sequences generated, a large percentage (59%) of ESTs was identified as known genes by identity comparisons. These 59 clones of known gene products represent transcriptional products of 30 genes. The 41 clones of unknown gene products represent 33 genes. Expression of gonadotropin (GtH) a-subunit and prolactin was slightly enhanced, 149% and 176% respectively, as a result of induced ovulation. Large increases in frequencies of several peptide hormones were observed as a result of induced ovulation: GtH b-I, 486%; GtH- b-II, 933%; growth hormone (GH), 393%; proopiomelanocortin (POMC), 345%. This indicates that GtH I, GtH II, and GH may be important for ovulation in channel catfish. POMC represented about 21% of all transcriptional activity in the pituitaries after induced ovulation. It is possible that increased POMC expression is simply a result of stress caused by injection, containment, and handling, and/or it may be up-regulated to coup with the overwhelming increase in GtH b expression during induced ovulation. This is the first study addressing physiological changes after injection of carp pituitary extract, a procedure widely used in catfish hatcheries.