Biology subjects

Crump, G.

Publications and source records attributed to Crump, G..

7 recordsLinked to original sources

bioRxiv2026

Signal triangulation coordinates cell fate decisions in the developing jaw

Development of the vertebrate lower jaw depends on spatially precise cell fate decisions by cranial neural crest-derived cells (CNCCs) of the mandibular arch. From closer to the mouth (oral) to farther away (aboral), CNCCs adopt bone, cartilage, tendon, and stromal fates to shape the jaw skeleton and ensure proper connectivity to the musculature. How signaling pathways impact downstream transcriptional programs to generate distinct cell fates along the oral-aboral axis remains incompletely understood. Using photoconversion-based lineage tracing of CNCCs in zebrafish, we show that oral cells contribute to the lower jaw skeleton and aboral cells primarily to tendon, ligament, and stromal tissues. During embryogenesis, the oral domain is partitioned into lateral pitx1+ and medial foxf1+ subdomains distinct from an aboral nr5a2+, gsc+ domain. Using pharmacological inhibition and transgenic misexpression, we find that Bmp signaling establishes aboral nr5a2 and gsc expression, Fgf signaling oral-lateral pitx1 expression, and Hedgehog signaling oral-medial foxf1 expression. Analysis of mutants for pitx1, nr5a2, and gsc reveal that their oral-aboral expression domains are established independently of each other. We also identify enhancers regulating oral-aboral expression of pitx1 and nr5a2, with mutagenesis showing roles for Fgf-dependent ETS motifs in oral pitx1 and Bmp-dependent E-box motifs in aboral nr5a2 enhancer activity, consistent with dependence of nr5a2 expression on the Bmp-dependent E-box factor Hand2. These findings reveal how triangulation of three major signaling pathways converge on distinct gene regulatory modules to establish distinct oral-aboral cell fate decisions in the developing jaw.

developmental biology↗

bioRxiv2024

Retinoic acid signaling suppresses chondrocyte identity during cartilage development and regeneration

Cartilage is a dynamic tissue during development, repair, and disease. Within developing endochondral bones, chondrocytes at growth plate edges transition to osteoblasts, adipocytes, and other connective tissue in the marrow cavity, and in diseases such as Multiple Osteochondromas (MO) chondrocytes form abnormally around growth plates and contribute to ectopic bone. On the other hand, the inability to form new chondrocytes to maintain damaged joints contributes to the high incidence of osteoarthritis. In order to assess the ability of zebrafish to regenerate cartilage, we developed a nitroreductase-based cartilage ablation model. Following ablation at larval to adult stages, we observed new chondrocytes forming around the dead cartilage matrix, with cartilage outgrowths in ablated endochondral bones resembling the exostoses of MO. By generating a perichondrium-restricted hyal4:GFP transgenic line, we show that new chondrocytes arise from the perichondrium surrounding the ablated cartilage. In addition, we observe enriched expression of the retinoic acid (RA) synthesis gene aldh1a2 in the perichondrium following ablation, and the RA degrading enzyme gene cyp26b1 in newly forming chondrocytes. Consistent with RA signaling suppressing chondrogenesis, treatment with the RA receptor gamma agonist palovarotene, which has been used to treat MO, prevented ablation-induced chondrogenesis. Although we find that BMP signaling is also required for ablation-induced chondrogenesis, we show a distinct role for RA signaling in suppressing sox9a expression and chondrogenesis. Moreover, palovarotene resulted in a near complete loss of growth plates in uninjured zebrafish, which was due to the precocious dedifferentiation and exit of chondrocytes from the growth plate. Our findings suggest a common chondrocyte suppressive role of RA signaling within the developing growth plates and regenerating perichondrium, which may explain the growth plate defects observed when using RA agonists to treat MO.

developmental biology↗

bioRxiv2021

Embryonic requirements for Tcf12 in the development of the mouse coronal suture

A major feature of Saethre-Chotzen syndrome is coronal craniosynostosis, the fusion of the frontal and parietal bones at the coronal suture. It is caused by heterozygous loss-of-function mutations in the basic HLH transcription factors TWIST1 and TCF12. While compound heterozygous Tcf12; Twist1 mice display severe coronal synostosis, the individual role of Tcf12 has remained unexplored. Here we show that Tcf12 controls several key processes in calvarial development, including the rate of frontal and parietal bone growth, and the boundary between sutural and osteogenic cells. Genetic analysis supports an embryonic requirement for Tcf12 in suture formation, as combined deletion of Tcf12 in the embryonic neural crest and mesoderm, but not in the postnatal suture mesenchyme, disrupts the coronal suture. We also detect asymmetric distribution of Grem1 + mesenchymal cells on opposing sides of the wild-type frontal and parietal bones, which prefigures later bone overlap at the sutures. In Tcf12 mutants, reduced asymmetry correlates with lack of bone overlap. Our results indicate a largely embryonic function of Tcf12 in controlling the rate and asymmetrical growth of calvarial bones and establishment of suture boundaries, which together ensure the proper formation of the overlapping coronal suture.

developmental biology↗

bioRxiv2020

osr1 couples intermediate mesoderm cell fate with temporal dynamics of vessel progenitor cell differentiation

Transcriptional regulatory networks refine gene expression boundaries throughout embryonic development to define the precise dimensions of organ progenitor territories. Kidney progenitors originate within the intermediate mesoderm (IM), but the pathways that establish the boundary between the IM and its neighboring vessel progenitors are poorly understood. Here, we delineate new roles for the zinc finger transcription factor Osr1 in kidney and vessel progenitor development. Zebrafish osr1 mutants display decreased IM formation and premature emergence of neighboring lateral vessel progenitors (LVPs). These phenotypes contrast with the increased IM and absent LVPs observed with loss of the bHLH transcription factor Hand2, and loss of hand2 partially suppresses the osr1 mutant phenotypes. hand2 and osr1 are both expressed in the posterior lateral mesoderm, but osr1 expression decreases dramatically prior to LVP emergence. Overexpressing osr1 inhibits LVP development while enhancing IM formation. Together, our data demonstrate that osr1 modulates both the extent of IM formation and the temporal dynamics of LVP development, suggesting that a balance between levels of osr1 and hand2 expression is essential to demarcate the dimensions of kidney and vessel progenitor territories. SUMMARY STATEMENTAnalysis of the osr1 mutant phenotype reveals roles in determining the extent of intermediate mesoderm formation while inhibiting premature differentiation of neighboring vessel progenitors.

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↗

bioRxiv2019

nkx3.2 mutant zebrafish accommodate the jaw joint loss through a phenocopy of the head shapes of Paleozoic agnathans

The vertebrate jaw is a versatile feeding apparatus that facilitated explosive diversification. To function, it requires a joint between the upper and lower jaws, so jaw joint defects - such as osteoarthritis or even ankylosis - are often highly disruptive and difficult to study. To describe consequences of jaw-joint dysfunction, we engineered two independent null alleles of a single jaw-joint marker gene, nkx3.2, in zebrafish. These mutations caused zebrafish to become functionally jawless via fusion of the upper and lower jaw cartilages (ankylosis). Despite lacking jaw joints, nkx3.2 mutants survive to adulthood and accommodate this defect by: a) remodeling their skulls; and b) altering their behavior from suction feeding to ram feeding. As a result of remodeling, nkx3.2 mutants developed superficial similarities to the skull shapes observed in two lineages of ancient jawless vertebrates (anaspids and furcacaudiid thelodonts), including: a fixed open gape, reduced snout, and enlarged branchial region. However, no homology exists in individual skull elements between these taxa, and most of the modified elements in the mutant zebrafish occur outside known expression domains of nkx3.2. Therefore, we interpret the adult nkx3.2 phenotype not as a reversal to an ancestral state, but as convergence due to similar functional requirement of feeding without moveable jaws. This remarkable convergence strongly suggests that jaw movements themselves dramatically influence the development of jawed vertebrate skulls, which implies that functionally viable skull morphologies are finite, with or without functional jaws. Because nkx3.2 null zebrafish display prominent joint ankylosis, drastically modified skull shape, and altered feeding behaviors, these mutants provide a unique model with which to investigate mechanisms of skeletal remodeling and joint diseases.

evolutionary 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↗