Expression profiles of growth-related genes in two Nile tilapia strains and their crossbred provide insights into introgressive breeding effects.

The Nile tilapia (Oreochromis niloticus) is a prominent farmed fish in aquaculture worldwide. Crossbreeding has recently been carried out between the Red-Stirling and the wt Chitralada strains of Nile tilapia, producing a heterotic hybrid (7/8 Chitralada and 1/8 Red-Stirling) that combines the superior growth performance of the Chitralada with the reddish coloration of the Red-Stirling strain. While classical selective breeding and crossbreeding strategies are well known, the molecular mechanisms underlying the phenotypic expression of economically advantageous traits in tilapia remain largely unknown. Molecular investigations have shown that variable expression of growth hormone (gh), insulin-like growth factors (igf1 and 2) and somatolactin (smtla) - components of the growth hormone/insulin-like growth factor (GH/IGF) axis - and myostatin (mstn) genes can affect traits of economic relevance in farmed animals. The aim of this study was to assess and compare the gene expression signature among Chitralada, Red-Stirling and their backcross hybrid in order to gain insights into the effects of introgressive breeding in modulation of the GH/IGF axis. Gene expression analyses in distinct tissues showed that most genes of the GH/IGF axis were up-regulated and mstn was down-regulated in backcross animals in comparison with Red-Stirling and Chitralada animals. These gene expression profiles revealed that backcross animals displayed a distinctive expression signature, which attests to the effectiveness of the introgressive breeding technique. Our findings also suggest that the GH/IGF axis and mstn genes might be candidate markers for fish performance and prove useful within genetic improvement programs aimed at the production of superior-quality tilapia strains using introgressive breeding.

Evaluation of the genetic diversity of microsatellite markers among four strains of Oreochromis niloticus.

Different strains of Nile tilapia can be found worldwide. To successfully use them in breeding programs, they must be genetically characterized. In this study, four strains of Nile tilapia - UFLA, GIFT, Chitralada and Red-Stirling - were genetically characterized using 10 noncoding microsatellite loci and two microsatellites located in the promoter and first intron of the growth hormone gene (GH). The two microsatellites in the GH gene were identified at positions -693 to -679 in the promoter [motif (ATTCT)8 ] and in intron 1 at positions +140 to +168 [motif (CTGT)7 ]. Genetic diversity was measured as mean numbers of alleles and expected heterozygosity, which were 4 and 0.60 (GIFT), 3.5 and 0.71 (UFLA), 4.5 and 0.57 (Chitralada) and 2.5 and 0.42 (Red-Stirling) respectively. Genetic differentiation was estimated both separately and in combination for noncoding and GH microsatellites markers using Jost's DEST index. The UFLA and GIFT strains were the least genetically divergent (DEST  = 0.10), and Chitralada and Red-Stirling were the most (DEST  = 0.58). The UFLA strain was genetically characterized for the first time and, because of its unique origin and genetic distinctness, may prove to be an important resource for genetic improvement of Nile tilapia. This study shows that polymorphisms found in coding gene regions might be useful for assessing genetic differentiation among strains.

Genetic parameters for carcass traits and body weight using a Bayesian approach in the Canchim cattle.

Correlation between genetic parameters and factors such as backfat thickness (BFT), rib eye area (REA), and body weight (BW) were estimated for Canchim beef cattle raised in natural pastures of Brazil. Data from 1648 animals were analyzed using multi-trait (BFT, REA, and BW) animal models by the Bayesian approach. This model included the effects of contemporary group, age, and individual heterozygosity as covariates. In addition, direct additive genetic and random residual effects were also analyzed. Heritability estimated for BFT (0.16), REA (0.50), and BW (0.44) indicated their potential for genetic improvements and response to selection processes. Furthermore, genetic correlations between BW and the remaining traits were high (P > 0.50), suggesting that selection for BW could improve REA and BFT. On the other hand, genetic correlation between BFT and REA was low (P = 0.39 ± 0.17), and included considerable variations, suggesting that these traits can be jointly included as selection criteria without influencing each other. We found that REA and BFT responded to the selection processes, as measured by ultrasound. Therefore, selection for yearling weight results in changes in REA and BFT.