Extremely different behaviours in high and low body weight lines of chicken are associated with differential expression of genes involved in neuronal plasticity.

Long-term selection (> 45 generations) for low or high body weight from the same founder population has generated two extremely divergent lines of chickens, the low (LWS) and high weight (HWS) lines, which at the age of selection (56 days) differs by more than nine-fold in body weight. The HWS line chickens are compulsive feeders, whereas, in the LWS line, some individuals are anorexic and others have very low appetites. The involvement of the central nervous system in these behavioural differences has been experimentally supported. We compared a brain region at 0 and 56 days of age containing the major metabolic regulatory regions, including the hypothalamus and brainstem, using a global cDNA array expression analysis. The results obtained show that the long-term selection has produced minor but multiple expression differences. Genes that regulate neuronal plasticity, such as actin filament polymerisation and brain-derived neurotrophic factor, were identified as being differentially expressed. Genes involved in lipid metabolism were over-represented among differentially expressed genes. The expression data confirm that neural systems regulating feeding behaviours in these lines are different. The results suggest that the lines are set in separate developmental trajectories equipped with slightly different nervous systems. We suggest that the lines adapt behaviourally different to changing situations post hatch, such as the transition from dependence on yolk to feeding, in order to obtain energy. The present study has identified and exemplifies the kind of changes that may underlie the extreme differences in such behaviours.

A high-resolution linkage map for the Z chromosome in chicken reveals hot spots for recombination.

A comprehensive linkage map for chicken chromosome Z was constructed as the result of a large-scale screening of single nucleotide polymorphisms (SNPs). A total of 308 SNPs were assigned to Z based on the genotype distribution among 182 birds representing several populations. A linkage map comprising 210 markers and spanning 200.9 cM was established by analyzing a small Red junglefowl/White Leghorn intercross. There was excellent agreement between the linkage map for Z and a recently released assembly of the chicken genome (May 2006). Almost all SNPs assigned to chromosome Z in the present study are on Z in the new genome assembly. The remaining 12 loci are all found on unassigned contigs that can now be assigned to Z. The average recombination rate was estimated at 2.7 cM/Mb but there was a very uneven distribution of recombination events with both cold and hot spots of recombination. The existence of one of the major hot spots of recombination, located around position 39.4 Mb, was supported by the observed pattern of linkage disequilibrium. Thirteen markers from unassigned contigs were shown to be located on chromosome W. Three of these contigs included genes that have homologues on chromosome Z. The preliminary assignment of three more genes to the gene-poor W chromosome may be important for studies on the mechanism of sex determination and dosage compensation in birds.