Worm Breeder's Gazette 5(1): 29

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.

Origin of Spatial Organization in Early Embryos

J. Laufer, P. Bazzicalupo, B. Wood

We have continued experiments on the cleavage patterns of partial 
embryos and isolated blastomeres obtained by crushing early N2 eggs in 
embryonic culture medium supplemented with Ascaris coelomic fluid (W.B.
G.  June 1978).  Neither isolated somatic precursor cells (blast cells)
nor isolated P cells give rise to the spatial patterns formed by 
their progeny in intact embryos.  However, all our results so far are 
consistent with the following simple hypothesis.  The blast cells, and 
their progeny, are internally determined to cleave in a simple helical 
pattern.  The P cells are internally determined to cleave linearly, 
maintaining the spindle orientation of preceding P-cell divisions 
parallel to the anterior-posterior axis.  In the intact embryo, 
interactions of cells with each other (and perhaps with the eggshell) 
combine with these two intrinsic cleavage patterns to dictate normal 
cellular organization, which therefore depends upon both extracellular 
and intracellular cues.
Cleavage of an isolated P2 blastomere results in an approximately 
linear chain of cells in the order C, C, D, P4.  This result, together 
with the approximately anterior-posterior orientation of the preceding 
cleavages that give rise to the AB, EMSt, E, and MSt cells suggests 
the possibility that in the zygote, determinants for blast-cell 
primary differentiation are arranged along the posterior-anterior axis 
in the order C (ectoderm), D (mesoderm), P4 (germ line), E (endoderm), 
MSt (mesoderm), AB (ectoderm).  This arrangement corresponds to that 
of a fate map proposed for the Ascaris des zygote 
by Zur Strassen (1896).  It differs from that of the fate map proposed 
for the C.  elegans zygote by Schierenberg (1978), who postulated the 
order P4, D, C, E, MSt, AB based on observations of division 
orientation in intact embryos,cytoplasmic streaming,and cell movements 
during early cleavage.