Changes in sialylation in homozygous Sp2H mouse mutant embryos

The splotch (Sp(2H)), Pax-3 mutant mice are characterized by neurulation defects, neural crest deficiencies, and altered somitogenesis. A link connecting all morphological abnormalities in the Pax-3 homozygous embryos is the composition of extracellular matrix and misexpression of cell adhesion molecules. The neural cell adhesion molecule (NCAM) is one of the Pax-3 target genes. Its adhesive properties depend on the attached polysialic acid (PSA). We have studied whether NCAM sialylation has been affected in the Pax-3 mutant embryos.

Genotyping of embryos was determined using polymerase chain reaction. The periodate-resorcinol method was used for quantitative determination of sialic acid. Immunoblotting was used to detect sialylated NCAM isoforms and sialic acids on the blot. This antibody was also used to detect PSA-NCAM spatial expression.

Quantitative determination of sialic acid at days 10.5-13.5 showed decreased sialic acid content in Sp(2H) homozygotes. The results of both techniques used in evaluating the expression of PSA-NCAM isoforms in our study indicate that the 180-kDa isoform is decreased in homozygous Splotch (Sp(2H)) embryos. Immunohistochemistry showed decreased staining in the neural tube, ganglion VIII, (day 13.5), frontal lobe, olfactory bulb, and neuroblastic retinal cells (day 18.5).

PSA-NCAM is present in Sp(2H) embryos of all genotypes, starting on developmental day 9.5. Sialylation of the 180-kDa NCAM isoform begins to decrease on day 12.5 in Sp(2H) homozygotes. Reduced NCAM sialylation could contribute to the decreased migration of cells in the sensory organs.