The gene for cytoplasmatic malate dehydrogenase, Mor2, is closely linked to the wobbler spinal muscular atrophy gene (wr)

Integrated radiation hybrid map of human chromosome 2p13: possible involvement of dynactin in neuromuscular diseases

The genes for the human neuromuscular diseases limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy are located on chromosome 2p13-p14, and two neuromuscular mutations of the mouse have been mapped to regions homologous to human chromosome 2p13 by conserved synteny, wobbler (wr) on proximal Chr 11 and motor neuron degeneration 2 (mnd2) on Chr 6. Neither one is a mouse homologue of LGMD2B. Recently the gene DCTN1, coding for the large subunit of the cytoskeletal protein dynactin, was shown by FISH to be located in this region and therefore should be considered a candidate for all these disease genes. Here we present mapping data based on radiation hybrid and physical mapping that more precisely define the location of nine genetic markers in the critical region and the homology relationship of human chromosome 2p with mouse proximal Chr 11 and Chr 6. The human dynactin gene was mapped between markers TGFA and D2S1394, implying that the mouse dynactin gene Dctn1 is located on Chr 6, distal to mnd2. Thus DCTN1/Dctn1 is a candidate for LGMD2B but not for mnd2 or wr.

Spinal muscular atrophy gene wobbler of the mouse: evidence from chimeric spinal cord and testis for cell-autonomous function

Human hereditary neurodegenerative diseases are genetically and mechanistically very heterogeneous and so are spinal muscular atrophies and cerebellar ataxias in the mouse, despite the common phenomenon of neuronal death. In this species, a number of mutations impair spermiogenesis in addition to neuron survival. Among these, the wobbler mutation on proximal chromosome 11 of the mouse leads to motoneuron degeneration in brain stem and spinal cord and to a defect of spermiogenesis. Chimeric mice of the type wr?/wr? <--> +/+ were produced, and their allelic status at the wr locus was determined by PCR diagnosis of a closely linked marker. Two overt chimeras, one female (XX <--> XX) and one male (XY <--> XY) were identified as wr/wr <--> +/+ and analyzed with respect to their pathological phenotype. Although there was patchy astrogliosis in the spinal cords of both chimeras, their motor performances were overtly normal and muscles were without signs of denervation. The male's testes revealed a mosaic pattern of normal and pathological spermatids. As no progeny was derived from wr spermatids, the spermatocytes appear as a primary target of the wr mutation in testis. Our results argue against a humoral mechanism of the wobbler disease and indicate a cell-autonomous action of the wr gene both in testis and in spinal cord.