Cell fate decisions in the Drosophila dorsal vessel depend on the multiadapter protein inscuteable

Antagonistic function of Lmd and Zfh1 fine tunes cell fate decisions in the Twi and Tin positive mesoderm of Drosophila melanogaster

In this study we show that cell fate decisions in the dorsal and lateral mesoderm of Drosophila melanogaster depend on the antagonistic action of the Gli-like transcription factor Lame duck (Lmd) and the zinc finger homeodomain factor Zfh1. Lmd expression leads to the reduction of Zfh1 positive cell types, thereby restricting the number of Odd-skipped (Odd) positive and Tinman (Tin) positive pericardial cells in the dorsal mesoderm. In more lateral regions, ectopic activation of Zfh1 or loss of Lmd leads to an excess of adult muscle precursor (AMP) like cells. We also observed that Lmd is co-expressed with Tin in the early dorsal mesoderm and leads to a reduction of Tin expression in cells destined to become dorsal fusion competent myoblasts (FCMs). In the absence of Lmd function, these cells remain Tin positive and develop as Tin positive pericardial cells although they do not express Zfh1. We show further that Tin repression and pericardial restriction in the dorsal mesoderm facilitated by Lmd is instructed by a late Decapentaplegic (Dpp) signal that is abolished in embryos carrying the disk region mutation dpp(d6).

Proliferating mesodermal cells in murine embryos exhibiting macrophage and lymphendothelial characteristics

BACKGROUND

The data on the embryonic origin of lymphatic endothelial cells (LECs) from either deep embryonic veins or mesenchymal (or circulating) lymphangioblasts presently available remain inconsistent. In various vertebrates, markers for LECs are first expressed in specific segments of embryonic veins arguing for a venous origin of lymph vessels. Very recently, studies on the mouse have strongly supported this view. However, in the chick, we have observed a dual origin of LECs from veins and from mesodermal lymphangioblasts. Additionally, in murine embryos we have detected mesenchymal cells that co-express LEC markers and the pan-leukocyte marker CD45. Here, we have characterized the mesoderm of murine embryos with LEC markers Prox1, Lyve-1 and LA102 in combination with macrophage markers CD11b and F4/80.

RESULTS

We observed cells co-expressing both types of markers (e.g. Prox1 - Lyve-1 - F4/80 triple-positive) located in the mesoderm, immediately adjacent to, and within lymph vessels. Our proliferation studies with Ki-67 antibodies showed high proliferative capacities of both the Lyve-1-positive LECs of lymph sacs/lymphatic sprouts and the Lyve-1-positive mesenchymal cells.

CONCLUSION

Our data argue for a dual origin of LECs in the mouse, although the primary source of embryonic LECs may reside in specific embryonic veins and mesenchymal lymphangioblasts integrated secondarily into lymph vessels. The impact of a dual source of LECs for ontogenetic, phylogenetic and pathological lymphangiogenesis is discussed.

Drosophila flies combine periodic heartbeat reversal with a circulation in the anterior body mediated by a newly discovered anterior pair of ostial valves and 'venous' channels

Heartbeat activity in tethered adult drosophilids was recorded using a linear optosensor chip and an IR-light beam. Recording from two to five sensor elements within 250 mum along the anterior heart, it was possible to analyze periodic reversals. In intact Drosophila melanogaster and D. hydei, longer anterograde pulse periods with lower pulse rates generally alternated with shorter retrograde pulse periods having higher pulse rates. These differences are dependent on heart anatomy: a newly discovered first pair of ostia is connected to bilateral thoraco-abdominal hemolymph channels. These channels are part of a venous space separated from the abdominal hemocoel by a septum, consisting of a metanotal ridge and the pericardial diaphragm lined by a special form of fat body. The channels are sealed, and their lumen is possibly controlled by the metathoracic tergo-pleural muscle. During retrograde pulses, the heart chamber works like a suction pump, aspiring hemolymph through the first ostia from the venous channels and discharging it through a newly described caudal opening. During forward beating, the anterior chamber receives hemolymph via all inflow ostia from the entire heart and drives it like a pressure pump through the narrow aorta. Also, during forward pulses, a lateral circulation occurs in the thorax as a result of the venous supply. Inhibition of abdominal mobility leads to an irregular heart rate, with pulse-wise alternating heartbeat reversals. The possible involvement of slow abdominal movements in heartbeat periodicity is discussed. The heartbeat periods are superimposed with intermittent bouts of abdominal pumping movements.

The ADAM metalloprotease Kuzbanian is crucial for proper heart formation in Drosophila melanogaster

We have screened a collection of EMS mutagenized fly lines in order to identify genes involved in cardiogenesis. In the present work, we have studied a group of alleles exhibiting a hypertrophic heart. Our analysis revealed that the ADAM protein (A Disintegrin And Metalloprotease) Kuzbanian, which is the functional homologue of the vertebrate ADAM10, is crucial for proper heart formation. ADAMs are a family of transmembrane proteins that play a critical role during the proteolytic conversion (shedding) of membrane bound proteins to soluble forms. Enzymes harboring a sheddase function recently became candidates for causing several congenital diseases, like distinct forms of the Alzheimer disease. ADAMs play also a pivotal role during heart formation and vascularisation in vertebrates, therefore mutations in ADAM genes potentially could cause congenital heart defects in humans. In Drosophila, the zygotic loss of an active form of the Kuzbanian protein results in a dramatic excess of cardiomyocytes, accompanied by a loss of pericardial cells. Our data presented herein suggest that Kuzbanian acts during lateral inhibition within the cardiac primordium. Furthermore we discuss a second function of Kuzbanian in heart cell morphogenesis.