Glycobiology Advance Access originally published online on June 15, 2005
Glycobiology 2005 15(10):912-923; doi:10.1093/glycob/cwi094
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Characterization of the LARGE family of putative glycosyltransferases associated with dystroglycanopathies
Institute of Genetics, Queen’s Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK
1 These authors contributed equally to this work.
2 To whom correspondence should be addressed; e-mail: jane.hewitt{at}nottingham.ac.uk
3 Present address: Howard Hughes Medical Institute, 9500 Gilman Drive-0625, University of California San Diego, La Jolla, CA 92093
Received on December 15, 2004; revised on June 6, 2005; accepted on June 10, 2005
The Largemyd mouse has a loss-of-function mutation in the putative glycosyltransferase gene Large. Mutations in the human homolog (LARGE) have been described in a form of congenital muscular dystrophy (MDC1D). Other genes (POMT1, POMGnT1, fukutin, and FKRP) that encode known or putative glycosylation enzymes are also causally associated with human congenital muscular dystrophies. All these diseases are associated with hypoglycosylation of the membrane protein 
-dystroglycan (-DG) and consequent loss of extracellular ligand binding. Hence, they are termed dystroglycanopathies. A paralogous gene for LARGE (LARGE2 or GYLTL1B) may also have a role in DG glycosylation. Using database interrogation and reverse-transcriptase polymerase chain reaction (RT–PCR), we identified vertebrate orthologs of each of these LARGE genes in many vertebrates, including human, mouse, dog, chicken, zebrafish, and pufferfish. However, within invertebrate genomes, we were able to identify only single homologs. We suggest that vertebrate LARGE orthologs be referred to as LARGE1. RT–PCR, dot-blot, and northern analysis indicated that LARGE2 has a more restricted tissue-expression profile than LARGE1. Using epitope-tagged proteins, we show that both LARGE1 and LARGE2 localize to the Golgi apparatus. The high similarity between the LARGE paralogs suggests that LARGE2 may also act on DG. Overexpression of LARGE2 in mouse C2C12 myoblasts results in increased glycosylation of -DG accompanied by an increase in laminin binding. Thus, there may be functional redundancy between LARGE1 and LARGE2. Consistent with this idea, we show that -DG is still fully glycosylated in kidney (a tissue that expresses a high level of LARGE2 mRNA) of Largemyd mutant mice.
Key words: dystroglycan / glycosyltransferase / Golgi / muscular dystrophy