Formation and function of intracardiac valve cells in the Drosophila heart.

Drosophila harbours a simple tubular heart that ensures haemolymph circulation within the body. The heart is built by a few different cell types, including cardiomyocytes that define the luminal heart channel and ostia cells that constitute openings in the heart wall allowing haemolymph to enter the heart chamber. Regulation of flow directionality within a tube, such as blood flow in arteries or insect haemolymph within the heart lumen, requires a dedicated gate, valve or flap-like structure that prevents backflow of fluids. In the Drosophila heart, intracardiac valves provide this directionality of haemolymph streaming, with one valve being present in larvae and three valves in the adult fly. Each valve is built by two specialised cardiomyocytes that exhibit a unique histology. We found that the capacity to open and close the heart lumen relies on a unique myofibrillar setting as well as on the presence of large membranous vesicles. These vesicles are of endocytic origin and probably represent unique organelles of valve cells. Moreover, we characterised the working mode of the cells in real time. Valve cells exhibit a highly flexible shape and, during each heartbeat, oscillating shape changes result in closing and opening of the heart channel. Finally, we identified a set of novel valve cell markers useful for future in-depth analyses of cell differentiation in wild-type and mutant animals.

Adhesive pad differentiation in Drosophila melanogaster depends on the Polycomb group gene Su(z)2.

The ability of many insects to walk on vertical smooth surfaces such as glass or even on the ceiling has fascinated biologists for a long time, and has led to the discovery of highly specialized adhesive organs located at the distal end of the animals' legs. So far, research has primarily focused on structural and ultrastructural investigations leading to a deeper understanding of adhesive organ functionality and to the development of new bioinspired materials. Genetic approaches, e.g. the analysis of mutants, to achieve a better understanding of adhesive organ differentiation have not been used so far. Here, we describe the first Drosophila melanogaster mutant that develops malformed adhesive organs, resulting in a complete loss of climbing ability on vertical smooth surfaces. Interestingly, these mutants fail to make close contact between the setal tips and the smooth surface, a crucial condition for wet adhesion mediated by capillary forces. Instead, these flies walk solely on their claws. Moreover, we were able to show that the mutation is caused by a P-element insertion into the Su(z)2 gene locus. Remobilization of the P-element restores climbing ability. Furthermore, we provide evidence that the P-element insertion results in an artificial Su(z)2 transcript, which most likely causes a gain-of-function mutation. We presume that this transcript causes deregulation of yet unknown target genes involved in pulvilli differentiation. Our results nicely demonstrate that the genetically treatable model organism Drosophila is highly suitable for future investigations on adhesive organ differentiation.

Drosophila metalloproteases in development and differentiation: the role of ADAM proteins and their relatives.

ADAM metalloproteases are membrane bound glycoproteins that control many biological processes during development and differentiation, mainly by acting as ectodomain sheddases. The Drosophila genome contains five genes that code for classical ADAM proteins which are characterized by a highly conserved domain structure with the respective catalytic domains facing the extracellular space. More than 50 genes encode related proteins such as those that have lost their primary enzymatic activity while retaining, e.g., their adhesive properties. The physiological relevance of many Drosophila ADAMs and their relatives is still unknown, however for others, a striking role during organogenesis and tissue maintenance has been demonstrated during the last few years. We have carried out genetic screenings combined with candidate approaches, aiming to identify new components involved in cardiogenesis and muscle differentiation. Herein we summarize our results with a particular focus on metalloproteases with known or potential roles in tissue differentiation.