Molecular Basis of Maintaining Circannual Rhythm in the Skin of Cashmere Goat
Abstract BackgroundThe cashmere goat (Capra hircus) is famous for the fine quality cashmere wool. The cashmere is produced by secondary hair follicle that shows seasonal rhythm in growth. Thus, in this study, the skin of cashmere goat was selected as a model to illustrate the circannual rhythm of skin. ResultsThe skin whole length transcriptome obtained by PacBio single-molecule long-read sequencing (SMRT) technology were mixed from four selected months. The transcriptome yielded 82,382 high quality non-redundant transcripts belonging to 193,310 genes, including 4,237 novel genes. Other 39 skin transcriptomes sequenced by Illumina Hi-Seq2500 were sampled from Dec. 2014 to Dec. 2015, from which we found 980 genes were differentially expressed. Of these genes, 403 seasonal rhythm genes (SRGs) were expressed and exhibited a seasonal pattern in skin. Some SRG genes related to the hormone secretion and eyes morphogenesis were enriched in skin. These SRG genes gradually increased their expression level under short light, reached the peak near the summer solstice, and then began to decline. We found that the expression of Dio1 gene may be affected by the photoperiod that induces transformation from the inactive T4 to active thyroid hormone T3 in the skin and led to the difference between the skin circannual rhythm and the core circannual rhythm. The results also showed that miRNAs were differentially expressed as the daylight length changed throughout a year. Furthermore, the skin expressed eye morphogenesis-related genes and miRNAs, which suggested some cells in the skin could have the potential of light sensitivity. ConclusionTaking together, these results revealed that SRGs could regulate the downstream gene expression and physiological process in the skin to adapt to the season change. We provided a hypothesis to describe how goat skin makes the own rhythm and gets the clue from the environment factor.