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.

Localization of the fertilized germinal disc in the chicken egg before incubation

At the time of oviposition, the embryo in the fertilized chicken egg has developed the germinal disc on top of the yolk and contains thousands of blastodermal cells. The germinal disc escapes exact localization because it is surrounded by albumen and shell membranes under a calcified shell. This study investigated whether or not ultrasonography or nuclear magnetic resonance imaging (MRI) are suited to localize the germinal disc and, if so, to estimate the accuracy of localization. Hatchability of treated eggs was also recorded. The ultrasound waves were reflected by the shell. The germinal disc could be seen only after removal of the eggshell and the outer shell membrane. In all, 39 intact eggs, MRI localized the germinal disc within 2 mm thick image slices. The mean position of the germinal disc deviated 3.0+/-2.1 mm from the maximum vertical plane of the egg with a mean distance to the inner surface of the shell of 2.7+/-1.1 mm. Incubation resulted in 84.2 and 77.5% hatched chicks for imaged eggs and controls, respectively. The localization results of MRI were verified manually in 38 open shell cultures. Correlation coefficients for the position of the germinal disc were r = 0.86 to 0.99 for the x-axis, r = 0.75 to 0.89 for the y-axis, and r = 0.63 to 0.76 for the z-axis. The study thus shows that MRI is a reliable tool to localize the germinal disc within the intact freshly laid egg.

A model for population growth of laboratory animals subjected to marker-assisted introgression: how many animals do we need?

This study provides methods for calculating the mean and variance of the number of animals with the desired genotype in each backcross generation for a marker-assisted introgression experiment. The ultimate goal is to produce animals which are homozygous for the desired loci. The methods have been developed specifically for experiments with inbred lines. The model assumes a Poisson distribution for litter size, and is similar to that used in stochastic versions of population dynamics models. Certain biological parameters must be specified as well as parameters under the control of the breeder. These methods can be utilized in designing an experiment to determine the number of founder animals required, given the number of animals required at the completion of the backcross process and vice versa. Consideration is given to minimizing the total amount of genotyping over the entire experiment, by varying the number of times each backcrossed male is used. In addition, an outline is given for an adaptive design that allows for changes in male usage to be made during the experiment.

Gordon Memorial Lecture. A holistic view of poultry science from a reductionist perspective

1. The success of the poultry industry has been dependent upon development of a precise understanding of poultry biology. 2. The advent of tools and probes that reveal the molecular and cellular organisation of complex physiological systems should be embraced by the poultry industry to gain insights into recurring problems such as egg shell quality and ascites. 3. The ability to modify the genome of chickens provides an opportunity to breed chickens with unprecedented precision. 4. The judicious use of time and resources will require a working knowledge of molecular and cellular biology and the poultry industry. There is an urgent need for educational facilities that provide both perspectives.

Transgenic chickens--methods and potential applications

The development of techniques for the genetic manipulation of poultry has lagged behind the technology available in mammalian systems, although several different approaches are being taken to overcome the problems associated with the manipulation of avian embryos. Several methods being developed for generating transgenic chickens are giving promising results, and the production of transgenic chickens by DNA microinjection has recently been demonstrated. Exploitation of this technology, in both basic and applied research, is now a possibility, and many applications of transgenic technology to poultry breeding and novel uses of transgenic chickens have been suggested.