Anti-apoptotic effects of IGF-I on mortality and dysmorphogenesis in tbx5-deficient zebrafish embryos

BACKGROUND

Tbx5 deficiency in zebrafish causes several abnormal phenotypes of the heart and pectoral fins. It has been reported that exogenous human growth hormone can enhance expression of downstream mediators in the growth hormone and insulin-like growth factor I (IGF-I) pathway and partially restore dysmorphogenesis in tbx5 morphants. This study aimed to further evaluate the effects of IGF-I on cell apoptosis and dysmorphogenesis in zebrafish embryos deficient for tbx5.

RESULTS

Among the five studied groups of zebrafish embryos (wild-type embryos [WT], tbx5 morphants [MO], mismatched tbx5 morpholino-treated wild-type embryos [MIS], IGF-I-treated wild-type embryos [WTIGF1], and IGF-I-treated tbx5 morphants [MOIGF1]), the expression levels of the ifg1, igf1-ra, ifg-rb, erk1, and akt2 genes as well as the ERK and AKT proteins were significantly reduced in the MO group, but were partially restored in the MOIGF1 group. These expression levels remained normal in the WT, MIS, and WTIGF1 groups. Exogenous human IGF-I also reduced the incidence of phenotypic anomalies, decreased the expression levels of apoptotic genes and proteins, suppressed cell apoptosis, and improved survival of the MOIGF1 group.

CONCLUSIONS

These results suggest that IGF-I has an anti-apoptotic protective effect in zebrafish embryos with tbx5 deficiency.

Ablation of miR-10b Suppresses Oncogene-Induced Mammary Tumorigenesis and Metastasis and Reactivates Tumor-Suppressive Pathways

The invasive and metastatic properties of many human tumors have been associated with upregulation of the miRNA miR-10b, but its functional contributions in this setting have not been fully unraveled. Here, we report the generation of miR-10b-deficient mice, in which miR-10b is shown to be largely dispensable for normal development but critical to tumorigenesis. Loss of miR-10b delays oncogene-induced mammary tumorigenesis and suppresses epithelial-mesenchymal transition, intravasation, and metastasis in a mouse model of metastatic breast cancer. Among the target genes of miR-10b, the tumor suppressor genes Tbx5 and Pten and the metastasis suppressor gene Hoxd10 are significantly upregulated by miR-10b deletion. Mechanistically, miR-10b promotes breast cancer cell proliferation, migration, and invasion through inhibition of the expression of the transcription factor TBX5, leading to repression of the tumor suppressor genes DYRK1A and PTEN In clinical specimens of breast cancer, the expression of TBX5, HOXD10, and DYRK1A correlates with relapse-free survival and overall survival outcomes in patients. Our results establish miR-10b as an oncomiR that drives metastasis, termed a metastamiR, and define the set of critical tumor suppressor mechanisms it overcomes to drive breast cancer progression. Cancer Res; 76(21); 6424-35. ©2016 AACR.

Molecular shifts in limb identity underlie development of feathered feet in two domestic avian species

Birds display remarkable diversity in the distribution and morphology of scales and feathers on their feet, yet the genetic and developmental mechanisms governing this diversity remain unknown. Domestic pigeons have striking variation in foot feathering within a single species, providing a tractable model to investigate the molecular basis of skin appendage differences. We found that feathered feet in pigeons result from a partial transformation from hindlimb to forelimb identity mediated by cis-regulatory changes in the genes encoding the hindlimb-specific transcription factor Pitx1 and forelimb-specific transcription factor Tbx5. We also found that ectopic expression of Tbx5 is associated with foot feathers in chickens, suggesting similar molecular pathways underlie phenotypic convergence between these two species. These results show how changes in expression of regional patterning genes can generate localized changes in organ fate and morphology, and provide viable molecular mechanisms for diversity in hindlimb scale and feather distribution.

Generating and evaluating a ranked candidate gene list for potential vertebrate heart field regulators

The vertebrate heart develops from two distinct lineages of cardiomyocytes that arise from the first and second heart fields (FHF and SHF, respectively). The FHF forms the primitive heart tube, while adding cells from the SHF allows elongation at both poles of the tube. Initially seen as an exclusive characteristic of higher vertebrates, recent work has demonstrated the presence of a distinct FHF and SHF in lower vertebrates, including zebrafish. We found that key transcription factors that regulate septation and chamber formation in higher vertebrates, including Tbx5 and Pitx2, influence relative FHF and SHF contributions to the zebrafish heart tube. To identify molecular modulators of heart field migration, we used microarray-based expression profiling following inhibition of tbx5a and pitx2ab in embryonic zebrafish (Mosimann & Panakova, et al, 2015; GSE70750). Here, we describe in more detail the procedure used to process, prioritize, and analyze the expression data for functional enrichment.

Distinct tissue-specific requirements for the zebrafish tbx5 genes during heart, retina and pectoral fin development

The transcription factor Tbx5 is expressed in the developing heart, eyes and anterior appendages. Mutations in human TBX5 cause Holt-Oram syndrome, a condition characterized by heart and upper limb malformations. Tbx5-knockout mouse embryos have severely impaired forelimb and heart morphogenesis from the earliest stages of their development. However, zebrafish embryos with compromised tbx5 function show a complete absence of pectoral fins, while heart development is disturbed at significantly later developmental stages and eye development remains to be thoroughly analysed. We identified a novel tbx5 gene in zebrafish--tbx5b--that is co-expressed with its paralogue, tbx5a, in the developing eye and heart and hypothesized that functional redundancy could be occurring in these organs in embryos with impaired tbx5a function. We have now investigated the consequences of tbx5a and/or tbx5b downregulation in zebrafish to reveal that tbx5 genes have essential roles in the establishment of cardiac laterality, dorsoventral retina axis organization and pectoral fin development. Our data show that distinct relationships between tbx5 paralogues are required in a tissue-specific manner to ensure the proper morphogenesis of the three organs in which they are expressed. Furthermore, we uncover a novel role for tbx5 genes in the establishment of correct heart asymmetry in zebrafish embryos.

The paracrine effect of exogenous growth hormone alleviates dysmorphogenesis caused by tbx5 deficiency in zebrafish (Danio rerio) embryos

BACKGROUND

Dysmorphogenesis and multiple organ defects are well known in zebrafish (Danio rerio) embryos with T-box transcription factor 5 (tbx5) deficiencies, mimicking human Holt-Oram syndrome.

METHODS

Using an oligonucleotide-based microarray analysis to study the expression of special genes in tbx5 morphants, we demonstrated that GH and some GH-related genes were markedly downregulated. Zebrafish embryos microinjected with tbx5-morpholino (MO) antisense RNA and mismatched antisense RNA in the 1-cell stage served as controls, while zebrafish embryos co-injected with exogenous growth hormone (GH) concomitant with tbx5-MO comprised the treatment group.

RESULTS

The attenuating effects of GH in tbx5-MO knockdown embryos were quantified and observed at 24, 30, 48, 72, and 96 h post-fertilization. Though the understanding of mechanisms involving GH in the tbx5 functioning complex is limited, exogenous GH supplied to tbx5 knockdown zebrafish embryos is able to enhance the expression of downstream mediators in the GH and insulin-like growth factor (IGF)-1 pathway, including igf1, ghra, and ghrb, and signal transductors (erk1, akt2), and eventually to correct dysmorphogenesis in various organs including the heart and pectoral fins. Supplementary GH also reduced apoptosis as determined by a TUNEL assay and decreased the expression of apoptosis-related genes and proteins (bcl2 and bad) according to semiquantitative reverse-transcription polymerase chain reaction and immunohistochemical analysis, respectively, as well as improving cell cycle-related genes (p27 and cdk2) and cardiomyogenetic genes (amhc, vmhc, and cmlc2).

CONCLUSIONS

Based on our results, tbx5 knockdown causes a pseudo GH deficiency in zebrafish during early embryonic stages, and supplementation of exogenous GH can partially restore dysmorphogenesis, apoptosis, cell growth inhibition, and abnormal cardiomyogenesis in tbx5 knockdown zebrafish in a paracrine manner.

Stat3 directly controls the expression of Tbx5, Nkx2.5, and GATA4 and is essential for cardiomyocyte differentiation of P19CL6 cells

The transcription factor Stat3 (signal transducer and activator of transcription 3) mediates many physiological processes, including embryogenesis, stem cell self-renewal, and postnatal survival. In response to gp130 receptor activation, Stat3 becomes phosphorylated by the receptor-associated Janus kinase, forms dimers, and enters the nucleus where it binds to Stat3 target genes and regulates their expression. In this report, we demonstrate that Stat3 binds directly to the promoters and regulates the expression of three genes that are essential for cardiac differentiation: Tbx5, Nkx2.5, and GATA4. We further demonstrate that Tbx5, Nkx2.5, and GATA4 expression is dependent on Stat3 in response to ligand treatment and during ligand-independent differentiation of P19CL6 cells into cardiomyocytes. Finally, we show that Stat3 is necessary for the differentiation of P19CL6 cells into beating cardiomyocytes. All together, these results demonstrate that Stat3 is required for the differentiation of cardiomyocytes through direct transcriptional regulation of Tbx5, Nkx2.5, and GATA4.

Molecular genetics of congenital atrial septal defects

Congenital heart defects (CHD) are the most common developmental errors in humans, affecting 8 out of 1,000 newborns. Clinical diagnosis and treatment of CHD has dramatically improved in the last decades. Hence, the majority of CHD patients are now reaching reproductive age. While the risk of familial recurrence has been evaluated in various population studies, little is known about the genetic pathogenesis of CHD. In recent years significant progress has been made in uncovering genetic processes during cardiac development. Data from human genetic studies in CHD patients indicate that the genetic aetiology was presumably underestimated in the past. Inherited mutations in genes encoding cardiac transcription factors and sarcomeric proteins were found as an underlying cause for familial recurrence of non-syndromic CHD in humans, in particular cardiac septal defects. Notably, the cardiac phenotypes most frequently seen in mutation carriers are ostium secundum atrial septal defects (ASDII). This review outlines experimental approaches employed for the detection of CHD-related genes in humans and summarizes recent findings in molecular genetics of congenital cardiac septal defects with an emphasis on ASDII.

Transcriptional regulation of the murine Connexin40 promoter by cardiac factors Nkx2-5, GATA4 and Tbx5

OBJECTIVE

Connexin40 (Cx40) is a gap junction protein expressed specifically in developing and mature atrial myocytes and cells of the conduction system. In this report, we identify cis-acting elements within the mouse Cx40 promoter and unravel part of the complex pathways involved in the cardiac expression of this gene.

METHODS

To identify the factors involved in the cardiac expression of Cx40, we used transient transfections in mammalian cells coupled with electrophoretic mobility shift assays (EMSA) and RT-PCR.

RESULTS

Within the promoter region, we identified the minimal elements required for transcriptional activity within 150 base pairs (bp) upstream of the transcriptional start site. Several putative regulatory sites for transcription factors were predicted within this region by computer analysis, and we demonstrated that the nuclear factors Sp1, Nkx2-5, GATA4 and Tbx5 could interact specifically with elements present in the minimal promoter region of the Cx40. Furthermore, co-transfection experiments showed the ability of Nkx2-5 and GATA4 to transactivate the minimal Cx40 promoter while Tbx5 repressed Nkx2-5/GATA4-mediated activation. Mutagenesis of the Nkx2-5 core site in the Cx40 promoter led to significantly decreased activity in rat smooth muscle cell line A7r5. Consistent with this, mouse embryos lacking Nkx2-5 showed a marked decrease in Cx40 expression.

CONCLUSION

In this work, we cloned the promoter region of the Cx40 and demonstrated that the core promoter was modulated by cardiac transcriptional factors Nkx2-5, Tbx5 and GATA4 acting together with ubiquitous Sp1.