Developmental Expression of a Sialyltransferase Responsible for Sialylation of Cortical Alveolus Glycoprotein during Oogenesis in Rainbow Trout (<i>Oncorhynchus mykiss</i>)

  • Asahina Shinji
    Department of Regulation of Biological Signals, Nagoya University Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University
  • Sato Chihiro
    Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University Bioscience and Biotechnology Center, Nagoya University
  • Kitajima Ken
    Department of Regulation of Biological Signals, Nagoya University Bioscience and Biotechnology Center, Nagoya University Institute for Advanced Research, Nagoya University

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  • Developmental Expression of a Sialyltransferase Responsible for Sialylation of Cortical Alveolus Glycoprotein during Oogenesis in Rainbow Trout (Oncorhynchus mykiss)

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Abstract

Polysialoglycoprotein (PSGP) is a major cortical alveolus glycoprotein of rainbow trout eggs that is characterized by the attachment of a polysialic acid structure to its O-glycan chains. It has been demonstrated that the polysialic acid structure is synthesized by at least three sialyltransferases mostly localized in cortical alveoli. Here we have cloned a cDNA encoding the sialyltransferase, designated rtST6GaINAc, responsible for the transfer of the first sialic acid residue onto the O-glycan chain of PSGP. This enzyme belongs to the vertebrate ST6GaINAc II family, and is strongly expressed in ovaries. Of those O-glycoproteins tested as substrates, asialo-PSGP is the best substrate. These results indicate that rtST6GalNAc is the enzyme responsible for the sialylation of PSGP during oogenesis. Furthermore, the rtST6GalNAc mRNA is expressed throughout oogenesis, is down-regulated at the late yolk vesicle stage (May), and then up-regulated during vitellogenesis (until August). This developmental profile is highly similar to that of STL2, a cortical alveolus lectin, while it is quite different from that of PSGP, which is extensively expressed at the yolk vesicle stage and down-regulated at later stages. Thus, not all cortical alveolus components are transcribed concomitantly. This is the first description of a developmental change in the transcription of a glycosyltransferase during oogenesis.

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