Hum. Reprod. Advance Access originally published online on November 24, 2006
Human Reproduction 2007 22(3):798-806; doi:10.1093/humrep/del424
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The axis of polarity of the mouse blastocyst is specified before blastulation and independently of the zona pellucida
Mammalian Development Laboratory, University of Oxford, Department of Zoology, South Parks Road, Oxford, UK
E-mail: richard.gardner{at}zoo.ox.ac.uk
BACKGROUND: Rather than being prepatterned, orientation of the embryonic–abembryonic (Em–Ab) axis of the mouse blastocyst has been claimed to depend on the conceptus being constrained by its zona pellucida (ZP) during blastulation. This hypothesis merited closer scrutiny, because it seemed at variance with observations on living conceptuses. METHODS: Two-cell conceptuses with an oil drop injected into the lesser diameter (LD) of the ZP at the first cleavage plane were cultured until shortly before blastulation when the blastomere underlying the drop was labelled with carbocyanine dye. After removing the ZP, conceptuses were re-cultured to the blastocyst stage for recording the position along the axis of the centres of the patches of labelled cells. RESULTS: These centres showed significant bias towards the equatorial (Eq) region of the axis compared with those resulting from labelling a blastomere at random, even following softening of the ZP at the 2-cell stage. This was also true if conceptuses were denuded at the 2-cell stage and the blastomere underlying an intact second polar body (PB) labelled in morulae. CONCLUSIONS: These findings further support the view that the Em–Ab axis of the mouse blastocyst is normally prepatterned and provide no evidence of a role for the ZP in its specification.
Key words: blastocyst/axis of polarity/prepatterning/zona pellucida
Submitted on July 7, 2006; resubmitted on September 20, 2006; accepted on September 29, 2006.
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