imaging-cell-shape-alteration-cell-movement-drosophila-gastrulation

Imaging of Cell Shape Alteration and Cell Movement in <em>Drosophila</em> Gastrulation Using DE-cadherin Reporter Transgenic Flies

Gastrulation is the first set of morphologically dynamic events that occur during the embryonic development of multicellular animals such as Drosophila. ...

JT Biohistory Research Hall

The formation of the ventral furrow during Drosophila gastrulation is driven by coordinated apical constriction. Cell-cell adhesion is thought to regulate apical constriction, but the mechanisms are poorly understood. DE-cadherin, an epithelial classic cadherin, has in its membrane-proximal extracellular region a suite of domains absent from vertebrate/urochordate classic cadherins. We constructed DEΔP, a DE-cadherin derivative that lacks the membrane-proximal half of the extracellular region but retains the entire cytoplasmic domain and still exhibits strong cell-cell binding ability. The extracellular region of DEΔP consists of only cadherin repeats, mimicking vertebrate/urochordate classic cadherins. In animals lacking DE-cadherin, DEΔP organized adherens junction assembly and functioned fully in many cadherin-dependent processes, including oogenesis. Embryos in which DE-cadherin was entirely replaced by DEΔP established the blastoderm epithelium but failed to form a ventral furrow. Apical constrictions were initiated relatively normally but subsequently decelerated. These were then followed by catastrophic disruption of the junctional network. Our results suggest that although the membrane-proximal half of the DE-cadherin extracellular region is dispensable for many developmental events, it is essential for efficient and robust apical constriction during ventral furrow formation.

The proximal half of the Drosophila E-cadherin extracellular region is dispensable for many cadherin-dependent events but required for ventral furrow formation.

Paramyosin is a myosin-binding protein characteristic of invertebrate animals, while troponin is a Ca(2+)-dependent regulator of muscle contraction. Both proteins are widely distributed in protostomes, while in deuterostomes, their distribution is limited; namely, presence of paramyosin and absence of troponin are common features in echinoderm muscles, while muscles of chordates contain troponin but lack paramyosin. In this study, we examined the muscle of a hemichordate, acorn worm, to clarify whether this animal is like echinoderms or like the other deuterostome animals. We found a 100-kDa protein in the smooth muscle of acorn worm. This protein was identified with paramyosin, since the purified protein formed paracrystals with a constant axial periodicity in the presence of divalent cations as paramyosin of other animals, showed ability to interact with myosin and shared common antigenicity with echinoderm paramyosin. On the other hand, troponin band was not detected in isolated thin filaments, and the filaments increased myosin-ATPase activity in a Ca(2+)-independent manner. The results indicate that troponin is lacking in thin filaments of acorn worm muscle just as in those of echinoderms. The muscle of hemichordate acorn worm is quite similar to echinoderm muscles, but different from chordate muscles.

Tomohiro Haruta

JT Biohistory Research Hall

Imaging of Cell Shape Alteration and Cell Movement in Drosophila Gastrulation Using DE-cadherin Reporter Transgenic Flies