The examination was performed whether aquaporin (AQP) 9 is expressed in normal skeletal muscle at mRNA and protein levels. Gel electrophoresis of the reverse transcription-polymerase chain reaction (RT-PCR) product of total RNA samples of human normal muscles by oligonucleotide primers for human AQP9 showed a band of 221 basepairs, which corresponded to the basepair length between two primers of AQP9. The nucleotide sequence of RT-PCR product coincided with that of human AQP9. Immunoblot analysis revealed that the rabbit and sheep antibodies against the synthetic peptide of the C-terminal cytoplasmic domain of human AQP9 molecule reacted with a protein of approximately 30 kDa molecular weight in extracts of human normal skeletal muscles. Immunohistochemistry with our anti-AQP9 antibodies showed an immunoreaction at the myofiber surface of both type 1 and type 2 fibers with almost equal staining intensity in human skeletal muscles. The implication of AQP9 expression in skeletal myofibers was discussed.

Previous study has suggested that distinct populations of myeloid cells exist in the anterior ventral blood islands (aVBI) and posterior ventral blood islands (pVBI) in Xenopus neurula embryo. However, details for differentiation programs of these two populations have not been elucidated. In the present study, we examined the role of Wnt, vascular endothelial growth factor (VEGF) and fibroblast growth factor signals in the regulation of myeloid cell differentiation in the dorsal marginal zone and ventral marginal zone explants that are the sources of myeloid cells in the aVBI and pVBI. We found that regulation of Wnt activity is essential for the differentiation of myeloid cells in the aVBI but is not required for the differentiation of myeloid cells in the pVBI. Endogenous activity of the VEGF signal is necessary for differentiation of myeloid cells in the pVBI but is not involved in the differentiation of myeloid cells in the aVBI. Overall results reveal that distinct mechanisms are involved in the myeloid, erythroid and endothelial cell differentiation in the aVBI and pVBI.

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Aquaporin (AQP) 4 is a water-specific channel protein and is abundant in central nervous tissues and skeletal muscles. Recently, the AQP4 molecule has been increasingly highlighted in its pathophysiological role of several neurological diseases, such as stroke, muscular dystrophy and neuromyelitis optica. We therefore measured the levels of AQP4 mRNA and glyceraldehyde-3 phosphate dehydrogenase mRNA (an internal control) in muscle and brain tissues of wild-type mice (C57BL10/ScSn) and age-matched dystrophindeficient mdx mice (C57BL10/ScSn mdx) by real-time quantitative RT-PCR. The relative AQP4 mRNA level was highest in the spinal cord among the neuromuscular tissues examined in wild-type mice. Among the muscle tissues of wild-type mice, the relative AQP4 mRNA level was higher in extensor digitorum longus (EDL) muscles, and its descending order was EDL, quadriceps femoris, soleus and heart muscles. It is noteworthy that there was no difference in the relative AQP4 mRNA levels in the brain tissues between wildtype mice and age-matched mdx mice. In contrast, the AQP4 mRNA level in the quadriceps femoris muscle was significantly lower in mdx mice than in wild-type mice. The fact that the spinal cord contains the highest AQP4 mRNA may be related to the pathogenesis of neuromyelitis optica, in which AQP4 protein is the target antigen. In addition, the low expression level of AQP4 mRNA in the mdx mouse muscle suggests a functional link between AQP4 and dystrophin in the muscle tissue. We suggest that a similar pathomechanism may underlie the phenotypic consequences of the mdx mouse and Duchenne muscular dystrophy. The water molecule is essential for the living organism. Aquaporins (AQPs) comprise a large family of integral membrane proteins that form a water channel in animals, plants and microorganisms. They play a role in bidirectional water movement in response to osmotic gradients created by ion pumping and are expressed widely in mammalian epithelia and endothelia. In skeletal muscle cells (Rash and Ellisman 1974) and brain astrocytes (Landis and Reese 1981), the freeze fracture electron microscopy revealed the presence of many orthogonal arrays (OAs) which are identified as aggregates of 4 or more 6-nm diameter particles in the P face and as aggregates of 4 or