Fur-developmental Adaptation Study Of Sable(Martes Zibellina) Based On Genomic And Transcriptomic Sequencing

The sable(Martes zibellina),a kind of small mammals widely distributed in the mountain and plain taiga,has developed several survival strategies,such as fur development and energy metabolism,to adapt to the cold environment.The sable had been hunting for its high quality fur in a long period in the past,which resulted in the dramactically decline of their popolations.In this study,we focused on the adaptive evolution of fur development in the severe environment and try to characterize the molecular mechanism under it.We sequenced the whole-genome of the sable,then the KRT and KRTAP gene families were identified in this genome,and molecular evolution analyses were performed.Additionally,comparative transcriptome analysis was employed to explore the mechanism of hair cycle and hair traits regulation,and we also checked for the candidate genes that related with the high quality fur traits.The genome size of the sable was estimated as 2.3Gb and was assembled from 276.9Gb(approximately 110-fold coverage)of clean data.The contig and scaffold N50 lengths reached 41.7kb and 5.2Mb,respectively,and we annotated a total of 19,505 protein-coding genes.We characterized 60 KRTs in the sable genome,and expression analysis indicated that KRT14,KRT5,KRT10 and KRT17 showed high expression level in the skin of the sable,which implied that these genes were important to the skin integrity and hair follicles morphogenesis.The hair and hair follicle-specific KRTs were all up-regulation in the period of anagen,in which KRT37,KRT38 and KRT41 obtained the highest folds change.The KRT gene family was highly conserved in gene number,arrangement and organization among Carnivora.KRT89 and KRT15 were under positive selection in mustelids,which indicated that they might have evolved in the function of fur development and epidermal differentiation.Much more positive selection signals were identified in the KRTs of pinnipeds,which might be helpful in the formation of the various hair and skin pattern in these aquatic animals and help them to adapt to the aquatic environment.We also identified 85 KRTAPs in the sable genome.Comparative analyses implied that this family was similiar in number among carnivores,and genes in some subfamilies have evolved by concerted evolution.The number of KRTAP6 in the sable was less than other mustelids,which might be related to the gloss and other traits of hair.We also found that the aquatic carnivores had less HGT-KRTAP and KRTAP 1-3 than the terrestrial,and the expression of these genes might affect the mechanical property of hair.Furthermore,strong positive selection was detected among carnivores,especially among pinnipeds in KRTAP27,which indicated that this gene might be helpful for the modifying of the hair traits in the pinnipeds.On the other hand,comparative transcriptome analysis was employed to investigate the gene expression in the sable skin between different periods.The expression level of ribosomal protein genes was high,which may indicate that there was higher level of translational activities in the sable skin.The differential expressed genes were identified and the enrichment analyses were performed,which implied that Wnt signal pathway,some regulators and energy metabolism were involved in the regulation of hair development,skin renewal and hair pigmentation.In addition,genes related to cornification,fibrosis and lipid metabolism were up-regulated in winter samples,which may be helpful to the development of hardy fur.We also found that the testis-spetific FABP9 was highly expressed in the summer samples.At last,we performed selection pressure analyses on highly expressed and differential expressed genes;the results showed that some genes such as CCDC80,which played vital roles in the formation of high quality fur were under positive selection.Besides,the CCDC80 was involved in the process of adipogenesis and this gene may be helpful to the low body fat content in the sable.