Bmp2 and Bmp4 genetically interact to support multiple aspects of mouse development including functional heart development

Identification of two miRNAs regulating cardiomyocyte proliferation in an Antarctic icefish

The hemoglobinless Antarctic icefish develop large hearts to compensate for reduced oxygen-carrying capacity, which serves as a naturally occurred model to explore the factors regulating cardiogenesis. Through miRNAome and microRNAome comparisons between an icefish (Chionodraco hamatus) and two red-blooded notothenioids, we discovered significant upregulation of factors in the BMP signaling pathways and altered expression of many miRNAs, including downregulation of 14 miRNAs in the icefish heart. Through knocking down of these miRNAs, we identified two of them, miR-458-3p and miR-144-5p, involved in enlarged heart development. The two miRNAs were found to regulate cardiomyocyte proliferation by targeting bone morphogenetic protein-2 (bmp2). We further validated that activation of the miRNA-bmp2 signaling in the fish heart could be triggered by hypoxic exposure. Our study suggested that a few miRNAs play important roles in the hypoxia-induced cardiac remodeling of the icefish which shed new light on the mechanisms regulating cardiomyocyte proliferation in heart.

Discovery and functional investigation of BMP4 as a new causative gene for human congenital heart disease

OBJECTIVE

Aggregating evidence highlights the strong genetic basis underpinning congenital heart disease (CHD). Here BMP4 was chosen as a prime candidate gene causative of human CHD predominantly because BMP4 was amply expressed in the embryonic hearts and knockout of Bmp4 in mice led to embryonic demise mainly from multiple cardiovascular developmental malformations. The aim of this retrospective investigation was to discover a novel BMP4 mutation underlying human CHD and explore its functional impact.

METHODS

A sequencing examination of BMP4 was implemented in 212 index patients suffering from CHD and 236 unrelated non-CHD individuals as well as the family members available from the proband carrying a discovered BMP4 mutation. The impacts of the discovered CHD-causing mutation on the expression of NKX2-5 and TBX20 induced by BMP4 were measured by employing a dual-luciferase analysis system.

RESULTS

A new heterozygous BMP4 mutation, NM_001202.6:c.318T>G;p.(Tyr106*), was found in a female proband affected with familial CHD. Genetic research of the mutation carrier's relatives unveiled that the truncating mutation was in co-segregation with CHD in the pedigree. The nonsense mutation was absent from 236 unrelated non-CHD control persons. Quantitative biologic measurement revealed that Tyr106*-mutant BMP4 failed to induce the expression of NKX2-5 and TBX20, two genes whose expression is lost in CHD.

CONCLUSION

The current findings indicate BMP4 as a new gene predisposing to human CHD, allowing for improved prenatal genetic counseling along with personalized treatment of CHD patients.

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.

Investigation of the Role of BMP2 and -4 in ASD, VSD and Complex Congenital Heart Disease

Congenital heart malformations (CHMs) make up between 2 and 3% of annual human births. Bone morphogenetic proteins (BMPs) signalling is required for chamber myocardium development. We examined for possible molecular defects in the bone morphogenetic protein 2 and 4 (BMP2, -4) genes by sequencing analysis of all coding exons, as well as possible transcription or protein expression deregulation by real-time PCR and ELISA, respectively, in 52 heart biopsies with congenital malformations (atrial septal defect (ASD), ventricular septal defect (VSD), tetralogy ofFallot (ToF) and complex cases) compared to 10 non-congenital heart disease (CHD) hearts. No loss of function mutations was found; only synonymous single nucleotide polymorphisms (SNPs) in the BMP2 and BMP4 genes were found. Deregulation of the mRNA expression and co-expression profile of the two genes (BMP2/BMP4) was observed in the affected compared to the normal hearts. BMP2 and -4 protein expression levels were similar in normal and affected hearts. This is the first study assessing the role of BMP-2 and 4 in congenital heart malformations. Our analysis did not reveal molecular defects in the BMP2 and -4 genes that could support a causal relationship with the congenital defects present in our patients. Importantly, sustained mRNA and protein expression of BMP2 and -4 in CHD cases compared to controls indicates possible temporal epigenetic, microRNA or post-transcriptional regulation mechanisms governing the initial stages of cardiac malformation.

Ferroptosis in life: To be or not to be

Ferroptosis is a novel type of programmed cell death, characterized by a dysregulated iron metabolism and accumulation of lipid peroxides. It features the alteration of mitochondria and aberrant accumulation of excessive iron as well as loss of the cysteine-glutathione-GPX4 axis. Eventually, the accumulated lipid peroxides result in lethal damage to the cells. Ferroptosis is induced by the overloading of iron and the accumulation of ROS and can be inhibited by the activation of the GPX4 pathway, FS1-CoQ10 pathway, GCH1-BH4 pathway, and the DHODH pathway, it is also regulated by the oncogenes and tumor suppressors. Ferroptosis involves various physiological and pathological processes, and increasing evidence indicates that ferroptosis play a critical role in cancers and other diseases. It inhibits the proliferation of malignant cells in various types of cancers and inducing ferroptosis may become a new method of cancer treatment. Many inhibitors targeting the key factors of ferroptosis such as SLC7A11, GPX4, and iron overload have been developed. The application of ferroptosis is mainly divided into two directions, i.e. to avoid ferroptosis in healthy cells and selectively induce ferroptosis in cancers. In this review, we provide a critical analysis of the concept, and regulation pathways of ferroptosis and explored its roles in various diseases, we also summarized the compounds targeting ferroptosis, aiming to promote the speed of clinical use of ferroptosis induction in cancer treatment.

[Joint regulation of Wnt and bone morphogenetic protein signaling pathways to promote differentiation of human induced pluripotent stem cells into cardiomyocytes]

Objective

To explore the role of joint regulation of Wnt and bone morphogenetic protein (BMP) signaling pathways in the differentiation of human induced pluripotent stem cells (hiPSCs) into cardiomyocytes.

Methods

HiPSCs were cultured and observed under inverted phase contrast microscope. Immunofluorescence staining was used to observe the expressions of hiPSCs pluripotent markers (OCT3/4, NANOG, and TRA-1-60). HiPSCs were passaged which were taken for subsequent experiments within the 35th passage. When the fusion degree of hiPSCs was close to 100%, the CHIR99021 (Wnt pathway activator) was added on the 0th day of differentiation. Different concentrations of IWP4 (inhibitor of Wnt production) were added on the 3rd day of differentiation, and the best concentration of IWP4 was added at different time points. The optimal concentration and the best effective period of IWP4 were obtained by detecting the expression of troponin T (TNNT2) mRNA by real-time fluorescence quantitative PCR. Then, on the basis of adding CHIR99021 and IWP4, different concentrations of BMP-4 were added on the 5th day of differentiation, and the best concentration of BMP-4 was added at different time points. The optimal concentration and best effective period of BMP-4 were obtained by detecting the expression of TNNT2 mRNA. Finally, hiPSCs were divided into three groups: Wnt group, BMP group, and Wnt+BMP group. On the basis of adding CHIR99021 on the 0th day of differentiation, IWP4, BMP-4, and IWP4+BMP-4 were added into Wnt group, BMP group, and Wnt+BMP group respectively according to the screening results. Cells were collected on the 7th and the 15th days of differentiation. The expressions of myocardial precursor cell markers [ISL LIM homeobox 1 (ISL1), NK2 homeobox 5 (NKX2-5)] and cardiomyocyte specific markers [myocyte enhancer factor 2C (MEF2C), myosin light chain 2 (MYL2), MYL7, and TNNT2] were detected by real-time fluorescent quantitative PCR. Cells were collected on the 28th day of differentiation, and the expression of cardiac troponin T (cTnT) was detected by flow cytometry and immunofluorescence staining.

Results

The results of cell mophology and immunoflurescence staining showed that the OCT3/4, NANOG, and TRA-1-60 were highly expressed in hiPSCs, which suggested that hiPSCs had characteristics of pluripotency. The optimal concentration of IWP4 was 10.0 μmol/L ( P<0.05) and the best effective period was the 3rd day ( P<0.05) in inducing hiPSCs to differentiate into cardiomyocytes. The optimal concentration of BMP-4 was 20.0 ng/mL ( P<0.05) and the best effective period was the 3rd day ( P<0.05). The relative expressions of ISL1, NKX2-5, MEF2C, MYL2, MYL7, and TNNT2 mRNAs, the positive expression ratio of cTnT detected by flow cytometry, and sarcomere structure detected by immunofluorescence staining of Wnt+BMP group were superior to those of Wnt group ( P<0.05).

Conclusion

Joint regulation of Wnt and BMP signaling pathways can improve the differentiation efficiency of hiPSCs into cardiomyocytes.

Bone Morphogenetic Protein-2 in Development and Bone Homeostasis

Bone morphogenetic proteins (BMPs) are multi-functional growth factors belonging to the Transforming Growth Factor-Beta (TGF-β) superfamily. These proteins are essential to many developmental processes, including cardiogenesis, neurogenesis, and osteogenesis. Specifically, within the BMP family, Bone Morphogenetic Protein-2 (BMP-2) was the first BMP to be characterized and has been well-studied. BMP-2 has important roles during embryonic development, as well as bone remodeling and homeostasis in adulthood. Some of its specific functions include digit formation and activating osteogenic genes, such as Runt-Related Transcription Factor 2 (RUNX2). Because of its diverse functions and osteogenic potential, the Food and Drug Administration (FDA) approved usage of recombinant human BMP-2 (rhBMP-2) during spinal fusion surgery, tibial shaft repair, and maxillary sinus reconstructive surgery. However, shortly after initial injections of rhBMP-2, several adverse complications were reported, and alternative therapeutics have been developed to limit these side-effects. As the clinical application of BMP-2 is largely implicated in bone, we focus primarily on its role in bone. However, we also describe briefly the role of BMP-2 in development. We then focus on the structure of BMP-2, its activation and regulation signaling pathways, BMP-2 clinical applications, and limitations of using BMP-2 as a therapeutic. Further, this review explores other potential treatments that may be useful in treating bone disorders.

BMP7 functions predominantly as a heterodimer with BMP2 or BMP4 during mammalian embryogenesis

BMP7/BMP2 or BMP7/BMP4 heterodimers are more active than homodimers in vitro, but it is not known whether these heterodimers signal in vivo. To test this, we generated knock in mice carrying a mutation (Bmp7^R-GFlag) that prevents proteolytic activation of the dimerized BMP7 precursor protein. This mutation eliminates the function of BMP7 homodimers and all other BMPs that normally heterodimerize with BMP7. While Bmp7 null homozygotes are live born, Bmp7^R-GFlag homozygotes are embryonic lethal and have broadly reduced BMP activity. Furthermore, compound heterozygotes carrying the Bmp7^R-G allele together with a null allele of Bmp2 or Bmp4 die during embryogenesis with defects in ventral body wall closure and/or the heart. Co-immunoprecipitation assays confirm that endogenous BMP4/7 heterodimers exist. Thus, BMP7 functions predominantly as a heterodimer with BMP2 or BMP4 during mammalian development, which may explain why mutations in either Bmp4 or Bmp7 lead to a similar spectrum of congenital defects in humans.

Functional and structural studies of tolloid-like 1 mutants associated with atrial-septal defect 6

Inactive mammalian tolloid-like 1 (tll1) and mutations detected in tolloid-like 1 (TLL1) have been linked to the lack of the heart septa formation in mice and to a similar human inborn condition called atrial-septal defect 6 (ASD6; OMIM 613087, formerly ASD II). Previously, we reported four point mutations in TLL1 found in approximately 20% of ASD6 patients. Three mutations in the coding sequence were M182L, V238A, and I629V. In this work, we present the effects of these mutations on TLL1 function. Three recombinant cDNA constructs carrying the mutations and one wild-type construct were prepared and then expressed in HT-1080 cells. Corresponding recombinant proteins were analyzed for their metalloendopeptidase activity using a native substrate, chordin. The results of these assays demonstrated that in comparison with the native TLL1, mutants cleaved chordin and procollagen I at significantly lower rates. CD analyses revealed significant structural differences between the higher order structure of wild-type and mutant variants. Moreover, biosensor-based assays of binding interactions between TLL1 variants and chordin demonstrated a significant decrease in the binding affinities of the mutated variants. The results from this work indicate that mutations detected in TLL1 of ASD6 patients altered its metalloendopeptidase activity, structure, and substrate-binding properties, thereby suggesting a possible pathomechanism of ASD6.

Ciliary margin-derived BMP4 does not have a major role in ocular development

Heterozygous Bmp4 mutations in humans and mice cause severe ocular anterior segment dysgenesis (ASD). Abnormalities include pupil displacement, corneal opacity, iridocorneal adhesions, and variable intraocular pressure, as well as some retinal and vascular defects. It is presently not known what source of BMP4 is responsible for these defects, as BMP4 is expressed in several developing ocular and surrounding tissues. In particular, BMP4 is expressed in the ciliary margins of the optic cup which give rise to anterior segment structures such as the ciliary body and iris, making it a good candidate for the required source of BMP4 for anterior segment development. Here, we test whether ciliary margin-derived BMP4 is required for ocular development using two different conditional knockout approaches. In addition, we compared the conditional deletion phenotypes with Bmp4 heterozygous null mice. Morphological, molecular, and functional assays were performed on adult mutant mice, including histology, immunohistochemistry, in vivo imaging, and intraocular pressure measurements. Surprisingly, in contrast to Bmp4 heterozygous mutants, our analyses revealed that the anterior and posterior segments of Bmp4 conditional knockouts developed normally. These results indicate that ciliary margin-derived BMP4 does not have a major role in ocular development, although subtle alterations could not be ruled out. Furthermore, we demonstrated that the anterior and posterior phenotypes observed in Bmp4 heterozygous animals showed a strong propensity to co-occur, suggesting a common, non-cell autonomous source for these defects.

Effect of bone morphogenetic proteins 2 and 4 on survival and development of bovine secondary follicles cultured in vitro

This study evaluated the effect of bone morphogenetic proteins 2 (BMP2) and 4 (BMP2) on follicle development and mRNA expression for GDF9, Cyclin B1, BMPR1A, BMPR1B, BMPRII, FSHR and SMAD1 in bovine secondary follicles cultured in vitro. Isolated secondary follicles were cultured for 18 days in TCM199⁺ medium alone or supplemented with BMP2 (10 ng/mL), BMP4 (100 ng/mL) or combination of both BMP2 and 4. Real-time PCR was used to analyze mRNA levels in fresh and cultured follicles. After 18 days of culture, follicles cultured with BMP2 alone or with BMP4 alone had larger diameters when compared to control (P < .05). In addition, all treatments promoted antrum formation and maintained a high viability rate through the growing period. The presence of BMP2, BMP4 or both together did not influence mRNA expression for the tested genes. However, the in vitro culture induces down-regulation for mRNA expression of BMPR1A. In conclusion, the addition of BMP2 or BMP4 alone in cultured medium promotes follicular growth and antrum formation in bovine follicles after 18 days of in vitro culture.

BMP2 expression in the endocardial lineage is required for AV endocardial cushion maturation and remodeling

Distal outgrowth, maturation and remodeling of the endocardial cushion mesenchyme in the atrioventricular (AV) canal are the essential morphogenetic events during four-chambered heart formation. Mesenchymalized AV endocardial cushions give rise to the AV valves and the membranous ventricular septum (VS). Failure of these processes results in several human congenital heart defects. Despite this clinical relevance, the mechanisms governing how mesenchymalized AV endocardial cushions mature and remodel into the membranous VS and AV valves have only begun to be elucidated. The role of BMP signaling in the myocardial and secondary heart forming lineage has been well studied; however, little is known about the role of BMP2 expression in the endocardial lineage. To fill this knowledge gap, we generated Bmp2 endocardial lineage-specific conditional knockouts (referred to as Bmp2 cKO^Endo) by crossing conditionally-targeted Bmp2^flox/flox mice with a Cre-driver line, Nfatc1^Cre, wherein Cre-mediated recombination was restricted to the endocardial cells and their mesenchymal progeny. Bmp2 cKO^Endo mouse embryos did not exhibit failure or delay in the initial AV endocardial cushion formation at embryonic day (ED) 9.5-11.5; however, significant reductions in AV cushion size were detected in Bmp2 cKO^Endo mouse embryos when compared to control embryos at ED13.5 and ED16.5. Moreover, deletion of Bmp2 from the endocardial lineage consistently resulted in membranous ventricular septal defects (VSDs), and mitral valve deficiencies, as evidenced by the absence of stratification of mitral valves at birth. Muscular VSDs were not found in Bmp2 cKO^Endo mouse hearts. To understand the underlying morphogenetic mechanisms leading to a decrease in cushion size, cell proliferation and cell death were examined for AV endocardial cushions. Phospho-histone H3 analyses for cell proliferation and TUNEL assays for apoptotic cell death did not reveal significant differences between control and Bmp2 cKO^Endo in AV endocardial cushions. However, mRNA expression of the extracellular matrix components, versican, Has2, collagen 9a1, and periostin was significantly reduced in Bmp2 cKO^Endo AV cushions. Expression of transcription factors implicated in the cardiac valvulogenesis, Snail2, Twist1 and Sox9, was also significantly reduced in Bmp2 cKO^Endo AV cushions. These data provide evidence that BMP2 expression in the endocardial lineage is essential for the distal outgrowth, maturation and remodeling of AV endocardial cushions into the normal membranous VS and the stratified AV valves.

Characterization of new bone morphogenetic protein (Bmp)-2 regulatory alleles

Bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) is a classical morphogen; a molecule that acts at a distance and whose concentration influences cell proliferation, differentiation, and apoptosis. Key events requiring precise Bmp2 regulation include heart specification and morphogenesis and neural development. In mesenchymal cells, the concentration of BMP2 influences myogenesis, adipogenesis, chondrogenesis, and osteogenesis. Because the amount, timing, and location of BMP2 synthesis influence pattern formation and organogenesis, the mechanisms that regulate Bmp2 are crucial. A sequence within the 3'UTR of the Bmp2 mRNA termed the "ultra-conserved sequence" (UCS) has been largely unchanged since fishes and mammals diverged. Cre-lox mediated deletion of the UCS in a reporter transgene revealed that the UCS may repress Bmp2 in proepicardium, epicardium, and epicardium-derived cells (EPDC) and in tissues with known epicardial contributions (coronary vessels and valves). The UCS also repressed the transgene in the aorta, outlet septum, posterior cardiac plexus, cardiac and extra-cardiac nerves, and neural ganglia. We used homologous recombination and conditional deletion to generate three new alleles in which the Bmp2 3'UTR was altered as follows: a UCS flanked by loxP sites with or without a neomycin resistance targeting vector, or a deleted UCS. Deletion of the UCS was associated with elevated Bmp2 mRNA and BMP signaling levels, reduced fitness, and embryonic malformations.

ISL1 is a major susceptibility gene for classic bladder exstrophy and a regulator of urinary tract development

Previously genome-wide association methods in patients with classic bladder exstrophy (CBE) found association with ISL1, a master control gene expressed in pericloacal mesenchyme. This study sought to further explore the genetics in a larger set of patients following-up on the most promising genomic regions previously reported. Genotypes of 12 markers obtained from 268 CBE patients of Australian, British, German Italian, Spanish and Swedish origin and 1,354 ethnically matched controls and from 92 CBE case-parent trios from North America were analysed. Only marker rs6874700 at the ISL1 locus showed association (p = 2.22 × 10⁻⁰⁸). A meta-analysis of rs6874700 of our previous and present study showed a p value of 9.2 × 10⁻¹⁹. Developmental biology models were used to clarify the location of ISL1 activity in the forming urinary tract. Genetic lineage analysis of Isl1-expressing cells by the lineage tracer mouse model showed Isl1-expressing cells in the urinary tract of mouse embryos at E10.5 and distributed in the bladder at E15.5. Expression of isl1 in zebrafish larvae staged 48 hpf was detected in a small region of the developing pronephros. Our study supports ISL1 as a major susceptibility gene for CBE and as a regulator of urinary tract development.

Epispadias and the associated embryopathies: genetic and developmental basis

The abnormalities in the urogenital organs are frequently observed as human developmental diseases. Among such diseases, the defects in the upper part of external genitalia are rather rare named epispadias. The cleft in the dorsal part of external genitalia often reaches to the urethra. In general, the urogenital abnormalities accompany defects in the adjacent tissues and organs. The ventral body wall and bladder can also be affected in the patients with dorsal defects of the external genitalia. Therefore, such multiple malformations are often classified as bladder exstrophy and epispadias complex (BEEC). Because of the lower frequency of such birth defects and their early embryonic development, animal models are required to analyze the pathogenic mechanisms and the functions of responsible genes. Mutant mouse analyses on various signal cascades for external genitalia and body wall development are increasingly performed. The genetic interactions between growth factors such as bone morphogenetic proteins (Bmp) and transcription factors such as Msx1/2 and Isl1 have been suggested to play roles for such organogenesis. The significance of epithelial-mesenchymal interaction (EMI) is suggested during development. In this review, we describe on such local interactions and developmental regulators. We also introduce some mutant mouse models displaying external genitalia-body wall abnormalities.

The Dorsal Mesenchymal Protrusion and the Pathogenesis of Atrioventricular Septal Defects

Congenital heart malformations are the most common type of defects found at birth. About 1% of infants are born with one or more heart defect on a yearly basis. Congenital Heart Disease (CHD) causes more deaths in the first year of life than any other congenital abnormality, and each year, nearly twice as many children die in the United States from CHD as from all forms of childhood cancers combined. Atrioventricular septal defects (AVSD) are congenital heart malformations affecting approximately 1 in 2000 live births. Babies born with an AVSD often require surgical intervention shortly after birth. However, even after successful surgery, these individuals typically have to deal with lifelong complications with the most common being a leaky mitral valve. In recent years the understanding of the molecular etiology and morphological mechanisms associated with the pathogenesis of AVSDs has significantly changed. Specifically, these studies have linked abnormal development of the Dorsal Mesenchymal Protrusion (DMP), a Second Heart Field-derived structure, to the development of this congenital defect. In this review we will be discuss some of the latest insights into the role of the DMP in the normal formation of the atrioventricular septal complex and in the pathogenesis of AVSDs.

Mainstream smoke and sidestream smoke affect the cardiac differentiation of mouse embryonic stem cells discriminately

Epidemiology studies suggest that maternal smoking and passive smoking have strongly resulted in the occurrence of congenital heart defects (CHD) in offspring. Cigarette smoke (CS) can be divided into mainstream smoke (MS) and sidestream smoke (SS); CS chemistry study indicates that significant differences exist in the composition of MS and SS. Therefore, MS and SS were suspected to process toxicity dissimilarly. However, much less was known about the difference in the developmental effects induced by MS and SS. In the current study, heart development was mimicked by mouse embryonic stem cells (ESCs) differentiation. After MS and SS exposure, by tracing the bone morphogenetic protein (BMP)-Smad4 signalling pathway, interruption of downstream gene expression was observed, including Gata4, Mef2c and Nkx2.5, as well as myosin heavy chain and myosin light chain. Specifically, SS caused inhibition of Gata4 expression, even at non-cytotoxic concentration. Further, SS-induced hypoacetylation in promoter regions of Gata4 reflected the orchestration of CS-gene modulation-epigenetic regulation. Even though SS induced apoptosis in ESC-derived cardiomyocytes, the partial clearance in cells with down-regulated Gata4 caused these cells to survive and undergo further differentiation, which laid potential risk for abnormal heart development. These data uncovered the difference between MS and SS on heart development preliminarily.

Establishment of Immortalized BMP2/4 Double Knock-Out Osteoblastic Cells Is Essential for Study of Osteoblast Growth, Differentiation, and Osteogenesis

Bone morphogenetic proteins 2 and 4 (BMP2/4) are essential for osteoblast differentiation and osteogenesis. Generation of a BMP2/4 dual knock‐out (^ko/ko) osteoblastic cell line is a valuable asset for studying effects of BMP2/4 on skeletal development. In this study, our goal was to create immortalized mouse deleted BMP2/4 osteoblasts by infecting adenoviruses with Cre recombinase and green fluorescent protein genes into immortalized murine floxed BMP2/4 osteoblasts. Transduced BMP2/4^ko/ko cells were verified by green immunofluorescence and PCR. BMP2/4^ko/ko osteoblasts exhibited small size, slow cell proliferation rate and cell growth was arrested in G1 and G2 phases. Expression of bone‐relate genes was reduced in the BMP2/4^ko/ko cells, resulting in delay of cell differentiation and mineralization. Importantly, extracellular matrix remodeling was impaired in the BMP2/4^ko/ko osteoblasts as reflected by decreased Mmp‐2 and Mmp‐9 expressions. Cell differentiation and mineralization were rescued by exogenous BMP2 and/or BMP4. Therefore, we for the first time described establishment of an immortalized deleted BMP2/4 osteoblast line useful for study of mechanisms in regulating osteoblast lineages. J. Cell. Physiol. 231: 1189–1198, 2016. © 2015 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Endothelium-derived essential signals involved in pancreas organogenesis

Endothelial cells (ECs) are essential for pancreas differentiation, endocrine specification, and endocrine function. They are also involved in the physiopathology of type 1 and type 2 diabetes. During embryogenesis, aortic ECs provide specific factors that maintain the expression of key genes for pancreas development such as pancreatic and duodenal homeobox-1. Other unknown factors are also important for pancreatic endocrine specification and formation of insulin-producing beta cells. Endocrine precursors proliferate interspersed with ductal cells and exocrine precursors and, at some point of development, these endocrine precursors migrate to pancreatic mesenchyme and start forming the islets of Langerhans. By the end of the gestation and close to birth, these islets contain immature beta cells with the capacity to express vascular endothelial growth factor and therefore to recruit ECs from the surrounding microenvironment. ECs in turn produce factors that are essential to maintain insulin secretion in pancreatic beta cells. Once assembled, a cross talk between endocrine cells and ECs maintain the integrity of islets toward an adequate function during the whole life of the adult individual. This review will focus in the EC role in the differentiation and maturation of pancreatic beta cells during embryogenesis as well as the current knowledge about the involvement of endothelium to derive pancreatic beta cells in vitro from mouse or human pluripotent stem cells.

Signaling molecules, transcription growth factors and other regulators revealed from in-vivo and in-vitro models for the regulation of cardiac development

Several in-vivo heart developmental models have been applied to decipher the cardiac developmental patterning encompassing early, dorsal, cardiac and visceral mesoderm as well as various transcription factors such as Gata, Hand, Tin, Dpp, Pnr. The expression of cardiac specific transcription factors, such as Gata4, Tbx5, Tbx20, Tbx2, Tbx3, Mef2c, Hey1 and Hand1 are of fundamental significance for the in-vivo cardiac development. Not only the transcription factors, but also the signaling molecules involved in cardiac development were conserved among various species. Enrichment of the bone morphogenic proteins (BMPs) in the anterior lateral plate mesoderm is essential for the initiation of myocardial differentiation and the cardiac developmental process. Moreover, the expression of a number of cardiac transcription factors and structural genes initiate cardiac differentiation in the medial mesoderm. Other signaling molecules such as TGF-beta, IGF-1/2 and the fibroblast growth factor (FGF) play a significant role in cardiac repair/regeneration, ventricular heart development and specification of early cardiac mesoderm, respectively. The role of the Wnt signaling in cardiac development is still controversial discussed, as in-vitro results differ dramatically in relation to the animal models. Embryonic stem cells (ESC) were utilized as an important in-vitro model for the elucidation of the cardiac developmental processes since they can be easily manipulated by numerous signaling molecules, growth factors, small molecules and genetic manipulation. Finally, in the present review the dynamic role of the long noncoding RNA and miRNAs in the regulation of cardiac development are summarized and discussed.

Bone morphogenetic protein-2 antagonizes bone morphogenetic protein-4 induced cardiomyocyte hypertrophy and apoptosis

Our previous work showed that the expression of bone morphogenetic protein-4 (BMP4) was up-regulated in pathological cardiac hypertrophy models and BMP4 induced cardiomyocyte hypertrophy and apoptosis. Bone morphogenetic protein-2 (BMP2) and BMP4 share greater than 80% amino acid homology and there exists an interaction between BMP2 and BMP4, so the aim of the present study was to elucidate the changes of BMP2 in the cardiac hypertrophy models and the effects of BMP2 on BMP4-induced cardiomyocyte hypertrophy and apoptosis. The in vivo cardiac hypertrophy models were induced by pressure-overload and swimming exercise in mice. BMP2 mRNA and protein expressions increased in pressure-overload and swimming-exercise induced cardiac hypertrophy. BMP2 itself did not elicit cardiomyocyte hypertrophy and apoptosis, but antagonized BMP4-induced cardiomyocyte hypertrophy and apoptosis. BMP2 stimulated Akt in cardiomyocytes and Akt inhibitor prevented the antagonism of BMP2 on BMP4-induced cardiomyocyte apoptosis. Furthermore, BMP2 inhibited BMP4-induced JNK activation in cardiomyocytes. In conclusion, BMP2 antagonizes BMP4-induced cardiomyocyte hypertrophy and apoptosis. The anti-apoptotic effects of BMP2 on BMP4-induced cardiomyocyte apoptosis might be through activating Akt and inhibiting JNK activation.

Combination of BMP-2 and 5-AZA is advantageous in rat bone marrow-derived mesenchymal stem cells differentiation into cardiomyocytes

Bone morphogenetic protein-2 (BMP-2) has a crucial role in the development of cardiogenesis, and is used in inducing bone marrow mesenchymal stem cells (BMMSCs) to differentiate into cardiomyocytes. We have examined a combination of BMP-2 and 5-azacytidine (5-AZA) in inducing these differentiation effects. BMMSCs were collected and purified from bone marrow of 4-week-old Sprague-Dawley (SD) rats by density-gradient centrifugation and differential attachment. The fourth passage subculture of BMMSCs, selected by cytometry for purity and identification, was divided into four groups: a control group, BMP-2 treated, 5-AZA treated, and a combination of BMP-2 and 5-AZA treatment. Expression of cardiac Troponin I (cTnI) and Connexin 43 (CX-43) in BMMSCs after induction were detected by immunofluorescence and Western blot. Flow cytometry analysis was used for differentiation rates and apoptosis of induced BMMSCs, through the expression of cardiac Troponin T (cTnT) and Annexin V-FITC & PI kit, respectively. BMP-2 can ameliorate apoptosis of BMMSCs caused by 5-AZA and promote the differentiation of BMMSCs into cardiomyocyte-like cells. Thus a combination of BMP-2 and 5-AZA can significantly improve the cardiac differentiation with fewer cell damage effects, making it a safe and effective method of induction in vitro.

Bone morphogenetic protein-2/-4 upregulation promoted by endothelial cells in coculture enhances mouse embryoid body differentiation

Endothelial cells (ECs) provide inductive signals for cell differentiation in vivo. However, it is unknown if these cells promote such differentiation in vitro and the signals involved. We investigated whether ECs are able to enhance the differentiation of the three germ layers and the underlying mechanisms. We established a coculture system of mouse embryoid bodies (EBs) and ECs. Then, we analyzed the expression of markers representative of the three germ layers, such as PDX-1, proinsulin, insulin1 (endoderm), nestin, neurofilament light (ectoderm), CD31, cardiotin, and cardiac troponin I (mesoderm) in EBs cultured alone (controls) or with ECs. A significant increase of these markers was observed in EBs cocultured with ECs compared to controls. The cocultured EBs also exhibited more robust vascular networks similar to those EBs treated with bone morphogenetic protein-2 or -4 (BMP-2 or -4). Therefore, the role of these peptides in the differentiation was investigated. We found a significant upregulation of BMP-2/-4 and BMP receptor 1A in EBs treated with EC conditioned medium (EC-CM) at early or middle stages of EB development. Recombinant human BMP-2 and BMP-4 exerted similar effects than EC-CM in the expression of BMPs or in the upregulation of the three germ layer specific markers. BMP-2/-4 antagonists, such as noggin and chordin-like-1, respectively inhibited the EC-CM inductive effects. These results demonstrate that ECs enhance the differentiation in vitro of cells that derived from the three germ layers and that BMP-2/-4 play a central role in this process.

Co-ordinating Notch, BMP, and TGF-β signaling during heart valve development

Congenital heart defects affect approximately 1-5 % of human newborns each year, and of these cardiac defects 20-30 % are due to heart valve abnormalities. Recent literature indicates that the key factors and pathways that regulate valve development are also implicated in congenital heart defects and valve disease. Currently, there are limited options for treatment of valve disease, and therefore having a better understanding of valve development can contribute critical insight into congenital valve defects and disease. There are three major signaling pathways required for early specification and initiation of endothelial-to-mesenchymal transformation (EMT) in the cardiac cushions: BMP, TGF-β, and Notch signaling. BMPs secreted from the myocardium set up the environment for the overlying endocardium to become activated; Notch signaling initiates EMT; and both BMP and TGF-β signaling synergize with Notch to promote the transition of endothelia to mesenchyme and the mesenchymal cell invasiveness. Together, these three essential signaling pathways help form the cardiac cushions and populate them with mesenchyme and, consequently, set off the cascade of events required to develop mature heart valves. Furthermore, integration and cross-talk between these pathways generate highly stratified and delicate valve leaflets and septa of the heart. Here, we discuss BMP, TGF-β, and Notch signaling pathways during mouse cardiac cushion formation and how they together produce a coordinated EMT response in the developing mouse valves.

Cardiac responses to 24 hrs hyperoxia in Bmp2 and Bmp4 heterozygous mice

BACKGROUND

Hyperoxia or clinical oxygen (O2) therapy is known to result in increased oxidative burden. Therefore, understanding susceptibility to hyperoxia exposure is clinically important. Bone morphogenetic proteins (BMPs) 2 and 4 are involved in cardiac development and may influence responses to hyperoxia.

METHODS

Bmp2(+/)(-). Bmp4(+/)(-) and wild-type mice were exposed to hyperoxia (100% O2) for 24 hrs. Electrocardiograms (ECG) were recorded before and during exposure by radio-telemetry.

RESULTS

At baseline, a significantly higher low frequency (LF) and total power (TP) heart rate variability (HRV) were found in Bmp2(+/)(-) mice only (p < 0.05). Twenty-four hours hyperoxia-induced strain-independent reductions in heart rate, QTcB and ST-interval and increases in QRS, LF HRV and standard deviation of RR-intervals were observed. In Bmp4(+/)(-) mice only, increased PR-interval (PR-I) (24 hrs), P-wave duration (P-d; 18 and 21-24 hrs), PR-I minus P-d (PR - Pd; 24 hrs) and root of the mean squared differences of successive RR-intervals (24 hrs) were found during hyperoxia (p < 0.05).

DISCUSSION

Elevated baseline LF and TP HRV in Bmp2(+/)(-) mice suggests an altered autonomic nervous system regulation of cardiac function in these mice. However, this was not related to strain specific differences in responses to 24 hrs hyperoxia. During hyperoxia, Bmp4(+/-) mice were the most susceptible in terms of atrioventricular conduction changes and risk of atrial fibrillation, which may have important implications for patients treated with O2 who also harbor Bmp4 mutations. This study demonstrates significant ECG and HRV responses to 24 hrs hyperoxia in mice, which highlights the need to further work on the genetic mechanisms associated with cardiac susceptibility to hyperoxia.

Bone morphogenetic protein-4 mediates cardiac hypertrophy, apoptosis, and fibrosis in experimentally pathological cardiac hypertrophy

Identifying the key factor mediating pathological cardiac hypertrophy is critically important for developing the strategy to protect against heart failure. Bone morphogenetic protein-4 (BMP4) is a mechanosensitive and proinflammatory gene. In this study, we investigated the role of BMP4 in cardiac hypertrophy, apoptosis, and fibrosis in experimentally pathological cardiac hypertrophy. The in vivo pathological cardiac hypertrophy models were induced by pressure-overload and angiotensin (Ang) II constant infusion in mice, and the in vitro model was induced by Ang II exposure to cultured cardiomyocytes. The expression of BMP4 increased in pressure overload, Ang II constant infusion-induced pathological cardiac hypertrophy, but not in swimming exercise-induced physiological cardiac hypertrophy in mice. BMP4 expression also increased in Ang II-induced cardiomyocyte hypertrophy in vitro. In turn, BMP4 induced cardiomyocyte hypertrophy, apoptosis, and cardiac fibrosis, and these pathological consequences were inhibited by the treatment with BMP4 inhibitors noggin and DMH1. Moreover, Ang II-induced cardiomyocyte hypertrophy was inhibited by BMP4 inhibitors. The underlying mechanism that BMP4-induced cardiomyocyte hypertrophy and apoptosis was through increasing NADPH oxidase 4 expression and reactive oxygen species-dependent pathways. Lentivirus-mediated overexpression of BMP4 recapitulated hypertrophy and apoptosis in cultured cardiomyocytes. BMP4 inhibitor DMH1 inhibited pressure overload-induced cardiac hypertrophy in mice in vivo. The plasma BMP4 level of heart failure patients was increased compared with that of subjects without heart failure. In summary, we conclude that BMP4 is a mediator and novel therapeutic target for pathological cardiac hypertrophy.

BMPER regulates cardiomyocyte size and vessel density in vivo

BACKGROUND

BMPER, an orthologue of Drosophila melanogaster Crossveinless-2, is a secreted factor that regulates bone morphogenetic protein activity in endothelial cell precursors and during early cardiomyocyte differentiation. Although previously described in the heart, the role of BMPER in cardiac development and function remain unknown.

METHODS

BMPER-deficient hearts were phenotyped histologically and functionally using echocardiography and Doppler analysis. Since BMPER -/- mice die perinatally, adult BMPER +/- mice were challenged to pressure-overload-induced cardiac hypertrophy and hindlimb ischemia to determine changes in angiogenesis and regulation of cardiomyocyte size.

RESULTS

We identify for the first time the cardiac phenotype associated with BMPER haploinsufficiency. BMPER messenger RNA and protein are present in the heart during cardiac development through at least E14.5 but is lost by E18.5. BMPER +/- ventricles are thinner and less compact than sibling wild-type hearts. In the adult, BMPER +/- hearts present with decreased anterior and posterior wall thickness, decreased cardiomyocyte size and an increase in cardiac vessel density. Despite these changes, BMPER +/- mice respond to pressure-overload-induced cardiac hypertrophy challenge largely to the same extent as wild-type mice.

CONCLUSION

BMPER appears to play a role in regulating both vessel density and cardiac development in vivo; however, BMPER haploinsufficiency does not result in marked effects on cardiac function or adaptation to pressure overload hypertrophy.

Cleft palate in a multigenerational family with a microdeletion of 20p12.3 involving BMP2

Cleft palate (CP) is a frequent and recognizable birth defect attributed to a variety of etiologies including genetic abnormalities and environmental exposures. Bone morphogenetic proteins (BMPs) are involved in embryonic signaling important for a number of developmental processes including bone formation and palate morphogenesis. Recently, haploinsufficiency of BMP2 was associated with syndromic forms of CP. Here, we report on a multigenerational family with a history of CP as a result of a 2.3 Mb deletion of chromosome 20p12.3, including the BMP2 gene. In addition to a submucous CP, the proband's clinical phenotype included failure to thrive (FTT), global developmental delays (DD), and dysmorphic features. The affected father exhibited an overt CP, with a facial gestalt and minor dysmorphic features similar to the proband. The father was otherwise healthy with no history of FTT or DD, suggesting high penetrance, yet variable expressivity for haploinsufficiency of BMP2. The findings presented here provide further evidence for the role of BMP2 in syndromic forms of CP.

Endothelial cells in co-culture enhance embryonic stem cell differentiation to pancreatic progenitors and insulin-producing cells through BMP signaling

Endothelial cells (ECs) represent the major component of the embryonic pancreatic niche and play a key role in the differentiation of insulin-producing β cells in vivo. However, it is unknown if ECs promote such differentiation in vitro. We investigated whether interaction of ECs with mouse embryoid bodies (EBs) in culture promotes differentiation of pancreatic progenitors and insulin-producing cells and the mechanisms involved. We developed a co-culture system of mouse EBs and human microvascular ECs (HMECs). An increase in the expression of the pancreatic markers PDX-1, Ngn3, Nkx6.1, proinsulin, GLUT-2, and Ptf1a was observed at the interface between EBs and ECs (EB-EC). No expression of these markers was found at the periphery of EBs cultured without ECs or those co-cultured with mouse embryonic fibroblasts (MEFs). At EB-EC interface, proinsulin and Nkx6.1 positive cells co-expressed phospho-Smad1/5/8 (pSmad1/5/8). Therefore, EBs were treated with HMEC conditioned media (HMEC-CM) suspecting soluble factors involved in bone morphogenetic protein (BMP) pathway activation. Upregulation of PDX-1, Ngn3, Nkx6.1, insulin-1, insulin-2, amylin, SUR1, GKS, and amylase as well as down-regulation of SST were detected in treated EBs. In addition, higher expression of BMP-2/-4 and their receptor (BMPR1A) were also found in these EBs. Recombinant human BMP-2 (rhBMP-2) mimicked the effects of the HMEC-CM on EBs. Noggin (NOG), a BMP antagonist, partially inhibited these effects. These results indicate that the differentiation of EBs to pancreatic progenitors and insulin-producing cells can be enhanced by ECs in vitro and that BMP pathway activation is central to this process.

Signaling pathways in early cardiac development

Cardiomyocyte differentiation is a complex multistep process requiring the proper temporal and spatial integration of multiple signaling pathways. Previous embryological and genetic studies have identified a number of signaling pathways that are critical to mediate the initial formation of the mesoderm and its allocation to the cardiomyocyte lineage. It has become clear that some of these signaling networks work autonomously, in differentiating myocardial cells whereas others work non-autonomously, in neighboring tissues, to regulate cardiac differentiation indirectly. Here, we provide an overview of three signaling networks that mediate cardiomyocyte specification and review recent insights into their specific roles in heart development. In addition, we demonstrate how systems level, 'omic approaches' and other high-throughput techniques such as small molecules screens are beginning to impact our understanding of cardiomyocyte specification and, to identify novel signaling pathways involved in this process. In particular, it now seems clear that at least one chemokine receptor CXCR4 is an important marker for cardiomyocyte progenitors and may play a functional role in their differentiation. Finally, we discuss some gaps in our current understanding of early lineage selection that could be addressed by various types of omic analysis.

Characterization of microvascular endothelial cells isolated from the dermis of adult mouse tails

Dermal microvascular endothelial cells (DMECs) play an important role in physiological and pathophysiological processes such as wound healing, cell differentiation, antigen-presentation, inflammation, tumor metastasis, and diabetes. The study of these processes requires a suitable and accessible in vitro model, such as murine DMECs (mDMECs). However, since these cells are difficult to isolate and propagate, some of their properties are not fully characterized. We isolated these cells from C57BL/6J adult mouse tail skin and purified them using magnetic sorting. Then, we tested several culture conditions and oxygen concentrations for mDMEC growth and propagation. After obtaining optimal culture conditions, we characterized the expression of EC markers and compared such expression with an established murine microvascular EC line (EOMA). Our results indicate that mDMECs isolated from mouse tails expressed most of the characteristic EC markers such as von Willebrand Factor (vWF), CD31, Tie1, Tie2, ANGPT1, ANGPT2, FLK-1, FLT-1, and VEGF-A. Further characterization demonstrated that these cells also expressed proteins involved in organogenesis such as bone morphogenetic proteins-2, -4 (BMP-2/-4), and their receptor (BMPR1A). Surprisingly, higher expression of vWF, ANGPT1, and BMP-2 was observed in mDMECs compared to EOMA cells. For mDMEC in vitro propagation, we found a twofold increase in cell proliferation in cells that grew at 1% O(2) compared to those cells that grew at standard 20% O(2.) Therefore, the method described herein for mDMECs isolation and propagation allowed us to analyze in more detail their biological properties that can be relevant for the study of pathological processes using mouse models.

An autonomous BMP2 regulatory element in mesenchymal cells

BMP2 is a morphogen that controls mesenchymal cell differentiation and behavior. For example, BMP2 concentration controls the differentiation of mesenchymal precursors into myocytes, adipocytes, chondrocytes, and osteoblasts. Sequences within the 3'untranslated region (UTR) of the Bmp2 mRNA mediate a post-transcriptional block of protein synthesis. Interaction of cell and developmental stage-specific trans-regulatory factors with the 3'UTR is a nimble and versatile mechanism for modulating this potent morphogen in different cell types. We show here, that an ultra-conserved sequence in the 3'UTR functions independently of promoter, coding region, and 3'UTR context in primary and immortalized tissue culture cells and in transgenic mice. Our findings indicate that the ultra-conserved sequence is an autonomously functioning post-transcriptional element that may be used to modulate the level of BMP2 and other proteins while retaining tissue specific regulatory elements.

BMP signaling in congenital heart disease: new developments and future directions

Congenital heart malformations are the most common of all congenital human birth anomalies. During the past decade, research with zebrafish, chick, and mouse models have elucidated many fundamental genetic pathways that govern early cardiac patterning and differentiation. This review highlights the roles of the bone morphogenetic protein (BMP) signaling pathway in cardiogenesis and how defective BMP signals can disrupt the intricate steps of cardiac formation and cause congenital heart defects.

Transforming growth factor beta2 is negatively regulated by endogenous retinoic acid during early heart morphogenesis

Vitamin A-deficient (VAD) quail embryos lack the vitamin A-active form, retinoic acid (RA) and are characterized by a phenotype that includes a grossly abnormal cardiovascular system that can be rescued by RA. Here we report that the transforming growth factor, TGFbeta2 is involved in RA-regulated cardiovascular development. In VAD embryos TGFbeta2 mRNA and protein expression are greatly elevated. The expression of TGFbeta receptor II is also elevated in VAD embryos but is normalized by treatment with TGFbeta2-specific antisense oligonucleotides (AS). Administration of this AS or an antibody specific for TGFbeta2 to VAD embryos normalizes posterior heart development and vascularization, while the administration of exogenous active TGFbeta2 protein to normal quail embryos mimics the excessive TGFbeta2 status of VAD embryos and induces VAD cardiovascular phenotype. In VAD embryos pSmad2/3 and pErk1 are not activated, while pErk2 and pcRaf are elevated and pSmad1/5/8 is diminished. We conclude that in the early avian embryo TGFbeta2 has a major role in the retinoic acid-regulated posterior heart morphogenesis for which it does not use Smad2/3 pathways, but may use other signaling pathways. Importantly, we conclude that retinoic acid is a critical negative physiological regulator of the magnitude of TGFbeta2 signals during vertebrate heart formation.

Mice lacking Alkbh1 display sex-ratio distortion and unilateral eye defects

Background

Eschericia coli AlkB is a 2-oxoglutarate- and iron-dependent dioxygenase that reverses alkylated DNA damage by oxidative demethylation. Mouse AlkB homolog 1 (Alkbh1) is one of eight members of the newly discovered family of mammalian dioxygenases.

Methods and Findings

In the present study we show non-Mendelian inheritance of the Alkbh1 targeted allele in mice. Both Alkbh1^−/− and heterozygous Alkbh1^+/− offspring are born at a greatly reduced frequency. Additionally, the sex-ratio is considerably skewed against female offspring, with one female born for every three to four males. Most mechanisms that cause segregation distortion, act in the male gametes and affect male fertility. The skewing of the sexes appears to be of paternal origin, and might be set in the pachythene stage of meiosis during spermatogenesis, in which Alkbh1 is upregulated more than 10-fold. In testes, apoptotic spermatids were revealed in 5–10% of the tubules in Alkbh1^−/− adults. The deficiency of Alkbh1 also causes misexpression of Bmp2, 4 and 7 at E11.5 during embryonic development. This is consistent with the incompletely penetrant phenotypes observed, particularly recurrent unilateral eye defects and craniofacial malformations.

Conclusions

Genetic and phenotypic assessment suggests that Alkbh1 mediates gene regulation in spermatogenesis, and that Alkbh1 is essential for normal sex-ratio distribution and embryonic development in mice.

Myocardial deletion of Smad4 using a novel α skeletal muscle actin Cre recombinase transgenic mouse causes misalignment of the cardiac outflow tract

SMAD4 acts as the converging point for TGFβ and BMP signaling in heart development. Here, we investigated the role of SMAD4 in heart development using a novel α skeletal muscle actin Cre recombinase (MuCre) transgenic mouse strain. Lineage tracing using MuCre/ROSA26^LacZ reporter mice indicated strong Cre-recombinase expression in developing and adult heart and skeletal muscles. In heart development, significant MuCre expression was noted at E11.5 in the atrial, ventricular, outflow tract and atrioventricular canal myocardium, but not in the endocardial cushions. MuCre-driven conditional deletion of Smad4 in mice caused double outlet right ventricle (DORV), ventricular septal defect (VSD), impaired trabeculation and thinning of ventricular myocardium, and mid-gestational embryonic lethality. In conclusion, MuCre mice effectively delete genes in both heart and skeletal muscles, thus enabling the discovery that myocardial Smad4 deletion causes misalignment of the outflow tract and DORV.

A comparative analysis of extra-embryonic endoderm cell lines

Prior to gastrulation in the mouse, all endodermal cells arise from the primitive endoderm of the blastocyst stage embryo. Primitive endoderm and its derivatives are generally referred to as extra-embryonic endoderm (ExEn) because the majority of these cells contribute to extra-embryonic lineages encompassing the visceral endoderm (VE) and the parietal endoderm (PE). During gastrulation, the definitive endoderm (DE) forms by ingression of cells from the epiblast. The DE comprises most of the cells of the gut and its accessory organs. Despite their different origins and fates, there is a surprising amount of overlap in marker expression between the ExEn and DE, making it difficult to distinguish between these cell types by marker analysis. This is significant for two main reasons. First, because endodermal organs, such as the liver and pancreas, play important physiological roles in adult animals, much experimental effort has been directed in recent years toward the establishment of protocols for the efficient derivation of endodermal cell types in vitro. Conversely, factors secreted by the VE play pivotal roles that cannot be attributed to the DE in early axis formation, heart formation and the patterning of the anterior nervous system. Thus, efforts in both of these areas have been hampered by a lack of markers that clearly distinguish between ExEn and DE. To further understand the ExEn we have undertaken a comparative analysis of three ExEn-like cell lines (END2, PYS2 and XEN). PYS2 cells are derived from embryonal carcinomas (EC) of 129 strain mice and have been characterized as parietal endoderm-like [1], END2 cells are derived from P19 ECs and described as visceral endoderm-like, while XEN cells are derived from blastocyst stage embryos and are described as primitive endoderm-like. Our analysis suggests that none of these cell lines represent a bona fide single in vivo lineage. Both PYS2 and XEN cells represent mixed populations expressing markers for several ExEn lineages. Conversely END2 cells, which were previously characterized as VE-like, fail to express many markers that are widely expressed in the VE, but instead express markers for only a subset of the VE, the anterior visceral endoderm. In addition END2 cells also express markers for the PE. We extended these observations with microarray analysis which was used to probe and refine previously published data sets of genes proposed to distinguish between DE and VE. Finally, genome-wide pathway analysis revealed that SMAD-independent TGFbeta signaling through a TAK1/p38/JNK or TAK1/NLK pathway may represent one mode of intracellular signaling shared by all three of these lines, and suggests that factors downstream of these pathways may mediate some functions of the ExEn. These studies represent the first step in the development of XEN cells as a powerful molecular genetic tool to study the endodermal signals that mediate the important developmental functions of the extra-embryonic endoderm. Our data refine our current knowledge of markers that distinguish various subtypes of endoderm. In addition, pathway analysis suggests that the ExEn may mediate some of its functions through a non-classical MAP Kinase signaling pathway downstream of TAK1.

Gene expression profiling in the fetal cardiac tissue after folate and low-dose trichloroethylene exposure

BACKGROUND

Previous studies show gene expression alterations in rat embryo hearts and cell lines that correspond to the cardio-teratogenic effects of trichloroethylene (TCE) in animal models. One potential mechanism of TCE teratogenicity may be through altered regulation of calcium homeostatic genes with a corresponding inhibition of cardiac function. It has been suggested that TCE may interfere with the folic acid/methylation pathway in liver and kidney and alter gene regulation by epigenetic mechanisms. According to this hypothesis, folate supplementation in the maternal diet should counteract TCE effects on gene expression in the embryonic heart.

APPROACH

To identify transcriptional targets altered in the embryonic heart after exposure to TCE, and possible protective effects of folate, we used DNA microarray technology to profile gene expression in embryonic mouse hearts with maternal TCE exposure and dietary changes in maternal folate.

RESULTS

Exposure to low doses of TCE (10 ppb) caused extensive alterations in transcripts encoding proteins involved in transport, ion channel, transcription, differentiation, cytoskeleton, cell cycle, and apoptosis. Exogenous folate did not offset the effects of TCE exposure on normal gene expression, and both high and low levels of folate produced additional significant changes in gene expression.

CONCLUSIONS

A mechanism by which TCE induces a folate deficiency does not explain altered gene expression patterns in the embryonic mouse heart. The data further suggest that use of folate supplementation, in the presence of this toxin, may be detrimental and not protective of the developing embryo.