Saccharide structures of the mouse embryo during the first eight days of development: Inferences from immunocytochemical studies using monoclonal antibodies in conjunction with glycosidases

Monoclonal anti-carbohydrate antibodies have been used in conjunction with glycosidases in immunofluorescence studies to derive information about the structures and in situ distribution of saccharides of the mouse embryo during the first 8 days of development. The salient findings are as follows:

• Branched poly-N-acetyllactosamine sequences of I-antigen type are detectable from the first day onwards and are widely distributed in cells of the endoderm, ectoderm and mesoderm.

• Linear poly-N-acetyllactosamine sequences of i-antigen type are detectable from the fifth day onwards in cells of all three lineages, but have a more restricted distribution than the sequences of I-type.

• Poly-N-acetyllactosamine sequences that are susceptible to digestion with endoβ-galactosidase are the main carriers of the SSEA-1, C14 and the blood group B-like antigens, which have the following structures

  

  and are found in endoderm and ectoderm but not in mesoderm cells. In the trophoblast however, these antigens are borne on saccharides that are resistant to endo-β-galactosidase.
• A proportion of the poly-N-acetyllactosamine structures in the endoderm and the ectoderm of the 5- and 6-day embryos may contain the following novel structures:

  

  in which antigenicities of SSEA-1 and C14 determinants are masked.

• There are several types of sialyl-oligosaccharides: (1) those reactive with anti-Gd, which has a specificity for NeuAc α2 –3Gal β1 –4GlcNAc sequence in the extraembryonic mesoderm and the heart; (2) those reactive with anti-Pr₂ but not with anti-Gd, which may correspond to other N-acetylneuraminic acid containing sequences such as NeuAc α2 –3Gal β1 –3GalNAc or NeuAc α2 –6Gal in preimplantation embryos and in the yolk sac, neural ectoderm and mesenchyme of the 8-day embryo; (3) those with other sialic acid forms or linkages that do not react with anti-Gd and Pr₂; among these are sialosyl-i sequences in the extraembryonic ectoderm, and sialosyl-I sequences in most cell types during the first 8 days. The latter are the main poly-N-acetyllactosamine structures in the neural ectoderm of the 8-day embryo.

• The sequence Gal β1 –3GlcNAc β1 –3Gal βl –4Glc/GlcNAc, or cross-reactive structures, which bind FC10.2 antibody occur in the extraembryonic endoderm and yolk sac.

The roles of specific carbohydrate structures as receptors during embryonic development and cell growth are important topics of current research. The cytochemical approach with monoclonal antibodies in conjunction with glycosidases, as in the present study, provides a unique opportunity to visualize the in situ disposition of specific carbohydrate sequences in individual cells of the whole organism, and should facilitate systematic investigations of their functions.