The role of N-glycans in spermatogenesis.
Many proteins, in particular those in the plasma membranes, are glycosylated with carbohydrates, which are grouped into O-glycans and N-glycans. O-glycans are synthesized step by step by glycosyltransferases, whereas N-glycans are synthesized by en-bloc transfer of the so-called high-mannose-type oligosaccharide from lipid-linked precursor to polypeptide. The high-mannose-type N-glycans are then modified by processing alpha-mannosidases. Alpha-mannosidase IIx (MX) was identified as the gene product of processing alpha-mannosidase II (MII)-related gene. MX apparently plays subsidiary role for MII in many cell types, as N-glycan patterns of MX null mouse tissues are not altered significantly. Surprisingly MX null male mice are infertile due to a failure of spermatogenesis. This review provides a brief overview of the in vivo role of N-glycans which are revealed by the gene knockout mouse approach, and introduce our studies on the MX gene knockout mouse. The MX gene knockout experiments unveiled a novel function of a specific N-glycan, which is N-acetylglucosamine-terminated and has a fucosylated triantennary structure, in the adhesion between germ cells and Sertoli cells. The study of MX is a good example of how the in vivo roles of an apparently redundant gene product are determined by the gene knockout approach.
Fukuda
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MN
Glycobiology Program, Cancer Research Center, The Burnham Institute, La Jolla, CA 92037, USA. michiko@burnham.org
Akama
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TO
D000818:Animals; D015894:Genome, Human; D006801:Humans; D008297:Male; D008361:Mannosidases / Q000235:genetics / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D011134:Polysaccharides / Q000502:physiology*; D013091:Spermatogenesis
D011134:Polysaccharides; D008361:Mannosidases; C445059:MAN2A2 protein, human; C499170:Man2a2 protein, mouse