We used Pacific Biosciences long-read isoform sequencing to generate full-length transcript sequences in equine bronchoalveolar lavage fluid (BALF) cells. Our dataset consisted of 313,563 HiFi reads comprising 805 Mb of polished sequence information. The resulting equine BALF transcriptome consisted of 14,234 full-length transcript isoforms originating from 7017 unique genes. These genes consisted of 6880 previously annotated genes and 137 novel genes. We identified 3428 novel transcripts in addition to 10,806 previously known transcripts. These included transcripts absent from existing genome annotations, transcripts mapping to putative novel (unannotated) genes and fusion transcripts incorporating exons from multiple genes. We provide transcript-level data for equine BALF cells as a resource to the scientific community.

/pdf/long-read-transcriptome-of-equine-bronchoalveolar-cells-3df4ljjz.pdf

Long-Read Transcriptome of Equine Bronchoalveolar Cells

Behavioural plasticity enables horses entering an exercise training programme to adapt with reduced stress. We characterised SNPs associated with behaviour in yearling Thoroughbred horses using genomics analyses for two phenotypes: (1) handler-assessed coping with early training events [coping] (n = 96); and (2) variation in salivary cortisol concentration at the first backing event [cortisol] (n = 34). Using RNA-seq derived gene expression data for amygdala and hippocampus tissues from n = 2 Thoroughbred stallions, we refined the SNPs to those with functional relevance to behaviour by cross-referencing to the 500 most highly expressed genes in each tissue. The SNPs of high significance (q < 0.01) were in proximity to genes (coping - GABARAP, NDM, OAZ1, RPS15A, SPARCL1, VAMP2; cortisol - CEBPA, COA3, DUSP1, HNRNPH1, RACK1) with biological functions in social behaviour, autism spectrum disorder, suicide, stress-induced anxiety and depression, Alzheimer's disease, neurodevelopmental disorders, neuroinflammatory disease, fear-induced behaviours and alcohol and cocaine addiction. The strongest association (q = 0.0002) was with NDN, a gene previously associated with temperament in cattle. This approach highlights functionally relevant genes in the behavioural adaptation of Thoroughbred horses that will contribute to the development of genetic markers to improve racehorse welfare.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/age.13320

Integrative genomics analysis highlights functionally relevant genes for equine behaviour.

LINE-1 is an active transposable element encoding proteins capable of inserting host gene retrocopies, resulting in retro-copy number variants (retroCNVs) between individuals. Here, we performed retroCNV discovery using 86 equids and identified 437 retrocopy insertions. Only 5 retroCNVs were shared between horses and other equids, indicating that the majority of retroCNVs inserted after the species diverged. A large number (17–35 copies) of segmentally duplicated Ligand Dependent Nuclear Receptor Corepressor Like (LCORL) retrocopies were present in all equids but absent from other extant perissodactyls. The majority of LCORL transcripts in horses and donkeys originate from the retrocopies. The initial LCORL retrotransposition occurred 18 million years ago (17–19 95% CI), which is coincident with the increase in body size, reduction in digit number, and changes in dentition that characterized equid evolution. Evolutionary conservation of the LCORL retrocopy segmental amplification in the Equidae family, high expression levels and the ancient timeline for LCORL retrotransposition support a functional role for this structural variant.

/pdf/ancient-segmentally-duplicated-lcorl-retrocopies-in-equids-18gf609u.pdf

Ancient segmentally duplicated LCORL retrocopies in equids

A high-quality reference genome assembly, a biobank of diverse equine tissues from the Functional Annotation of the Animal Genome (FAANG) initiative, and incorporation of long-read sequencing technologies, have enabled efforts to build a comprehensive and tissue-specific equine transcriptome. The equine FAANG transcriptome reported here provides up to 45% improvement in transcriptome completeness across tissue types when compared to either RefSeq or Ensembl transcriptomes. This transcriptome also provides major improvements in the identification of alternatively spliced isoforms, novel noncoding genes, and 3’ transcription termination site (TTS) annotations. The equine FAANG transcriptome will empower future functional studies of important equine traits while providing future opportunities to identify allele-specific expression and differentially expressed genes across tissues.

https://www.biorxiv.org/content/biorxiv/early/2022/06/09/2022.06.07.495038.full.pdf

L. Orlando

Papers

Long-read RNA Sequencing Improves the Annotation of the Equine Transcriptome