Biology subjects

Herbert, A. L.

Publications and source records attributed to Herbert, A. L..

5 recordsLinked to original sources

bioRxiv2024

The fourspine stickleback (Apeltes quadracus) has an XY sex chromosome system with polymorphic inversions on both X and Y chromosomes

Teleost fish are well-known for possessing a diversity of sex chromosomes and for undergoing frequent turnovers of these sex chromosomes. However, previous studies have mainly focused on variation between species, while comparatively little attention has been given to sex chromosome polymorphisms within species, which may capture early stages of sex chromosome changes. To better understand the evolution of sex chromosomes, we used the fourspine stickleback (Apeltes quadracus) as a model organism. Previously, it was believed that females of this species possessed a ZW heteromorphic sex chromosome system. However, genetic crosses and our whole-genome sequencing of wild populations revealed that A. quadracus has an XY sex chromosome on chromosome 23. This chromosome has not previously been identified as a sex chromosome in other stickleback species, indicating a recent sex chromosome turnover. We also identified two genes - rxfp2a and zar1l - as novel candidate sex determination genes. Notably, we observed inversions on both the X and Y chromosomes in different populations, resulting in distinctive patterns of differentiation between the X and Y chromosomes across populations. We propose that the inversion on the X chromosome may have been favored by sexually antagonistic selection. The new sex chromosome and intraspecies inversion polymorphisms observed in A. quadracus provide an excellent system for studying the evolution of sex chromosomes and their turnovers. Author SummaryAs compared to mammals and birds, teleost fish exhibit a very high level of diversity in their sex chromosomes, even among closely related species. Thus far, little attention has been paid to variation within species, although it offers a valuable opportunity to advance our understanding of the mechanisms underlying the formation and turnover of sex chromosomes. Through a quantitative trait locus (QTL) cross and sequencing diverse populations, we determined that instead of the previously reported ZW system, A. quadracus has an XY sex determination system on chromosome 23. Within the sex determining region, we identified rxfp2a and zar1l as putative sex determining genes. Notably, we also observed polymorphic inversions present on both the X and Y chromosomes that differ among populations. Based on our findings, we hypothesize that the X-linked inversions are favored by selection that differs between males and females. These observations represent a rare situation in which sex chromosomes are still polymorphic for sex-linked inversions, which offers important insights into the early stages of sex chromosome evolution.

evolutionary biology↗

bioRxiv2023

Evolution of novel sensory organs in fish with legs

How do animals evolve new traits? Sea robins are unusual "walking" fishes that use leg-like appendages to navigate the seafloor. Here, we show that legs are bona fide sense organs that mediate the unique ability to localize and uncover buried prey. We then probe the developmental and physiological basis of these novel sense organs as a striking example of a major trait gain in evolution. We find certain sea robin species have legs with unique end-organs called papillae that mediate enhanced mechanical and chemical sensitivity to enable predatory digging behavior. Papillae exhibit dense innervation from touch-sensitive neurons, noncanonical epithelial taste receptors, and chemical sensitivity that drives predatory digging behavior. Using a combination of developmental analyses, crosses between species with and without papillae, and interspecies comparisons of sea robins from around the world, we demonstrate that papillae represent a key evolutionary innovation associated with behavioral niche expansion on the seafloor. These discoveries provide a conceptual framework for understanding how molecular, cellular, and tissue-scale adaptations integrate to produce novel organismic traits and behavior.

evolutionary biology↗

bioRxiv2023

The genetic basis of novel trait gain in walking fish

A major goal in biology is to understand how organisms evolve novel traits. Multiple studies have identified genes contributing to regressive evolution, the loss of structures that existed in a recent ancestor. However, fewer examples exist for genes underlying constructive evolution, the gain of novel structures and capabilities in lineages that previously lacked them. Sea robins are fish that have evolved enlarged pectoral fins, six mobile locomotory fin rays (legs) and six novel macroscopic lobes in the central nervous system (CNS) that innervate the corresponding legs. Here, we establish successful husbandry and use a combination of transcriptomics, CRISPR-Cas9 editing, and behavioral assays to identify key transcription factors that are required for leg formation and function in sea robins. We also generate hybrids between two sea robin species with distinct leg morphologies and use allele-specific expression analysis and gene editing to explore the genetic basis of species-specific trait diversity, including a novel sensory gain of function. Collectively, our study establishes sea robins as a new model for studying the genetic basis of novel organ formation, and demonstrates a crucial role for the conserved limb gene tbx3a in the evolution of chemosensory legs in walking fish.

evolutionary biology↗

bioRxiv2021

Evolution of stickleback spines through independent cis-regulatory changes at HOXDB

Understanding the genetic mechanisms leading to new traits is a fundamental goal of evolutionary biology. We show that HOXDB regulatory changes have been used repeatedly in different stickleback fish species to alter the length and number of bony dorsal spines. In Gasterosteus aculeatus, a variant HOXDB allele is genetically linked to shortening an existing spine and adding a spine. In Apeltes quadracus, a variant allele is associated with lengthening an existing spine and adding a spine. The alleles alter the same conserved non-coding HOXDB enhancer by diverse molecular mechanisms, including SNPs, deletions, and transposable element insertions. The independent cis-acting regulatory changes are linked to anterior expansion or contraction of HOXDB expression. Our findings support the long-standing hypothesis that natural Hox gene variation underlies key morphological patterning changes in wild populations and illustrate how different mutational mechanisms affecting the same region may produce opposite gene expression changes with similar phenotypic outcomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=154 SRC="FIGDIR/small/472698v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@8e6675org.highwire.dtl.DTLVardef@e89e13org.highwire.dtl.DTLVardef@1e1f1dcorg.highwire.dtl.DTLVardef@cdb6f8_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2018

Fbxw7 is a critical regulator of Schwann cell myelinating potential

Myelin insulates and protects axons in vertebrate nervous systems. In the central nervous system (CNS), oligodendrocytes (OLs) make numerous myelin sheaths on multiple axons, whereas in the peripheral nervous system (PNS) myelinating Schwann cells (SCs) make just one myelin sheath on a single axon. Why the myelinating potentials of OLs and SCs are so fundamentally different is unclear. Here, we find that loss of Fbxw7, an E3 ubiquitin ligase component, enhances the myelinating potential of SCs. Fbxw7 mutant SCs are seen myelinating multiple axons in a fashion reminiscent of OLs as well as aberrantly myelinating large axons while simultaneously ensheathing small unmyelinated axons - typically distinct roles of myelinating SCs and non-myelinating Remak SCs, respectively. We found that several of the Fbxw7 mutant phenotypes, including the ability to generate thicker myelin sheaths, were due to dysregulation of mTOR. However, the remarkable ability of mutant SCs to either myelinate multiple axons or myelinate some axons while simultaneously encompassing other unmyelinated axons is independent of mTOR signaling. This indicates distinct roles for Fbxw7 in regulating multiple aspects of SC behavior and that novel Fbxw7-regulated mechanisms control modes of myelination previously thought to fundamentally distinguish myelinating SCs from non-myelinating SCs and OLs. Our data reveal unexpected plasticity in the myelinating potential of SCs, which may have important implications for our understanding of both PNS and CNS myelination and myelin repair.

neuroscience↗