Abstract
The number of vertebrae, especially thoracic vertebrae, is an important economic trait that may influence carcass length and meat production in animals. However, the genetic basis of vertebrae number in sheep is still poorly understood. To detect the candidate genes, 400 increased number of thoracic vertebrae (T14L6) and 200 normal (T13L6) Kazakh sheep were collected. We generated and sequenced 60 pools of genomic DNA (each pool prepared by mixing genomic DNA from 10 sheep with the same thoracic traits), with an average depth of coverage of 25.65×. We identified a total of 42,075,402 SNPs and 11 putatively selected genomic regions, including the VRTN gene and the HoxA gene family that regulate vertebral development. The most prominent areas of selective elimination were located in a region of chromosome 7, including VRTN, which regulates spinal development and morphology. Further investigation indicated that the expression level of the VRTN gene during fetal development was significantly higher in sheep with more thoracic vertebrae than in those with a normal number of thoracic vertebrae. A genome-wide comparison between sheep with increased and normal numbers of thoracic vertebrae showed that the VRTN gene is the major selection locus for the number of thoracic vertebrae in sheep and has the potential to be utilized in sheep breeding in the future.
Highlights
The mammalian spine is divided into different vertebral regions based on morphology and function along the head-to-tail axis, and these regions include the cervical (C), thoracic (T), lumbar (L), sacral (S), and caudal (Cd) regions (Schimandle and Boden, 1994)
Sequencing of pools of genomic DNA was performed with 25.65fold coverage of the sheep genome using an Illumina HiSeq PE150 system (Supplementary Table S3), which generated a total of 4,215.15 Gb of raw data
To identify the selected signals associated with an increase in the number of thoracic vertebrae in sheep, large-scale resequencing of Kazak sheep with T14L6 and T13L6 traits was performed in this study
Summary
The mammalian spine is divided into different vertebral regions based on morphology and function along the head-to-tail axis, and these regions include the cervical (C), thoracic (T), lumbar (L), sacral (S), and caudal (Cd) regions (Schimandle and Boden, 1994). A study of European sheep breeds (Texel, Scottish Blackface, Texel × Mule, and Poll Dorset × Mule) by Donaldson et al have shown that multi-vertebral traits can significantly increase the length of the body (and carcass) (Donaldson et al, 2013; Donaldson et al, 2014). The results of these studies are consistent with those of our previous reports showing that multi-vertebral variation may contribute to the performance of Kazakh sheep (Li et al, 2017), but one study showed that the number of rib pairs has little impact on meat production traits. An increased number of thoracic vertebrae will result in an increased number of rib pairs, which is a valuable economic trait in sheep due to the preference for lamb chops
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