RESUMEN
Labeo rohita (Ham.) also called rohu is the most important freshwater aquaculture species on the Indian sub continent. Monsoon dependent breeding restricts its seed production beyond season indicating a strong genetic control about which very limited information is available. Additionally, few genomic resources are publicly available for this species. Here we sought to identify reproduction-relevant genes from normalized cDNA libraries of the brain-pituitary-gonad-liver (BPGL-axis) tissues of adult L. rohita collected during post preparatory phase. 6161 random clones sequenced (Sanger-based) from these libraries produced 4642 (75.34%) high-quality sequences. They were assembled into 3631 (78.22%) unique sequences composed of 709 contigs and 2922 singletons. A total of 182 unique sequences were found to be associated with reproduction-related genes, mainly under the GO term categories of reproduction, neuro-peptide hormone activity, hormone and receptor binding, receptor activity, signal transduction, embryonic development, cell-cell signaling, cell death and anti-apoptosis process. Several important reproduction-related genes reported here for the first time in L. rohita are zona pellucida sperm-binding protein 3, aquaporin-12, spermine oxidase, sperm associated antigen 7, testis expressed 261, progesterone receptor membrane component, Neuropeptide Y and Pro-opiomelanocortin. Quantitative RT-PCR-based analyses of 8 known and 8 unknown transcripts during preparatory and post-spawning phase showed increased expression level of most of the transcripts during preparatory phase (except Neuropeptide Y) in comparison to post-spawning phase indicating possible roles in initiation of gonad maturation. Expression of unknown transcripts was also found in prolific breeder common carp and tilapia, but levels of expression were much higher in seasonal breeder rohu. 3631 unique sequences contained 236 (6.49%) putative microsatellites with the AG (28.16%) repeat as the most frequent motif. Twenty loci showed polymorphism in 36 unrelated individuals with allele frequency ranging from 2 to 7 per locus. The observed heterozygosity ranged from 0.096 to 0.774 whereas the expected heterozygosity ranged from 0.109 to 0.801. Identification of 182 important reproduction-related genes and expression pattern of 16 transcripts in preparatory and post-spawning phase along with 20 polymorphic EST-SSRs should be highly useful for the future reproductive molecular studies and selection program in Labeo rohita.