Grewal Prabhjit K, McLaughlan Jennifer M, Moore Christopher J, Browning Claudia A, Hewitt Jane E
Institute of Genetics, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK.
Glycobiology. 2005 Oct;15(10):912-23. doi: 10.1093/glycob/cwi094. Epub 2005 Jun 15.
The Large(myd) 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 alpha-dystroglycan (alpha-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 alpha-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 alpha-DG is still fully glycosylated in kidney (a tissue that expresses a high level of LARGE2 mRNA) of Large(myd) mutant mice.
大（myd）小鼠在假定的糖基转移酶基因Large中存在功能丧失突变。人类同源基因（LARGE）的突变已在一种先天性肌营养不良（MDC1D）中被描述。其他编码已知或假定糖基化酶的基因（POMT1、POMGnT1、福库亭和FKRP）也与人类先天性肌营养不良有因果关系。所有这些疾病都与膜蛋白α- dystroglycan（α-DG）的低糖基化以及随之而来的细胞外配体结合丧失有关。因此，它们被称为糖基化肌营养不良症。LARGE的一个旁系同源基因（LARGE2或GYLTL1B）可能也在DG糖基化中起作用。通过数据库查询和逆转录聚合酶链反应（RT-PCR），我们在许多脊椎动物中鉴定出了这些LARGE基因中每一个的脊椎动物直系同源基因，包括人类、小鼠、狗、鸡、斑马鱼和河豚。然而，在无脊椎动物基因组中，我们只能鉴定出单个同源基因。我们建议将脊椎动物LARGE直系同源基因称为LARGE1。RT-PCR、斑点印迹和Northern分析表明，LARGE2的组织表达谱比LARGE1更受限。使用表位标记蛋白我们发现，LARGE1和LARGE2都定位于高尔基体。LARGE旁系同源基因之间的高度相似性表明LARGE2可能也作用于DG。在小鼠C2C12成肌细胞中过表达LARGE2会导致α-DG糖基化增加，同时层粘连蛋白结合增加。因此，LARGE1和LARGE2之间可能存在功能冗余。与此观点一致，我们发现大（myd）突变小鼠的肾脏（一种表达高水平LARGE2 mRNA的组织）中的α-DG仍然完全糖基化。
