Hum. Reprod. Advance Access originally published online on February 2, 2005
Human Reproduction 2005 20(3):672-682; doi:10.1093/humrep/deh652
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Human Reproduction Vol. 20 No. 3 © The Author 2005; all rights reserved
Spindle abnormalities in normally developing and arrested human preimplantation embryos in vitro identified by confocal laser scanning microscopy
1 The London Bridge Fertility, Gynaecology and Genetics Centre, One St Thomas Street, London SE1 9RY, 2 CRUK Clinical Centre at Leeds, Division of Cancer Medicine Research, St James’ University Hospital, Leeds LS9 7TF, UK, 3 Iakentro Advanced Medical Centre, Thessaloniki, 542 50, Greece and 4 School of Biology, University of Leeds, Leeds LS2 9JT, UK
5 To whom correspondence should be addressed. Email: katerinachatzime{at}hotmail.com
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 
-tubulin, 
-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.
Key words: cell cycle checkpoints/confocal laser scanning microscopy/human preimplantation embryo/mitotic spindle/nuclear abnormalities
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