Biology subjects

Hillier, L. W.

Publications and source records attributed to Hillier, L. W..

5 recordsLinked to original sources

bioRxiv2025

Genomic resources for comparative analyses of obligate avian brood parasitism

Examples of convergent evolution, wherein distantly related organisms evolve similar traits, including behaviors, underscore the adaptive power of natural selection. In birds, obligate brood parasitism, and the associated loss of parental care behaviors, has evolved independently in seven different lineages, though little is known about the genetic basis of the complex suite of traits associated with this rare life history strategy. We generated genome assemblies for ten brood parasitic species plus eight species representatives of their parental/nesting outgroups. This includes nine long-read chromosome-level assemblies, with scaffold N50 sizes ranging from 38.1 to 72.6 MB, and gene representation completeness measures >97%. Leveraging this new catalog of avian genomes, we constructed clade-level alignments that reveal variation in chromosomal synteny, provide first-time or improved annotations of protein-coding and non-coding genes, and define cross-species ortholog reference sets. We also refine estimates for the timing of the seven independent origins of brood parasitism, ranging from recent events such as 1.6 to 4.5 million years ago in Molothrus cowbirds to much earlier origins over 30 million years ago in two of the three cuckoo lineages. These genomic resources lay the foundation for investigating the genetic and genomic underpinnings of brood parasitism, including the loss of parental care, shifts in mating systems, perhaps resulting in heightened sperm competition, elevated annual fecundity, improved spatial cognition related to nest-finding, and the diverse adaptations shaped by intense coevolution with host species.

genomics↗

bioRxiv2024

Lineage-resolved analysis of embryonic gene expression evolution in C. elegans and C. briggsae

What constraints govern the evolution of gene expression patterns across development remains a fundamental question of evolutionary biology. The advent of single-cell sequencing opens the possibility of learning these constraints by systematically profiling homologous cells across different organisms. The nematode C. elegans is a well-studied model for embryonic development, and its invariant lineage that is conserved with other Caenorhabditis species makes it an ideal model to directly compare gene expression between homologous progenitor and terminal cell types across evolution. We have measured the spatiotemporal divergence of gene expression across embryogenesis by collecting, annotating, and comparing the transcriptomes of homologous embryonic progenitors and terminal cell types, using a dataset comprising >200,000 C. elegans cells and >190,000 C. briggsae cells. We find a high level of similarity in gene expression programs between the species despite tens of millions of years of evolutionary divergence, consistent with their conserved developmental lineages. Even still, thousands of genes show divergence in their cell-type specific expression patterns, and these are enriched for categories involved in environmental response and behavior. Comparing the degree of expression conservation across cell types reveals that certain cell types such as neurons, have diverged more than others such as the intestine and body wall muscle. Taken together, this work identifies likely constraints on the evolution of developmental gene expression and provides a powerful resource for addressing diverse evolutionary questions.

evolutionary biology↗

bioRxiv2022

Patterns of lineage-specific genome evolution in the brood parasitic black-headed duck (Heteronetta atricapilla)

Occurring independently at seven separate origins across the avian tree of life, obligate brood parasitism is a unique suite of traits observed in only approximately 1% of all bird species. Obligate brood parasites exhibit varied physiological, morphological, and behavioural traits across lineages, but common among all obligate brood parasites is that the females lay their eggs in the nest of other species. Unique among these species is the black-headed duck (Heteronetta atricapilla), a generalist brood parasite that is the only obligate brood parasite among waterfowl. This provides an opportunity to assess evolutionary changes in traits associated with brood parasitism, notably the loss of parental care behaviours, with an unspecialized brood parasite. We generated new high-quality genome assemblies and genome annotations of the black-headed duck and three related non-parasitic species (freckled duck, African pygmy-goose, and ruddy duck). With these assemblies and existing public genome assemblies, we produced a whole genome alignment across Galloanserae to identify conserved non-coding regions with atypical accelerations in the black-headed duck and coding genes with evidence of positive selection, as well as to resolve uncertainties in the duck phylogeny. To complement these data, we sequenced a population sample of black-headed ducks, allowing us to conduct McDonald-Kreitman tests of lineage-specific selection. We resolve the existing polytomy between our focal taxa with concordance from coding and non-coding sequences, and we observe stronger signals of evolution in non-coding regions of the genome than in coding regions. Collectively, the new high-quality genomes, comparative genome alignment, and population genomics provide a detailed picture of genome evolution in the only brood parasitic duck.

evolutionary biology↗

bioRxiv2021

An integrated analysis tool reveals intrinsic biases in gene set enrichment

Generating meaningful interpretations of gene lists remains a challenge for all large-scale studies. Many approaches exist, often based on evaluating gene enrichment among pre-determined gene classes. Here, we conceived and implemented yet another analysis tool (YAAT), specifically for data from the widely-used model organism C. elegans. YAAT extends standard enrichment analyses, using a combination of co-expression data and profiles of phylogenetic conservation, to identify groups of functionally-related genes. It additionally allows class clustering, providing inference of functional links between groups of genes. We give examples of the utility of YAAT for uncovering unsuspected links between genes and show how the approach can be used to prioritise genes for in-depth study. Our analyses revealed several limitations to the meaningful interpretation of gene lists, specifically related to data sources and the "universe" of gene lists used. We hope that YAAT will represent a model for integrated analysis that could be useful for large-scale exploration of biological function in other species.

bioinformatics↗

bioRxiv2020

A new domestic cat genome assembly based on long sequence reads empowers feline genomic medicine and identifies a novel gene for dwarfism.

The domestic cat (Felis catus) numbers over 94 million in the USA alone, occupies households as a companion animal, and, like humans, suffers from cancer and common and rare diseases. However, genome-wide sequence variant information is limited for this species. To empower trait analyses, a new cat genome reference assembly was developed from PacBio long sequence reads that significantly improve sequence representation and assembly contiguity. The whole genome sequences of 54 domestic cats were aligned to the reference to identify single nucleotide variants (SNVs) and structural variants (SVs). Across all cats, 16 SNVs predicted to have deleterious impacts and in a singleton state were identified as high priority candidates for causative mutations. One candidate was a stop gain in the tumor suppressor FBXW7. The SNV is found in cats segregating for feline mediastinal lymphoma and is a candidate for inherited cancer susceptibility. SV analysis revealed a complex deletion coupled with a nearby potential duplication event that was shared privately across three unrelated dwarfism cats and is found within a known dwarfism associated region on cat chromosome B1. This SV interrupted UDP-glucose 6-dehydrogenase (UGDH), a gene involved in the biosynthesis of glycosaminoglycans. Importantly, UGDH has not yet been associated with human dwarfism and should be screened in undiagnosed patients. The new high-quality cat genome reference and the compilation of sequence variation demonstrate the importance of these resources when searching for disease causative alleles in the domestic cat and for identification of feline biomedical models. Author summaryThe practice of genomic medicine is predicated on the availability of a high quality reference genome and an understanding of the impact of genome variation. Such resources have lead to countless discoveries in humans, however by working exclusively within the framework of human genetics, our potential for understanding diseases biology is limited, as similar analyses in other species have often lead to novel insights. The generation of Felis_catus_9.0, a new high quality reference genome for the domestic cat, helps facilitate the expansion of genomic medicine into the felis lineage. Using Felis_catus_9.0 we analyze the landscape of genomic variation from a collection of 54 cats within the context of human gene constraint. The distribution of variant impacts in cats is correlated with patterns of gene constraint in humans, indicating the utility of this reference for identifying novel mutations that cause phenotypes relevant to human and cat health. Moreover, structural variant analysis revealed a novel variant for feline dwarfism in UGDH, a gene that has not been associated with dwarfism in any other species, suggesting a role for UGDH in cases of undiagnosed dwarfism in humans.

genomics↗