Transcripts of the myotonic dystrophy protein kinase (DMPK) gene, a member of the Rho kinase family, are subject to cell-type specific alternative splicing. An imbalance in the splice isoform profile of DMPK may play a role in the pathogenesis of DM1, a severe multisystemic disorder. Here, we report how structural subdomains determine biochemical properties and subcellular distribution of DMPK isoforms. A newly developed kinase assay revealed that DMPK is a Lys/Arg-directed kinase. Individual DMPK isoforms displayed comparable transphosphorylation activity and sequence preference for peptide substrates. However, DMPK autophosphorylation and phosphorylation of MYPT1 (as putative in vivo target of DMPK), were dependent on presence of an alternatively spliced VSGGG motif and the nature of the C terminus. In-gel effects of the VSGGG motif on the migration behavior of full-length kinase provide evidence for a model in which this motif mediates 3-D-conformational changes in DMPK isoforms. Finally, different C termini endow DMPK with the ability to bind to either endoplasmic reticulum or mitochondria or to adopt a cytosolic location. Our results suggest that DMPK isoforms have cell-type and location dependent substrate specificities with a role in organellar and cytoarchitectural dynamics.Myotonic dystrophy (DM1) is the most common form of muscular dystrophy in adults (23), caused by amplification of an unstable (CTG) n repeat in the 3Ј untranslated region (3Ј-UTR) of the DM1 protein kinase (DMPK) gene (10,20,29). The severity of the disease is correlated to the length of this repeat expansion, whereas there is an inverse correlation to the age of onset. The favored explanation for the DM1 phenotype is a gain-of-function at the RNA level (reviewed in references 41 and 53), whereby long (CUG) n repeat tracts in DMPK transcripts cause a global perturbation of RNA processing events in the nucleus. Reports of cis-effects on the accumulation of (CUG) n repeat containing DMPK transcripts in the nucleus and trans-effects on alternative splicing of transcripts encoding other muscle or brain proteins support this hypothesis (15,16,30,40,43,45).It is widely accepted, nonetheless, that the highly variable and complex DM1 phenotype is not caused solely by detrimental effects of (CUG) n expansion at the RNA level, but that also direct effects on DMPK gene products and local gene effects are involved in specific disease features. Various studies have shown that expansion of the (CTG) n repeat results in reduced appearance of DMPK in the cytoplasm (53). Studies in knockout mouse and myocyte cell models indicated that lack of DMPK protein may be associated with typical DM1 symptoms like myopathy and heart conduction defects, perhaps via effects on Ca 2ϩ or Na ϩ ion homeostasis (5,6,25,35,42).DMPK is a member of the AGC group of serine/threonine kinases (31) and is most homologous to the p21-activated kinases MRCK (28) and ROCK/rho-kinase/ROK (4). Other mammalian homologues are NDR1 (32), warts/lats (26, 55), and citron kinase (17). DM...

We have cloned and characterized two distinct types of alphoid DNA elements. Probe pG-Xbal 1/340 was obtained by random cloning of human satellite DNA and contains two basic units with overall 88% homology to the 171 -bp consensus alphoid sequence. pG-Xball/340-like elements are represented about 2,000-4,000 times in the haploid genome and, by in situ hybridization, are found exclusively at the primary constrictions of chromosomes 4 and 9. Probe pG-A16 was cloned from a chromosome 19-specific cosmid library and represents a 2.25-kb higher-order DNA element which is present at roughly 75-150 copies per haploid genome and which hybridizes to the centromeres of chromosomes 5 and 19. Using the pG-A16 probe, further genetic and physical dissection of the central area of chromosome 19 can be envisaged.

We have studied genetic linkage between the gene for creatine kinase muscle type (CKMM) and the gene for myotonic dystrophy (DM). In a panel of 65 myotonic dystrophy families from Canada and the Netherlands, a maximum lod score (Zmax) of 22.8 at a recombination frequency (theta) of 0.03 was obtained. Tight linkage was also demonstrated for CKMM and the gene for apolipoprotein C2 (ApoC2). This establishes CKMM as a useful marker for myotonic dystrophy.

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We identified a large kindred that shows classical myotonic dystrophy (MyD), together with hereditary motor and sensory neuropathy (HMSN) in some individuals, and HMSN alone in others. A previous study of this family has shown cosegregation of the MyD and HMSN phenotypes with the Lutheran and secretor loci in some branches of the family, indicating linkage to chromosome 19. We reanalyzed this family with 2 recombinant DNA marker systems from the ApoC2 locus on chromosome 19. Our results demonstrate that all affected individuals have inherited a unique ApoC2 haplotype that was not found in their clinically and electrophysiologically normal sibs. We also obtained evidence against involvement of the HMSN I locus on chromosome 17. In this family, a moderately severe neuropathy may be the only clinical sign of MyD for many years. Our results are consistent with an unusual neuropathic mutation at the MyD gene. However, involvement of 2 closely linked genes (1 for MyD and the other for HMSN) can also explain our findings.