Identification of the Core Protein Carrying the Tn Antigen in Mouse Brain: Specific Expression on Syndecan-3.

Abstract

ABSTRACT. We isolated glycoproteins carrying the Tn antigen, which was expressed spatiotemporally in the developing mouse brain. The Tn antigen was expressed on two molecular species with a molecular weight from 200 to 350 kDa and 110 to 160 kDa, as judged on SDS-PAGE. Although the two glycoproteins showed different susceptibilities to heparitinase I and solubilities in a salt solution, after treatment with V8 protease they showed the same mobility corresponding to a molecular weight of 90 kDa on SDS-PAGE, suggesting that these two molecules shared a common core protein. Partial N-terminal sequences of the glycoproteins were determined, i.e. AQRXRNENFERPV and ALAAPXAPAMLP, which were identified as the sequences of the N-terminal and central portions of syndecan-3, respectively. Both glycoproteins were reactive to anti-mouse syndecan-3 antibody. These results suggest that one is a soluble syndecan-3 cleaved between mucin-like domain and transmembrane domain, and the other is a membrane-bound syndecan-3 lacking N-terminal glycosaminoglycan attachment sites, and that both glycoproteins have a mucin-like domain characteristic of syndecan-3, in which the Tn antigen may be expressed.

Cloning and Characterization of a New Human UDP-N-Acetyl-α-d-galactosamine:PolypeptideN-Acetylgalactosaminyltransferase, Designated pp-GalNAc-T13, That Is Specifically Expressed in Neurons and Synthesizes GalNAc α-Serine/Threonine Antigen

“…In addition, cell bodies of neuronal cells in the internal granular layer also exhibited positive reactivity. According to the previous studies (24,44), internal granular layer cells were not likely stained with MLS128, and this was different from our present results using HB-Tn1. In contrast, the pp-GalNAc-T13 null mouse showed a remarkable decrease in HB-Tn1 reactivity both in Purkinje cells and in internal granular layer cells (Fig.…”

“…antibody (24,44). It was reported that the triplet Tn antigen is present in late embryonic brain with an expression peak in the early postnatal brain (postnatal 3-7 days, P3-P7), and immunoreactivity for MLS128 was restricted to the cell bodies of Purkinje cells in the P7 mouse brain (44).…”

“…pp-GalNAc-T9 is an exception in that it is mainly expressed in the brain; however, its activity has yet to be examined (8). Very recently, it was reported that certain proteins in neurons, such as a neurite outgrowth receptor, human ␣-synuclein related to Parkinson's disease, and human syndecan-3, are modified by O-linked glycosylation (23,24). It is of interest to identify the pp-GalNAc-T(s) responsible for the O-linked glycosylation of proteins in neurons.…”

“…In this sense, syndecan-3 may be a natural substrate for pp-GalNAc-T13. It has been reported that syndecan-3 carries an antigenic epitope that reacts with an anti-Tn antibody, MLS128, and the reactivity is regulated during development in the mouse brain (24,44,45). The epitope structure recognized by MLS128 has also been reported to compose three or four consecutive sequences of GalNAc-Ser/Thr (46,47).…”

Differential expression of syndecan isoforms during mouse incisor amelogenesis

“…Tissue slices along the longitudinal axis of incisors were stained with rabbit polyclonal antibodies raised against extracellular portions of mouse syndecan core proteins. The specificity of the antibodies was confirmed in the previous study (17,18).…”