First cleavage plane in zebrafish zygote

R_FLUCK at ACAD.FANDM.EDU R_FLUCK at ACAD.FANDM.EDU
Thu Jan 12 09:30:24 EST 1995


In his 1938 paper (Biol. Bull. 75:119-133), Roosen-Runge reported the following
observation (pp. 121-122): "Before entering into a detailed description of
these early events it is necessary to say something about the method of
orienting the egg.  There is a polar axis in the mature egg of the zebra fish
just as in other teleosts, though it is less conspicuous.  Immediately after
the membrane [chorion] is lifted off (Fig. 1), the egg appears somewhat oval in
shape with the long axis as the polar axis and the animal pole marked by a
little depression, where the sperm entered.  But it is far more important for
the orientation of the egg that, in addition to this, the direction of the
first cleavage plane seems also be be established very early.  The cavity on
the animal pole is from the first moment of observation slightly elongated, so
that it appears deepest when seen along the long axis.  It is therefore
possible to orient the egg during the earliest stages by turning it around the
polar axis, until the cavity appears most excavated.  If this is done (Fig. 1
in this paper, Fig. 1a in Roosen-Runge, 1936), it is almost certain that the
first cleavage plane will appear perpendicular to the plane of observation."

Roosen-Runge did not report any controls.  For example, he did describe
cleavage in eggs in which the long axis of the depression was more or less in
the plane of observation.  Perhaps the correlation he observed was an effect of
compression of the egg.

Has anyone repeated duplicated Roosen-Runge's studies or extended them?




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