Biology subjects

Barske, L.

Publications and source records attributed to Barske, L..

6 recordsLinked to original sources

bioRxiv2026

Pax9 governs anterior identity and deployment of sclerotome to the median fins

The caudal fin is an anomaly among vertebrate locomotory appendages: its internal skeleton is as asymmetric as the human hand, but it lacks the Shh-secreting Zone of Polarizing Activity (ZPA) and the Gli3/HoxD/Hand2 programs that govern anterior-posterior patterning in other appendages. As the caudal fin was also the first appendage to evolve, deciphering its alternative patterning program may provide clues to the ancestral state. Pax9 is one of few conserved appendage patterning factors reported to also be active in the caudal fin, specifically in the anterior domain. We report that loss of pax9 function in zebrafish not only disrupts anterior-specific caudal fin anatomy, but also results in a spectacular fusion of the caudal and anal fins along the ventral midline. The dorsal fin is also expanded to a lesser degree, the paired fins not at all. The mutant caudal fin initially forms as an irregularly patterned structure lacking anterior molecular identity, with supernumerary elements spilling out beyond the normal anterior boundary. Unexpectedly, this phenotype is subsequently compounded by neighboring trunk somites erroneously deploying skeletal mesenchyme in the normally finless caudal peduncle region, completing the ectopic skeleton. scRNAseq analysis at caudal fin bud stage indicates that pax9 mutants gain skeletal mesenchyme at the expense of a specialized type of fibroblast involved in the formation of fin fold actinotrichia. Median fin skeletal mesenchyme and fin fold fibroblasts both arise from the sclerotome, a somite compartment that also robustly expresses pax9. We propose that, within the sclerotome, Pax9 pushes progenitors towards fin fold fibroblast fate, limiting how many cells will later be available to make median fin skeleton. Within the fin bud, it drives anterior identity, with the strongest impact on the ZPA-free caudal fin bud. These dual sites of action make Pax9 a uniquely powerful governor of median fin development.

Developmental Biology↗

bioRxiv2024

Midfacial retrusion and loss of facial appendages caused by mutation of Pax9 in zebrafish

Loss of dentition has occurred repeatedly throughout vertebrate evolution. Cyprinid fish, including zebrafish, form teeth only deep within the pharynx, not on their oral jaws. However, zebrafish still robustly express transcription factors associated with mammalian tooth development in the neural crest-derived mesenchyme surrounding the mouth. We investigated whether this expression is vestigial or whether these factors contribute to the formation of non-tooth mesenchymal structures in the oral region, using Pax9 as a test case. Zebrafish homozygous for two different pax9 mutant alleles develop the normal complement of pharyngeal teeth but fail to form the premaxilla bone, most of the maxilla, and nasal and maxillary barbels. Lack of most of the upper jaw complex does not preclude effective feeding in the laboratory environment. We observed a significant deficit of sp7:EGFP+ osteoblasts and adjacent alx4a:DsRed+ condensing mesenchyme where the maxilla forms, and no accumulation of either in the premaxillary domain. These phenotypes are not presaged by major disruptions in early facial patterning, Wnt signaling, proliferation, or cell death; however, loss of a small population of Wnt-responsive cells around the maxilla correlates with its stalled growth in mutants. We conclude that Pax9 is not unequivocally required for all vertebrate tooth development, but instead may be broadly involved in the development of a variety of organs forming through mesenchymal condensation around the mouth.

developmental biology↗

bioRxiv2024

Cadherin 16 promotes sensory gating via the endocrine corpuscles of Stannius

Sensory thresholds enable animals to regulate their behavioral responses to environmental threats. Despite the importance of sensory thresholds for animal behavior and human health, we do not yet have a full appreciation of the underlying molecular-genetic and circuit mechanisms. The larval zebrafish acoustic startle response provides a powerful system to identify molecular mechanisms underlying establishment of sensory thresholds and plasticity of thresholds through mechanisms like habituation. Using this system, we identify Cadherin 16 as a previously undescribed regulator of sensory gating. We demonstrate that Cadherin 16 regulates sensory thresholds via an endocrine organ, the corpuscle of Stannius (CS), which is essential in zebrafish for regulating Ca2+ homeostasis. We further show that Cadherin 16 regulates whole-body calcium and ultimately behavior through the hormone Stanniocalcin 1L, and the IGF-regulatory metalloprotease, Papp-aa. Finally, we demonstrate the importance of the CS through ablation experiments that reveal its role in promoting normal acoustic sensory gating. Together, our results uncover a previously undescribed brain non-autonomous pathway for the regulation of behavior and establish Ca2+ homeostasis as a critical process underlying sensory gating in vivo.

genetics↗

bioRxiv2024

Sox10 is required for systemic initiation of bone mineralization

Heterozygous variants in the gene encoding the SOX10 transcription factor cause congenital syndromes affecting pigmentation, digestion, hearing, and neural function. Most of these symptoms are attributable to failed differentiation and loss of neural crest cells. Extensive research on mouse and zebrafish models has confirmed that Sox10 is essential for most non-skeletal crest derivatives, but seemingly dispensable for skeletal development. We challenge that concept here by revealing a novel requirement for Sox10 in skeletal mineralization. Neither neural crest- nor mesoderm-derived bones initiate mineralization on time in zebrafish sox10 mutants, despite normal osteoblast differentiation and matrix production. We show that mutants are deficient in the ionocyte subpopulation tasked with taking up calcium from the environment through the Trpv6 epithelial calcium channel, leading to a severe calcium deficit that explains the lack of mineralization. As these ionocytes do not derive from a sox10+ lineage, we hypothesized that the primary defect instead resides in a separate organ that regulates ionocyte numbers or calcium uptake at a systemic level. Screening of the endocrine hormones known to regulate calcium homeostasis in adult vertebrates revealed significantly elevated levels of stanniocalcin (Stc1a), an anti-hypercalcemic hormone, in larval sox10 mutants. Previous studies demonstrated that Stc1a inhibits calcium uptake in fish by repressing trpv6 expression and blocking proliferation of Trpv6+ ionocytes. Our epistasis assays indicate that excess Stc1a is the proximate cause of the calcium deficit in sox10 mutants. Lineage tracing shows that the pronephros-derived glands that synthesize Stc1a interact with sox10+ neural crest-derived cells, and that the latter are missing in mutants. We conclude that a subpopulation of Sox10+ neural crest non-cell-autonomously limit Stc1a production to allow the inaugural wave of calcium uptake necessary for the initiation of bone mineralization.

developmental biology↗

bioRxiv2020

Evolution of vertebrate gill covers via shifts in an ancient Pou3f3 enhancer

Whereas the gill chambers of extant jawless vertebrates (lampreys and hagfish) open directly into the environment, jawed vertebrates evolved skeletal appendages that promote the unidirectional flow of oxygenated water over the gills. A major anatomical difference between the two jawed vertebrate lineages is the presence of a single large gill cover in bony fishes versus separate covers for each gill chamber in cartilaginous fishes. Here we find that these divergent gill cover patterns correlate with the pharyngeal arch expression of Pou3f3 orthologs. We identify a Pou3f3 arch enhancer that is deeply conserved from cartilaginous fish through humans but undetectable in lampreys, with minor sequence differences in the bony versus cartilaginous fish enhancers driving the corresponding single versus multiple gill arch expression patterns. In zebrafish, loss of Pou3f3 gene function disrupts gill cover formation, and forced expression of Pou3f3b in the gill arches generates ectopic skeletal elements resembling the multiple gill cover pattern of cartilaginous fishes. Emergence of this Pou3f3 enhancer >430 mya and subsequent modifications may thus have contributed to the acquisition and diversification of gill covers and respiratory strategies during gnathostome evolution.

developmental biology↗

bioRxiv2017

Genome-Wide Analysis of Facial Regionalization in Zebrafish

Patterning of the facial skeleton involves the precise deployment of thousands of genes in distinct regions of the pharyngeal arches. Despite the significance for craniofacial development, how genetic programs drive this regionalization remains incompletely understood. Here we use combinatorial labeling of zebrafish cranial neural crest-derived cells (CNCCs) to define global gene expression along the dorsoventral axis of the developing arches. Intersection of region-specific transcriptomes with expression changes in response to signaling perturbations demonstrates complex roles for Endothelin1 (Edn1) signaling in the intermediate joint-forming region yet a surprisingly minor role in ventral-most regions. Analysis of co-variance across multiple sequencing experiments further reveals clusters of coregulated genes, with in situ hybridization confirming the domain-specific expression of novel genes. We then performed mutational analysis of a number of these genes, which uncovered antagonistic functions of two new Edn1 targets, follistatin a (fsta) and emx2, in regulating cartilaginous joints in the hyoid arch. Our unbiased discovery and functional analysis of genes with regional expression in zebrafish arch CNCCs reveals complex regulation by Ednl and points to novel candidates for craniofacial disorders.\n\nSummary StatementUsing zebrafish to purify distinct groups of embryonic cells, Askary et al. have created a detailed map of how thousands of genes are deployed to shape the developing face.

developmental biology↗