As a major source of high-quality protein, the global demand for meat is on the rise. The meat industry is a primary driver of many economies, including that of New Zealand, and compared to other animal species, sheep are ideal as a meat source as there are fewer global religious restrictions its consumption.
The production of better quality meat is of commercial importance and interest to consumers and farmers alike. While the selective breeding of livestock for desirable traits has been employed in agriculture for centuries, it was previously based on an appraisal of the animal’s performance. This approach is now being supplemented with more reliable marker-assisted selection (MAS) approaches. MAS depends on analysis of candidate genes found within the quantitative trait loci (QTL) associated with production traits, and specifically finding and selecting for the underlying variation in those genes that improves the traits.
PROP paired-like homeobox 1 (PROP1) is a pituitary-specific factor that is vital to the development of the pituitary during embryonic development. Dependent upon the PROP1 gene (PROP1) expression is the proper functioning of pituitary cells that secrete growth hormone (GH), luteinizing hormone (LH), and thyroid stimulating hormone (TSH). PROP1 mutations documented in humans present with similar phenotypic characteristics, including stunted growth, pituitary hypoplasia, and diminished musculature. The biological function of the PROP1 protein product in affecting growth, skeletal muscle development and metabolism, as well as its previously reported impact on meat quality traits in cattle and pig breeds, makes it worth investigating in sheep.
Ekegbu et al., (2018) examined sequence variations in PROP1 using a combination of molecular methods. A target DNA fragment was amplified using the Polymerase Chain Reaction (PCR), then analyzed using SSCP where the amplified DNA is denatured, and individual strands form three-dimensional structures that differ if there is variation in the nucleotide sequence. Nucleotide sequencing determined the specific nature of any variation in the SSCP patterns and thus gene sequences.
In the study, three single nucleotide polymorphisms (SNPs, c.45A>G, c.109+40T>C, and c.109+207C>T), forming three distinct sequence variants (A1, B1, and C1) were identified. The c.45A>G SNP putatively leads to a silent Glu15Glu substitution, while the latter two SNPs are in introns. In decades past, silent and intronic DNA sequence variation was dismissed as unimportant if it did not change the amino acid sequence of the protein. However, ample scientific evidence now exists to challenge this notion, as silent and intronic variation have been found to have an indirect effect on proteins, including altering their level of expression, charge characteristics, and stability.
All three gene variants in the study were found to influence growth traits in young sheep. Lambs possessing the A1 haplotype grew faster, and weighed more at tailing and weaning, than lambs that did not. The C1 haplotype was however antagonistic, being associated with a decrease in growth rate and weaning weight. Faster-growing animals are highly desirable in the animal breeding/farming industry, due to their greater efficiency at converting feed into muscle (or meat) and lower carbon footprint.
The importance of this novel research and its potential value to the meat industry cannot be stressed enough. The genetic variation identified could be used as genetic markers in breeding for sheep with superior growth, thus aiding farmers in making a more informed decision during selection. This would also mean more value for money, as meat production is enhanced.
These findings are described in the article entitled Gene polymorphisms in PROP1 associated with growth traits in sheep, recently published in the journal Gene. This work was conducted by Ugonna J. Ekegbu, Lucy Burrows, Hamed Amirpour-Najafabadi, Huitong Zhou, and Jon G.H. Hickford from Lincoln University.