Biology subjects

Trainor, P. A.

Publications and source records attributed to Trainor, P. A..

7 recordsLinked to original sources

bioRxiv2026

Loss of polr1c disrupts myelination in a zebrafish model of POLR1C-associated disease

Pathogenic variants in POLR1C, which encodes a shared subunit of RNA Polymerases (Pols) I and III, cause Treacher Collins syndrome (TCS) and POLR3-related leukodystrophy. While Pol I and Tp53-dependent mechanisms have been implicated in the pathogenesis of TCS, the basis of hypomyelination in POLR1C-associated POLR3-related leukodystrophy remains incompletely understood. Here, we show that polr1c mutant zebrafish exhibit reduced myelination in addition to previously described craniofacial anomalies. Oligodendrocyte precursor cells exhibit increased activation of the Tp53 pathway; however, these cells do not undergo apoptosis. Consistent with this finding, tp53 inhibition reduces cell death in polr1c mutants but fails to restore myelination, indicating that myelination deficits are not driven by Tp53-dependent progenitor loss in this model. polr1c mutants also exhibit reduced rRNA transcription by Pol I and reduced expression of some Pol III-transcribed tRNAs. Altogether, these data indicate distinct tissue-specific responses to polr1c deficiency and suggest persistent impairment of rRNA transcription contributes to deficient myelin development. These findings expand the developmental consequences of polr1c loss and advance our understanding of the molecular basis of POLR1C-associated diseases.

developmental biology↗

bioRxiv2026

Retinoid signaling promotes frontonasal identity while repressing maxillary identity during craniofacial development

Vertebrate facial development depends on the correct specification of embryonic facial prominences, a process known to be governed by region-specific reciprocal signaling pathways between the craniofacial ectoderm, endoderm and mesenchyme. This process is further modulated by transcriptional and epigenetic mechanisms that regulate the expression of essential genes in mesenchymal progenitors derived from cranial neural crest cells. Retinoid signaling plays a critical role in facial development, and both gain-and loss-of-function results in a wide spectrum of facial defects, including orofacial clefts. In this study, we identified retinoid signaling as a critical regulator of cranial neural crest cell specification toward a frontonasal process identity in mice. Rdh10 oxidizes vitamin A (all-trans retinol) to retinal, which is a rate limiting step in the synthesis of retinoic acid. Rdh10 loss-of-function resulted in ectopic formation of whisker pads - a derivative of the maxillary process - within the frontonasal process region. This transformation was evidenced by the mis-expression of maxillary specific transcription factors including Meis2 and Lhx6 in the frontonasal mesenchyme. Furthermore, these transcription factors exhibited increased chromatin accessibility at their consensus binding sites following the loss of retinoid signaling in frontonasal cranial neural crest cells. These results indicate that retinoid signaling acts as a critical regulator specifying frontonasal identity and fate of cranial neural crest cells as they migrate into the frontonasal process, while concomitantly repressing maxillary process fate. These results not only advance our understanding of frontonasal prominence specification and the evolutionary development of craniofacial structures but also offers valuable insights into the etiology and pathogenesis of craniofacial malformations such as orofacial clefts.

developmental biology↗

bioRxiv2025

Loss of SPECC1L in cranial neural crest cells results in increased hedgehog signaling and frontonasal dysplasia

SPECC1L encodes a cytoskeletal scaffolding protein that interacts with filamentous actin, microtubules, and cell junctional components. In humans, autosomal dominant mutations in SPECC1L cause a syndrome characterized by craniofrontonasal anomalies including broad nasal bridge, ocular hypertelorism, prominent forehead, and cleft lip/palate. Complete loss of SPECC1L in mice on a homogenous genetic background results in perinatal lethality, accompanied by subtle cranial differences and incompletely penetrant cleft palate. This lethality limits postnatal analysis of craniofacial development. Because cranial neural crest cells (CNCCs) contribute extensively to the formation of anterior craniofacial structures, we investigated whether disruption of SPECC1L in CNCCs contributes to the craniofrontonasal phenotypes observed in SPECC1L-related syndrome. We generated a Specc1l-floxed allele and crossed it with the Wnt1-Cre2 deleter strain, which drives Cre recombinase expression in the dorsal neuroectoderm and NCCs. Most homozygous mutant Specc1l{Delta}CNCC mutants survived postnatally and exhibited hallmark features of the human SPECC1L-related syndrome, including shortened skulls, reduced frontal bone area, nasal defects, and midface hypoplasia. The cranial mesenchyme of Specc1l{Delta}CNCC mice displayed shortened primary cilia and increased Hedgehog (Hh) signaling activity at E13.5, as evidenced by enhanced GLI1 immunostaining. These defects were also observed early in E9.5 facial prominences, indicating that they are etiologic in nature. Collectively, Specc1l{Delta}CNCC mice provide a novel model for investigating the roles of CNCCs, primary cilia, and Hh signaling in frontonasal prominence and midfacial development.

developmental biology↗

bioRxiv2025

Epiblast Lumenogenesis is not a mammalian-specific trait

Epiblast lumenogenesis, which leads to amniotic cavity formation, is a hallmark of mammalian embryogenesis, and required for crucial developmental processes such as anterior-posterior patterning and gastrulation. Based on avian model-organisms, the epiblast in reptiles is thought to form a monolayered flat disc that undergoes anterior-posterior patterning and gastrulation. Here, we report that the squamate, veiled chameleon (Chameleo calyptratus), exhibits epiblast lumenogenesis and amniogenesis prior to anterior-posterior patterning. Using SEM, immunofluorescence, and histology techniques, we demonstrate that chameleon epiblast lumenogenesis occurs via a purse-string-like mechanism involving the formation of supracellular actin cables in concentric rings around the epiblast followed by constriction that closes the epiblast lumen. Through expression analyses of Nodal1, Nodal2, Cerberus, Lefty, Brachyury, Wnt3A, and Bmp2, and immunostaining for Brachyury, we uncovered a Wnt3a- and Brachyury-positive ring at the edge of the epiblast concomitant with lumenogenesis, and preceding anterior-posterior patterning and gastrulation. Furthermore, we report anterior-posterior patterning in veiled chameleons occurs independently of Cerberus and Lefty. These processes that mediate epiblast lumenogenesis in chameleons, result in a morphology remarkably similar to human embryos, despite 300 million years of evolutionary separation. Taken together, we show that pre-gastrulation epiblast lumenogenesis is not mammalian-specific, but also occurs in some non-avian reptiles.

developmental biology↗

bioRxiv2023

Identification and characterization of intermediate states in mammalian neural crest cell epithelial to mesenchymal transition and delamination

Epithelial to mesenchymal transition (EMT) is a cellular process that converts epithelial cells to mesenchymal cells with migratory potential in both developmental and pathological processes. Although originally considered a binary event, EMT in cancer progression involves intermediate states between a fully epithelial and a fully mesenchymal phenotype, which are characterized by distinct combinations of epithelial and mesenchymal markers. This phenomenon has been termed epithelial to mesenchymal plasticity (EMP), however, the intermediate states remain poorly described and its unclear whether they exist during developmental EMT. Neural crest cells (NCC) are an embryonic progenitor cell population that gives rise to numerous cell types and tissues in vertebrates, and their formation is a classic example of developmental EMT. An important feature of NCC development is their delamination from the neuroepithelium via EMT, following which NCC migrate throughout the embryo and undergo differentiation. NCC delamination shares similar changes in cellular state and structure with cancer cell invasion. However, whether intermediate states also exist during NCC EMT and delamination remains unknown. Through single cell RNA sequencing, we identified intermediate NCC states based on their transcriptional signature and then spatially defined their locations in situ in the dorsolateral neuroepithelium. Our results illustrate the progressive transcriptional and spatial transitions from premigratory to migratory cranial NCC during EMT and delamination. Of note gene expression and trajectory analysis indicate that distinct intermediate populations of NCC delaminate in either S phase or G2/M phase of the cell cycle, and the importance of cell cycle regulation in facilitating mammalian cranial NCC delamination was confirmed through cell cycle inhibition studies. Additionally, transcriptional knockdown revealed a functional role for the intermediate stage marker Dlc1 in regulating NCC delamination and migration. Overall, our work identifying and characterizing the intermediate cellular states, processes, and molecular signals that regulate mammalian NCC EMT and delamination furthers our understanding of developmental EMP and may provide new insights into mechanisms regulating pathological EMP.

developmental biology↗

bioRxiv2021

Specification of axial identity by Hoxa2 distinguishes between a phenotypic and molecular ground state in mouse cranial neural crest cells

Hox genes play a key role in head formation by specifying the axial identity of neural crest cells (NCCs) migrating into embryonic pharyngeal arches. In the absence of Hoxa2, NCC derivatives of the second pharyngeal arch (PA2) undergo a homeotic transformation and duplicate structures formed by first arch (PA1) NCCs. Current models postulate that PA1 represents a NCC ground state and loss of Hoxa2 causes a reversion of PA2 NCCs to the PA1 ground state. We use bulk and single-cell RNAseq to investigate the molecular mechanisms driving this phenotypic transformation in the mouse. In Hoxa2-/- mutants, PA2 NCCs generally maintain expression of the PA2 transcriptional signature and fail to strongly upregulate a PA1 transcriptional signature. Our analyses identify putative HOXA2 targets and suggest that subsets of NCCs may respond to HOXA2 activity in distinct manners. This separation of phenotypic and molecular states has significant implications for understanding craniofacial development.

developmental biology↗

bioRxiv2021

Ocular elongation and retraction in foveated reptiles

BackgroundPronounced asymmetric changes in ocular globe size during eye development have been observed in a number of species ranging from humans to lizards. In contrast, largely symmetric changes in globe size have been described for other species like rodents. We propose that asymmetric changes in the three-dimensional structure of the developing eye correlate with the types of retinal remodeling needed to produce areas of high photoreceptor density. To test this idea, we systematically examined three-dimensional aspects of globe size as a function of eye development in the bifoveated brown anole, Anolis sagrei. ResultsDuring embryonic development, the anole eye undergoes dynamic changes in ocular shape. Initially spherical, the eye elongates in the presumptive foveal regions of the retina and then proceeds through a period of retraction that returns the eye to its spherical shape. During this period of retraction, pit formation and photoreceptor cell packing are observed. We found a similar pattern of elongation and retraction associated with the single fovea of the veiled chameleon, Chamaeleo calyptratus. ConclusionsThese results, together with those reported for other foveated species, support the idea that areas of high photoreceptor packing occur in regions where the ocular globe asymmetrically elongates and retracts during development. Key FindingsO_LIThe eyes of the brown anole, Anolis sagrei, and veiled chameleon, Chamaeleo calyptratus undergo dynamic asymmetrical changes in ocular shape during development. C_LIO_LIIn both species, asymmetric elongation and retraction of the ocular globe is associated with fovea morphogenesis. C_LIO_LIPit formation and photoreceptor cell packing in the foveal area occur when the corresponding region of the ocular globe is retracting relative to adjacent regions. C_LI

developmental biology↗