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Transcription initiates at the core promoter, which contains distinct core promoter elements. Here, we highlight the complexity of transcriptional regulation by outlining the effect of core promoterdependent regulation on embryonic development and the proper function of an organism. We demonstrate in vivo the importance of the downstream core promoter element (DPE) in complex heart formation in Drosophila. Pioneering a novel approach using both CRISPR and nascent transcriptomics, we show the effects of mutating a single core promoter element within the natural context. Specifically, we targeted the downstream core promoter element (DPE) of the endogenous tin gene, encoding the Tinman transcription factor, a homologue of human NKX2-5 associated with congenital heart diseases. The 7 bp substitution mutation results in massive perturbation of the Tinman regulatory network that orchestrates dorsal musculature, which is manifested as physiological and anatomical changes in the cardiac system, impaired specific activity features, and significantly compromised viability of adult flies. Thus, a single motif can have a critical impact on embryogenesis and, in the case of DPE, functional heart formation. Transcription initiates at the core promoter, which contains distinct core promoter elements. Here, we highlight the complexity of transcriptional regulation by outlining the effect of core promoterdependent regulation on embryonic development and the proper function of an organism. We demonstrate in vivo the importance of the downstream core promoter element (DPE) in complex heart formation in Drosophila. Pioneering a novel approach using both CRISPR and nascent transcriptomics, we show the effects of mutating a single core promoter element within the natural context. Specifically, we targeted the downstream core promoter element (DPE) of the endogenous tin gene, encoding the Tinman transcription factor, a homologue of human NKX2-5 associated with congenital heart diseases. The 7 bp substitution mutation results in massive perturbation of the Tinman regulatory network that orchestrates dorsal musculature, which is manifested as physiological and anatomical changes in the cardiac system, impaired specific activity features, and significantly compromised viability of adult flies. Thus, a single motif can have a critical impact on embryogenesis and, in the case of DPE, functional heart formation. [ABSTRACT FROM AUTHOR]

Flying insects oscillate their wings at high frequencies of up to 1,000 Hz (1,2) and produce large mechanical forces of 80 W per kilogram of muscle (3). They utilize a pair of perpendicularly oriented indirect flight muscles that contain fibrillar, stretch-activated myofibres. In contrast, all other, more slowly contracting, insect body muscles have a tubular muscle morphology (4). Here we identify the transcription factor Spalt major (Salm) as a master regulator of fibrillar flight muscle fate in Drosophila. salm is necessary and sufficient to induce fibrillar muscle fate. salm switches the entire transcriptional program from tubular to fibrillar fate by regulating the expression and splicing of key sarcomeric components specific to each muscle type. Spalt function is conserved in insects evolutionarily separated by 280 million years. We propose that Spalt proteins switch myofibres from tubular to fibrillar fate during development, a function potentially conserved in the vertebrate heart--a stretch-activated muscle sharing features with insect flight muscle., To generate fast wing oscillations, both indirect flight muscle (IFM) units are attached to the thoracic exoskeleton. The contraction of one unit, the dorsal-longitudinal flight muscles (DLMs), deforms the thorax [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.08.024 Byline: Patrick C.H. Lo (a), Stephane Zaffran (b), Sebastien Senatore (b), Manfred Frasch (a) Keywords: Drosophila; bHLH factor; Heart; Midgut; Metamorphosis Abstract: The Hand proteins of the bHLH family of transcriptional factors play critical roles in vertebrate cardiogenesis. In Drosophila, the single orthologous Hand gene is expressed in the developing embryonic dorsal vessel (heart), lymph glands, circular visceral musculature, and a subset of CNS cells. We demonstrate that the absence of Hand activity causes semilethality during the early larval instars. The dorsal vessel and midgut musculature are unaffected in null mutant embryos, but in a large fraction the lymph glands are missing. However, homozygous adult flies lacking Hand possess morphologically abnormal dorsal vessels characterized by a disorganized myofibrillar structure, reduced systolic and diastolic diameter, and abnormal heartbeat contractions, and suffer from premature lethality. In addition, their midguts are highly deformed; in the most severe cases, there is midgut blockage and a massive excess of ectopic peritrophic membrane tubules exiting a rupture in an anterior midgut bulge. Nevertheless, the visceral musculature appears to be relatively normal. Based on these phenotypes, we conclude that the expression of the Drosophila Hand gene in the dorsal vessel and circular visceral muscles is mainly required during pupal stages, when Hand participates in the proper hormone-dependent remodeling of the larval aorta into the adult heart and in the normal morphogenesis of the adult midgut endoderm during metamorphosis. Author Affiliation: (a) Brookdale Department of Molecular, Cell and Developmental Biology, Box 1020, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA (b) Developmental Biology Institute of Marseille-Luminy, CNRS URM 6216, Campus de Luminy, Case 907, 13009 Marseille, France Article History: Received 6 July 2007; Accepted 1 August 2007

Author(s): Hsiu-Hsiang Lee [1]; Audra Norris [2]; Joseph B. Weiss (corresponding author) [2, 3]; Manfred Frasch (corresponding author) [1, 3] The secreted protein Jelly belly (Jeb) is required for an [...]

The embryonic dorsal vessel in Drosophila possesses anteroposterior polarity and is subdivided into two chamber-like portions, the aorta in the anterior and the heart in the posterior. The heart portion features a wider bore as compared with the aorta and develops inflow valves (ostia) that allow the pumping of hemolymph from posterior toward the anterior. Here, we demonstrate that homeotic selector genes provide positional information that determines the anteroposterior subdivision of the dorsal vessel. Antennapedia (Antp), Ultrabithorax (Ubx), abdominal-A (abd-A), and Abdominal-B (Abd-B) are expressed in distinct domains along the anteroposterior axis within the dorsal vessel, and, in particular, the domain of abd-A expression in cardioblasts and pericardial cells coincides with the heart portion. We provide evidence that loss of abd-A function causes a transformation of the heart into aorta, whereas ectopic expression of abd-A in more anterior cardioblasts causes the aorta to assume heart-like features. These observations suggest that the spatially restricted expression and activity of abd-A determine heart identities in cells of the posterior portion of the dorsal vessel. We also show that Abd-B, which at earlier stages is expressed posteriorly to the cardiogenic mesoderm, represses cardiogenesis. In light of the developmental and morphological similarities between the Drosophila dorsal vessel and the primitive heart tube in early vertebrate embryos, these data suggest that Hox genes may also provide important anteroposterior cues during chamber specification in the developing vertebrate heart. Key Words: cardiogenesis; heart patterning; dorsal vessel; homeotic genes; abd-A; Abd-B; Hox genes.

Results show that biniou, the Drosophila equivalent of the FoxF subfamily of forkhead domain genes, is involved in the development of visceral mesoderm and helps maintain the distinction between splanchnic and somatic mesoderm. Data indicate that the splanchnic mesoderm layers develop into musculature and other visceral organs.

Smad proteins function with synergistic and antagonistic regulators to send Dpp responses to the mesoderm for Drosophila. Integration of positive and negative regulators on enhancers of target genes seems to be a significant way for TGF-beta molecules to achieve tissue-specific induction. Dpp is in the TGF-beta superfamily and a signaling molecule.

Adhesion of cells to one another and to extracellular matrices has major roles in morphogenetic processes during development. One important family of cell adhesion receptors are the integrins, which in Drosophila have crucial functions in at least two adhesion-mediated developmental events: embryonic muscle attachment and adhesion of the wing epithelia. We have cloned and characterized a gene (struthio) that is expressed in embryonic mesodermal and muscle cells, including cardioblasts, and epidermal muscle attachment sites in a pattern that is reminiscent of the expression pattern of the PS integrins. Maternal and zygotic transcripts are produced by this gene and encode similar proteins with two alternative carboxy tails. Both proteins contain identical KH domains, a protein sequence motif that is found in numerous proteins that interact with RNA. The struthio protein is highly homologous in a region including the KH domain to the mouse quaking and C. elegans gld-1 proteins, two developmentally important genes. Somatic homozygous clones of an embryonic lethal mutation in this gene ([stru.sup.1A122]) cause wing blisters and flight impairment, phenotypes which are associated with PS integrin subunit mutations. Thus, the struthio gene encodes a putative RNA-binding protein that appears to regulate some aspects of Drosophila integrin functioning.

The transforming growth factor-beta Decapentaplegic (Dpp) determines which mesodermal cells in the Drosophila embryo will form the visceral mesoderm and the heart. Dpp is a signal molecule which is necessary for the stimulation of the tinman homeobox gene in the mesoderm. The tinman gene in turn stimulates another homeobox gene bagpipe in certain mesodermal cells which form the visceral mesoderm. Heart formation is controlled by the expression of tinman. Mutants lacking Dpp show normal tinman expression in the beginning which is lost after migration of mesodermal cells.

This review discusses the role of cell type-specific cell surface molecules in the process of myoblast fusion using Drosophila as a model. Data indicate that in Drosophila, founder cells recruit the fusion-competent cells which eventually fuse with the former and initiate muscle differentiation.

A significant role of the Drosophila counterpart of a heterochronic miRNA gene from Caenorhabditis elegans gene let7 in regulation of stage-specific developmental events in neuromuscular tissues during the transition from larval to adult stage is reported. The findings from the research provide insight into widespread usage of miRNA in temporal regulation of animal development.

A study is conducted on the requirement of FGF receptors, pyramus and thisbe, for the differentiation of a variety of mesodermal tissues in the Drosophila embryo. The results reveal that the two genes exhibit dynamic patterns of expression in tissues that influence the development of different mesoderm lineages.