Human Reproduction, Vol 13, 1307-1311, Copyright © 1998 by Oxford University Press
D Dozortsev, A Ermilov, DM El-Mowafi and M Diamond
It has been demonstrated previously that removal of acellular debris from
the preimplantation mouse embryo is beneficial for subsequent development
to the hatched blastocyst stage. We have studied the impact of cellular
fragmentation induced in the mouse embryo during the late pronuclei and
8-cell stages on the hatching frequency and total cell number at the
blastocyst stage. At the late pronuclei stage about one- quarter of the
cytoplasm was removed from embryos in the experimental group, in four to
six steps, thus creating four to six cytoplasts that were subsequently
returned as anucleated fragments under the zona pellucida. Embryos with
one-quarter of the cytoplasm removed and with intact cytoplasm after
partial zona dissection (PZD) served as controls. At the 8-cell stage,
embryos with their nucleoplast removed from two blastomeres served as an
experimental group. Groups of embryos with part of the cytoplast removed
from two blastomeres (nucleated fragments), embryos with two blastomeres
removed and embryos after PZD alone served as controls. After manipulation
all embryos were left in culture and analysed at about 100 h after human
chorionic gonadotrophin administration. Fragments induced at the late
pronuclei stage did not participate in compaction and were often
spontaneously expelled from the embryo during hatching. Neither embryo
hatching rate nor total cell number was affected when compared with zygotes
with reduced cytoplasm. Although both nucleated and anucleated fragments
induced at the 8-cell stage participated in recompaction, hatching was not
compromised and there was no interference in further development as
assessed by the cell number or hatching rate at the blastocyst stage, as
compared with embryos with blastomeres removed. We conclude that anucleated
cellular fragments formed in an otherwise healthy embryo, both before and
after acquisition of the ability for compaction, are benign and that their
removal provides no benefit for embryo development, at least to the hatched
blastocyst stage.
ARTICLES
The impact of cellular fragmentation induced experimentally at different stages of mouse preimplantation development
Department of Obstetrics and Gynaecology, Hutzel Hospital/Wayne State University, Detroit, MI 48201, USA.
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