Melissa Ann Wilson

Speciation in marine taxa is dynamic and complex, often occurring in the absence of absolute geographic barriers to gene flow. Boobies comprise a clade of seven highly mobile seabird species with high diversity in the eastern Pacific Ocean, where no land barriers separate extant sister species and hybridization is widespread. They exhibit striking diversity in bare-part coloration, an important signal of mate quality, and possess a novel multiple sex chromosome system (Z ₁ Z ₂ Z ₁ Z ₂ / Z ₁ Z ₂ W), likely resulting from a fusion between an ancestral autosomal microchromosome and the W chromosome. To understand speciation processes in the context of gene flow, we sequenced and analyzed 29 short-read booby genomes and assembled a reference northern gannet genome to (1) test for introgression, (2) characterize genomic patterns of divergence across species, and (3) investigate the gene content and evolution of the neo-sex chromosome. We found that divergence among eastern Pacific sister taxa is temporally associated with periods of glacial maxima. Between periods of glacial maxima, two pairs of sister species (blue-footed and Peruvian boobies; masked and Nazca boobies) exhibit strong signatures of episodic introgression, indicating that speciation has occurred over multiple periods of divergence followed by gene flow. However, in the third pair of sister species, genomic signatures showed higher divergence within brown booby populations than between brown and Cocos boobies. We also identified the epidermal differentiation complex – a gene cassette involved in skin, feather, beak, and claw development – on the neo-sex region of the W chromosome, where it spans the boundary between the putatively recombining and non-recombining regions, with interspecific variation in the exact recombination suppression boundary. We inferred that this complex may contribute to diversity in feather and bare part coloration across boobies. Together, these results reveal that diversification and speciation in a clade of highly mobile seabirds emerged from a complex evolutionary history involving historical climate dynamics, introgression, and sex chromosome evolution.

The Vertebrate Genomes Project (VGP) aims to produce complete and near-error-free reference genomes for all ∼70,000 extant vertebrate species. Organized in four phases, it progressively targets all vertebrate orders, families, genera, and eventually all species. Here we present the completion of VGP Phase I, delivering reference genomes for ∼97% of vertebrate orders, along with additional lineages within those orders, totaling 815 species and 1.6 trillion base pairs of main haplotype sequence. These genomes were assembled and annotated over an 8-year period (2018-2026) of rapid advances in genome sequencing, assembly, and annotation methods, alongside the growth of associated consortium initiatives and international collaborations. They represent some of the highest-quality vertebrate genomes currently available, and most have become the primary reference for their respective species in public databases. Comparative analyses across a subset of 579 species when we reached a threshold of 85% of orders allowed us to reconstruct the genome of the last common ancestor of all vertebrates 500 million years ago, identify diverse modes of sex chromosome evolution, reveal clade-specific three-dimensional genome architecture, discover methylated epigenetic landscapes across vertebrates, and provide a framework for studying gene and pseudogene evolution, immune loci, cancer-associated genes, and other trait-associated loci. Approximately a quarter of this subset are listed as Vulnerable to Critically Endangered by the IUCN Red List of Threatened Species, and have enabled more advanced genomic investigations of extinction risk. VGP Phase I delivers the reference backbone for vertebrate genomics, enabling discoveries that would otherwise remain out of reach across evolution, conservation, and medicine.

The human Y chromosome is among the most structurally dynamic chromosomes in the human genome, yet much of its diversity remains unresolved because of extensive palindromes, ampliconic gene families, satellite-rich heterochromatin and large segmental duplications. What remained unclear was how these diverse forms of variation fit together across the full chromosome, how often similar structures recur in different lineages, and which aspects of organization remain constrained despite rapid sequence turnover. Here, we generated and analyzed 142 nearly complete human Y chromosome assemblies from 17 major haplogroups spanning approximately 180,000 years of evolution, creating a population-scale resource for studying Y chromosome biology and diversity. These assemblies show that structural change on the Y chromosome is recurrent but constrained, even in its most repetitive regions. In the fertility-associated azoospermia factor c (AZFc) region, recurrent inversions, deletions, and complex rearrangements generate a limited repertoire of structural haplotypes. Multicopy ampliconic gene families follow distinct evolutionary paths: DAZ paralogues differ in structural constraint, RBMY evolves within a modular array, and TSPY copy number varies mainly through local expansion and contraction. The centromere and Yq12 heterochromatin vary greatly in size but retain a stable higher-order organization, including a single hypomethylated centromeric core and conserved Yq12 repeat composition and orientation. Methylation across palindromic and ampliconic regions is likewise structured by repeat class, copy order and local architecture. Together, these results provide a population-scale resource for the human Y chromosome and show that its rapid structural evolution is repeatedly funneled into a limited set of architectural outcomes.

In most animal species, the sex-determining pathway is typically initiated by the presence/absence of a primary genetic cue at a critical point during development. This primary genetic cue is often located on a single locus—referred to as sex chromosomes—and can be limited to females (in a ZZ/ZW system) or males (in an XX/XY system). One trademark of sex chromosomes is a restriction or cessation of recombination surrounding the sex-limited region (to prevent its inheritance in the homogametic sex). This may lead to—through a variety of mechanisms—higher amounts of genetic divergence within this region, ie between the X/Z and Y/W chromosomes, especially when compared with their autosomal counterparts. Recent advances in genome sequencing and computation have brought with them the ability to resolve haplotypes within a diploid individual, permitting assembly of previously challenging genomic regions like sex chromosomes. Leveraging these advances, we identified replicable diagnostic characteristics between typical autosomes and sex chromosomes (within a single genome assembly). Under this framework, we can use this information to identify putative sex chromosome linkage groups across divergent vertebrate taxa and simultaneously curate misassembled regions on autosomes. Here, we present this conceptual framework and associated tool for identifying candidate sex chromosome linkage groups from a single, diploid individual dubbed Sex Chromosome Identification by Negating Kmer Densities.

Background: Preeclampsia is a hypertensive disorder of pregnancy with major maternal and fetal consequences. While the molecular basis of early-onset preeclampsia is well studied, the mechanisms underlying late-onset disease—and how they differ by fetal sex—remain poorly understood. Placental transcriptomic profiling at term can reveal persistent molecular alterations reflecting cumulative disease processes. Methods: We conducted a cross-sectional observational analysis of placental gene expression using RNA sequencing in a subset of 58 term placentas (21 male-bearing and 37 female-bearing pregnancies) drawn from two large prospective birth cohorts. Pregnancies were classified based on a clinical diagnosis of late-onset preeclampsia (diagnosed ≥ 20 weeks’ gestation according to ISSHP criteria) or as uncomplicated pregnancies. We then assessed for differential gene expression. Cell type proportions were estimated using CIBERSORTx from a placenta-specific reference single-cell dataset. Weighted gene co-expression network analysis identified modules of co-expressed genes associated with late-onset preeclampsia and fetal sex. Results: Differential gene expression analysis identified 150 genes with altered expression in male-bearing placentas from pregnancies with late-onset preeclampsia compared to those from uncomplicated pregnancies. No differentially expressed genes were identified in female-bearing placentas. Cell type deconvolution revealed increased abundance of CD14 + monocytes and CD8 + activated T cells (log odds of 1.42 and 1.44 respectively) and reduced fetal GZMK natural killer cells (log odds of 0.60) in male-bearing placentas from affected pregnancies. In female-bearing placentas, late-onset preeclampsia was associated with increased fetal nucleated red blood cells and maternal plasma cells (log odds of 1.33 and 1.40 respectively). Male-specific co-expression analysis identified gene modules enriched for biological processes including RNA processing, immune regulation, and metabolism. Conclusions: Placental transcription and cellular responses to late-onset preeclampsia differ by fetal sex. Evidence of altered immune cell composition and gene co-expression in male-bearing placentas suggests a sex-specific vulnerability. These findings highlight the importance of considering fetal sex in molecular investigation and clinical management of preeclampsia. Plain english summary: Preeclampsia is a common pregnancy complication marked by high blood pressure, but how it affects the placenta, especially in later pregnancy and depending on the baby’s sex, is not well understood. In this study, we analysed placental tissue from pregnancies with and without late-onset preeclampsia using RNA sequencing. By separating the data based on whether the neonate was male or female, we found striking differences in gene expression. Only placentas from male-bearing pregnancies showed significant changes in gene expression linked to preeclampsia. These changes involved genes related to immune response, metabolism and vascular function. We also used computational tools to estimate what types of cells were present in each placental sample. In male-bearing pregnancies affected by late-onset preeclampsia, there was a notable increase in certain immune cells, suggesting an altered immune response and increased inflammation. In contrast, female-bearing pregnancies affected by late-onset preeclampsia showed an increase in cell composition for two blood related cell types, but no significant gene expression differences. By grouping genes that worked together into networks, we identified several groups, especially in placentas from male-bearing pregnancies, that were strongly associated with biological processes known to be disrupted in preeclampsia, such as blood vessel formation, extracellular matrix remodelling, and hormone regulation. These findings emphasise the importance of considering fetal sex in pregnancy research and could help guide future sex-specific diagnostic or treatment strategies.

The short arms of human acrocentric chromosomes are characterized by nucleolar organizer regions essential for ribosome biogenesis, but their highly repetitive nature has hindered genomic analysis. Leveraging the recently completed genomes of all major ape lineages, we identified recurrent features of their acrocentrics, including enriched repeat classes, centromere repositioning by whole-arm inversion, interchromosomal sequence exchange, and birth-and-death evolution of multiple gene families. Together, these processes have enabled the repeated amplification and diversification of the FRG1 gene family over 25 million years of ape evolution, and, in gorilla, the formation and amplification of a novel IGSF3 - GGT fusion gene under positive selection. Similar evolutionary events also explain the distribution of segmental duplications and heterochromatin in the modern human genome, predisposing it to karyotypic abnormalities such as Robertsonian translocations. Our findings highlight acrocentric chromosomes as key drivers of evolution in the great apes, with implications for speciation, adaptation, and clinical genomics.

Poecilozonites bermudensis, the greater Bermuda land snail, is a critically endangered species and 1 of only 2 extant members in its genus. These snails are one of Bermuda's few endemic animal clades, and their rich fossil record was the basis for the punctuated equilibria model of speciation. Once thought extinct, recent conservation efforts have focused on the recovery of the species, yet no genomic information or other molecular sequences have been available to inform these initiatives. We present a high-quality, annotated genome for P. bermudensis generated using PacBio long reads and Hi-C long-range reads sequencing. The resulting assembly is approximately 1.36 Gb with a scaffold N50 of 44.8 Mb and 31 chromosome-length scaffolds. Nearly 43% of the genome was identified as repeat content. This assembly confirms that a whole genome duplication occurred near the base of Stylommatophora. The genome will serve as a resource for conservation efforts of the surviving Poecilozonites species and adds to the currently limited body of genomic data on gastropod evolution.

Microchimerism research has recently gained renewed attention despite known existence of these rare cells for decades. Fetal and maternal microchimeric‐derived cells may have functional capabilities, and are increasingly associated with both beneficial and adverse health outcomes. Yet, establishing the role of microchimerism in health has been largely constrained methodologically and theoretically. The Microchimerism, Human Health, and Evolution Project address these challenges by calling on 29 leading microchimerism experts to put forth key research questions that can substantially advance the field. Seven major categories are identified: function and mechanism; microchimerism in interventions, treatment, and transplant; mapping “generational microchimerism”; evolution; microchimerism detection; appropriate experimental model systems; and definition of microchimerism. Identifying these questions ‐ and continuing to find answers ‐ will be crucial for advancing the knowledge of microchimerism in health and disease.

Histopathologic diagnosis of thin, invasive cutaneous melanoma (CM) is only 34–62% accurate. Therefore, we sought to develop a transcriptomic biomarker to distinguish benign from malignant melanocytic neoplasms. We generated a targeted RNA-Sequencing dataset (TempO-Seq) of benign nevi (BN; n = 50) and CM (Breslow depth ≤ 1.0 mm; n = 51) and demonstrated enrichment of immune-related pathways among the 450 differentially expressed genes. Next, we trained a putative transcriptomic biomarker in two datasets, including BN and CM, and one dataset with CM in association with a nevus, macrodissected into CM and nevus regions. We refer to the nevus portion of CM in association with a nevus as progressing nevi (PN), since these nevi progressed to CM. Principal component analysis showed that PN samples clustered in a component intermediate to BN and CM. Ordinal regularized regression selected PYGL, AP000845.1, PHYHIP, WSCD1, FBXO7, TRPM1, SLC4A4, NALCN, FRMD4B, HHATL, COL1A1, CRYM, EPOP, RGS1, KRT6C, IGHG1, CNTN1, MMP11, GZMM, AP001880.1, TTYH3, TMEM132A, and PRAME; these genes were consistently selected in 1000 models using data from bootstrap resamples and had a single model predictive accuracy of at least 0.90 (area under the receiver operator characteristics curve). Linear regression models fit with these 23 genes in the TempO-Seq data, and publicly available microarray datasets from BN, dysplastic nevi, and CM, showed high consistency in the magnitude and directionality of gene expression differences between nevi and CM. Furthermore, immunohistochemical staining showed consistent protein-level changes in MMP11 and PYGL. These results illuminate the potential for a transcriptomic biomarker to differentiate benign from malignant melanocytic neoplasms and improve the accuracy of melanoma diagnosis.