R L Gardner1. 1. Mammalian Development Laboratory, University of Oxford, Department of Zoology, South Parks Road, Oxford, UK. richard.gardner@zoo.ox.ac.uk
Abstract
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.
BACKGROUND: Rather than being prepatterned, orientation of the embryonic-abembryonic (Em-Ab) axis of the mouseblastocyst 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 mouseblastocyst is normally prepatterned and provide no evidence of a role for the ZP in its specification.
Authors: Calvin R Simerly; Carlos A Castro; Ethan Jacoby; Kevin Grund; Janet Turpin; Dave McFarland; Jamie Champagne; Joe B Jimenez; Pat Frost; Cassondra Bauer; Laura Hewitson; Gerald Schatten Journal: Reprod Sci Date: 2010-07-14 Impact factor: 3.060
Authors: Agnieszka Jedrusik; David-Emlyn Parfitt; Guoji Guo; Maria Skamagki; Joanna B Grabarek; Martin H Johnson; Paul Robson; Magdalena Zernicka-Goetz Journal: Genes Dev Date: 2008-10-01 Impact factor: 11.361