Bioinformatic identification and validation of conservative microRNAs in Ictalurus punctatus

Catfish (Ictalurus spp.) is an important aquaculture species around the world, accounting for over 60 % of the domestic aquaculture output in the United States. However, little information is available about I. punctatus miRNAs which play an important role in the regulation of almost every biological process. In the present studies, we applied a bioinformatic strategy to identify 16 miRNAs which represent 12 miRNA families in I. punctatus by searching both expressed sequence tags and genome survey sequences databases. The A + U contents of the candidate pre-miRNA sequence range from 51 to 63 %, and the pre-miRNA sequences vary from 55 to 63 bp in length. To verify the predicted miRNAs, real-time PCR was used to profile the expression of 16 miRNAs with different tissues of I. punctatus. All the miRNA candidates were detectable in five tissues except for ipu-miR-9-3p. Based on sequence complementarity between miRNAs and their mRNA targets, potential targets for I. punctatus miRNAs were predicted. Due to the limited information for the I. punctatus transcripts, only one sequence targeted by ipu-miR-135 was identified to be an I. punctatus EB1 mRNA. Bioinformatic analyses indicated that the 3' untranslated region (3'-UTR) of EB1 mRNA contains an ipu-miR-135 target site, which are perfectly complementary to the seed region (positions 2-8) of the mature ipu-miR-135. I. punctatus miRNAs characterized in this study may provide useful information for the miRNAs research in I. punctatus and other aquaculture species.