Spindle abnormalities in normally developing and arrested human preimplantation embryos in vitro identified by confocal laser scanning microscopy.
BACKGROUND
Despite recent technical improvements, many human preimplantation embryos fail to develop to the blastocyst stage or implant after transfer to the uterus. A possible cause for this developmental arrest is the high incidence of nuclear and postzygotic chromosomal abnormalities observed during cleavage, including chaotic chromosome complements, suggestive of defects in mitotic chromosomal segregation. The underlying mechanisms are largely unknown, but similarities with chromosome instability in human cancers led to the proposal that cell cycle checkpoints may not operate at these early stages.


METHODS
To investigate this and to examine whether spindle abnormalities contribute to chromosome malsegregation, we have used fluorescence and confocal laser scanning microscopy, following immunolabelling with antibodies specific for alpha-tubulin, gamma-tubulin, or acetylated tubulin, combined with a DNA fluorochrome to visualize nuclei, spindle and chromosome configurations in normal and arrested human embryos, from cleavage to blastocyst stages.


RESULTS
In addition to frequent interphase nuclear abnormalities, we identify for the first time various spindle abnormalities including abnormal shape and chromosome loss and multipolar spindles at cleavage and blastocyst stages.


CONCLUSIONS
We propose that a major pathway leading to postzygotic chromosomal abnormalities is the formation of binucleate blastomeres with two centrosomes which result either in a bipolar spindle and division to two tetraploid blastomeres, or in a multipolar spindle, chromosome malsegregation and chromosomal chaos.
Chatzimeletiou
Katerina
K
The London Bridge Fertility, Gynaecology and Genetics Centre, One St Thomas Street, London SE1 9RY, UK. katerinachatzime@hotmail.com
Morrison
Ewan E
EE
Prapas
Nikos
N
Prapas
Yannis
Y
Handyside
Alan H
AH
D000107:Acetylation; D001755:Blastocyst / Q000502:physiology* / Q000648:ultrastructure*; D002467:Cell Nucleus / Q000648:ultrastructure; D002869:Chromosome Aberrations; D020090:Chromosome Segregation; D002970:Cleavage Stage, Ovum; D047108:Embryonic Development; D006801:Humans; D066298:In Vitro Techniques; D007399:Interphase; D018613:Microscopy, Confocal; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure*; D014018:Tissue Distribution; D014404:Tubulin / Q000378:metabolism
D014404:Tubulin