We. Hable et Dl. Kropf, ROLES OF SECRETION AND THE CYTOSKELETON IN CELL-ADHESION AND POLARITYESTABLISHMENT IN PELVETIA-COMPRESSA ZYGOTES, Developmental biology (Print), 198(1), 1998, pp. 45-56
During the establishment of polarity, fucoid algal zygotes adhere to t
he substratum and select a growth axis according to environmental cues
. Since little is known about the early events leading to axis selecti
on, we investigated the chronology of cell adhesion, adhesive depositi
on, and axis selection induced by light (photopolarization). The requi
rements for secretion and the cytoskeleton in these processes and in t
he process of changing the orientation of an axis in response to new e
nvironmental cues (axis realignment) were also tested. Adhesive deposi
tion occurred in two distinct stages: it was deposited uniformly on yo
ung zygotes (uniform primary adhesive) and later was deposited asymmet
rically (polar secondary adhesive). Uniform primary adhesive depositio
n, cell adhesion, and photopolarization occurred simultaneously, and s
hortly thereafter, polar secondary adhesive deposition occurred at the
future growth site. Uniform primary adhesive deposition and cell adhe
sion required secretion, but were independent of filamentous-actin (F-
actin) and microtubule function. Photopolarization of young zygotes an
d polar secondary adhesive deposition required secretion but not micro
tubules. F-actin served to localize secondary adhesive deposition at t
he rhizoid pole; its function in polarization was more complex. F-acti
n was required for axis selection; however, its role in realignment of
an axis depended on the light regime. The differing requirements for
F-actin during development indicates that the axis is not static, but
changes with time. These findings indicate that previous and future wo
rk on ''axis formation'' must be interpreted in the context of the dev
elopmental stage of the zygote. (C) 1998 Academic Press.