The Genetics of Axis Specification in Drosophila
To move anything takes force, and understanding the mechanical forces involved in morphogenesis has recently become an area of great interest to developmental biologists. Drosophila gastrulation presents many questions relevant to these areas of study. For example, what are the biomechanics driving invagination of mesoderm at the ventral furrow?
First, realize that the cellularized blastoderm is an epithelium, so its cells have strong junctional attachments (adhesion) to one another. This tissue, therefore, should not break under strain, but it may change shape. It was recently discovered that just prior to mesoderm invagination, myosin becomes most active in the cells at the ventral midline of the embryo. (As you likely already know, myosin is a motor protein that associates with actin filaments to build subcellular contractile machines—think muscle cells.) Over time, this highly active myosin not only accumulates in the apex of cells at the midline, but also becomes organized into arrays along the cells’ anterior-to-posterior axis. This axial orientation of actomyosin arrays concentrated in ventral cells along the midline causes anisotropic tension (i.e., asymmetric, not uniform) directed along the length of the future furrow (Figure 1; Chanet et al. 2017; Heer et al. 2017). The oriented apical constriction of the midline ventral cells causes them to become wedge-shaped rather than conical, resulting in a furrow rather than a pit. This is just one example of how force plays a role in controlling cellular behavior that changes the shape of a tissue. Keep the momentum going and seek out additional processes that are under the regulation of biophysical parameters—the reality is, they all are.
References
Chanet, S., C. J. Miller, E. D. Vaishnav, B. Ermentrout, L. A. Davidson and A. C. Martin. 2017. Actomyosin meshwork mechanosensing enables tissue shape to orient cell force. Nat. Commun. 8: 15014
PubMed Link
Heer, N. C., P. W. Miller, S. Chanet, N. Stoop, J. Dunkel and A. C. Martin. 2017. Actomyosin-based tissue folding requires a multicellular myosin gradient. Development 144: 1876–1886.
PubMed Link
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