Expression of cardiac myosin-binding protein-C (cMyBP-C) in Drosophila as a model for the study of human cardiomyopathies.

Mutations in the MYBPC3 gene encoding human cardiac myosin-binding protein-C (cMyBP-C) are associated with familial hypertrophic cardiomyopathy (FHC), but the molecular mechanisms involved are not fully understood. In addition, development of FHC is sensitive to genetic background, and the search for candidate modifier genes is crucial with a view to proposing diagnosis and exploring new therapies. We used Drosophila as the model to investigate the in vivo consequences of human cMyBP-C mutations. We first produced transgenic flies that specifically express human wild-type or two C-terminal truncated cMyBP-Cs in indirect flight muscles (IFM), a tissue particularly amenable to genetic and molecular analyses. First, incorporation of human cMyBP-C into the IFM led to sarcomeric structural abnormalities and to a flightless phenotype aggravated by age and human gene dosage. Second, transcriptome analysis of transgenic IFM using nylon microarrays showed the remodelling of a transcriptional program involving 97 out of 3570 Drosophila genes. Among them, the Calmodulin gene encoding a key component of muscle contraction, found up-regulated in transgenic IFM, was evaluated as a potential modifier gene. Calmodulin mutant alleles rescued the flightless phenotype, and therefore behave as dominant suppressors of the flightless phenotype suggesting that Calmodulin might be a modifier gene in the context of human FHC. In conclusion, we suggest that the combination of heterologous transgenesis and transcriptome analysis in Drosophila could be of great value as a way to glean insights into the molecular mechanisms underlying FHC and to propose potential candidate modifier genes.

The Drosophila cytokine receptor Domeless controls border cell migration and epithelial polarization during oogenesis.

In mammals, the JAK/STAT (Janus Kinase/Signal Transducer and Activator of Transcription) signaling pathway is activated in response to cytokines and growth factors to control blood cell development, proliferation and cell determination. In Drosophila, a conserved JAK/STAT signaling pathway controls segmentation in embryos, as well as blood cell development and other processes in larvae and adults. During embryogenesis, transduction of the Unpaired [Upd; also known as Outstretched (Os)] ligand through the JAK/STAT pathway requires Domeless, a putative membrane protein with distant homology to vertebrate type I cytokine receptors. We have isolated domeless (dome) in a screen to identify genes essential in epithelial morphogenesis during oogenesis. The level of dome activity is critical for proper border cell migration and is controlled in part through a negative feedback loop. In addition to its essential role in border cells, we show that dome is required in the germarium for the polarization of follicle cells during encapsulation of germline cells. In this process, dome controls the expression of the apical determinant Crumbs. In contrast to the ligand Upd, whose expression is limited to a pair of polar cells at both ends of the egg chamber, dome is expressed in all germline and follicle cells. However, the Dome protein is specifically localized at apicolateral membranes and undergoes ligand-dependent internalization in the follicle cells. dome mutations interact genetically with JAK/STAT pathway genes in border cell migration and abolish the nuclear translocation of Stat92E in vivo. We also show that dome functions downstream of upd and that both the extracellular and intracellular domains of Dome are required for JAK/STAT signaling. Altogether, our data indicate that Dome is an essential receptor molecule for Upd and JAK/STAT signaling during oogenesis.