Unknown,Transcriptomics,Genomics,Proteomics

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Next generation sequencing reveals the diversity and population-genetic properties of cattle CNVs

ABSTRACT: Structural and functional impacts of copy number variations (CNVs) on livestock genomes are not yet well understood. In this study, we have identified 1853 CNV regions (CNVRs) using population-scale sequencing data generated from 75 cattle of 8 breeds (Holstein, Angus, Jersey, Limousin, Romagnola, Brahman, Gir and Nelore). Individual genome sequence coverage ranged from 4 to 30 fold, with a mean of 11.8 fold. A total of 3.1% (87.5 Mb) of the cattle genome is predicted to be copy number variable, representing a substantial increase over the previous estimates (~2%). This dataset was highly correlated with array CGH data (r2 = 0.761) and was validated to be accurate with an estimated 12% false positive rate and a 19% false negative rate based on qPCR and array CGH, respectively. Hundreds of CNVs were found to be either breed specific or differentially variable across breeds, including the RICTOR gene in dairy breeds and the PNPLA3 gene in the beef breeds. In contrast, clusters of the PRP and PAG genes are duplicated in all sequenced animals, implicating that subfunctionalization, neofunctionalization or overdominance play a role in diversifying these fertility related genes. Further population-genetic analyses based on CNVs revealed the population structures of these taurine and indicine breeds and uncovered hundreds of positively selected CNV candidates near important functional genes. These CNV results provide a new glimpse of diverse selections during cattle speciation, domestication, breed formation, and recent genetic improvement. 25 animals were analyzed using a custom Nimblegen aCGH chip with 2.1 million probes. The reference animal chosen was L1 Dominette, a Hereford cow of European ancestry. The array was subjected to a dye-swap with the reference sample to test probe intensity fidelity. Single channel intensity data from the array was used in a digital aCGH analysis to compare aCGH copy number estimates to copy number estimates derived from sequence data. Briefly, the reference signal from all analyzed arrays was collected and a median signal intensity was calculated from probe intensities within the BTF3 gene. The copy number of the reference animal was then inferred by division of single channel probe intensities with the median intensity of the BTF3 gene. Next, test sample intensities were normalized by taking the log2 ratio of the test intensity divided by the normalized reference copy number for the probe. CN values derived from sequence data were also normalized in this fashion by taking the log2 of the ratio of NGS CN divided by aCGH reference copy number.

ORGANISM(S): Bos taurus

SUBMITTER: Derek Bickhart

PROVIDER: E-GEOD-62990 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Genomic structural variation is an important and abundant source of genetic and phenotypic variation. Here we describe the first systematic and genome-wide analysis of copy number variations (CNVs) in modern domesticated cattle using array comparative genomic hybridization (array CGH), quantitative PCR (qPCR) and fluorescent in situ hybridization (FISH). The array CGH panel included 90 animals from 11 Bos taurus, 3 Bos indicus and 3 composite breeds for beef, dairy or dual purpose. We identified over 200 candidate CNV regions (CNVRs) in total and 177 within known chromosomes, which harbor or are adjacent to gains or losses. These 177 high-confidence CNVRs cover 28.1 mega bases or ~1.07% of the genome. Over 50% of the CNVRs (89/177) were found in multiple animals or breeds and analysis revealed breed-specific frequency differences and reflected aspects of the known ancestry of these cattle breeds. Selected CNVs were further validated by independent methods using qPCR and FISH. Approximately 67% of the CNVRs (119/177) completely or partially span cattle genes and 61% of the CNVRs (108/177) directly overlap with segmental duplications. The CNVRs span about 400 annotated cattle genes that are significantly enriched for specific biological functions such as immunity, lactation, reproduction and rumination. Multiple gene families, including ULBP, have gone through ruminant lineage-specific gene amplification. We detected and confirmed marked differences in their CNV frequencies across diverse breeds, indicating that some cattle CNVs are likely to arise independently in breeds and contribute to breed differences. Our results provide a valuable resource beyond microsatellites and single nucleotide polymorphisms to explore the full dimension of genetic variability for future cattle genomic research. The custom aCGH chips that interrogated the whole genome CNVs were build for 90 cattles from diverse breeds, with Hereford L1 Dominette 01449 as refference sample.

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Next generation sequencing reveals the diversity and population-genetic properties of cattle CNVs

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