Summary:In vertebrates, different Wnt-signaling pathways are required in a temporally coordinated manner to promote cardiogenesis. In Drosophila, wingless holds an essential role in heart development. Among the known Drosophila Wnts is DWnt4, the function of which has been studied in various developmental processes except for heart development. We re-evaluated the expression pattern of DWnt4 during embryogenesis and show that transcripts are not restricted to the dorsal ectoderm but are also present in the cardiogenic mesoderm. Moreover, we detect DWnt4 mRNA transcripts in myocardial cells by stage 16. The heart phenotype in DWnt4 mutant embryos is characterized by various degrees of disrupted expression of different cardiac markers. Overexpression of Dwnt4 also affects heart marker expression, which can be partially rescued by simultaneous inhibition of PKC. Our data reveal a role for DWnt4 in cardiogenesis; however, integration of DWnt4 with other known signaling pathways that function in heart development still awaits further investigation. genesis 50:466-481 , 2012. V V C 2012 Wiley Periodicals, Inc.

The LIM-homeodomain transcription factor Tailup (Tup) is a component of the complex cardiac transcriptional network governing specification and differentiation of cardiac cells in Drosophila. LIM-domain containing factors are known to interact with the adaptor molecule Chip/Ldb1 to form higher order protein complexes to regulate gene expression thereby determining a cell's developmental fate. However, with respect to Drosophila heart development, it has not been investigated yet, whether Chip and tup interact to regulate the generation of different cardiac cell types. Here we show that Chip is required for normal heart development and that it interacts with tup in this context. Particularly the number of Odd skipped-expressing pericardial cells depends on balanced amounts of Chip and Tup. Data from luciferase assays using Hand- and even-skipped reporter constructs in Drosophila S2 cells indicate that Chip and Tup act as a tetrameric complex on the regulatory regions of Hand and even-skipped (eve). Finally we have identified and verified five Tup binding sites in the eve mesodermal enhancer, which adds Tup as novel factor to directly regulate eve expression. Taken together this study provides novel findings regarding cardiac gene expression regulation in Drosophila.