Developmental Expression And Function Of β-galactosyltransferase In Mouse Brain And Testis

Glycosylation changes occurring on cell surfaces during mammalian embryogenesis have been recognized for decades. Alterations in glycosylation have been proposed to participate in cell adhesion, receptor activation, cell differentiation and tissue morphogenesis. Because the early embryo is composed of cells that must adhere to other embryonic cells, it seems likely that glycans modulating this adhesion would have been indispensable for early development. Genetic elimination or partial abrogation of expression of some major classes of glycans, such as N-glycans, glycosphingolipids, hyaluronan and sialic acids, has been shown to be lethal during murine embryogenesis. The complex of glycan structure is synthesized by glycosyltransferases and the differential expression of glycans during development is due to the developmental expression and activity of glycosyltransferases. Two types of carbohydrate chains are known to exist in the lacto-series of oligosaccharides, type 1 chains that contain the Galβ1→3GlcNAc linkage and type 2 chains containing the Galβ1 → 4GlcNAc structure, β-1,3-galactosyltransferases family enable the formation of type 1 chains while the β-1, 4-galactosyltransferases family are involved in the type 2 chain synthesis. p4GalT-l-deficientmice were born normally and were fertile, but they exhibited growth retardation, endocrine insufficiency and neonatal-lethality. Epithelial cell proliferation of the skin and small intestine was also enhanced. No successful study of p3GalT-l knock-out mice has been reported to date. Northern analysis revealed that p3GalT-l was exclusively expressed in the brain while that p4GalT-l was expressed highly in testis, moreover, sperm surface p4GalT-l was suggested to play a significant role in signal transduction involving the acrosome reaction in the mouse. In the present study, we mainly detected the developmental expression and function of p-galactosyltransferases in mouse brain and testis.We first characterized the developmental expression of β3GalT-l in mouse brain. A significant level of β3GalT-1 transcript was present in the brains of 18-day-old mouse embryo, newborn and 1-week-old mice. Hereafter, its level decreased markedly. Densitometry analysis indicated that the p3GalT-l band was 10-fold more intensive in the 1-week-old mouse brain than that in the 12-week-old, indicating that β3GalT-l mRNA was expressed at a developmentally regulated way. Since the β-1, 3-galactosyltransferase family contains multiple isoforms involved in synthesis of type 1 chain lactosamine structure, we also examined the gene expression of two other important family members, β3GalT-2 and β3GalT-5. The expression of β3GalT-2 remained relatively low at each stage of development with the highest level in 1-week-old mouse brain while the levels of p3GalT-5 were not detected in mouse brain throughout development. These results indicate that β3GalT-l may be the key enzyme responsible for type 1 chain oligosaccharides synthesis in mouse brain. We further performed Northern blot hybridization to reveal the regional distribution of β3GalT-l transcripts in mouse brain. In cerebral cortex, p3GalT-l was expressed abundantly in newborn mice with a slight decrease in adult mice, and a similar expression pattern could also be detected in hippocampus. In contrast, the expression levels were low in diencephalon and brainstem in both newborn and adult mice. The cerebellum was the only area that differed significantly from the rest of the samples, with a higher expression in newborn mice, and a much lower expression in adult mice. The more accurate localization of β3GalT-l mRNA expression in mouse brain as studied by in situ hybridization was in good agreement with the general expression pattern seen with Northern blot hybridization. In newborn mice, the dense granular layer and the Purkinje cell showed a strong signal. However, in adult mice, strong signals were only detected in Purkinje cell layers and the levels in granular layers were barely detectable. The a...