A role for Drosophila Wnt-4 in heart development

Knockout of tnni1b in zebrafish causes defects in atrioventricular valve development via the inhibition of the myocardial wnt signaling pathway

The proper development of atrioventricular (AV) valves is critical for heart morphogenesis and for the formation of the cardiac conduction system. Defects in AV valve development are the most common type of congenital heart defect. Cardiac troponin I ( ctnni), a structural and regulatory protein involved in cardiac muscle contraction, is a subunit of the troponin complex, but the functions and molecular mechanisms of ctnni during early heart development remain unclear. We created a knockout zebrafish model in which troponin I type 1b ( tnni1b) ( Tnni-HC, heart and craniofacial) was deleted using the clustered regularly interspaced short palindromic repeat/clustered regularly interspaced short palindromic repeat-associated protein system. In the homozygous mutant, the embryos showed severe pericardial edema, malformation of the heart tube, reduction of heart rate without contraction and with almost no blood flow, heart cavity congestion, and lack of an endocardial ring or valve leaflet, resulting in 88.8 ± 6.0% lethality at 7 d postfertilization. Deletion of tnni1b caused the abnormal expression of several markers involved in AV valve development, including bmp4, cspg2, has2, notch1b, spp1, and Alcam. Myocardial re-expression of tnni1b in mutants partially rescued the pericardial edema phenotype and AV canal (AVC) developmental defects. We further showed that tnni1b knockout in zebrafish and ctnni knockdown in rat h9c2 myocardial cells inhibited cardiac wnt signaling and that myocardial reactivation of wnt signaling partially rescued the abnormal expression of AVC markers caused by the tnni1b deletion. Taken together, our data suggest that tnni1b plays a vital role in zebrafish AV valve development by regulating the myocardial wnt signaling pathway.-Cai, C., Sang, C., Du, J., Jia, H., Tu, J., Wan, Q., Bao, B., Xie, S., Huang, Y., Li, A., Li, J., Yang, K., Wang, S., Lu, Q. Knockout of tnni1b in zebrafish causes defects in atrioventricular valve development via the inhibition of myocardial wnt signaling pathway.

Conserved signaling mechanisms in Drosophila heart development

Signal transduction through multiple distinct pathways regulates and orchestrates the numerous biological processes comprising heart development. This review outlines the roles of the FGFR, EGFR, Wnt, BMP, Notch, Hedgehog, Slit/Robo, and other signaling pathways during four sequential phases of Drosophila cardiogenesis-mesoderm migration, cardiac mesoderm establishment, differentiation of the cardiac mesoderm into distinct cardiac cell types, and morphogenesis of the heart and its lumen based on the proper positioning and cell shape changes of these differentiated cardiac cells-and illustrates how these same cardiogenic roles are conserved in vertebrates. Mechanisms bringing about the regulation and combinatorial integration of these diverse signaling pathways in Drosophila are also described. This synopsis of our present state of knowledge of conserved signaling pathways in Drosophila cardiogenesis and the means by which it was acquired should facilitate our understanding of and investigations into related processes in vertebrates. Developmental Dynamics 246:641-656, 2017. © 2017 Wiley Periodicals, Inc.

The canonical Wingless signaling pathway is required but not sufficient for inflow tract formation in the Drosophila melanogaster heart

The inflow tracts of the embryonic Drosophila cardiac tube, termed ostia, arise in its posterior three segments from cardiac cells that co-express the homeotic transcription factor Abdominal-A (abdA), the orphan nuclear receptor Seven-up (Svp), and the signaling molecule Wingless (Wg). To define the roles of these factors in inflow tract development, we assessed their function in inflow tract formation. We demonstrate, using several criteria, that abdA, svp, and wg are each critical for normal inflow tract formation. We further show that Wg acts in an autocrine manner to impact ostia fate, and that it mediates this effect at least partially through the canonical Wg signaling pathway. By contrast, neither wg expression nor Wg signaling are sufficient for inflow tract formation when expressed in anterior Svp cells that do not normally form inflow tracts in the embryo. Instead, ectopic abd-A expression throughout the cardiac tube is required for the formation of ectopic inflow tracts, indicating that autocrine Wg signaling must be supplemented by additional Hox-dependent factors to effect inflow tract formation. Taken together, these studies define important cellular and molecular events that contribute to cardiac inflow tract development in Drosophila. Given the broad conservation of the cardiac regulatory network through evolution, our studies provide insight into mechanisms of cardiac development in higher animals.

On the Morphology of the Drosophila Heart

The circulatory system of Drosophilamelanogaster represents an easily amenable genetic model whose analysis at different levels, i.e., from single molecules up to functional anatomy, has provided new insights into general aspects of cardiogenesis, heart physiology and cardiac aging, to name a few examples. In recent years, the Drosophila heart has also attracted the attention of researchers in the field of biomedicine. This development is mainly due to the fact that several genes causing human heart disease are also present in Drosophila, where they play the same or similar roles in heart development, maintenance or physiology as their respective counterparts in humans. This review will attempt to briefly introduce the anatomy of the Drosophila circulatory system and then focus on the different cell types and non-cellular tissue that constitute the heart.

Transposon Dysregulation Modulates dWnt4 Signaling to Control Germline Stem Cell Differentiation in Drosophila

Germline stem cell (GSC) self-renewal and differentiation are required for the sustained production of gametes. GSC differentiation in Drosophila oogenesis requires expression of the histone methyltransferase dSETDB1 by the somatic niche, however its function in this process is unknown. Here, we show that dSETDB1 is required for the expression of a Wnt ligand, Drosophila Wingless type mouse mammary virus integration site number 4 (dWnt4) in the somatic niche. dWnt4 signaling acts on the somatic niche cells to facilitate their encapsulation of the GSC daughter, which serves as a differentiation cue. dSETDB1 is known to repress transposable elements (TEs) to maintain genome integrity. Unexpectedly, we found that independent upregulation of TEs also downregulated dWnt4, leading to GSC differentiation defects. This suggests that dWnt4 expression is sensitive to the presence of TEs. Together our results reveal a chromatin-transposon-Wnt signaling axis that regulates stem cell fate.

Wnt4 is required for ostia development in the Drosophila heart

The Drosophila ostia are valve-like structures in the heart with functional similarity to vertebrate cardiac valves. The Wnt/β-catenin signaling pathway is critical for valve development in zebrafish and mouse, but the key ligand(s) for valve induction remains unclear. We observed high levels of Wnt4 gene expression in Drosophila ostia progenitor cells, immediately prior to morphological differentiation of these cells associated with ostia formation. This differentiation was blocked in Wnt4 mutants and in flies expressing canonical Wnt signaling pathway inhibitors but not inhibitors of the planar cell polarity pathway. High levels of Wnt4 dependent activation of a canonical Wnt signaling reporter was observed specifically in ostia progenitor cells. In vertebrate valve formation Wnt signaling is active in cells undergoing early endothelial-mesenchymal transition (EMT) and the Wnt9 homolog of Drosophila Wnt4 is expressed in valve progenitors. In demonstrating an essential role for Wnt4 in ostia development we have identified similarities between molecular and cellular events associated with early EMT during vertebrate valve development and the differentiation and partial delamination of ostia progenitor cells in the process of ostia formation.

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.