Real-time RT-PCR and cDNA macroarray to study the impact of the genetic polymorphism at the α_s1-casein locus on the expression of genes in the goat mammary gland during lactation

Abstract

-Milk fat has a large effect on nutritional, technological and sensorial properties of milk products. The milk fat content and composition are modulated by genetics and nutritional factors and imply a large number of enzymes. The regulation of their gene expression in the mammary gland still needs to be clarified. An association between the extensive polymorphism at the a s1 -casein (a s1 -Cas) locus and both the lipid content and the characteristics of this fraction in caprine milk has been demonstrated. In order to decipher the mechanism responsible for this impact, a quantification of the transcripts of four lipogenic key enzymes (acetyl-CoA carboxylase, fatty acid synthase, lipoprotein lipase and stearoyl-CoA desaturase) was performed using real-time RT-PCR, suggesting an absence of association between the a s1 -Cas genotype and expression variability of the studied genes. This approach has been completed by a more global analysis using a first generation of ruminant macroarray gathering 400 gene probes. The comparison of the expression profiles of lactating goat a s1 -Cas A/A (strong allele) and F/F (defective allele) mammary gland allowed to confirm the expected variability in the expression of known genes (such as those encoding the α s1 -casein) in ruminant mammary tissues as well as to identify up-and down-regulated genes. A second generation of ruminant cDNA macroarray extended to a few thousands of genes is currently in progress and will be applied to study different factors such as the nutritional regulation of gene expression in the mammary gland.goat milk / casein / fatty acids / genetic polymorphism / macroarray / lipogenesis

Goat’s αS1-casein polymorphism affects gene expression profile of lactating mammary gland

“…The comparison of mammary transcriptome profiles between 'high' and 'low' CSN1S1 genotype goats made it possible to identify, among the 400 genes analyzed, 3% of differentially expressed genes, mainly involved in protein biosynthesis, DNA damage repair, cell trafficking or the cell cycle (Leroux et al, 2003). To supplement these investigations, we undertook gene expression profiling experiments to compare the mammary gland from lactating goats of different CSN1S1 genotypes using a bovine oligonucleotide microarray enlarged to 8379 gene probes.…”

Effects on Production Traits of Haplotypes Among Casein Genes in Norwegian Goats and Evidence for a Site of Preferential Recombination

“…CSN1S1 is the most complex and is highly polymorphic (Martin et al 2002b). As many as 18 different alleles have been identified for this gene (Leroux et al 2003;Devold 2004), including alleles with ''strong'' effects, ''medium'' effects, and ''weak'' effects and ''null'' alleles associated with no synthesis of the protein (Leroux et al 1990;Neveu et al 2002). Goats carrying the strong variants have been reported to produce milk with a significantly higher casein, total protein, and fat content than goats carrying the weak variants (Manfredi et al 1993;Remeuf 1993;Barbieri et al 1995).…”

“…One hypothesis is that when expression of one casein gene is downregulated, the others can be upregulated to compensate (Leroux et al 2003). Bovenhuis et al (1992) conflicting results of the effects of mutations in casein genes for cattle at least might be due to linkage between mutations in different caseins, as well as the different statistical models used in the analyses.…”

Genetic Factors that Regulate Milk Protein and Lipid Composition in Goats

“…Low-content alleles have also been linked to an increased mammary desaturase activity (Chilliard et al 2006). There is a certain controversy about the influence of CSN1S1 polymorphism on the mRNA expression of lipid metabolism genes, with studies that support a regulatory effect (Badaoui 2008) and others that do not (Leroux et al 2003). Since lipids and proteins are synthesized in the endoplasmic reticulum and their transport is, to a certain extent, coupled and co-regulated, it has been hypothesized that the perturbation of casein transport induced by the CSN1S1 genotype might also alter lipid trafficking resulting in a reduced fat secretion (Ollivier-Bousquet et al 2002).…”