Worm Breeder's Gazette 13(4): 48 (October 1, 1994)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Cell-Cell Contacts Controlling Early Cell Division Axes.

Bob Goldstein

MRC, Cambridge, England

  Cell division axes are often controlled precisely in embryos, by intracellular cues
(for example, Hyman and White, 1987; Dan, 1979), or by extracellular cues.
Extracellular cues have been found to work either by mechanical deformation of cell
shape (Symes and Weisblat, 1992) or by induction, as changes in cell fate are often
followed by changes in cell division patterns (Sternberg and Horvitz, 1986).
  I have found evidence that the division axes of some early cells, EMS and E, are
controlled by specific cell-cell contacts with their posterior neighbors (EMSP2 or E-P[3]
contact). Altering the orientation of contact between these cells(1) alters the orientation
in which the EMS or E cell divides. I have been following this up with timelapse
videomicroscopy of centrosome movements and anti-tubulin immunofluorescence to
visualize asters and centrosomes These have been done primarily in the EMS cell, in
both intact embryos and isolated cell pairs.
  Contact-dependent mitotic spindle orientation appears to work by establishing a
site of the type described by Hyman and White (1987) and Hyman (1989) in the cortex of
the responding cell: one centrosome moves toward the site of cell-cell contact during
rotation, both in intact embryos and re-oriented cell pairs(2). The effect is especially
apparent when two donor cells are placed on one side of the responding cell. Both
centrosomes are "captured", pulling the nucleus to one side of the cell. No centrosome
rotation occurs in the absence of cell-cell contact, nor in nocodazole-treated cell pairs.
  The relationship between gut induction and spindle orientation in EMS is being
examined, as both require contact between P[2] and EMS. When P[2] and EMS are
isolated in the first five minutes of the EMS cell cycle, neither effect occurs. Placing
P[2] onto EMS soon after this time still rescues gut induction, but can no longer rescue
the spindle orientation effect. In these cell pairs EMS divides in various orientations,
yet gut differentiation generally occurs, suggesting that proper spindle orientation is
not necessary for gut induction. There is however one spindle orientation which
appears to be incompatible with gut induction: when the EMS cleavage furrow forms
directly through the site of cell-cell contact, gut differentiation does not occur (0/10
cases, compared to 14/14 of other orientations).
  The results suggest that some of the cortical sites described by Hyman are
established cell-autonomously (in P[l], P[2], and P[3]), and some are established by
cell-cell contact (in EMS and E). Contact-dependent mitotic spindle orientation
appears to play a role in ensuring that developmental information received via
induction is partitioned between daughter cells. It might also play a role later in
morphogenesis, generating lines of cells in the embryo.
  (1) That orientation of cell pairs was altered has been confirmed by seeing that no
whole cell rotation occurs in high magnification timelapse recordings of cell pairs, and
by noting in live and fixed cells the random position of the centrosomes after cells are
  (2) The direction of rotation in EMS is at odds with Waddle's finding that
actin-capping protein localizes to the anterior side of EMS during rotation (Waddle et
al., 1994). Schierenberg previously noted that the nucleus in these cells moves
posteriorly to the site of cell-cell contact, and is dependent on contact with P2 in EMS
(Schierenberg, 1987).
 Dan (1979) Dev Growth Diff 21(6):527-535.
 Hyman and White (1987) J Cell Biol 105:2123-2135.
 Hyman (1989) J Cell Biol 109:1185-1193.
 Schierenberg (1987) Dev Biol 122:452-463.
 Sternberg and Horvitz (1986) Cell 44:761-772.
 Symes and Weisblat (1992) Dev Biol 150:203-218.
 Waddle et al. (1994) Development 120:2317-2328.