Question

Influential genes and proteins in dairy cattle:

Genetic methods have been used to examine regions of the dairy cattle genome that appear to have been under selection. A positive signature of selection in a given region implies the genes contained therein are potentially important for aspects of milk production such as yield.

Two such genes found to be of importance in dairy cattle are DGAT1 (which encodes the fat biosynthesis enzyme diacylglycerol o-acyltransferase 1) and GHR (which encodes the growth hormone receptor).

44. Why might these two genes be important for milk production?

Answer 1

44. DGAT1 is the gene whose Diacylglycerol O-acyltransferase 1 protein catalyzes the final step in synthesis of triglycerides. Milk has nearly 98% of its composition as fats, with bovine milk having short chain fatty acids. These short chain fatty acids have 4-6 C atoms. Triglycerides are synthesized by addition of fatty acids to sn-1 and sn-2 position of glycerol. DGAT1 enzyme adds the third fatty acid to the sn-3 position in glycerol. Short chain fatty acids with 4-6 C atoms are found in this position in glycerol while forming triglycerides. Lactation is found to be also impaired in female cows that have a deficiency of DGAT1. Polymorphisms in this gene affect percentage of milk fat and protein as well as overall milk volume. Some polymorphism such as DGAT1 A allele leads to milk production that has higher unsaturated fatty acids. Thus, DGAT1 is essential for milk production.

Growth hormone is required for lactation in cows. GHR binds to its receptor GHR to activate JAk2 kinase which phosphorylates STAT5. STAT5 enters the nucleus and activates transcription of target genes. Downstream signaling will increase the production of milk protein, lactose and milk volume in mammary gland. GHR in mammary gland thus, regulates the actions of GH. Thus DGAT1 and GHR are important for milk production.