Biology subjects

Lo, B.-W.

Publications and source records attributed to Lo, B.-W..

4 recordsLinked to original sources

bioRxiv2026

Evolution and mechanism of MEIS2-mediated forelimb specialization in bats

The genomic basis of limb adaptations in tetrapods is thought to be largely driven by changes in gene regulation. However, the mechanisms by which regulatory programs evolve are not well understood. In bats, wing membrane development has been shown to be associated with expression of the transcription factor MEIS2 in the interdigital tissue of the forelimb. However, MEIS2 alone is insufficient to recapitulate wing morphology, suggesting that its regulatory context has also undergone divergence. Here, we integrate functional genomics with sequence-to-function deep learning to dissect both the mechanistic and evolutionary roles of MEIS2 in bat forelimb development. Using models trained on embryonic limb data from bat and mouse, we identify a strong association between MEIS2 binding and the transcription factor TWIST1, a finding which is supported by single-cell transcriptomic analyses. To investigate the evolutionary dimension, we applied these models across more than 100 genomes, including extant bats, closely related species, and reconstructed ancestors. This analysis identified divergences in regulatory regions, which likely contribute to bat-specific forelimb expression of genes that lead to wing morphogenesis. Notably, these changes are prominent in the regulatory domains of the MEIS dimerization partner PBX1, indicating coordinated regulatory evolution. Together, our results demonstrate that the evolution of a complex morphological trait involves coordinated changes in both trans-regulatory environments and cis-regulatory landscapes. More broadly, this study provides a framework for integrating deep learning with comparative and functional genomics to investigate regulatory evolution.

evolutionary biology↗

bioRxiv2024

Genomes of Wiebesia fig wasps reveal the adaptation and codiversification in fig-fig wasp mutualism

Figs and fig wasps represent one of the most intimate examples of plant-pollinator coevolution. As figs diversified into geographically isolated populations, both figs and fig wasps underwent selective pressures driven by local adaptation and coevolution. Ficus pumila comprises two ecologically distinct varieties: the creeping fig (F. pumila var. pumila), which is widely distributed across the lowlands of East Asia, and the jelly fig (F. pumila var. awkeotsang), endemic to Taiwan and found at mid-elevations. To elucidate how codiversification with fig hosts influences the evolutionary trajectories of fig wasps, we analyzed the genomes of Wiebesia sp. 2 and sp. 3, the respective pollinators of creeping fig and jelly fig. Our demographic analysis indicates that vicariance during the Last Glacial Period facilitated ecological differentiation between these two fig-fig wasp pairs. Through comparative and population genomic analyses, we identified selection signals linked to habitat adaptation, with evolutionary rates corresponding to the life history traits of their host figs. Variations in host preference behavior, chemosensory gene expression, and adaptive duplications in olfactory receptors highlight potential mechanisms for adaptation to host floral scents. These findings collectively underscore how the obligate mutualism between figs and their pollinating wasps allows the ecological traits and habitat preferences of fig hosts to shape the evolutionary pathways of their pollinators, leaving distinct molecular imprints in the fig wasp genomes. This study demonstrates the capacity of tightly intertwined life cycles between plants and pollinators to drive adaptation and diversification.

evolutionary biology↗

bioRxiv2024

Comparative single-cell analyses reveal evolutionary repurposing of a conserved gene program in bat wing development

Bats are the only mammals capable of self-powered flight, an evolutionary innovation based on the transformation of forelimbs into wings. The bat wing is characterized by an extreme elongation of the second to fifth digits and a wing membrane called chiropatagium connecting them. Here we investigated the developmental and cellular origin of this structure by comparing bat and mouse limbs using omics tools and single-cell analyses. Despite the substantial morphological differences between the species, we observed an overall conservation of cell populations and gene expression patterns including interdigital apoptosis. Single-cell analyses of micro-dissected embryonic chiropatagium identified a specific fibroblast population, independent of apoptosis-associated interdigital cells, as the origin of this tissue. These distal cells express a conserved gene program including the transcription factors MEIS2 and TBX3, which are commonly known to specify and pattern the early proximal limb. Transgenic ectopic expression of MEIS2 and TBX3 in mouse distal limb cells resulted in the activation of genes expressed during wing development and phenotypic changes related to wing morphology, such as the fusion of digits. Our results elucidate fundamental molecular mechanisms of bat wing development and illustrate how drastic morphological changes can be achieved through repurposing of existing developmental programs during evolution.

evolutionary biology↗

bioRxiv2024

Conservation of Regulatory Elements with Highly Diverged Sequences Across Large Evolutionary Distances

Embryonic gene expression is remarkably conserved across vertebrates as observed, for instance, in the developing hearts of chicken and mouse which diverged >300 million years ago. However, most cis regulatory elements (CREs) are highly divergent, which makes orthology tracing based on sequence similarity difficult, especially at larger evolutionary distances. Some evidence suggests functional conservation of CREs despite sequence divergence. However, it remains unclear how widespread such functional conservation might be. Here, we address this question by profiling the regulatory genome in the embryonic hearts of chicken and mouse at equivalent developmental stages. Gene expression and 3D chromatin structure show remarkable similiarity, while the majority of CREs are non-alignable between the two species. To identify orthologous CREs independent of sequence alignability, we introduce a synteny-based strategy called Interspecies Point Projection (IPP). Compared to alignment-based approaches, IPP identifies up to 5-fold more putative orthologs in chicken, and up to 9-fold across distantly related vertebrates. We term these sequence-diverged orthologs indirectly conserved and characterize their functional conservation compared to sequence-alignable, directly conserved CREs. Indirectly and directly conserved elements show similar enrichment of functional chromatin signatures and cell-type specific enhancer sequence composition. Yet, shared transcription factor binding sites between orthologs are more heavily rearranged in indirectly conserved elements. Finally, we validate functional conservation of indirectly conserved chicken enhancers in mouse using in vivo reporter assays. Taken together, by overcoming the limitations of alignment-based methods our results reveal functional conservation of CREs across large evolutionary distances is more widespread than previously recognized.

genetics↗