Culture of postimplantation conceptuses was used in conjunction with microsurgery to investigate the timing, the mechanism and the developmental regulation of chorioallantoic fusion in the mouse. The timing of fusion was determined in both freshly recovered conceptuses and in those that had been cultured from as early as the mid-streak stage. Attachment of the allantois to the chorion was found to have occurred in most conceptuses by the 6-somite stage, irrespective of whether they had been cultured. In investigating the mechanism of fusion, we wished to determine whether it depended on directed growth of the allantoic bud or on its differential adhesion to the chorion. Microsurgery was used to transplant allantoic tissue into the exocoelomic cavity of conceptuses from which the resident allantois had been removed. In synchronous grafting experiments, transplanted allantoises typically attached to the chorion despite loss of their connection with the hindgut region of the fetus. Hence selective attachment of the allantois to the chorion clearly cannot depend simply on its directed growth. While the transplanted allantoic tissue attached to the chorion selectively, it did not attach to it precociously, despite being favourably positioned to do so. These findings argue that the initial attachment of the allantois to the chorion depends on a selective adhesive mechanism that is developmentally regulated. Further grafting experiments in which donor conceptuses were either more or less advanced than hosts revealed that attachment of the allantois to the chorion depends primarily on the stage of the allantois rather than on the stage of the chorion. Collectively, these findings support the hypothesis that the initial stage of chorioallantoic fusion depends on selective adhesion between regionally differentiated mesodermal surfaces which is governed principally by the stage of development of the allantois.

Reference

Beddington
R. S. P.
(
1981
)
An autoradiographic analysis of the potency of embryonic ectoderm in the 8th day postimplantation mouse embryo.
J. Embryol. Exp. Morph
64
,
87
104
Champlin
A. K.
,
Dorr
D. L.
,
Gates
A. H.
(
1973
)
Determining the stage of the estrous cycle in the mouse by the appearance of the vagina.
Biol. Reprod
8
,
491
494
Copp
A. J.
,
Roberts
H. M.
,
Polani
P. E.
(
1986
)
Chimaerism of primordial germ cells in the early postimplantation mouse embryo following microsurgical grafting of posterior primitive streak cells in vitro.
J. Embryol. Exp. Morph
95
,
95
115
Downs
K. M.
,
Davies
T. M.
(
1993
)
Staging of gastrulating mouse embryos by morphological landmarks in the dissecting microscope.
Development
118
,
1255
1266
Ellington
S. K. L.
(
1985
)
A morphological study of the development of the allantois of rat embryos in vivo.
J. Anat
142
,
1
11
Ellington
S. K. L.
(
1987
)
A morphological study of the development of the chorion of rat embryos.
J. Anat
150
,
247
263
Friedrich
G.
,
Soriano
P.
(
1991
)
Promoter traps in embryonic stem cells: a genetic screen to identify and mutate developmental genes in mice.
Genes Dev
5
,
1513
1523
Gardner
R. L.
(
1983
)
Origin and differentiation of extraembryonic tissues in the mouse.
Int. Rev. Exp. Path
24
,
63
133
Kelly
S. J.
,
Rossant
J.
(
1976
)
The effect of short-term labelling in [3H]-methyl thymidine on the viability of mouse blastomeres alone and incombination with unlabelled blastomeres.
J. Embryol. Exp. Morph
35
,
95
106
Lawson
K. A.
,
Meneses
J.
,
Pedersen
R. A.
(
1991
)
Clonal analysis of epiblast fate during germ layer formation in the mouse embryo.
Development
113
,
891
911
Rashbass
P.
,
Cooke
L. A.
,
Herrmann
B. G.
,
Beddington
R. S. P.
(
1991
)
A cell autonomous function of Brachyury in T/T embryonic stem cell chimeras.
Nature
353
,
348
350
Sanders
E. J.
,
Varedi
M.
,
French
A. S.
(
1993
)
Cell proliferation in the gastrulating chick embryo: a study using BrdU incorporation and PCNA localization.
Development
118
,
389
399
Tam
P. P. L.
,
Beddington
R. S. P.
(
1987
)
The formation of mesodermal tissues in the mouse embryo during gastrulation and early organogenesis.
Development
99
,
109
126
Yamaguchi
T. P.
,
Dumont
D. J.
,
Conlon
R. A.
,
Breitman
M. L.
,
Rossant
J.
(
1993
)
flk −1, an flt-related receptor tyrosine kinase is an early marker for endothelial cell precursors.
Development
118
,
489
498
This content is only available via PDF.