Biology subjects

Bronner, M. E.

Publications and source records attributed to Bronner, M. E..

25 records · Page 2Linked to original sources

bioRxiv2020

Hmx gene conservation identifies the evolutionary origin of vertebrate cranial ganglia

The evolutionary origin of vertebrates included innovations in sensory processing associated with the acquisition of a predatory lifestyle1. Vertebrates perceive external stimuli through sensory systems serviced by cranial sensory ganglia (CSG) which develop from cranial placodes; however understanding the evolutionary origin of placodes and CSGs is hampered by the gulf between living lineages and difficulty in assigning homology between cell types and structures. Here we use the Hmx gene family to address this question. We show Hmx is a constitutive component of vertebrate CSG development and that Hmx in the tunicate Ciona is able to drive the differentiation program of Bipolar Tail Neurons (BTNs), cells previously thought neural crest homologs2,3. Using Ciona and lamprey transgenesis we demonstrate that a unique, tandemly duplicated enhancer pair regulated Hmx in the stem-vertebrate lineage. Strikingly, we also show robust vertebrate Hmx enhancer function in Ciona, demonstrating that deep conservation of the upstream regulatory network spans the evolutionary origin of vertebrates. These experiments demonstrate regulatory and functional conservation between Ciona and vertebrate Hmx, and confirm BTNs as CSG homologs. Our analysis also identifies derived evolutionary changes, including a genetic basis for secondary simplicity in Ciona and unique regulatory complexity in vertebrates.

evolutionary biology↗

bioRxiv2020

P-bodies are sites of rapid RNA decay during the neural crest epithelial-mesenchymal transition

The epithelial--mesenchymal transition (EMT) drives cellular movements during development to create specialized tissues and structures in metazoans, using mechanisms often coopted during metastasis. Neural crest cells are a multipotent stem cell population that undergo a developmentally regulated EMT and are prone to metastasis in the adult, providing an excellent model to study cell state changes and mechanisms underlying EMT. A hallmark of neural crest EMT during avian development is temporally restricted expression followed by rapid down-regulation of the Wnt antagonist Draxin. Using live RNA imaging, here we demonstrate that rapid clearance of Draxin transcripts is mediated post-transcriptionally via localization to processing bodies (P-bodies), small cytoplasmic granules which are established sites of RNA processing. Contrasting with recent work in immortalized cell lines suggesting that P-bodies are sites of storage rather than degradation, we show that targeted decay of Draxin occurs within P-bodies during neural crest migration. Furthermore, P-body disruption via DDX6 knockdown inhibits not only endogenous Draxin down-regulation but also neural crest EMT in vivo. Together, our data highlight a novel and important role for P-bodies in an intact organismal context--controlling a developmental EMT program via post-transcriptional target degradation.

cell biology↗

bioRxiv2020

De novo enteric neurogenesis in post-embryonic zebrafish from Schwann cell precursors rather than resident cell types

The enteric nervous system is essential for normal gastrointestinal function, but evidence regarding postnatal enteric neurogenesis is conflicting. Using zebrafish as a model, we explored the origin of enteric neurons that arise in post-embryonic life in normal development and injury, and tested effects of the 5-HT4 receptor agonist, prucalopride. To assess enteric neurogenesis, all enteric neurons were photoconverted prior to time-lapse imaging to detect emergence of new neurons. Injury was modeled by two-photon laser ablation of enteric neurons. Lineage tracing was performed with neural tube injections of lipophilic dye and with an inducible Sox10-Cre line. Lastly, we tested prucaloprides effect on post-embryonic enteric neurogenesis. The post-embryonic zebrafish intestine appears to lack resident neurogenic precursors and enteric glia. However, enteric neurogenesis persists post-embryonically during development and after injury. New enteric neurons arise from trunk neural crest-derived Schwann cell precursors. Prucalopride increases enteric neurogenesis in normal development and after injury if exposure occurs prior to injury. Enteric neurogenesis persists in the post-embryonic period in both normal development and injury, appears to arise from gut-extrinsic Schwann cell precursors, and is promoted by prucalopride. SUMMARY STATEMENTTrunk crest-derived enteric neurogenesis is poorly understood. We find post-embryonic zebrafish lack resident neuronal precursors yet enteric neurogenesis from trunk crest-derived precursors occurs in development, injury, and is promoted by prucalopride.

developmental biology↗

bioRxiv2020

Cancer-associated HIF-2α impacts trunk neural crest stemness

The neural crest is a stem cell population that gives rise to sympathetic ganglia, the cell type of origin of neuroblastoma. Hypoxia Inducible Factor (HIF)-2 is associated with high risk neuroblastoma, however, little is known about its role in normal neural crest development. To address this important question, here we show that HIF-2 is expressed in trunk neural crest cells of human, murine and avian embryos. Modulating HIF-2 in vivo not only causes developmental delays but also induces proliferation and stemness of neural crest cells while altering the number of cells migrating ventrally to sympathoadrenal sites. Transcriptome changes after loss of HIF-2 reflect the in vivo phenotype. The results suggest that expression levels of HIF-2 must be strictly controlled and abnormal levels increase stemness and may promote metastasis. Our findings help elucidate the role of HIF-2 during normal development with implications also in tumor initiation at the onset of neuroblastoma.

developmental biology↗

bioRxiv2019

An atlas of anterior hox gene expression in the embryonic sea lamprey head: hox-code evolution in vertebrates

In the hindbrain and the adjacent cranial neural crest (NC) cells of jawed vertebrates (gnathostomes), nested and segmentally-restricted domains of Hox gene expression provide a combinatorial Hox-code for specifying regional properties during head development. Extant jawless vertebrates, such as the sea lamprey (Petromyzon marinus), can provide insights into the evolution and diversification of this Hox-code in vertebrates. There is evidence for gnathostome-like spatial patterns of Hox expression in lamprey; however, the expression domains of the majority of lamprey hox genes from paralogy groups (PG) 1-4 are yet to be characterized, so it is unknown whether they are coupled to hindbrain segments (rhombomeres) and NC. In this study, we systematically describe the spatiotemporal expression of all 14 sea lamprey hox genes from PG1-PG4 in the developing hindbrain and pharynx to investigate the extent to which their expression conforms to the archetypal gnathostome hindbrain and pharyngeal hox-codes. We find many similarities in Hox expression between lamprey and gnathostome species, particularly in rhombomeric domains during hindbrain segmentation and in the cranial neural crest, enabling inference of aspects of Hox expression in the ancestral vertebrate embryonic head. These data are consistent with the idea that a Hox regulatory network underlying hindbrain segmentation is a pan vertebrate trait. We also reveal differences in hindbrain domains at later stages, as well as expression in the endostyle and in pharyngeal arch (PA) 1 mesoderm. Our analysis suggests that many Hox expression domains that are observed in extant gnathostomes were present in ancestral vertebrates but have been partitioned differently across Hox clusters in gnathostome and cyclostome lineages after duplication.

developmental biology↗

bioRxiv2018

Draxin alters laminin expression during basement membrane reorganization to control cranial neural crest EMT

Premigratory neural crest cells arise within the dorsal neural tube and subsequently undergo an epithelial-to-mesenchymal transition (EMT) to leave the neuroepithelium and initiate migration. Draxin is a Wnt modulator that has been shown to control the timing of cranial neural crest EMT. Here we show that this process is accompanied by three stages of remodeling of the basement membrane protein laminin, from regression to expansion and channel formation. Loss of Draxin results in blocking laminin remodeling at the regression stage, whereas ectopic maintenance of Draxin blocks remodeling at the expansion stage. The latter effect is rescued by addition of Snail2, previously shown to be downstream of Draxin. Our results demonstrate an essential function for the Wnt modulator Draxin in regulating basement membrane remodeling during cranial neural crest EMT.\n\nHIGHLIGHTSO_LICranial neural crest migrate through a laminin-rich basement membrane channel\nC_LIO_LIPerturbation of Draxin, a Wnt antagonist, alters laminin channel formation\nC_LIO_LIDraxins effect on laminin channel formation is largely mediated by Snail2\nC_LI

developmental biology↗

bioRxiv2018

Maintaining trunk neural crest cells as crestospheres

Neural crest cells have broad migratory and differentiative ability that differs according to their axial level of origin. However, their transient nature has limited understanding of their stem cell and self-renewal properties. While an in vitro culture method has made it possible to maintain cranial neural crest cells as self-renewing multipotent crestospheres (Kerosuo et al., 2015), these same conditions failed to preserve trunk neural crest in a stem-like state. Here we optimize culture conditions for maintenance of trunk crestospheres, comprised of both neural crest stem and progenitor cells. Trunk crestospheres display elevated expression of neural crest cell markers as compared to those characteristic of neural tube or mesodermal fates. Moreover, trunk crestospheres have increased expression of trunk-related markers as compared to cranial genes. Finally, we use lentiviral transduction as a tool to manipulate gene expression in trunk crestospheres. Taken together, this method enables long-term in vitro maintenance and manipulation of trunk neural crest cells in a premigratory stem or early progenitor state to probe the mechanisms underlying their stemness and lineage decisions.\n\nHighlightsO_LITrunk-derived multipotent neural crest stem cells can be cultured as crestospheres\nC_LIO_LITrunk-derived crestospheres require different conditions than cranial\nC_LIO_LITrunk crestospheres consist of neural crest stem and progenitor cells\nC_LIO_LITrunk crestospheres can be efficiently transduced using lentiviral vectors\nC_LI

developmental biology↗