Molecular cloning of rat sperm galactosyl receptor, a C-type lectin with in vitro egg binding activity

Eugene Rivkin, Laura L. Tres, Ruth Kaplan-Kraicer, Ruth Shalgi, Abraham L. Kierszenbaum*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Rat sperm galactosyl receptor is a member of the C-type animal lectin family showing preferential binding to N-acetylgalactosamine compared to galactose. Binding is mediated by a Ca2+-dependent carbohydrate-recognition domain (CRD) identical to(hat of the minor variant of rat hepatic lectin receptor 2/3 (RHL-2/3). The molecular organization of the genomic DNA, cDNA, and derived amino acid sequence of rat testis galactosyl receptor have been determined and in vitro fertilization studies were conducted to ascertain its role. We have determined that the rat testis galactosyl receptor gene generates two mRNA species: one species, designated liver-type, is identical to RHL-2/3; the other, designated testis-type, contains one unspliced intron (86 nt) which alters the reading frame and changes the amino acid sequence of the carboxyl terminus. As a result, the CRD (glutamine-proline-aspartic acid/QPD) and flanked Ca2+-binding amino acid sequences were not present in the testis-type protein. Northern and Southern blots demonstrated presence of transcripts with unspliced intron in rat sperm but not liver. Similarly, antibody, raised against a synthetic 12-amino acid peptide (p12) encoded by the unspliced intron, recognized in immunoblots a 54 kDa receptor protein in protein extracts from testis but not from liver. Immunofluorescence and immunogold electron microscopy studies demonstrated that both protein species localized on the plasma membrane surface of the head and tail of rat sperm. Furthermore, capacitated rat sperm preincubated with polyclonal antisera to RHL-2/3 or to the CRD of the liver-type galactosyl receptor showed a statistically significant decrease in the in vitro fertilization rate. We conclude that rat sperm galactosyl receptor may play a role in egg binding and that an undetermined molecular mechanism operates to generate two proteins with identical intracellular amino terminal domain but only one of them displays a CRD and associated Ca2+-binding sites at the carboxyl terminal extracellular domain. (C) 2000 Wiley-Liss, Inc.

Original languageEnglish
Pages (from-to)401-411
Number of pages11
JournalMolecular Reproduction and Development
Volume56
Issue number3
DOIs
StatePublished - 2000

Funding

FundersFunder number
Eunice Kennedy Shriver National Institute of Child Health and Human DevelopmentR01HD027685

    Keywords

    • C-type lectin
    • Differential splicing
    • Fertilization
    • Immunoblocking
    • Sperm receptor
    • Sperm tail

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