Glial cell line-derived neurotrophic factor-responsive and neurotrophin-3-responsive neurons require the cytoskeletal linker protein dystonin for postnatal survival

We have investigated the fate of different neurotrophin-responsive subpopulations of dorsal root ganglion neurons in dystonia musculorum (dt) mice. These mice have a null mutation in the cytoskeletal linker protein, dystonin. Dystonin is expressed by all sensory neurons and cross links actin filaments, intermediate filaments, and microtubules. The dt mice undergo massive sensory neurodegeneration postnatally and die at around 4 weeks of age. We assessed the surviving and degenerating neuronal populations by comparing the dorsal root ganglion (DRG) neurons and central and peripheral projections in dt mice and wildtype mice. Large, neurofilament-H-positive neurons, many of which are muscle afferents and are neurotrophin-3 (NT-3)-responsive, were severely decreased in number in dt DRGs. The loss of muscle afferents was correlated with a degeneration of muscle spindles in skeletal muscle. Nerve growth factor (NGF)-responsive populations, which were visualized using calcitonin gene-related peptide and p75, appeared qualitatively normal in the lumbar spinal cord, DRG, and hindlimb skin. In contrast, glial cell line-derived neurotrophic factor (GDNF)-responsive populations, which were visualized using the isolectin B-4 and thiamine monophosphatase, were severely diminished in the lumbar spinal cord, DRG, and hindlimb skin. Analysis of NT-3, NGF, and GDNF mRNA levels using semiquantitative reverse transcriptase-polymerase chain reaction revealed normal trophin synthesis in the peripheral targets of dt mice, arguing against decreased trophic synthesis as a possible cause of neuronal degeneration. Thus, the absence of dystonin results in the selective survival of NGF-responsive neurons and the postnatal degeneration of many NT-3- and GDNF-responsive neurons. Our results reveal that the loss of this ubiquitously expressed cytoskeletal linker has diverse effects on sensory subpopulations. Moreover, we show that dystonin is critical for the maintenance of certain DRG neurons, and its function may be related to neurotrophic support. J. Comp. Neurol. 432:155-168, 2001. (C) 2001 Wiley-Liss. Inc.