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Fig. 8. Model of fog function in controlling cell shape change. (A) The
patterning gene twist (twi), a transcription factor,
specifies mesodermal fate of the ventral cells. As a consequence of
twi expression, these cells activate transcription of fog
(arrow), resulting in the production and secretion of fog protein
from the apical side of the cell (blue dots). (B) Reception of fog
signal on the apical side of the cell results in localized activation of ROK
(red asterisk) which in turn activates the contractility of myosin with actin.
This local source of actomyosin contractility drives myosin (pink) to the
apical side of the cell (arrows). (C) The actin-myosin cytoskeleton is
tethered to the cell surface through adherens junctions (orange). The force
generated by apically localized contraction of the actin-myosin cytoskeleton
therefore pulls down and flattens the domed apical cell surface and draws the
adherens junctions up to the apical edge of the cell (arrows). (D) The
continued contraction of apical actin-myosin exerts further force on the
adherens junctions, pulling them close together, and resulting in the apical
constriction of the cells.
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