Carbohydrate structures are altered according to spatially and temporally controlled developmental programs (Muramatsu, 1988). Some of the developmentally regulated carbohydrate structures, especially those in non-reducing termini of glycans in glycoproteins or glycolipids, are believed to play important roles in regulation of differentiation and development.
6-Sulfated GlcNAc residues have recently attracted considerable interest since they are located not only in keratan sulfate (Kjellén and Lindhal, 1991) but also in mucin-type as well as asparagine-linked glycans (Spiro and Bhoyroo, 1988; de Waard et al., 1991; Shilatifard et al., 1993; Lo-Guidice et al., 1994). Notably, 6-sulfo sialyl Lewis x and 6[prime]-sulfo sialyl Lewis x structures are present in GlyCAM-1, an endothelial ligand of L-selectin, which plays a key role in the initial stage of lymphocyte homing to lymph nodes (Hemmerich et al., 1994). Sulfation of the ligand is essential for recognition by L-selectin (Imai et al., 1993). Both 6-sulfo sialyl Lewis x and 6[prime]-sulfo sialyl Lewis x have been proposed to be important as the L-selectin ligand (Hemmerich and Rosen, 1994; Tsuboi et al., 1996; Maly et al., 1996; Ohmoto et al., 1996; Galustian et al., 1997; Mitsuoka et al., 1997, 1998). However, immunological (Mitsuoka et al., 1997, 1998), enzymological (Maly et al., 1996) and chemical studies (Ohmoto et al., 1996; Galustian et al., 1997), which have been carried out recently, favor the view that the former is the preferred structure.
We recently cloned mouse GlcNAc-6-O-sulfotransferase (Uchimura et al., 1998b). The enzyme transferred sulfate to GlcNAc exposed to the nonreducing end, but not to internally located GlcNAc. This specificity of the cloned enzyme agrees with that of the unpurified enzyme preparations recently studied (Spiro et al., 1996; Degroote et al., 1997). The cloned GlcNAc-6-O-sulfotransferase has been concluded to participate in synthesis of 6-sulfo sialyl Lewis x structures, and was detected in high endothelial venules of mesenteric lymph nodes, suggesting that the enzyme is involved in formation of L-selectin ligands (Uchimura et al., 1998b).
In the present study, we analyzed expression of GlcNAc-6-O-sulfotransferase during postimplantation embryogenesis in the mouse to obtain information regarding the developmental roles of the sulfotransferase and its products.
Overall mode of expression of GlcNAc-6-O-sulfotransferase mRNA during mouse embryogenesis
Figure 1. GlcNAc6ST mRNA expression in the embryo and uterus on E6.5 (A-C), 7.5 (D-F) and 10.5 (G-I). (A), (D), (G), hematoxylin and eosin staining; (B), (E), (H), GlcNAc6ST antisense probe; (C), (F), (I), GlcNAc6ST sense probe. Arrowheads in (E) show expression in the mesoderm; the arrow in (E) shows expression in the ectoplacental cone; the arrowhead in (H) shows expression in the spinal ganglion. Abbreviations: ec, ectoderm; ect, ectoplacental cone; ed, endoderm; ex, extraembryonic ectoderm; lv, lateral ventricle; mes, mesoderm; Sg, spinal ganglion; T, thalamus; Te, tectum; 4v, fourth ventricle. Bars in (A) and (D), 100 µm; bars in (G) 400 µm.
On embryonic day 6.5 (E6.5), GlcNAc-6-O-sulfotransferase mRNA was not detected in the embryo proper nor in extraembryonic tissues (Figure
Figure 2. GlcNAc6ST mRNA expression in sagittal sections of an E13.5 mouse embryo and its tissues. (A), (D), (E), (F), (J), hematoxylin and eosin staining; (B), (G), (H), (I), (K), GlcNAc6ST antisense probe; (C), (L), GlcNAc6ST sense probe. The arrowhead in (G) shows strong expression in the dental mesenchyme; arrowheads in (H) show expression in ductal precursor cells of the pancreas; arrowheads in (I) show expression in condensing mesenchyme of the lung; arrowheads in (K) show expression in the mesenchyme around the salivary gland. Abbreviations: b, brain; de, dental epithelium; dm, dental mesenchyme; f, facial process; h, heart; k, kidney; l, lung; o, olfactory organ; p, pancreas; s, salivary gland; sb, segmental bronchi; t, tooth. Bars in (A), 500 µm; bars in (D-F) and (J), 100 µm.
Table I.
Figure 3. GlcNAc6ST mRNA expression during tooth development. (A), (C), (E), (G), hematoxylin and eosin staining; (B), (D), (F), (H), GlcNAc6ST antisense probe. (A) and (B), E12.5. (C) and (D), E13.5. (E) and (F), E14.5, the mRNA expression decreased in the dental papilla mesenchyme (arrowhead). Stars show GlcNAc6ST mRNA expression in the mesenchymal cells of the mandible. (G) and (H), E15.5, weak expression was detected in the inner enamel epithelium (arrowhead). Abbreviations: de, dental epithelium; dm, dental mesenchyme; dp, dental papilla mesenchyme; ie, inner enamel epithelium; Mc, Meckel's cartilage. Bars, 100 µm.
Figure 4. GlcNAc6ST mRNA expression during pancreas development. (A), (C), (E), (G), hematoxylin and eosin; (B), (D), (F), (H), GlcNAc6ST antisense probe. (A) and (B), E12.5. (C) and (D), E13.5. (E) and (F), E14.5. (G) and (H), E15.5. Ductal structures are indicated by arrowheads. Abbreviations: li, liver; p, pancreas. Bars, 100 µm.
Figure 5. GlcNAc6ST is expressed in particular regions of the embryonic central nervous system. (A), (B), (D-F), (G), GlcNAc6ST antisense probe; (C) and (H), GlcNAc6ST sense probe. (A) E10.5. (B-F) E12.5. (G) and (H), E15.5. Insets in (B) are expanded in (D-F). No specific signals were seen with the sense probe (C). The arrowhead in (B) shows GlcNAc6ST mRNA expression in the posterior pons. Arrow and arrowhead in (G) indicate the mRNA expression in the hypoglossal nucleus and the thalamus, respectively. Abbreviations: C, neocortex; Hi, hippocampus; Hli, intermediate hypothalamic neuroepithelium; Hlm, hypothalamus mammillary neuroepithelium; Is, isthmus; Is*, differentiating field of isthmus; It, inferior tectal neuroepithelium; lv, lateral ventricle; Med, medulla; Nc, neocortex; o, olfactory bulb; Pn, pons; St, strionuclear neuroepithelium of basal ganglia; T, thalamus; Te, tectum; 3v, third ventricle; 4v, fourth ventricle; 4vi, isthmal fourth ventricle. Bars, 100 µm.
Figure 6. Northern blotting analysis of GlcNAc6ST gene expression in developing mouse embryos. Aliquots of ten µg of total RNA from E 9.5, E11.5, E13.5, E15.5, and E17.5 mouse embryos were hybridized with a 32P-labeled mouse GlcNAc6ST cDNA probe. As a control, the same blot was rehybridized with a mouse GAPDH cDNA probe (bottom).
The mode of developmentally regulated expression of the sulfotransferase mRNA is more fully explained in 3 sites, namely the tooth, pancreas, and brain, in the following sections.
Degree of expression
Whisker follicles
ep
++
mes
+
Nose
ep
+
mes
+
Inner ear
ep
+
mes
+
Eye
ep
NS
mes
NS
Tooth
ep
-
mes
+++
Salivary gland
ep
-
mes
+++
Lung
ep
-
mes
++
Esophagus
ep
-
mes
-
Stomach
ep
-
mes
-
Intestine
ep
-
mes
-
Kidney
ep
++
mes
-
Ureter
ep
-
mes
-
Pancreas
ep
+++
mes
-
Heart
-
Liver
-
Testis
NS
Central nervous system
Telencephalon
++
Thalamus
+++
Mesencephalon
++
Myelencephalon
++
Choroid plexus
+
Peripheral nervous system
Dorsal root ganglia
-
Neuronal projection (tail)
++
Dermal epithelium
-
Oral epithelium
-
Tongue epithelium
+
Facial mesenchyme
++
Digital mesenchyme
++
Muscles
-
GlcNAc-6-O-sulfotransferase expression during tooth development.
The tooth is a good model in which to study the molecular mechanisms of inductive interactions of two tissues, the epithelial layer and the mesenchymal layer. On E12.5, there was no detectable expression of the sulfotransferase mRNA in the epithelium or mesenchyme (Figure
GlcNAc-6-O-sulfotransferase expression during pancreatic development.
Ductal epithelium of the pancreas expressed the mRNA on E12.5 (Figure
GlcNAc-6-O-sulfotransferase expression during brain development.
On E10.5, strong signals were observed in the telencephalon (neocortex, Nc) and the inferior tectal neuroepithelium (It), and moderate signals were seen in the anterior thalamus (Figure
Distribution of 6-sulfo Lewis x and 6-sulfo sialyl Lewis x antigens in E12.5-E15.5 embryos
N-Acetylglucosamine-6-O-sulfotransferase is expected to be involved in synthesis of a variety of glycan structures. Among them, we investigated the distribution of 6-sulfo Lewis x and 6-sulfo sialyl Lewis x antigens, since monoclonal antibodies specific to these structures are available.
The antigenically positive sites on E13.5 and E15.5 are summarized in Table II, and typical mode of expression in E13.5 brain is demonstrated in Figure
Figure 7. Expression of 6-sulfo Lewis x (AG223), 6-sulfo sialyl Lewis x (G152) and 6-sulfo poly-N-acetyllactosamine (5D4) antigens in E13.5 mouse brain. (A), (C), (E), neocortex; (B), (D), (F), thalamus. Arrows indicate expression in neocortical neuroepithelium. (A) and (B), AG223; (C) and (D), G152; (E) and (F), 5D4. T, thalamus, lv, lateral ventricle. Bars, 100 µm.
Figure 8. Expression of 6-sulfo sialyl Lewis x (G152) and 6-sulfo Lewis x (AG223) antigens in organs of E12.5 mice. (A) G152 in the tongue epithelium; (B) G152 in the lung epithelium; (C) AG223 in the intestinal mucosal epithelium. e, Epithelium. Bars, 100 µm.
By immunostaining we also examined the possible expression of L-selectin, which is a candidate molecule to recognize 6-sulfo sialyl Lewis x, but it was not detected in tissue sections of E13.5 and E15.5 embryos. The immunostaining procedure was valid, since intense staining of lymphocytes was observed when sections of the spleen from adult mice fixed under identical conditions were reacted with anti-L-selectin antibody.
The expression of GlcNAc-6-O-sulfotransferase was found to be strictly regulated both spatially and temporally during mouse embryogenesis. This restricted mode of expression implies that the enzyme may not be a sulfotransferase involved in synthesis of keratan sulfate in a wide variety of tissues. Indeed, the chromosomal location of human GlcNAc-6-O-sulfotransferase is different from that of the causative gene of macular corneal dystrophy (Uchimura et al., 1998c), which is probably due to hindrance of GlcNAc-6-O-sulfation of corneal keratan sulfate (Vance et al., 1996). However, the possibility that the GlcNAc-6-O-sulfotransferase studied here participates in keratan sulfate biosynthesis in specific tissues can not be excluded.
The developmentally regulated expression of GlcNAc-6-O-sulfotransferase is of special interest for the following reasons. First, the sulfotransferase is frequently expressed in one of two tissues undergoing epithelial-mesenchymal interactions, which is one of the fundamental processes in organogenesis, e.g., in the condensing mesenchyme of the tooth at E13.5. Among the interacting tissues, mesenchymal expression was also observed in the lungs and the salivary glands. However, in the pancreas, whisker follicles and kidney, epithelial tissues strongly expressed the message. Second, restricted regions of the brain showed distinct expression of the mRNA between E12.5 and 15.5. In particular, segmental sulfotransferase expression was observed in the inferior tectal neuroepithelium on E10.5 and the strionuclear neuroepithelium, intermediate hypothalamic neuroepithelium, and dorsal isthmal neuroepithelium on E12.5.
The results described in this paper clearly indicated the importance of 6-sulfo-N-acetyllactosamine-containing epitopes in mouse development. These findings raised three major questions to be answered by subsequent studies. First, the proteins which recognize the 6-sulfo-N-acetyllactosamine-containing epitopes in specific regions of mouse embryos should be identified, since L-selectin, which recognizes sulfated sialy Lewis x structures (Imai et al., 1993), has not been detected in embryonic tissues. Second, it is necessary to determine the structure of the sulfated epitopes formed by the sulfotransferase localized in developmentally significant regions; 6-sulfo sialyl Lewis x, 6-sulfo Lewis x and/or 6-sulfo-N-acetyllactosamine are possible candidates. In E15.5 and E13.5 embryonic brain, the thalamus expressed AG223(6-sulfo Lewis x) antigen, and the neocortex AG223 and G152(6-sulfo sialyl Lewis x) antigen. Miller et al., (1997) reported the presence of 6-sulfo poly N-acetyllactosamine antigenic epitope, 5D4, in these regions of E14-E16 rat embryos, and we confirmed its expression in the regions of E13.5 mouse embryos. The thalamus strongly expressed GlcNAc-6-O-sulfotransferase and the neocortex did it moderately. Therefore, in the brain, the region-specific expression of the sulfotransferase mRNA correlated, at least partly, with the distribution of arrays of 6-sulfo-N-acetyllactosamine containing structures. However, in other organs, the mode of the antigenic distribution did not correlate with the mRNA. Our own studies using 5D4 antibody revealed specific antigenic localization only in the brain and the heart (unpublished observations). In other words, at the present time, in situ hybridization to detect the mRNA is the only one method capable of implying stage-specific expression of 6-sulfo-N-acetyllactosamine-containing structures in embryonic organs other than the brain. Lastly, and most importantly, the developmental roles of 6-sulfo-N-acetyllactosamine-containing structures in embryogenesis should be investigated. To address this question, gene manipulation studies of the sulfotransferase are currently in progress in our laboratory.
Table II.
Antigenic expression | ||||
E13.5 | E15.5 | |||
Tissues and organs | AG223 | G152 | AG223 | G152 |
Brain | ||||
Neocortex | + | + | + | + |
Thalamus | ++ | - | + | - |
Choroid plexus of lateral ventricle | ++ | ++ | + | + |
Choroid plexus of the fourth ventricle | ++ | ++ | + | + |
Other organs | ||||
Tongue epithelium | ++ | + | ++ | + |
Lung epithelium | ++ | + | ++ | + |
Intestinal mucosal epithelium | ++ | + | ++ | + |
Adrenal glands | ++ | + | ++ | + |
Heart | + | + | + | + |
In situ hybridization
Embryos were collected from the inbred mouse strain C57BL6J. The morning when vaginal plugs were detected was designated as day 0.5 of gestation. Mice were anesthetized with Nembutal and perfused with 10 ml of saline followed by 50 ml of 4% paraformaldehyde in Dulbecco's phosphate-buffered saline (PBS). Both the embryos and those in their decidua were fixed in 4% paraformaldehyde in PBS at 4°C overnight. After embedding in paraffin, sections 5 µm thick were cut and placed on silane-coated slide glasses. They were then subjected to in situ hybridization or to hematoxylin-eosin staining to localize the site of signals.
For generation of in situ hybridization probes, a 0.6 kb PstI fragment of the cDNA encoding mouse GlcNAc-6-O-sulfotransferase (Uchimura et al., 1998b, nucleotide number 962-1561; GenBank accession number AB011451) was inserted into pBluescript II SK-(Stratagene, CA). After linearizing the template plasmid by digestion with appropriate restriction enzymes, T3 or T7 RNA polymerase was used to perform in vitro transcription. Digoxigenin-11-dUTP-labeled single-stranded RNA was prepared using a DIG RNA labeling Kit (Boehringer Mannheim, Germany). After ethanol precipitation, the products were dissolved in 50 µl of H2O, 20 U of RNase inhibitor, and 50 µl of deionized formamide, and then stored at -80°C until use. in situ hybridization was performed as described previously (Fan et al., 1998).
Immunohistochemistry
Monoclonal antibodies AG223 and G152 (mouse IgM) were produced as described previously (Mitsuoka et al., 1998), while 5D4 (rat IgG) was purchased from Seikagaku Kogyo, Japan. MEL-14, a monoclonal antibody to mouse L-selectin (mouse IgG), was purchased from Parmingen, CA.
Fluorescein isothiocyanate (FITC)-labeled IgG fraction of rabbit anti-mouse IgM, rabbit anti-mouse IgG, and of goat anti-rat IgG were purchased from Cappel Laboratories (Cochranville, PA).
For indirect immunofluorescence microscopy, two µm thick frozen sections of mouse embryos were cut with a cryocut and were fixed in cold acetone for 10 min. Indirect immunofluorescence staining was performed according to the method previously described (Akahori et al., 1997). The sections were immersed in 0.01 M phosphate-buffered saline (PBS) containing 1% normal rabbit or normal goat serum for 20 min to avoid nonspecific binding of the secondary antibodies. After washing with PBS, the sections were incubated with an optimal concentration of the first antibodies followed by the incubation with FITC labeled secondary antibodies. All the sections were mounted with 90% glycerol in PBS containing p-phenylenediamine (Platt et al., 1983), and were observed with Olympus BH2 epifluorescence microscopy.
Northern blotting analysis
RNA was extracted from C57BL/6J mouse embryos as described previously (Chomczynski and Sacchi, 1987), and electrophoresed on a 1.0% agarose gel containing 5% formaldehyde (v/v). Hybridization was performed as described (Uchimura et al., 1998a) using a 368 bp fragment of mouse GlcNAc-6-O-sulfotransferase cDNA (Uchimura et al., 1998b, nucleotide number 1139-1506) as a probe.
This work was supported by grants from the Ministry of Education, Science Sports and Culture, Japan (grant number 10178102 and Grant-in-aid for COE Research). We thank Ms. A.Horisawa and M.Ishihara for secretarial assistance. K.U. is a Research Fellow of the Japanese Society for the Promotion of Science.
E, embryonic day; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; GlcNAc, N-acetylglucosamine; GlcNAc6ST, N-acetylglucosamine-6-O-sulfotransferase; PBS, Dulbecco's phosphate-buffered saline; 6-sulfo sialyl Lewis x, NeuAc[alpha]2-3Gal[beta]1-4(Fuc[alpha]1-3)(SO4-6)GlcNAc; 6[prime]-sulfo sialyl Lewis x, NeuAc[alpha]2-3(SO4-6)Gal[beta]1-4GlcNAc.
This page is run by Oxford University Press, Great Clarendon Street, Oxford OX2 6DP, as part of the OUP Journals
Comments and feedback: jnl.info{at}oup.co.uk
Last modification: 25 Aug 1999
Copyright©Oxford University Press, 1999.