TBX2 and TBX3 act downstream of canonical WNT signaling in patterning and differentiation of the mouse ureteric mesenchyme

TBX3 is essential for establishment of the posterior boundary of anterior genes and upregulation of posterior genes together with HAND2 during the onset of limb bud development

During limb bud formation, axis polarities are established as evidenced by the spatially restricted expression of key regulator genes. In particular, the mutually antagonistic interaction between the GLI3 repressor and HAND2 results in distinct and non-overlapping anterior-distal Gli3 and posterior Hand2 expression domains. This is a hallmark of the establishment of antero-posterior limb axis polarity, together with spatially restricted expression of homeodomain and other transcriptional regulators. Here, we show that TBX3 is required for establishment of the posterior expression boundary of anterior genes in mouse limb buds. ChIP-seq and differential gene expression analysis of wild-type and mutant limb buds identifies TBX3-specific and shared TBX3-HAND2 target genes. High sensitivity fluorescent whole-mount in situ hybridisation shows that the posterior expression boundaries of anterior genes are positioned by TBX3-mediated repression, which excludes anterior genes such as Gli3, Alx4, Hand1 and Irx3/5 from the posterior limb bud mesenchyme. This exclusion delineates the posterior mesenchymal territory competent to establish the Shh-expressing limb bud organiser. In turn, HAND2 is required for Shh activation and cooperates with TBX3 to upregulate shared posterior identity target genes in early limb buds.

Single-Cell Analyses Offer Insights into the Different Remodeling Programs of Arteries and Veins

Arteries and veins develop different types of occlusive diseases and respond differently to injury. The biological reasons for this discrepancy are not well understood, which is a limiting factor for the development of vein-targeted therapies. This study contrasts human peripheral arteries and veins at the single-cell level, with a focus on cell populations with remodeling potential. Upper arm arteries (brachial) and veins (basilic/cephalic) from 30 organ donors were compared using a combination of bulk and single-cell RNA sequencing, proteomics, flow cytometry, and histology. The cellular atlases of six arteries and veins demonstrated a 7.8× higher proportion of contractile smooth muscle cells (SMCs) in arteries and a trend toward more modulated SMCs. In contrast, veins showed a higher abundance of endothelial cells, pericytes, and macrophages, as well as an increasing trend in fibroblasts. Activated fibroblasts had similar proportions in both types of vessels but with significant differences in gene expression. Modulated SMCs and activated fibroblasts were characterized by the upregulation of MYH10, FN1, COL8A1, and ITGA10. Activated fibroblasts also expressed F2R, POSTN, and COMP and were confirmed by F2R/CD90 flow cytometry. Activated fibroblasts from veins were the top producers of collagens among all fibroblast populations from both types of vessels. Venous fibroblasts were also highly angiogenic, proinflammatory, and hyper-responders to reactive oxygen species. Differences in wall structure further explain the significant contribution of fibroblast populations to remodeling in veins. Fibroblasts are almost exclusively located outside the external elastic lamina in arteries, while widely distributed throughout the venous wall. In line with the above, ECM-targeted proteomics confirmed a higher abundance of fibrillar collagens in veins vs. more basement ECM components in arteries. The distinct cellular compositions and transcriptional programs of reparative populations in arteries and veins may explain differences in acute and chronic wall remodeling between vessels. This information may be relevant for the development of antistenotic therapies.

Modulation of canonical Wnt signaling regulates peribiliary mesenchymal identity during homeostasis and injury

BACKGROUND

The matrix and associated mesenchyme of the extrahepatic bile ducts are distinct, which could drive diseases with a predilection for these ducts, such as primary sclerosing cholangitis. We aimed to understand the molecular drivers of peribiliary mesenchymal cell (PMC) identity in the extrahepatic bile ducts and dissect how this changed in the context of injury using an entirely in vivo approach with transcriptomic analysis.

METHODS AND RESULTS

Single-cell sequencing with a receptor-ligand analysis showed that PMCs had the most interactions with surrounding cells. Wnt4, Wnt5a, and Wnt7b were identified as the major ligands secreted from PMCs and cholangiocytes that interacted in both paracrine and autocrine fashion. Bile duct ligation caused an increase in all 3 Wingless/Integrated ligands and Axin2 with an associated increase in the transcription factors T-box transcription factor (Tbx)2 and Tbx3. Conversely, Indian hedgehog secretion decreased without an associated decrease in hedgehog signaling effectors. Loss of smoothened within PMCs did not impact hedgehog signaling effectors or cellular identity, whereas smoothened gain of function led to myofibroblast transdifferentiation with upregulation of Tbx2 and Tbx3 without injury. Loss of β-catenin caused a decrease in expression of all 3 Gli transcription factors and associated mesenchymal gene expression, which was phenocopied with compound Gli2 and Gli3 loss in uninjured PMCs. With injury, loss of β-catenin resulted in decreased myofibroblast transdifferentiation with reduced Tbx2 and Tbx3 expression.

CONCLUSIONS

Our results show how modulation of canonical Wingless/Integrated signaling in PMCs is important for regulating basal mesenchymal gene expression and initiating a myogenic gene transcriptional program during injury. They also highlight reciprocating interactions between the hedgehog and Wingless/Integrated signaling pathways within PMCs.

The urothelial gene regulatory network: understanding biology to improve bladder cancer management

The urothelium is a stratified epithelium composed of basal cells, one or more layers of intermediate cells, and an upper layer of differentiated umbrella cells. Most bladder cancers (BLCA) are urothelial carcinomas. Loss of urothelial lineage fidelity results in altered differentiation, highlighted by the taxonomic classification into basal and luminal tumors. There is a need to better understand the urothelial transcriptional networks. To systematically identify transcription factors (TFs) relevant for urothelial identity, we defined highly expressed TFs in normal human bladder using RNA-Seq data and inferred their genomic binding using ATAC-Seq data. To focus on epithelial TFs, we analyzed RNA-Seq data from patient-derived organoids recapitulating features of basal/luminal tumors. We classified TFs as "luminal-enriched", "basal-enriched" or "common" according to expression in organoids. We validated our classification by differential gene expression analysis in Luminal Papillary vs. Basal/Squamous tumors. Genomic analyses revealed well-known TFs associated with luminal (e.g., PPARG, GATA3, FOXA1) and basal (e.g., TP63, TFAP2) phenotypes and novel candidates to play a role in urothelial differentiation or BLCA (e.g., MECOM, TBX3). We also identified TF families (e.g., KLFs, AP1, circadian clock, sex hormone receptors) for which there is suggestive evidence of their involvement in urothelial differentiation and/or BLCA. Genomic alterations in these TFs are associated with BLCA. We uncover a TF network involved in urothelial cell identity and BLCA. We identify novel candidate TFs involved in differentiation and cancer that provide opportunities for a better understanding of the underlying biology and therapeutic intervention.

Abnormal activation of the Wnt3a/β-catenin signaling pathway promotes the expression of T-box transcription factor 3(TBX3) and the epithelial-mesenchymal transition pathway to mediate the occurrence of adenomyosis

BACKGROUND

T-box transcription factor 3(TBX3) is a transcription factor that can regulate cell proliferation, apoptosis, invasion, and migration in different tumor cells; however, its role in adenomyosis (ADM) has not been previously studied. Some of ADM's pathophysiological characteristics are similar to those of malignant tumors (e.g., abnormal proliferation, migration, and invasion).

METHODS AND RESULTS

We hypothesized that TBX3 might have a role in ADM. We used tamoxifen-induced Institute of Cancer research (ICR) mice to establish ADM disease model. The study procedure included western blotting and immunohistochemistry to analyze protein levels; additionally, we used intraperitoneal injection of Wnt/β-catenin pathway inhibitor XAV-939 to study the relationship between TBX3 and Wnt/β-catenin pathway as well as Anti-proliferation cell nuclear antigen( PCNA) and TUNEL to detect cell proliferation and apoptosis, respectively. TBX3 overexpression and epithelial-to-mesenchymal transition (EMT) in ADM mice was found to be associated with activation of the Wnt3a/β-catenin pathway. Treatment with XAV-939 in ADM mice led to the inhibition of both TBX3 and EMT; moreover, abnormal cell proliferation was suppressed, the depth of invasion of endometrium cells was limited. Thus, the use of XAV-939 effectively inhibited further invasion of endometrial cells.

CONCLUSION

These findings suggest that TBX3 may play an important role in the development of ADM. The expression of TBX3 in ADM was regulated by the Wnt3a/β-catenin pathway. The activation of the Wnt3a/β-catenin pathway in ADM promoted TBX3 expression and induced the occurrence of EMT, thus promoting cell proliferation and inhibiting apoptosis, ultimately accelerating the development of ADM. The study provides a reference for the diagnosis of ADM.

Loss of Tbx3 in Mouse Eye Causes Retinal Angiogenesis Defects Reminiscent of Human Disease

Purpose

Familial exudative vitreoretinopathy (FEVR) and Norrie disease are examples of genetic disorders in which the retinal vasculature fails to fully form (hypovascular), leading to congenital blindness. While studying the role of a factor expressed during retinal development, T-box factor Tbx3, we discovered that optic cup loss of Tbx3 caused the retina to become hypovascular. The purpose of this study was to characterize how loss of Tbx3 affects retinal vasculature formation.

Methods

Conditional removal of Tbx3 from both retinal progenitors and astrocytes was done using the optic cup-Cre recombinase driver BAC-Dkk3-Cre and was analyzed using standard immunohistochemical techniques.

Results

With Tbx3 loss, the retinas were hypovascular, as seen in patients with retinopathy of prematurity (ROP) and FEVR. Retinal vasculature failed to form the stereotypic tri-layered plexus in the dorsal-temporal region. Astrocyte precursors were reduced in number and failed to form a lattice at the dorsal-temporal edge. We next examined retinal ganglion cells, as they have been shown to play a critical role in retinal angiogenesis. We found that melanopsin expression and Islet1/2-positive retinal ganglion cells were reduced in the dorsal half of the retina. In previous studies, the loss of melanopsin has been linked to hyaloid vessel persistence, which we also observed in the Tbx3 conditional knockout (cKO) retinas, as well as in infants with ROP or FEVR.

Conclusions

To the best of our knowledge, these studies are the first demonstration that Tbx3 is required for normal mammalian eye formation. Together, the results provide a potential genetic model for retinal hypovascular diseases.

Role of T-box transcription factor 3 in gastric cancers

The expression of T-box transcription factor 3 (TBX3) has been identified in various cancers, including gastric cancers. Its role in breast cancers and melanomas has been intensively studied, and its contribution to the progression of cancers through suppressing senescence and promoting epithelial-mesenchymal transition has been reported. Recent reports on the role of TBX3 in gastric cancers have implied its involvement in gastric carcinogenesis. Considering its pivotal role in the initiation and progression of cancers, TBX3 could be a promising therapeutic target for gastric cancers.

Single-cell transcriptomics uncovers a non-autonomous Tbx1-dependent genetic program controlling cardiac neural crest cell development

Disruption of cardiac neural crest cells (CNCCs) results in congenital heart disease, yet we do not understand the cell fate dynamics as these cells differentiate to vascular smooth muscle cells. Here we performed single-cell RNA-sequencing of NCCs from the pharyngeal apparatus with the heart in control mouse embryos and when Tbx1, the gene for 22q11.2 deletion syndrome, is inactivated. We uncover three dynamic transitions of pharyngeal NCCs expressing Tbx2 and Tbx3 through differentiated CNCCs expressing cardiac transcription factors with smooth muscle genes. These transitions are altered non-autonomously by loss of Tbx1. Further, inactivation of Tbx2 and Tbx3 in early CNCCs results in aortic arch branching defects due to failed smooth muscle differentiation. Loss of Tbx1 interrupts mesoderm to CNCC cell-cell communication with upregulation and premature activation of BMP signaling and reduced MAPK signaling, as well as alteration of other signaling, and failed dynamic transitions of CNCCs leading to disruption of aortic arch artery formation and cardiac outflow tract septation.

TBX3 is dynamically expressed in pancreatic organogenesis and fine-tunes regeneration

BACKGROUND

The reactivation of genetic programs from early development is a common mechanism for injury-induced organ regeneration. T-box 3 (TBX3) is a member of the T-box family of transcription factors previously shown to regulate pluripotency and subsequent lineage commitment in a number of tissues, including limb and lung. TBX3 is also involved in lung and heart organogenesis. Here, we provide a comprehensive and thorough characterization of TBX3 and its role during pancreatic organogenesis and regeneration.

RESULTS

We interrogated the level and cell specificity of TBX3 in the developing and adult pancreas at mRNA and protein levels at multiple developmental stages in mouse and human pancreas. We employed conditional mutagenesis to determine its role in murine pancreatic development and in regeneration after the induction of acute pancreatitis. We found that Tbx3 is dynamically expressed in the pancreatic mesenchyme and epithelium. While Tbx3 is expressed in the developing pancreas, its absence is likely compensated by other factors after ablation from either the mesenchymal or epithelial compartments. In an adult model of acute pancreatitis, we found that a lack of Tbx3 resulted in increased proliferation and fibrosis as well as an enhanced inflammatory gene programs, indicating that Tbx3 has a role in tissue homeostasis and regeneration.

CONCLUSIONS

TBX3 demonstrates dynamic expression patterns in the pancreas. Although TBX3 is dispensable for proper pancreatic development, its absence leads to altered organ regeneration after induction of acute pancreatitis.

Mesenchymal FGFR1 and FGFR2 control patterning of the ureteric mesenchyme by balancing SHH and BMP4 signaling

The coordinated development of the mesenchymal and epithelial progenitors of the murine ureter depends on a complex interplay of diverse signaling activities. We have recently shown that epithelial FGFR2 signaling regulates stratification and differentiation of the epithelial compartment by enhancing epithelial Shh expression, and mesenchymal SHH and BMP4 activity. Here, we show that FGFR1 and FGFR2 expression in the mesenchymal primordium impinges on the SHH/BMP4 signaling axis to regulate mesenchymal patterning and differentiation. Mouse embryos with conditional loss of Fgfr1 and Fgfr2 in the ureteric mesenchyme exhibited reduced mesenchymal proliferation and prematurely activated lamina propria formation at the expense of the smooth muscle cell program. They also manifested hydroureter at birth. Molecular profiling detected increased SHH, WNT and retinoic acid signaling, whereas BMP4 signaling in the mesenchyme was reduced. Pharmacological activation of SHH signaling in combination with inhibition of BMP4 signaling recapitulated the cellular changes in explant cultures of wild-type ureters. Additional experiments suggest that mesenchymal FGFR1 and FGFR2 act as a sink for FGF ligands to dampen activation of Shh and BMP receptor gene expression by epithelial FGFR2 signaling.

GATA6 is a crucial factor for Myocd expression in the visceral smooth muscle cell differentiation program of the murine ureter

Smooth muscle cells (SMCs) are a crucial component of the mesenchymal wall of the ureter, as they account for the efficient removal of the urine from the renal pelvis to the bladder by means of their contractile activity. Here, we show that the zinc-finger transcription factor gene Gata6 is expressed in mesenchymal precursors of ureteric SMCs under the control of BMP4 signaling. Mice with a conditional loss of Gata6 in these precursors exhibit a delayed onset and reduced level of SMC differentiation and peristaltic activity, as well as dilatation of the ureter and renal pelvis (hydroureternephrosis) at birth and at postnatal stages. Molecular profiling revealed a delayed and reduced expression of the myogenic driver gene Myocd, but the activation of signaling pathways and transcription factors previously implicated in activation of the visceral SMC program in the ureter was unchanged. Additional gain-of-function experiments suggest that GATA6 cooperates with FOXF1 in Myocd activation and SMC differentiation, possibly as pioneer and lineage-determining factors, respectively.

Wnt signaling regulates hepatocyte cell division by a transcriptional repressor cascade

As a general model for cell cycle control, repressors keep cells quiescent until growth signals remove the inhibition. For S phase, this is exemplified by the Retinoblastoma (RB) protein and its inactivation. It was unknown whether similar mechanisms operate in the M phase. The Wnt signaling pathway is an important regulator of cell proliferation. Here, we find that Wnt induces expression of the transcription factor Tbx3, which in turn represses mitotic inhibitors E2f7 and E2f8 to permit mitotic progression. Such a cascade of transcriptional repressors may be a general mechanism for cell division control. These findings have implications for tissue homeostasis and disease, as the function for Wnt signaling in mitosis is relevant to its widespread role in stem cells and cancer.

Cell proliferation is tightly controlled by inhibitors that block cell cycle progression until growth signals relieve this inhibition, allowing cells to divide. In several tissues, including the liver, cell proliferation is inhibited at mitosis by the transcriptional repressors E2F7 and E2F8, leading to formation of polyploid cells. Whether growth factors promote mitosis and cell cycle progression by relieving the E2F7/E2F8-mediated inhibition is unknown. We report here on a mechanism of cell division control in the postnatal liver, in which Wnt/β-catenin signaling maintains active hepatocyte cell division through Tbx3, a Wnt target gene. The TBX3 protein directly represses transcription of E2f7 and E2f8, thereby promoting mitosis. This cascade of sequential transcriptional repressors, initiated by Wnt signals, provides a paradigm for exploring how commonly active developmental signals impact cell cycle completion.

Complex functional redundancy of Tbx2 and Tbx3 in mouse limb development

The limb phenotypes of Tbx2 and Tbx3 mutants are distinct: loss of Tbx2 results in isolated duplication of digit 4 in the hindlimb while loss of Tbx3 results in anterior polydactyly and posterior oligodactly in the forelimb. In the face of such disparate phenotypes, we sought to determine whether Tbx2 and Tbx3 have functional redundancy during development of the mouse limb. We found that sequential loss of alleles generates defects that are not simply additive of those observed in single mutants and that multiple structures in both the forelimb and hindlimb display compound sensitivity to decreased gene dosage. This article is protected by copyright. All rights reserved.

Tbx2 is a master regulator of inner versus outer hair cell differentiation

The cochlea uses two types of mechanosensory cell to detect sounds. A single row of inner hair cells (IHCs) synapse onto neurons to transmit sensory information to the brain, and three rows of outer hair cells (OHCs) selectively amplify auditory inputs¹. So far, two transcription factors have been implicated in the specific differentiation of OHCs, whereas, to our knowledge, none has been identified in the differentiation of IHCs^2-4. One such transcription factor for OHCs, INSM1, acts during a crucial embryonic period to consolidate the OHC fate, preventing OHCs from transdifferentiating into IHCs². In the absence of INSM1, embryonic OHCs misexpress a core set of IHC-specific genes, which we predict are involved in IHC differentiation. Here we find that one of these genes, Tbx2, is a master regulator of IHC versus OHC differentiation in mice. Ablation of Tbx2 in embryonic IHCs results in their development as OHCs, expressing early OHC markers such as Insm1 and eventually becoming completely mature OHCs in the position of IHCs. Furthermore, Tbx2 is epistatic to Insm1: in the absence of both genes, cochleae generate only OHCs, which suggests that TBX2 is necessary for the abnormal transdifferentiation of INSM1-deficient OHCs into IHCs, as well as for normal IHC differentiation. Ablation of Tbx2 in postnatal, largely differentiated IHCs makes them transdifferentiate directly into OHCs, replacing IHC features with those of mature and not embryonic OHCs. Finally, ectopic expression of Tbx2 in OHCs results in their transdifferentiation into IHCs. Hence, Tbx2 is both necessary and sufficient to make IHCs distinct from OHCs and maintain this difference throughout development.

The WNT7A/WNT7B/GPR124/RECK signaling module plays an essential role in mammalian limb development

In central nervous system vascular endothelial cells, signaling via the partially redundant ligands WNT7A and WNT7B requires two co-activator proteins, GPR124 and RECK. WNT7A and RECK have been shown previously to play a role in limb development, but the mechanism of RECK action in this context is unknown. The roles of WNT7B and GPR124 in limb development have not been investigated. Using combinations of conventional and/or conditional loss-of-function alleles for mouse Wnt7a, Wnt7b, Gpr124 and Reck, including a Reck allele that codes for a protein that is specifically defective in WNT7A/WNT7B signaling, we show that reductions in ligand and/or co-activator function synergize to cause reduced and dysmorphic limb bone growth. Two additional limb phenotypes – loss of distal Lmx1b expression and ectopic growth of nail-like structures – occur with reduced Wnt7a/Wnt7b gene copy number and, respectively, with Reck mutations and with combined Reck and Gpr124 mutations. A third limb phenotype – bleeding into a digit – occurs with the most severe combinations of Wnt7a/Wnt7b, Reck and Gpr124 mutations. These data imply that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system functions as an integral unit in limb development.

Summary: Genetic analyses in mice show that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system, first defined in the context of CNS angiogenesis and barrier development, also functions as an integral unit in limb development.

Notch signaling is a novel regulator of visceral smooth muscle cell differentiation in the murine ureter

The contractile phenotype of smooth muscle cells (SMCs) is transcriptionally controlled by a complex of the DNA-binding protein SRF and the transcriptional co-activator MYOCD. The pathways that activate expression of Myocd and of SMC structural genes in mesenchymal progenitors are diverse, reflecting different intrinsic and extrinsic signaling inputs. Taking the ureter as a model, we analyzed whether Notch signaling, a pathway previously implicated in vascular SMC development, also affects visceral SMC differentiation. We show that mice with a conditional deletion of the unique Notch mediator RBPJ in the undifferentiated ureteric mesenchyme exhibit altered ureter peristalsis with a delayed onset, and decreased contraction frequency and intensity at fetal stages. They also develop hydroureter 2 weeks after birth. Notch signaling is required for precise temporal activation of Myocd expression and, independently, for expression of a group of late SMC structural genes. Based on additional expression analyses, we suggest that a mesenchymal JAG1-NOTCH2/NOTCH3 module regulates visceral SMC differentiation in the ureter in a biphasic and bimodal manner, and that its molecular function differs from that in the vascular system.

TBX2 controls a proproliferative gene expression program in melanoma

Senescence shapes embryonic development, plays a key role in aging, and is a critical barrier to cancer initiation, yet how senescence is regulated remains incompletely understood. TBX2 is an antisenescence T-box family transcription repressor implicated in embryonic development and cancer. However, the repertoire of TBX2 target genes, its cooperating partners, and how TBX2 promotes proliferation and senescence bypass are poorly understood. Here, using melanoma as a model, we show that TBX2 lies downstream from PI3K signaling and that TBX2 binds and is required for expression of E2F1, a key antisenescence cell cycle regulator. Remarkably, TBX2 binding in vivo is associated with CACGTG E-boxes, present in genes down-regulated by TBX2 depletion, more frequently than the consensus T-element DNA binding motif that is restricted to Tbx2 repressed genes. TBX2 is revealed to interact with a wide range of transcription factors and cofactors, including key components of the BCOR/PRC1.1 complex that are recruited by TBX2 to the E2F1 locus. Our results provide key insights into how PI3K signaling modulates TBX2 function in cancer to drive proliferation.

Diversity of developing peripheral glia revealed by single-cell RNA sequencing

The peripheral nervous system responds to a wide variety of sensory stimuli, a process that requires great neuronal diversity. These diverse neurons are closely associated with glial cells originating from the neural crest. However, the molecular nature and diversity among peripheral glia are not understood. Here, we used single-cell RNA sequencing to profile developing and mature glia from somatosensory dorsal root ganglia and auditory spiral ganglia. We found that glial precursors (GPs) in these two systems differ in their transcriptional profiles. Despite their unique features, somatosensory and auditory GPs undergo convergent differentiation to generate molecularly uniform myelinating and non-myelinating Schwann cells. By contrast, somatosensory and auditory satellite glial cells retain system-specific features. Lastly, we identified a glial signature gene set, providing new insights into commonalities among glia across the nervous system. This survey of gene expression in peripheral glia constitutes a resource for understanding functions of glia across different sensory modalities.

Single-Cell Epigenomics and Functional Fine-Mapping of Atherosclerosis GWAS Loci

Supplemental Digital Content is available in the text.

Genome-wide association studies have identified hundreds of loci associated with coronary artery disease (CAD). Many of these loci are enriched in cisregulatory elements but not linked to cardiometabolic risk factors nor to candidate causal genes, complicating their functional interpretation.

Regulation of otocyst patterning by Tbx2 and Tbx3 is required for inner ear morphogenesis in the mouse

All epithelial components of the inner ear, including sensory hair cells and innervating afferent neurons, arise by patterning and differentiation of epithelial progenitors residing in a simple sphere, the otocyst. Here, we identify the transcriptional repressors TBX2 and TBX3 as novel regulators of these processes in the mouse. Ablation of Tbx2 from the otocyst led to cochlear hypoplasia, whereas loss of Tbx3 was associated with vestibular malformations. The loss of function of both genes (Tbx2/3cDKO) prevented inner ear morphogenesis at midgestation, resulting in indiscernible cochlear and vestibular structures at birth. Morphogenetic impairment occurred concomitantly with increased apoptosis in ventral and lateral regions of Tbx2/3cDKO otocysts around E10.5. Expression analyses revealed partly disturbed regionalisation, and a posterior-ventral expansion of the neurogenic domain in Tbx2/3cDKO otocysts at this stage. We provide evidence that repression of FGF signalling by TBX2 is important to restrict neurogenesis to the anterior-ventral otocyst and implicate another T-box factor, TBX1, as a crucial mediator in this regulatory network.

Combined genomic and proteomic approaches reveal DNA binding sites and interaction partners of TBX2 in the developing lung

BACKGROUND

Tbx2 encodes a transcriptional repressor implicated in the development of numerous organs in mouse. During lung development TBX2 maintains the proliferation of mesenchymal progenitors, and hence, epithelial proliferation and branching morphogenesis. The pro-proliferative function was traced to direct repression of the cell-cycle inhibitor genes Cdkn1a and Cdkn1b, as well as of genes encoding WNT antagonists, Frzb and Shisa3, to increase pro-proliferative WNT signaling. Despite these important molecular insights, we still lack knowledge of the DNA occupancy of TBX2 in the genome, and of the protein interaction partners involved in transcriptional repression of target genes.

METHODS

We used chromatin immunoprecipitation (ChIP)-sequencing and expression analyses to identify genomic DNA-binding sites and transcription units directly regulated by TBX2 in the developing lung. Moreover, we purified TBX2 containing protein complexes from embryonic lung tissue and identified potential interaction partners by subsequent liquid chromatography/mass spectrometry. The interaction with candidate proteins was validated by immunofluorescence, proximity ligation and individual co-immunoprecipitation analyses.

RESULTS

We identified Il33 and Ccn4 as additional direct target genes of TBX2 in the pulmonary mesenchyme. Analyzing TBX2 occupancy data unveiled the enrichment of five consensus sequences, three of which match T-box binding elements. The remaining two correspond to a high mobility group (HMG)-box and a homeobox consensus sequence motif. We found and validated binding of TBX2 to the HMG-box transcription factor HMGB2 and the homeobox transcription factor PBX1, to the heterochromatin protein CBX3, and to various members of the nucleosome remodeling and deacetylase (NuRD) chromatin remodeling complex including HDAC1, HDAC2 and CHD4.

CONCLUSION

Our data suggest that TBX2 interacts with homeobox and HMG-box transcription factors as well as with the NuRD chromatin remodeling complex to repress transcription of anti-proliferative genes in the pulmonary mesenchyme.

Roles for urothelium in normal and aberrant urinary tract development

Congenital anomalies of the kidney and urinary tract (CAKUTs) represent the leading cause of chronic kidney disease and end-stage kidney disease in children. Increasing evidence points to critical roles for the urothelium in the developing urinary tract and in the genesis of CAKUTs. The involvement of the urothelium in patterning the urinary tract is supported by evidence that CAKUTs can arise as a result of abnormal urothelial development. Emerging evidence indicates that congenital urinary tract obstruction triggers urothelial remodelling that stabilizes the obstructed kidney and limits renal injury. Finally, the diagnostic potential of radiological findings and urinary biomarkers derived from the urothelium of patients with CAKUTs might aid their contribution to clinical care.

Delayed onset of smooth muscle cell differentiation leads to hydroureter formation in mice with conditional loss of the zinc finger transcription factor gene Gata2 in the ureteric mesenchyme

The establishment of the peristaltic machinery of the ureter is precisely controlled to cope with the onset of urine production in the fetal kidney. Retinoic acid (RA) has been identified as a signal that maintains the mesenchymal progenitors of the contractile smooth muscle cells (SMCs), while WNTs, SHH, and BMP4 induce their differentiation. How the activity of the underlying signalling pathways is controlled in time, space, and quantity to activate coordinately the SMC programme is poorly understood. Here, we provide evidence that the Zn-finger transcription factor GATA2 is involved in this crosstalk. In mice, Gata2 is expressed in the undifferentiated ureteric mesenchyme under control of RA signalling. Conditional deletion of Gata2 by a Tbx18^cre driver results in hydroureter formation at birth, associated with a loss of differentiated SMCs. Analysis at earlier stages and in explant cultures revealed that SMC differentiation is not abrogated but delayed and that dilated ureters can partially regain peristaltic activity when relieved of urine pressure. Molecular analysis identified increased RA signalling as one factor contributing to the delay in SMC differentiation, possibly caused by reduced direct transcriptional activation of Cyp26a1, which encodes an RA-degrading enzyme. Our study identified GATA2 as a feedback inhibitor of RA signalling important for precise onset of ureteric SMC differentiation, and suggests that in a subset of cases of human congenital ureter dilatations, temporary relief of urine pressure may ameliorate the differentiation status of the SMC coat. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.