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Cerebral water accumulation was studied during induction of brain edema in dystrophin-null transgenic mice (mdx-[beta]geo) and control mice. Immunofluorescence and immunoelectron microscopic analyses of dystrophin-null brains revealed a dramatic reduction of AQP4 (aquaporin-4) in astroglial end-feet surrounding capillaries (blood--brain barrier) and at the gila limitans (cerebrospinal fluid-brain interface). The AQP4 protein is mislocalized, because immunoblotting showed that the total AQP4 protein abundance was unaltered. Brain edema was induced by i.p. injection of distilled water and 8-deamino-arginine vasopressin. Changes in cerebral water compartments were assessed by diffusion-weighted MRI with determination of the apparent diffusion coefficient (ADC). In dystrophin-null mice and control mice, ADC gradually decreased by 5-6% from baseline levels during the first 35 min, indicating the initial phase of intracellular water accumulation is similar in the two groups. At this point, the control mice sustained an abrupt, rapid decline in ADC to 58% [+ or -] 2.2% of the baseline at 52.5 min, and all of the animals were dead by 56 min. After a consistent delay, the dystrophin-null mice sustained a similar decline in ADC to 55% [+ or -] 3.4% at 66.5 min, when all of the mice were dead. These results demonstrate that dystrophin is necessary for polarized distribution of AQP4 protein in brain where facilitated movements of water occur across the blood--brain barrier and cerebrospinal fluid--brain interface. Moreover, these results predict that interference with the subcellular localization of AQP4 may have therapeutic potential for delaying the onset of impending brain edema.

It has been possible to use positional cloning to isolate the t-responder (Tcr). It was established that Tcr belongs to a novel protein kinase gene family, known as Smok, expressed during late spermiogenesis. The identification of Tcr as a member of a protein kinase gene family indicates that Smok and Tcr could be elements of a signal cascade that controls flagellar function. The relationship of Smok/Tcr proteins to MARK2 kinase, which phosphorylates microtubule-associated proteins, may also suggest a function for Smok/Tcr on the axoneme.

Experimental analyses of the M-twist gene activities to determine if the gene suppresses muscle differentiation show that mouse twist gene suppresses muscle differentiation in a reversible manner. Stable M-twist expression vector transfection in myogenic mouse cells damages differentiation in 75% of muscle cells and completely inhibits differentiation in 15% of cells. Application of antisense oligonucleotides revives the ability of the cells to differentiate.