Transcriptomic analysis of eyelid pigmentation in Hereford cattle.

The study of skin color in cattle holds both economic and scientific interest. Several ocular diseases of cattle have been associated with low pigmentation of the eyelids, including ocular squamous cell carcinoma and infectious keratoconjunctivitis, the two most common ocular diseases affecting cattle production. Although low eyelid pigmentation is a well-known risk factor for various ocular diseases, the genetic and biological basis of this relationship is largely unknown. We investigated the transcriptome of eyelid skin in Hereford cattle using RNA-sequencing technology. Two contrasting groups were evaluated: steers that were completely pigmented and steers with no pigmentation in both eyelids. Most of the up-regulated genes in pigmented samples are directly implicated in melanogenesis and melanosome development, whereas up-regulated genes in non-pigmented samples are implicated in cancer development and the immune system, among other functions. Interestingly, network analysis comparing pigmented vs. non-pigmented samples revealed significant differences in the co-expression patterns of genes related to melanosome, pigmentation and defense response to bacteria, showing higher gene activity, greater co-expression patterns and tighter co-regulation mechanisms in pigmented samples. Overall, our findings indicate that bovine eyelid pigmentation depends on the expression of many genes involved not only in pigmentation and melanosome function but also related to inflammatory response, infection and tumoral pathways.