The PDGF alpha receptor is required for neural crest cell development and for normal patterning of the somites

Transcriptome Profiling of Trabecular Meshwork Progenitor Cells

The loss and dysfunction of trabecular meshwork (TM) cells are implicated in aging and primary open-angle glaucoma. TM progenitor cells (TMPCs) contribute to the population and function of the TM, but their identity is not well elucidated. This study aimed to identify the expression profile of differentially expressed genes (DEGs) in human TM cell cultures, TM-derived spheres, and their differentiated progeny. Primary normal human TM cells (PTM) from three donors were cultured, de-differentiated into spheres, and re-differentiated into TM cells (DTM). RNA-Seq was performed using Illumina NGS, and bioinformatics analysis was conducted with Tuxedo, Bowtie2, Tophat, Cufflinks, and Ingenuity Pathway Analysis (IPA). DEGs were validated via Nanostring, RT-qPCR (in five independent donors), immunocytochemistry, and western blotting. RNA-seq identified significant DEGs in PTM, TM progenitor cells (TMPCs), and DTM cells. Gene expression in TMPCs differed significantly from PTM and DTM cells. Nanostring and RT-qPCR confirmed 70 DEGs upregulated in TMPCs (P < 0.05). Immunocytochemistry highlighted distinct markers in TMPCs (SOX2, NOTCH1, ANKG, MGP) versus PTM and DTM cells (TAGLN, TEM7, SPARC). Western blotting further analyzed MGP, TAGLN, and SPARC proteins, revealing significant upregulation of MGP in TMPCs and downregulation of TAGLN and SPARC in spheres compared to PTM cells. Pathway analysis revealed activation of cell cycle checkpoint regulation, SUMOylation, and STAT3 pathways in TMPCs, with HGF, MMP9, KDR, IGF1, and FOS as key node genes in TMPC development. RNA-Seq identified novel expression profile of potential TM markers and activated pathways in TMPCs, providing insights into TMPC behaviours in physiological and pathological conditions.

PDGFRα/β heterodimer activation negatively affects downstream ERK1/2 signaling and cellular proliferation

The platelet-derived growth factor receptor (PDGFR) family of receptor tyrosine kinases consists of two receptors, PDGFRα and PDGFRβ, that homodimerize and heterodimerize upon ligand binding. Here, we tested the hypothesis that differential internalization and trafficking dynamics of the various PDGFR dimers underlie differences in downstream intracellular signaling and cellular behavior. Using a bimolecular fluorescence complementation approach, we demonstrated that PDGFRα/β heterodimers are rapidly internalized into early endosomes. We showed that PDGFRα/β heterodimer activation does not induce downstream phosphorylation of ERK1/2 and significantly inhibits cell proliferation. Further, we identified MYO1D as a protein that preferentially binds PDGFRα/β heterodimers and demonstrated that knockdown of MYO1D leads to retention of PDGFRα/β heterodimers at the plasma membrane, increased phosphorylation of ERK1/2 and increased cell proliferation. Collectively, our findings impart valuable insight into the molecular mechanisms by which specificity is introduced downstream of PDGFR activation to differentially propagate signaling and generate distinct cellular responses.

PDGFRα signaling regulates cartilage and fibrous tissue differentiation during synovial joint development

Synovial joints develop from mesenchymal structures called interzones, with progenitor cells differentiating into specialized cartilaginous and fibrous tissues of the joint. Platelet-derived growth factor receptor-α (PDGFRα) is a tyrosine kinase expressed by cells of the limb bud, but its role in limb development is unknown. To investigate PDGFRα function, we generated mice expressing mutant PDGFRα with a point mutation (D842V) that increases receptor signaling. Mutant hindlimbs are immobile with knee joints fused by cartilage and lacking ligaments and menisci. The interzone marker Gdf5 is initially expressed at E12.5 but is downregulated thereafter, suggesting a defect in interzone maintenance. Omics analysis of the joint tissues identifies ectopic cartilage matrix expressing genes for cartilage and fibrotic tissue. Thus, elevated PDGFRα signaling corrupts joint development by downregulating Gdf5 and redirecting interzone progenitors into a fibrocartilage fate. This suggests that tight regulation of tyrosine kinase activity is necessary for the development of the mouse knee joint.

Tyrosine kinase inhibitors in Ewing's sarcoma: a systematic review

Ewing's sarcoma (ES) is a highly aggressive primary bone malignancy that primarily affects children and adolescents. Several tyrosine kinase receptors (RTKs) have been found to be overexpressed in ES samples, and it was demonstrated that some play significant roles in driving the malignant phenotype of ES. Specifically, ES with insulin-like growth factor 1 (IGF1R) or vascular endothelial growth factor (VEGFR) overexpression were correlated with more aggressive ES and worse outcomes. Other RTKs that were determined to be overexpressed in ES include platelet-derived growth factor receptor, stem cell factor receptor, and hepatocyte growth factor. Overexpression of these molecules suggests their possible tumor-driving role, making them potential targets for intervention. Various tyrosine kinase inhibitors (TKIs), including apatinib, anlotinib, and cabozantinib have shown clinical promise in patients with recurrent ES who have progressed on previous lines of therapy. The findings reported in this review emphasize the importance of assessing IGF1R-focused inhibitors and combinational therapeutic regimens in future research. Furthermore, biomarkers predictive of response are necessary to improve patient outcomes. In order to optimize ES care, considerations for patient eligibility on the basis of positivity for biomarkers predictive of response, and the inclusion of quality-of-life evaluations in studies must be addressed.

Dopamine in the tail of the striatum facilitates avoidance in threat-reward conflicts

Responding appropriately to potential threats before they materialize is critical to avoiding disastrous outcomes. Here we examine how threat-coping behavior is regulated by the tail of the striatum (TS) and its dopamine input. Mice were presented with a potential threat (a moving object) while pursuing rewards. Initially, the mice failed to obtain rewards but gradually improved in later trials. We found that dopamine in TS promoted avoidance of the threat, even at the expense of reward acquisition. Furthermore, the activity of dopamine D1 receptor-expressing neurons promoted threat avoidance and prediction. In contrast, D2 neurons suppressed threat avoidance and facilitated overcoming the potential threat. Dopamine axon activation in TS not only potentiated the responses of dopamine D1 receptor-expressing neurons to novel sensory stimuli but also boosted them acutely. These results demonstrate that an opponent interaction of D1 and D2 neurons in the TS, modulated by dopamine, dynamically regulates avoidance and overcoming potential threats.

The primary cilia: Orchestrating cranial neural crest cell development

Primary cilia (hereafter "cilia") are microtubule-based antenna-like organelles projecting from the surface of vertebrate cells. Cilia can serve as cellular antennae controlling cell growth and differentiation. Absent or dysfunctional cilia frequently lead to craniofacial anomalies known as craniofacial ciliopathies. However, the detailed pathological mechanisms of craniofacial ciliopathies remain unclear. This perspective discusses our current understanding of the role of cilia in cranial neural crest cells. We also describe potential mechanisms of ciliogenesis in cranial neural crest cells, which may contribute to unraveling the complex pathogenesis of craniofacial ciliopathies.

Mouse scalp development requires Rac1 and SRF for the maintenance of mechanosensing mesenchyme

Regulation of essential cellular responses like proliferation, migration, and differentiation is crucial for normal development. Rac1, a ubiquitously expressed small GTPase, executes these responses under the regulation of guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GTPases). Mutations in specific GEFs (DOCK6) and GTPases (AHGAP31) that regulate Rac1 are associated with Adams-Oliver syndrome (AOS), a developmental syndrome characterized by congenital scalp defects and limb truncations. Genetic ablation of Rac1 in the mouse embryonic limb ectoderm results in limb truncation. However, the etiology of Rac1-associated cranial defects is unknown. To investigate the origin and nature of cranial defects, we used a mesenchymal Cre line ( Pdgfra-Cre ) to delete Rac1 in cranial mesenchyme. Rac1 -KO mice died perinatally and lacked the apical portion of the calvarium and overlying dermis, resembling cranial defects seen in severe cases of AOS. In control embryos, α-smooth muscle actin (αSMA) expression was spatially restricted to the apical mesenchyme, suggesting a mechanical interaction between the growing brain and the overlying mesenchyme. In Rac1 -KO embryos there was reduced proliferation of apical mesenchyme, and reduced expression of αSMA and its regulator, serum response factor (SRF). Remarkably, Srf -KO mice generated with Pdgfra-Cre recapitulated the cranial phenotype observed in Rac1- KO mice. Together, these data suggest a model where Rac1 and SRF are critical to maintaining apical fibroblasts in a mechano-sensitive and proliferative state needed to complete cranial development.

Ventral body wall closure: Mechanistic insights from mouse models and translation to human pathology

The ventral body wall (VBW) that encloses the thoracic and abdominal cavities arises by extensive cell movements and morphogenetic changes during embryonic development. These morphogenetic processes include embryonic folding generating the primary body wall; the initial ventral cover of the embryo, followed by directed mesodermal cell migrations, contributing to the secondary body wall. Clinical anomalies in VBW development affect approximately 1 in 3000 live births. However, the cell interactions and critical cellular behaviors that control VBW development remain little understood. Here, we describe the embryonic origins of the VBW, the cellular and morphogenetic processes, and key genes, that are essential for VBW development. We also provide a clinical overview of VBW anomalies, together with environmental and genetic influences, and discuss the insight gained from over 70 mouse models that exhibit VBW defects, and their relevance, with respect to human pathology. In doing so we propose a phenotypic framework for researchers in the field which takes into account the clinical picture. We also highlight cases where there is a current paucity of mouse models for particular clinical defects and key gaps in knowledge about embryonic VBW development that need to be addressed to further understand mechanisms of human VBW pathologies.

FAPs orchestrate homeostasis of muscle physiology and pathophysiology

As a common clinical manifestation, muscle weakness is prevalent in people with mobility disorders. Further studies of muscle weakness have found that patients with muscle weakness present with persistent muscle inflammation, loss of muscle fibers, fat infiltration, and interstitial fibrosis. Therefore, we propose the concept of muscle microenvironment homeostasis, which explains the abnormal pathological changes in muscles through the imbalance of muscle microenvironment homeostasis. And we identified an interstitial progenitor cell FAP during the transition from normal muscle microenvironment homeostasis to muscle microenvironment imbalance caused by muscle damage diseases. As a kind of pluripotent stem cell, FAPs do not participate in myogenic differentiation, but can differentiate into fibroblasts, adipocytes, osteoblasts, and chondrocytes. As a kind of mesenchymal progenitor cell, it is involved in the generation of extracellular matrix, regulate muscle regeneration, and maintain neuromuscular junction. However, the muscle microenvironment is disrupted by the causative factors, and the abnormal activities of FAPs eventually contribute to the complex pathological changes in muscles. Targeting the mechanisms of these muscle pathological changes, we have identified appropriate signaling targets for FAPs to improve and even treat muscle damage diseases. In this review, we propose the construction of muscle microenvironmental homeostasis and find the key cells that cause pathological changes in muscle after homeostasis is broken. By studying the mechanism of abnormal differentiation and apoptosis of FAPs, we found a strategy to inhibit the abnormal pathological changes in muscle damage diseases and improve muscle regeneration.

PDGFRα signaling regulates Srsf3 transcript binding to affect PI3K signaling and endosomal trafficking

Signaling through the platelet-derived growth factor receptor alpha (PDGFRα) plays a critical role in craniofacial development. Phosphatidylinositol 3-kinase (PI3K)/Akt is the primary effector of PDGFRα signaling during mouse skeletal development. We previously demonstrated that Akt phosphorylates the RNA-binding protein serine/arginine-rich splicing factor 3 (Srsf3) downstream of PI3K-mediated PDGFRα signaling in mouse embryonic palatal mesenchyme (MEPM) cells, leading to its nuclear translocation. We further showed that ablation of Srsf3 in the murine neural crest lineage results in severe midline facial clefting and widespread alternative RNA splicing (AS) changes. Here, we demonstrated via enhanced UV-crosslinking and immunoprecipitation of MEPM cells that PDGF-AA stimulation leads to preferential binding of Srsf3 to exons and loss of binding to canonical Srsf3 CA-rich motifs. Through the analysis of complementary RNA-seq data, we showed that Srsf3 activity results in the preferential inclusion of exons with increased GC content and lower intron to exon length ratio. We found that Srsf3 activity downstream of PDGFRα signaling leads to retention of the receptor in early endosomes and increases in downstream PI3K-mediated Akt signaling. Taken together, our findings reveal that growth factor-mediated phosphorylation of an RNA-binding protein underlies gene expression regulation necessary for mammalian craniofacial development.

Discovery of Potential Candidate Genes for Coat Colour in Wuzhishan Pigs by Integrating SNPs and mRNA Expression Analysis

Despite identifying genes regulating the coat colour in Western pig breeds, the genetic basis of the coat colour in Chinese indigenous pigs is still not understood due to the diversity of indigenous breeds and their genetic differences from exotic pigs. In this study, 215 Wuzhishan pigs with three coat colour patterns (white, black, and black-back/white-belly) were used to conduct a genome-wide association analysis. We found that genes responsible for the coat colour in the Wuzhishan breed are located on chromosome 8. Ninety-seven genome-wide significant SNPs are related to the animal's coat colour. Using a haplotype-sharing analysis, we narrowed the potential candidate region to a 10.1 Mb interval encompassing only one gene, RAPGEF2, which participates in the regulation of melanogenesis. Two additional candidate genes, PDGFRA and KIT, are located within 1 Mb of the genome-wide significant SNPs. Gene ontology analysis and literature mining suggest that these candidate genes are associated with the animal's coat colour. mRNA expression results revealed that RAPGEF2 and PDGFRA had significantly higher expressions in black pigs than in white pigs and higher expressions in black skin than in white skin from the same black-back/white-belly pigs. These results suggest that RAPGEF2 and PDGFRA are potential candidate genes regulating the coat colour in Wuzhishan pigs. Interestingly, mutations of KIT (a gene duplication and a G to A substitution at the splicing site in intron 17) were detected in white Wuzhishan pigs but not in black-back/white-belly or black pigs, suggesting a close genetic relationship between white Wuzhishan pigs and Western white pig breeds. In summary, these results indicate that the expression of RAPGEF2 and PDGFRA may cause the coat colour variation by influencing the deposition of melanin, while the mutation of KIT causes the white coat colour. Our results may provide a theoretical basis for the breeding of white coat colour Wuzhishan pigs, and shed light on the complex genetic background of coat colour variations in indigenous Chinese pig breeds.

Functional and clinical roles of stromal PDGF receptors in tumor biology

PDGF receptors play pivotal roles in both developmental and physiological processes through the regulation of mesenchymal cells involved in paracrine instructive interactions with epithelial or endothelial cells. Tumor biology studies, alongside analyses of patient tissue samples, provide strong indications that the PDGF signaling pathways are also critical in various types of human cancer. This review summarizes experimental findings and correlative studies, which have explored the biological mechanisms and clinical relevance of PDGFRs in mesenchymal cells of the tumor microenvironment. Collectively, these studies support the overall concept that the PDGF system is a critical regulator of tumor growth, metastasis, and drug efficacy, suggesting yet unexploited targeting opportunities. The inter-patient variability in stromal PDGFR expression, as being linked to prognosis and treatment responses, not only indicates the need for stratified approaches in upcoming therapeutic investigations but also implies the potential for the development of PDGFRs as biomarkers of clinical utility, interestingly also in settings outside PDGFR-directed treatments.

PDGFRα signaling regulates Srsf3 transcript binding to affect PI3K signaling and endosomal trafficking

Signaling through the platelet-derived growth factor receptor alpha (PDGFRα) plays a critical role in craniofacial development, as mutations in PDGFRA are associated with cleft lip/palate in humans and Pdgfra mutant mouse models display varying degrees of facial clefting. Phosphatidylinositol 3-kinase (PI3K)/Akt is the primary effector of PDGFRα signaling during skeletal development in the mouse. We previously demonstrated that Akt phosphorylates the RNA-binding protein serine/arginine-rich splicing factor 3 (Srsf3) downstream of PI3K-mediated PDGFRα signaling in mouse embryonic palatal mesenchyme (MEPM) cells, leading to its nuclear translocation. We further showed that ablation of Srsf3 in the murine neural crest lineage results in severe midline facial clefting, due to defects in proliferation and survival of cranial neural crest cells, and widespread alternative RNA splicing (AS) changes. Here, we sought to determine the molecular mechanisms by which Srsf3 activity is regulated downstream of PDGFRα signaling to control AS of transcripts necessary for craniofacial development. We demonstrated via enhanced UV-crosslinking and immunoprecipitation (eCLIP) of MEPM cells that PDGF-AA stimulation leads to preferential binding of Srsf3 to exons and loss of binding to canonical Srsf3 CA-rich motifs. Through the analysis of complementary RNA-seq data, we showed that Srsf3 activity results in the preferential inclusion of exons with increased GC content and lower intron to exon length ratio. Moreover, we found that the subset of transcripts that are bound by Srsf3 and undergo AS upon PDGFRα signaling commonly encode regulators of PI3K signaling and early endosomal trafficking. Functional validation studies further confirmed that Srsf3 activity downstream of PDGFRα signaling leads to retention of the receptor in early endosomes and increases in downstream PI3K-mediated Akt signaling. Taken together, our findings reveal that growth factor-mediated phosphorylation of an RNA-binding protein underlies gene expression regulation necessary for mammalian craniofacial development.

Pleiotropy in FOXC1-attributable phenotypes involves altered ciliation and cilia-dependent signaling

Alterations to cilia are responsible for a wide range of severe disease; however, understanding of the transcriptional control of ciliogenesis remains incomplete. In this study we investigated whether altered cilia-mediated signaling contributes to the pleiotropic phenotypes caused by the Forkhead transcription factor FOXC1. Here, we show that patients with FOXC1-attributable Axenfeld-Rieger Syndrome (ARS) have a prevalence of ciliopathy-associated phenotypes comparable to syndromic ciliopathies. We demonstrate that altering the level of Foxc1 protein, via shRNA mediated inhibition, CRISPR/Cas9 mutagenesis and overexpression, modifies cilia length in vitro. These structural changes were associated with substantially perturbed cilia-dependent signaling [Hedgehog (Hh) and PDGFRα], and altered ciliary compartmentalization of the Hh pathway transcription factor, Gli2. Consistent with these data, in primary cultures of murine embryonic meninges, cilia length was significantly reduced in heterozygous and homozygous Foxc1 mutants compared to controls. Meningeal expression of the core Hh signaling components Gli1, Gli3 and Sufu was dysregulated, with comparable dysregulation of Pdgfrα signaling evident from significantly altered Pdgfrα and phosphorylated Pdgfrα expression. On the basis of these clinical and experimental findings, we propose a model that altered cilia-mediated signaling contributes to some FOXC1-induced phenotypes.

Requirement of Pdgfrα+ cells for calvarial bone repair

Platelet-derived growth factor receptor α (PDGFRα) is often considered as a general marker of mesenchymal cells and fibroblasts, but also shows expression in a portion of osteoprogenitor cells. Within the skeleton, Pdgfrα+ mesenchymal cells have been identified in bone marrow and periosteum of long bones, where they play a crucial role in participating in fracture repair. A similar examination of Pdgfrα+ cells in calvarial bone healing has not been examined. Here, we utilize Pdgfrα-CreERTM;mT/mG reporter animals to examine the contribution of Pdgfrα+ mesenchymal cells to calvarial bone repair through histology and single-cell RNA sequencing (scRNA-Seq). Results showed that Pdgfrα+ mesenchymal cells are present in several cell clusters by scRNA-Seq, and by histology a dramatic increase in Pdgfrα+ cells populated the defect site at early timepoints to give rise to healed bone tissue overtime. Notably, diphtheria toxin-mediated ablation of Pdgfrα reporter+ cells resulted in significantly impaired calvarial bone healing. Our findings suggest that Pdgfrα-expressing cells within the calvarial niche play a critical role in the process of calvarial bone repair.

TAD border deletion at the Kit locus causes tissue-specific ectopic activation of a neighboring gene

Topologically associated domains (TADs) restrict promoter-enhancer interactions, thereby maintaining the spatiotemporal pattern of gene activity. However, rearrangements of the TADs boundaries do not always lead to significant changes in the activity pattern. Here, we investigated the consequences of the TAD boundaries deletion on the expression of developmentally important genes encoding tyrosine kinase receptors: Kit, Kdr, Pdgfra. We used genome editing in mice to delete the TADs boundaries at the Kit locus and characterized chromatin folding and gene expression in pure cultures of fibroblasts, mast cells, and melanocytes. We found that although Kit is highly active in both mast cells and melanocytes, deletion of the TAD boundary between the Kit and Kdr genes results in ectopic activation only in melanocytes. Thus, the epigenetic landscape, namely the mutual arrangement of enhancers and actively transcribing genes, is important for predicting the consequences of the TAD boundaries removal. We also found that mice without a TAD border between the Kit and Kdr genes have a phenotypic manifestation of the mutation - a lighter coloration. Thus, the data obtained shed light on the principles of interaction between the 3D chromatin organization and epigenetic marks in the regulation of gene activity.

Identification of a Novel Frameshift Variant in MYF5 Leading to External Ophthalmoplegia with Rib and Vertebral Anomalies

Myogenic transcription factors with a basic helix-loop-helix (bHLH) such as MYOD, myogenin, MRF4, and MYF5 contribute to muscle differentiation and regulation. The MYF5 gene located on chromosome 12 encodes for myogenic factor 5 (MYF5), which has a role in skeletal and extraocular muscle development and rib formation. Variants in MYF5 were found to cause external ophthalmoplegia with rib and vertebral anomalies (EORVA), a rare recessive condition. To date, three homozygous variants in MYF5 have been reported to cause EORVA in six members of four unrelated families. Here, we present a novel homozygous MYF5 frameshift variant, c.596dupA p. (Asn199Lysfs*49), causing premature protein termination and presenting with external ophthalmoplegia, ptosis, and scoliosis in three siblings from a consanguineous family of Pakistani origin. With four MYF5 variants now discovered, genetic testing and paediatric assessment for extra-ocular features should be considered in all cases of congenital ophthalmoplegia.

CD74 supports accumulation and function of regulatory T cells in tumors

Regulatory T cells (Tregs) are plastic cells playing a pivotal role in the maintenance of immune homeostasis. Tregs actively adapt to the microenvironment where they reside; as a consequence, their molecular and functional profiles differ among tissues and pathologies. In tumors, the features acquired by Tregs remains poorly characterized. Here, we observe that human tumor-infiltrating Tregs selectively overexpress CD74, the MHC class II invariant chain. CD74 has been previously described as a regulator of antigen-presenting cell biology, however its function in Tregs remains unknown. CD74 genetic deletion in human primary Tregs reveals that CD74KO Tregs exhibit major defects in the organization of their actin cytoskeleton and intracellular organelles. Additionally, intratumoral CD74KO Tregs show a decreased activation, a drop in Foxp3 expression, a low accumulation in the tumor, and consistently, they are associated with accelerated tumor rejection in preclinical models in female mice. These observations are unique to tumor conditions as, at steady state, CD74KO-Treg phenotype, survival, and suppressive capacity are unaffected in vitro and in vivo. CD74 therefore emerges as a specific regulator of tumor-infiltrating Tregs and as a target to interfere with Treg anti-tumor activity.

Redox Regulation of LAT Enhances T Cell-Mediated Inflammation

The positional cloning of single nucleotide polymorphisms (SNPs) of the neutrophil cytosolic factor 1 (Ncf1) gene, advocating that a low oxidative burst drives autoimmune disease, demands an understanding of the underlying molecular causes. A cellular target could be T cells, which have been shown to be regulated by reactive oxygen species (ROS). However, the pathways by which ROS mediate T cell signaling remain unclear. The adaptor molecule linker for activation of T cells (LAT) is essential for coupling T cell receptor-mediated antigen recognition to downstream responses, and it contains several cysteine residues that have previously been suggested to be involved in redox regulation. To address the possibility that ROS regulate T cell-dependent inflammation through LAT, we established a mouse strain with cysteine-to-serine mutations at positions 120 and 172 (LATSS). We found that redox regulation of LAT through C120 and C172 mediate its localization and phosphorylation. LATSS mice had reduced numbers of double-positive thymocytes and naïve peripheral T cells. Importantly, redox insensitivity of LAT enhanced T cell-dependent autoimmune inflammation in collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis (RA). This effect was reversed on an NCF1-mutated (NCF1m1j), ROS-deficient, background. Overall, our data show that LAT is redox-regulated, acts to repress T cell activation, and is targeted by ROS induced by NCF1 in antigen-presenting cells (APCs).

Molecular Pathways and Animal Models of Atrioventricular Septal Defect

The development of a fully functional four-chambered heart is critically dependent on the correct formation of the structures that separate the atrial and ventricular chambers. Perturbation of this process typically results in defects that allow mixing of oxygenated and deoxygenated blood. Atrioventricular septal defects (AVSD) form a class of congenital heart malformations that are characterized by the presence of a primary atrial septal defect (pASD), a common atrioventricular valve (cAVV), and frequently also a ventricular septal defect (VSD). While AVSD were historically considered to result from failure of the endocardial atrioventricular cushions to properly develop and fuse, more recent studies have determined that inhibition of the development of other components of the atrioventricular mesenchymal complex can lead to AVSDs as well. The role of the dorsal mesenchymal protrusion (DMP) in AVSD pathogenesis has been well-documented in studies using animal models for AVSDs, and in addition, preliminary data suggest that the mesenchymal cap situated on the leading edge of the primary atrial septum may be involved in certain situations as well. In this chapter, we review what is currently known about the molecular mechanisms and animal models that are associated with the pathogenesis of AVSD.

PDGFRα/β heterodimer activation negatively affects downstream ERK1/2 signaling and cellular proliferation

The platelet-derived growth factor receptor (PDGFR) family of receptor tyrosine kinases allows cells to communicate with one another by binding to growth factors at the plasma membrane and activating intracellular signaling pathways to elicit responses such as migration, proliferation, survival and differentiation. The PDGFR family consists of two receptors, PDGFRα and PDGFRβ, that dimerize to form PDGFRα homodimers, PDGFRα/β heterodimers and PDGFRβ homodimers. Here, we overcame prior technical limitations in visualizing and purifying PDGFRα/β heterodimers by generating a cell line stably expressing C-terminal fusions of PDGFRα and PDGFRβ with bimolecular fluorescence complementation fragments corresponding to the N-terminal and C-terminal regions of the Venus fluorescent protein, respectively. We found that these receptors heterodimerize relatively quickly in response to PDGF-BB ligand treatment, with a peak of receptor autophosphorylation following 5 minutes of ligand stimulation. Moreover, we demonstrated that PDGFRα/β heterodimers are rapidly internalized into early endosomes, particularly signaling endosomes, where they dwell for extended lengths of time. We showed that PDGFRα/β heterodimer activation does not induce downstream phosphorylation of ERK1/2 and significantly inhibits cell proliferation. Further, we characterized the PDGFR dimer-specific interactome and identified MYO1D as a novel protein that preferentially binds PDGFRα/β heterodimers. We demonstrated that knockdown of MYO1D leads to retention of PDGFRα/β heterodimers at the plasma membrane, resulting in increased phosphorylation of ERK1/2 and increased cell proliferation. Collectively, our findings impart valuable insight into the molecular mechanisms by which specificity is introduced downstream of PDGFR activation to differentially propagate signaling and generate distinct cellular responses.

Characterization of a new mouse line triggering transient oligodendrocyte progenitor depletion

Oligodendrocyte progenitor cells (OPC) are the main proliferative cells in the healthy adult brain. They produce new myelinating oligodendrocytes to ensure physiological myelin remodeling and regeneration after various pathological insults. Growing evidence suggests that OPC have other functions. Here, we aimed to develop an experimental model that allows the specific ablation of OPC at the adult stage to unravel possible new functions. We generated a transgenic mouse expressing a floxed human diphtheria toxin receptor under the control of the PDGFRa promoter, crossed with an Olig2Cre mouse to limit the recombination to the oligodendrocyte lineage in the central nervous system. We determined a diphtheria toxin dose to substantially decrease OPC density in the cortex and the corpus callosum without triggering side toxicity after a few daily injections. OPC density was normalized 7 days post-treatment, showing high repopulation capacity from few surviving OPC. We took advantage of this strong but transient depletion to show that OPC loss was associated with behavioral impairment, which was restored by OPC recovery, as well as disruption of the excitation/inhibition balance in the sensorimotor cortex, reinforcing the hypothesis of a neuromodulatory role of OPC in the adult brain.

Tyrosine kinase inhibitors in osteosarcoma: Adapting treatment strategiesa

Osteosarcoma (OS) is an aggressive primary bone malignancy that metastasizes rapidly. The standard of care has changed little over the previous four decades, and survival rates have plateaued. In this context, tyrosine kinase inhibitors (TKIs) emerge as potential treatments. A literature search was conducted to collect data related to receptor tyrosine kinase genetic alterations and expression in OS specimens. Gene amplification and protein expression of these receptors were linked to prognosis and tumor behavior. Relevant TKIs were evaluated as monotherapies and as parts of combination therapies. Certain TKIs, such as apatinib, regorafenib, and cabozantinib, present a potential therapeutic avenue for OS patients, especially when combined with chemotherapy. Producing long-lasting responses and enhancing quality of life remain key goals in OS treatment. To this effect, optimizing the use of TKIs by identifying biomarkers predictive of response and assessing promising TKIs in larger-scale trials to validate the efficacy and safety outcomes relative to these drugs reported in phase II clinical trials. To this effect, it is necessary to identify biomarkers predictive of response to TKIs in larger-scale trials and to validate the efficacy and safety of these drugs reported in phase II clinical trials.

The macrophage genetic cassette inr/dtor/pvf2 is a nutritional status checkpoint for developmental timing

A small number of signaling molecules, used reiteratively, control differentiation programs, but the mechanisms that adapt developmental timing to environmental cues are less understood. We report here that a macrophage inr/dtor/pvf2 genetic cassette is a developmental timing checkpoint in Drosophila, which either licenses or delays biosynthesis of the steroid hormone in the endocrine gland and metamorphosis according to the larval nutritional status. Insulin receptor/dTor signaling in macrophages is required and sufficient for production of the PDGF/VEGF family growth factor Pvf2, which turns on transcription of the sterol biosynthesis Halloween genes in the prothoracic gland via its receptor Pvr. In response to a starvation event or genetic manipulation, low Pvf2 signal delays steroid biosynthesis until it becomes Pvr-independent, thereby prolonging larval growth before pupariation. The significance of this developmental timing checkpoint for host fitness is illustrated by the observation that it regulates the size of the pupae and adult flies.

Neural crest cells and fetal alcohol spectrum disorders: Mechanisms and potential targets for prevention

Fetal alcohol spectrum disorders (FASD) are a group of preventable and nongenetic birth defects caused by prenatal alcohol exposure that can result in a range of cognitive, behavioral, emotional, and functioning deficits, as well as craniofacial dysmorphology and other congenital defects. During embryonic development, neural crest cells (NCCs) play a critical role in giving rise to many cell types in the developing embryos, including those in the peripheral nervous system and craniofacial structures. Ethanol exposure during this critical period can have detrimental effects on NCC induction, migration, differentiation, and survival, leading to a broad range of structural and functional abnormalities observed in individuals with FASD. This review article provides an overview of the current knowledge on the detrimental effects of ethanol on NCC induction, migration, differentiation, and survival. The article also examines the molecular mechanisms involved in ethanol-induced NCC dysfunction, such as oxidative stress, altered gene expression, apoptosis, epigenetic modifications, and other signaling pathways. Furthermore, the review highlights potential therapeutic strategies for preventing or mitigating the detrimental effects of ethanol on NCCs and reducing the risk of FASD. Overall, this article offers a comprehensive overview of the current understanding of the impact of ethanol on NCCs and its role in FASD, shedding light on potential avenues for future research and intervention.

Research progress on the role of PDGF/PDGFR in type 2 diabetes

Platelet-derived growth factors (PDGFs) are basic proteins stored in the α granules of platelets. PDGFs and their receptors (PDGFRs) are widely expressed in platelets, fibroblasts, vascular endothelial cells, platelets, pericytes, smooth muscle cells and tumor cells. The activation of PDGFR plays a number of critical roles in physiological functions and diseases, including normal embryonic development, cellular differentiation, and responses to tissue damage. In recent years, emerging experimental evidence has shown that activation of the PDGF/PDGFR pathway is involved in the development of diabetes and its complications, such as atherosclerosis, diabetic foot ulcers, diabetic nephropathy, and retinopathy. Research on targeting PDGF/PDGFR as a treatment has also made great progress. In this mini-review, we summarized the role of PDGF in diabetes, as well as the research progress on targeted diabetes therapy, which provides a new strategy for the treatment of type 2 diabetes.

Mitochondrial DNA Deficiency and Supplementation in Sus scrofa Oocytes Influence Transcriptome Profiles in Oocytes and Blastocysts

Mitochondrial DNA (mtDNA) deficiency correlates with poor oocyte quality and fertilisation failure. However, the supplementation of mtDNA deficient oocytes with extra copies of mtDNA improves fertilisation rates and embryo development. The molecular mechanisms associated with oocyte developmental incompetence, and the effects of mtDNA supplementation on embryo development are largely unknown. We investigated the association between the developmental competence of Sus scrofa oocytes, assessed with Brilliant Cresyl Blue, and transcriptome profiles. We also analysed the effects of mtDNA supplementation on the developmental transition from the oocyte to the blastocyst by longitudinal transcriptome analysis. mtDNA deficient oocytes revealed downregulation of genes associated with RNA metabolism and oxidative phosphorylation, including 56 small nucleolar RNA genes and 13 mtDNA protein coding genes. We also identified the downregulation of a large subset of genes for meiotic and mitotic cell cycle process, suggesting that developmental competence affects the completion of meiosis II and first embryonic cell division. The supplementation of oocytes with mtDNA in combination with fertilisation improves the maintenance of the expression of several key developmental genes and the patterns of parental allele-specific imprinting gene expression in blastocysts. These results suggest associations between mtDNA deficiency and meiotic cell cycle and the developmental effects of mtDNA supplementation on Sus scrofa blastocysts.

Stromal regulation of the intestinal barrier

The intestinal barrier is a complex structure that allows the absorption of nutrients while ensuring protection against intestinal pathogens and balanced immunity. The development and maintenance of a functional intestinal barrier is a multifactorial process that is only partially understood. Here we review novel findings on the emerging role of mesenchymal cells in this process using insights gained from lineage tracing approaches, Cre-based gene deletion, and single-cell transcriptomics. The current evidence points toward a key organizer role for distinct mesenchymal lineages in intestinal development and homeostasis, regulating both epithelial and immune components of the intestinal barrier. We further discuss recent findings on functional mesenchymal heterogeneity and implications for intestinal regeneration and inflammatory intestinal pathologies.

Selective STING stimulation in dendritic cells primes antitumor T cell responses

T cells that recognize tumor antigens are crucial for mounting antitumor immune responses. Induction of antitumor T cells in immunogenic tumors depends on STING, the intracellular innate immune receptor for cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) and related cyclic dinucleotides (CDNs). However, the optimal way to leverage STING activation in nonimmunogenic tumors is still unclear. Here, we show that cGAMP delivery by intratumoral injection of virus-like particles (cGAMP-VLP) led to differentiation of circulating tumor-specific T cells, decreased tumor regulatory T cells (T_regs), and antitumoral responses that synergized with PD1 blockade. By contrast, intratumoral injection of the synthetic CDN ADU-S100 led to tumor necrosis and systemic T cell activation but simultaneously depleted immune cells from injected tumors and induced minimal priming of circulating tumor-specific T cells. The antitumor effects of cGAMP-VLP required type 1 conventional dendritic cells (cDC1), whereas ADU-S100 eliminated cDC1 from injected tumors. cGAMP-VLP preferentially targeted STING in dendritic cells at a 1000-fold smaller dose than ADU-S100. Subcutaneous administration of cGAMP-VLP showed synergy when combined with PD1 blockade or a tumor T_reg-depleting antibody to elicit systemic tumor-specific T cells and antitumor activity, leading to complete and durable tumor eradication in the case of tumor T_reg depletion. These findings show that cell targeting of STING stimulation shapes the antitumor T cell response and identify a therapeutic strategy to enhance T cell-targeted immunotherapy.

Cancer-Associated Fibroblast Heterogeneity, Activation and Function: Implications for Prostate Cancer

The continuous remodeling of the tumor microenvironment (TME) during prostate tumorigenesis is emerging as a critical event that facilitates cancer growth, progression and drug-resistance. Recent advances have identified extensive communication networks that enable tumor-stroma cross-talk, and emphasized the functional importance of diverse, heterogeneous stromal fibroblast populations during malignant growth. Cancer-associated fibroblasts (CAFs) are a vital component of the TME, which mediate key oncogenic events including angiogenesis, immunosuppression, metastatic progression and therapeutic resistance, thus presenting an attractive therapeutic target. Nevertheless, how fibroblast heterogeneity, recruitment, cell-of-origin and differential functions contribute to prostate cancer remains to be fully delineated. Developing our molecular understanding of these processes is fundamental to developing new therapies and biomarkers that can ultimately improve clinical outcomes. In this review, we explore the current challenges surrounding fibroblast identification, discuss new mechanistic insights into fibroblast functions during normal prostate tissue homeostasis and tumorigenesis, and illustrate the diverse nature of fibroblast recruitment and CAF generation. We also highlight the promise of CAF-targeted therapies for the treatment of prostate cancer.

The origins of skin diversity: lessons from dermal fibroblasts

Skin is largely composed of an epidermis that overlies a supporting dermis. Recent advancements in our understanding of how diverse groups of dermal fibroblasts regulate epidermal and hair follicle growth and differentiation have been fueled by tools capable of resolving molecular heterogeneity at a single-cell level. Fibroblast heterogeneity can be traced back to their developmental origin before their segregation into spatially distinct fibroblast subtypes. The mechanisms that drive this lineage diversification during development are being unraveled, with studies showing that both large- and small-scale positional signals play important roles during dermal development. Here, we first delineate what is known about the origins of the dermis and the central role of Wnt/β-catenin signaling in its specification across anatomical locations. We then discuss how one of the first morphologically recognizable fibroblast subtypes, the hair follicle dermal condensate lineage, emerges. Leveraging the natural variation of skin and its appendages between species and between different anatomical locations, these collective studies have identified shared and divergent factors that contribute to the extraordinary diversity of skin.

IL-2 and IL-15 drive intrathymic development of distinct periphery-seeding CD4+Foxp3+ regulatory T lymphocytes

Development of Foxp3-expressing regulatory T-lymphocytes (Treg) in the thymus is controlled by signals delivered in T-cell precursors via the TCR, co-stimulatory receptors, and cytokine receptors. In absence of IL-2, IL-15 or their receptors, fewer Treg apparently develop in the thymus. However, it was recently shown that a substantial part of thymic Treg are cells that had recirculated from the periphery back to the thymus, troubling interpretation of these results. We therefore reassessed the involvement of IL-2 and IL-15 in the development of Treg, taking into account Treg-recirculation. At the age of three weeks, when in wt and IL-15-deficient (but not in IL-2-deficient) mice substantial amounts of recirculating Treg are present in the thymus, we found similarly reduced proportions of newly developed Treg in absence of IL-2 or IL-15, and in absence of both cytokines even less Treg developed. In neonates, when practically no recirculating Treg were found in the thymus, the absence of IL-2 led to substantially more reduced Treg-development than deficiency in IL-15. IL-2 but not IL-15 modulated the CD25, GITR, OX40, and CD73-phenotypes of the thymus-egress-competent and periphery-seeding Treg-population. Interestingly, IL-2 and IL-15 also modulated the TCR-repertoire expressed by developing Treg. Upon transfer into Treg-less Foxp3^sf mice, newly developed Treg from IL-2- (and to a much lesser extent IL-15-) deficient mice suppressed immunopathology less efficiently than wt Treg. Taken together, our results firmly establish important non-redundant quantitative and qualitative roles for IL-2 and, to a lesser extent, IL-15 in intrathymic Treg-development.

PDGFR dimer-specific activation, trafficking and downstream signaling dynamics

Signaling through the platelet-derived growth factor receptors (PDGFRs) plays a critical role in multiple cellular processes during development. The two PDGFRs, PDGFRα and PDGFRβ, dimerize to form homodimers and/or heterodimers. Here, we overcome previous limitations in studying PDGFR dimer-specific dynamics by generating cell lines stably expressing C-terminal fusions of each PDGFR with bimolecular fluorescence complementation (BiFC) fragments corresponding to the N-terminal or C-terminal regions of the Venus fluorescent protein. We find that PDGFRβ receptors homodimerize more quickly than PDGFRα receptors in response to PDGF ligand, with increased levels of autophosphorylation. Furthermore, we demonstrate that PDGFRα homodimers are trafficked and degraded more quickly, whereas PDGFRβ homodimers are more likely to be recycled back to the cell membrane. We show that PDGFRβ homodimer activation results in a greater amplitude of phospho-ERK1/2 and phospho-AKT signaling, as well as increased proliferation and migration. Finally, we demonstrate that inhibition of clathrin-mediated endocytosis leads to changes in cellular trafficking and downstream signaling, particularly for PDGFRα homodimers. Collectively, our findings provide significant insight into how biological specificity is introduced to generate unique responses downstream of PDGFR engagement. This article has an associated First Person interview with the first author of the paper.

Cis interactions between CD2 and its ligands on T cells are required for T cell activation

CD2 is largely described to promote T cell activation when engaged by its ligands, CD48 in mice and CD58 in humans, that are present on antigen-presenting cells (APCs). However, both CD48 and CD58 are also expressed on T cells. By generating new knockout mouse strains lacking CD2 or CD48 in the C57BL/6 background, we determined that whereas CD2 was necessary on T cells for T cell activation, its ligand CD48 was not required on APCs. Rather, CD48 was also needed on T cells. One exception was during cytotoxicity, which required CD48 on T cells and APCs. Fluorescence resonance energy transfer (FRET) studies in nonimmune cells provided evidence that cis interactions between CD2 and CD48 existed within individual cells. CD2-CD48 interactions on T cells enabled more robust T cell receptor (TCR) signals, including protein tyrosine phosphorylation. Using T cells from a CD2 knock-in mouse in which a tag was inserted at the carboxyl terminus of CD2, mass spectrometry analyses revealed that the role of CD2 in T cell activation correlated with its ability to interact with components of the TCR complex and the protein tyrosine kinase Lck. CD2-CD58 provided a similar function in human T cells. Thus, our data imply that T cell-intrinsic cis interactions of CD2 with its ligands are required for TCR signaling and T cell activation. Interactions with ligands on APCs contribute during cytotoxicity.

Mesoderm-derived PDGFRA+ cells regulate the emergence of hematopoietic stem cells in the dorsal aorta

Mouse haematopoietic stem cells (HSCs) first emerge at embryonic day 10.5 (E10.5), on the ventral surface of the dorsal aorta, by endothelial-to-haematopoietic transition. We investigated whether mesenchymal stem cells, which provide an essential niche for long-term HSCs (LT-HSCs) in the bone marrow, reside in the aorta-gonad-mesonephros and contribute to the development of the dorsal aorta and endothelial-to-haematopoietic transition. Here we show that mesoderm-derived PDGFRA⁺ stromal cells (Mesp1^der PSCs) contribute to the haemogenic endothelium of the dorsal aorta and populate the E10.5-E11.5 aorta-gonad-mesonephros but by E13.5 were replaced by neural-crest-derived PSCs (Wnt1^der PSCs). Co-aggregating non-haemogenic endothelial cells with Mesp1^der PSCs but not Wnt1^der PSCs resulted in activation of a haematopoietic transcriptional programme in endothelial cells and generation of LT-HSCs. Dose-dependent inhibition of PDGFRA or BMP, WNT and NOTCH signalling interrupted this reprogramming event. Together, aorta-gonad-mesonephros Mesp1^der PSCs could potentially be harnessed to manufacture LT-HSCs from endothelium.

Potential ovarian toxicity and infertility risk following targeted anti-cancer therapies

Unlike traditional chemotherapy agents which are generally cytotoxic to all cells, targeted anti-cancer therapies are designed to specifically target proliferation mechanisms in cancer cells but spare normal cells, resulting in high potency and reduced toxicity. There has therefore been a rapid increase in their development and use in clinical settings, including in curative-intent treatment regimens. However, the targets of some of these drugs including kinases, epigenetic regulatory proteins, DNA damage repair enzymes and proteasomes, have fundamental roles in governing normal ovarian physiology. Inhibiting their action could have significant consequences for ovarian function, with potentially long-lasting adverse effects which persist after cessation of treatment, but there is limited evidence of their effects on reproductive function. In this review, we will use literature that examines these pathways to infer the potential toxicity of targeted anti-cancer drugs on the ovary.

Lay summary

Compared to traditional chemotherapy agents, anti-cancer therapies are thought to be highly effective at targeting cancer cells but sparing normal cells, resulting in reduced drug side effects. However, many of processes within the cells that these drugs affect are also important for the ovary to work normally, so suppressing them in this way could have long-lasting implications for female fertility. This review examines the potential toxicity of anti-cancer therapies on the ovary.

Development of ribs and intercostal muscles in the chicken embryo

In the thorax of higher vertebrates, ribs and intercostal muscles play a decisive role in stability and respiratory movements of the body wall. They are derivatives of the somites, the ribs originating in the sclerotome and the intercostal muscles originating in the myotome. During thorax development, ribs and intercostal muscles extend into the lateral plate mesoderm and eventually contact the sternum during ventral closure. Here, we give a detailed description of the morphogenesis of ribs and thoracic muscles in the chicken embryo (Gallus gallus). Using Alcian blue staining as well as Sox9 and Desmin whole‐mount immunohistochemistry, we monitor synchronously the development of rib cartilage and intercostal muscle anlagen. We show that the muscle anlagen precede the rib anlagen during ventrolateral extension, which is in line with the inductive role of the myotome in rib differentiation. Our studies furthermore reveal the temporary formation of a previously unknown eighth rib in the chicken embryonic thorax.

Diverse roles of tumor-stromal PDGFB-to-PDGFRβ signaling in breast cancer growth and metastasis

Over the last couple of decades, it has become increasingly apparent that the tumor microenvironment (TME) mediates every step of cancer progression and solid tumors are only able to metastasize with a permissive TME. This intricate interaction of cancer cells with their surrounding TME, or stroma, is becoming more understood with an ever greater knowledge of tumor-stromal signaling pairs such as platelet-derived growth factors (PDGF) and their cognate receptors. We and others have focused our research efforts on understanding how tumor-derived PDGFB activates platelet-derived growth factor receptor beta (PDGFRβ) signaling specifically in the breast cancer TME. In this chapter, we broadly discuss PDGF and PDGFR expression patterns and signaling in normal physiology and breast cancer. We then detail the expansive roles played by the PDGFB-to-PDGFRβ signaling pathway in modulating breast tumor growth and metastasis with a focus on specific cellular populations within the TME, which are responsive to tumor-derived PDGFB. Given the increasingly appreciated importance of PDGFB-to-PDGFRβ signaling in breast cancer progression, specifically in promoting metastasis, we end by discussing how therapeutic targeting of PDGFB-to-PDGFRβ signaling holds great promise for improving current breast cancer treatment strategies.

Platelet-derived growth factor-AA promotes placental choriocarcinoma JAR cell proliferation via primary cilia

OBJECTIVE

During early pregnancy, the proliferation placental cells is crucial for proper implantation and formation of maternal-fetal circulation. Platelet-derived growth factor-AA (PDGF-AA) has been detected in placenta during early pregnancy; however, the role of PDGF-AA in placental cell growth has not been studied extensively. Primary cilium, a centrosome-based cellular protrusion, is an signaling hub for regulating development and differentiation. Importantly, the receptor of PDGF-AA (Pdgfr-α) is detected in the primary cilium and primary cilia-mediated PDGF-AA signaling regulates development and differentiation. Here we would like to investigate whether PDGF-AA regulates placental cell growth and whether primary cilia play roles in this process.

MATERIALS AND METHODS

Human placental choriocarcinoma JAR cells were treated with PDGF-AA followed by examining cell growth. Primary cilia and subcellular localization of Pdgfr-α were observed by immunofluorescence staining. Manipulation of primary cilia was performed by treating cells with roscovitine or by transfecting cells with siRNA against IFT88.

RESULTS

Here we showed that PDGF-AA induced JAR cell proliferation. In addition, JAR cells grew primary cilia where Pdgfr-α was detected. More importantly, pharmacological inhibition of primary cilia formation or depletion of cilia-related gene, IFT88, alleviated PDGF-AA induced JAR cell proliferation.

CONCLUSION

Thus, our study show that PDGF-AA facilitates human placental choriocarcinomaJARcell growth via primary cilia.

Single-cell RNA sequencing reveals PDGFRα+ stromal cell subpopulations that promote proacinar cell differentiation in embryonic salivary gland organoids

Stromal cells can direct the differentiation of epithelial progenitor cells during organ development. Fibroblast growth factor (FGF) signaling is essential for submandibular salivary gland development. Through stromal fibroblast cells, FGF2 can indirectly regulate proacinar cell differentiation in organoids, but the mechanisms are not understood. We performed single-cell RNA-sequencing and identified multiple stromal cell subsets, including Pdgfra+ stromal subsets expressing both Fgf2 and Fgf10. When combined with epithelial progenitor cells in organoids, magnetic-activated cell-sorted PDGFRα+ cells promoted proacinar cell differentiation similarly to total stroma. Gene expression analysis revealed that FGF2 increased the expression of multiple stromal genes, including Bmp2 and Bmp7. Both BMP2 and BMP7 synergized with FGF2, stimulating proacinar cell differentiation but not branching. However, stromal cells grown without FGF2 did not support proacinar organoid differentiation and instead differentiated into myofibroblasts. In organoids, TGFβ1 treatment stimulated myofibroblast differentiation and inhibited the proacinar cell differentiation of epithelial progenitor cells. Conversely, FGF2 reversed the effects of TGFβ1. We also demonstrated that adult salivary stromal cells were FGF2 responsive and could promote proacinar cell differentiation. These FGF2 signaling pathways may have applications in future regenerative therapies.

Gene regulatory network from cranial neural crest cells to osteoblast differentiation and calvarial bone development

Calvarial bone is one of the most complex sequences of developmental events in embryology, featuring a uniquely transient, pluripotent stem cell-like population known as the cranial neural crest (CNC). The skull is formed through intramembranous ossification with distinct tissue lineages (e.g. neural crest derived frontal bone and mesoderm derived parietal bone). Due to CNC's vast cell fate potential, in response to a series of inductive secreted cues including BMP/TGF-β, Wnt, FGF, Notch, Hedgehog, Hippo and PDGF signaling, CNC enables generations of a diverse spectrum of differentiated cell types in vivo such as osteoblasts and chondrocytes at the craniofacial level. In recent years, since the studies from a genetic mouse model and single-cell sequencing, new discoveries are uncovered upon CNC patterning, differentiation, and the contribution to the development of cranial bones. In this review, we summarized the differences upon the potential gene regulatory network to regulate CNC derived osteogenic potential in mouse and human, and highlighted specific functions of genetic molecules from multiple signaling pathways and the crosstalk, transcription factors and epigenetic factors in orchestrating CNC commitment and differentiation into osteogenic mesenchyme and bone formation. Disorders in gene regulatory network in CNC patterning indicate highly close relevance to clinical birth defects and diseases, providing valuable transgenic mouse models for subsequent discoveries in delineating the underlying molecular mechanisms. We also emphasized the potential regenerative alternative through scientific discoveries from CNC patterning and genetic molecules in interfering with or alleviating clinical disorders or diseases, which will be beneficial for the molecular targets to be integrated for novel therapeutic strategies in the clinic.

Pulling back the curtain: The hidden functions of receptor tyrosine kinases in development

Receptor tyrosine kinases (RTKs) are a conserved superfamily of transmembrane growth factor receptors that drive numerous cellular processes during development and in the adult. Upon activation, multiple adaptors and signaling effector proteins are recruited to binding site motifs located within the intracellular domain of the RTK. These RTK-effector interactions drive subsequent intracellular signaling cascades involved in canonical RTK signaling. Genetic dissection has revealed that alleles of Fibroblast Growth Factor receptors (FGFRs) that lack all canonical RTK signaling still retain some kinase-dependent biological activity. Here we examine how genetic analysis can be used to understand the mechanism by which RTKs drive multiple developmental processes via canonical signaling while revealing noncanonical activities. Recent data from both FGFRs and other RTKs highlight potential noncanonical roles in cell adhesion and nuclear signaling. The data supporting such functions are discussed as are recent technologies that have the potential to provide valuable insight into the developmental significance of these noncanonical activities.

Expression and function of PDGF-C in development and stem cells

Platelet-derived growth factor C (PDGF-C) is a relatively new member of the PDGF family, discovered nearly 20 years after the finding of platelet-derived growth factor A (PDGF-A) and platelet-derived growth factor B (PDGF-B). PDGF-C is generally expressed in most organs and cell types. Studies from the past 20 years have demonstrated critical roles of PDGF-C in numerous biological, physiological and pathological processes, such as development, angiogenesis, tumour growth, tissue remodelling, wound healing, atherosclerosis, fibrosis, stem/progenitor cell regulation and metabolism. Understanding PDGF-C expression and activities thus will be of great importance to various research disciplines. In this review, however, we mainly discuss the expression and functions of PDGF-C and its receptors in development and stem cells.

Zebrafish models of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorder (FASD) describes a wide range of structural deficits and cognitive impairments. FASD impacts up to 5% of children born in the United States each year, making ethanol one of the most common teratogens. Due to limitations and ethical concerns, studies in humans are limited in their ability to study FASD. Animal models have proven critical in identifying and characterizing the mechanisms underlying FASD. In this review, we will focus on the attributes of zebrafish that make it a strong model in which to study ethanol-induced developmental defects. Zebrafish have several attributes that make it an ideal model in which to study FASD. Zebrafish produced large numbers of externally fertilized, translucent embryos. With a high degree of genetic amenability, zebrafish are at the forefront of identifying and characterizing the gene-ethanol interactions that underlie FASD. Work from multiple labs has shown that embryonic ethanol exposures result in defects in craniofacial, cardiac, ocular, and neural development. In addition to structural defects, ethanol-induced cognitive and behavioral impairments have been studied in zebrafish. Building upon these studies, work has identified ethanol-sensitive loci that underlie the developmental defects. However, analyses show there is still much to be learned of these gene-ethanol interactions. The zebrafish is ideally suited to expand our understanding of gene-ethanol interactions and their impact on FASD. Because of the conservation of gene function between zebrafish and humans, these studies will directly translate to studies of candidate genes in human populations and allow for better diagnosis and treatment of FASD.

Role of PDGF-A/B Ligands in Cardiac Repair After Myocardial Infarction

Platelet-derived growth factors (PDGFs) are powerful inducers of cellular mitosis, migration, angiogenesis, and matrix modulation that play pivotal roles in the development, homeostasis, and healing of cardiac tissues. PDGFs are key signaling molecules and important drug targets in the treatment of cardiovascular disease as multiple researchers have shown that delivery of recombinant PDGF ligands during or after myocardial infarction can reduce mortality and improve cardiac function in both rodents and porcine models. The mechanism involved cannot be easily elucidated due to the complexity of PDGF regulatory activities, crosstalk with other protein tyrosine kinase activators, and diversity of the pathological milieu. This review outlines the possible roles of PDGF ligands A and B in the healing of cardiac tissues including reduced cell death, improved vascularization, and improved extracellular matrix remodeling to improve cardiac architecture and function after acute myocardial injury. This review may highlight the use of recombinant PDGF-A and PDGF-B as a potential therapeutic modality in the treatment of cardiac injury.

Fibroblasts: Origins, definitions, and functions in health and disease

Fibroblasts are diverse mesenchymal cells that participate in tissue homeostasis and disease by producing complex extracellular matrix and creating signaling niches through biophysical and biochemical cues. Transcriptionally and functionally heterogeneous across and within organs, fibroblasts encode regional positional information and maintain distinct cellular progeny. We summarize their development, lineages, functions, and contributions to fibrosis in four fibroblast-rich organs: skin, lung, skeletal muscle, and heart. We propose that fibroblasts are uniquely poised for tissue repair by easily reentering the cell cycle and exhibiting a reversible plasticity in phenotype and cell fate. These properties, when activated aberrantly, drive fibrotic disorders in humans.

Srsf3 mediates alternative RNA splicing downstream of PDGFRα signaling in the facial mesenchyme

Signaling through the platelet-derived growth factor receptor alpha (PDGFRα) is crucial for mammalian craniofacial development, although the mechanisms by which the activity of downstream intracellular effectors is regulated to mediate gene expression changes have not been defined. We find that the RNA-binding protein Srsf3 is phosphorylated at Akt consensus sites downstream of PI3K-mediated PDGFRα signaling in mouse palatal mesenchyme cells, leading to its nuclear translocation. We further demonstrate that ablation of Srsf3 in the mouse neural crest lineage leads to facial clefting due to defective cranial neural crest cell proliferation and survival. Finally, we show that Srsf3 regulates the alternative RNA splicing of transcripts encoding protein kinases in the mouse facial process mesenchyme to regulate PDGFRα-dependent intracellular signaling. Collectively, our findings reveal that alternative RNA splicing is an important mechanism of gene expression regulation downstream of PI3K/Akt-mediated PDGFRα signaling in the facial mesenchyme and identify Srsf3 as a critical regulator of craniofacial development.

Lineage Contribution of PDGFRα-Expressing Cells in the Developing Mouse Eye

PDGFRα signaling is critically important in ocular development. Previous data on PDGFRα lacks an expression map with high spatial and temporal resolution and lineage information. In this study, we aim to present a detailed PDGFRα expression and lineage map from early embryogenesis to adulthood. PDGFRα-CreER; mT/mG reporter mice were analyzed. mEGFP-positive cells contributed to multiple ocular lineages in a spatiotemporally regulated manner. A dynamic PDGFRα expression was identified in corneal stromal cells, lens epithelial cells, lens fiber cells, and retinal astrocytes during the entire period of eye development, while PDGFRα expression in retinal astrocytes from E17.5 onwards and in Müller glial cells was identified within two weeks after birth. By revealing detailed characterization of gene expression and function, we present a comprehensive map of PDGFRα-expressing cells in the eye for a better understanding of PDGFRα signaling's role during eye development.

PDGFRα-Signaling Is Dispensable for the Development of the Sinoatrial Node After Its Fate Commitment

Palate-derived growth factor receptor α (Pdgfrα) signaling has been reported to play important roles in the cardiac development. A previous study utilizing Pdgfrα conventional knockout mice reported hypoplasia of the sinus venous myocardium including the sinoatrial node (SAN) accompanied by increased expression of Nkx2.5. This mouse line embryos die by E11.5 due to embryonic lethality, rendering them difficult to investigate the details. To elucidate the underlying mechanism, in this study, we revisited this observation by generation of specific ablation of Pdgfrα in the SAN by Shox2-Cre at E9.5, using a Shox2-Cre;Pdgfrα ^flox/flox conditional mouse line. Surprisingly, we found that resultant homozygous mutant mice did not exhibit any malformation in SAN morphology as compared to their wild-type littermates. Further analysis revealed the normal cardiac function in adult mutant mice assessed by the record of heart rate and electrocardiogram and unaltered expression of Nkx2.5 in the E13.5 SAN of Pdgfrα conditional knockout mice. Our results unambiguously demonstrate that Pdgfrα is dispensable for SAN development after its fate commitment in mice.

PDGF-PDGFR network differentially regulates the fate, migration, proliferation, and cell cycle progression of myogenic cells

Platelet-derived growth factors (PDGFs) regulate embryonic development, tissue regeneration, and wound healing through their binding to PDGF receptors, PDGFRα and PDGFRβ. However, the role of PDGF signaling in regulating muscle development and regeneration remains elusive, and the cellular and molecular responses of myogenic cells are understudied. Here, we explore the PDGF-PDGFR gene expression changes and their involvement in skeletal muscle myogenesis and myogenic fate. By surveying bulk RNA sequencing and single-cell profiling data of skeletal muscle stem cells, we show that myogenic progenitors and muscle stem cells differentially express PDGF ligands and PDGF receptors during myogenesis. Quiescent adult muscle stem cells and myoblasts preferentially express PDGFRβ over PDGFRα. Remarkably, cell culture- and injury-induced muscle stem cell activation altered PDGF family gene expression. In myoblasts, PDGF-AB and PDGF-BB treatments activate two pro-chemotactic and pro-mitogenic downstream transducers, RAS-ERK1/2 and PI3K-AKT. PDGFRs inhibitor AG1296 inhibited ERK1/2 and AKT activation, myoblast migration, proliferation, and cell cycle progression induced by PDGF-AB and PDGF-BB. We also found that AG1296 causes myoblast G0/G1 cell cycle arrest. Remarkably, PDGF-AA did not promote a noticeable ERK1/2 or AKT activation, myoblast migration, or expansion. Also, myogenic differentiation reduced the expression of both PDGFRα and PDGFRβ, whereas forced PDGFRα expression impaired myogenesis. Thus, our data highlight PDGF signaling pathway to stimulate satellite cell proliferation aiming to enhance skeletal muscle regeneration and provide a deeper understanding of the role of PDGF signaling in non-fibroblastic cells.