Knockdown of the Drosophila fused in sarcoma (FUS) homologue causes deficient locomotive behavior and shortening of motoneuron terminal branches

Mutations in the fused in sarcoma/translated in liposarcoma gene (FUS/TLS, FUS) have been identified in sporadic and familial forms of amyotrophic lateral sclerosis (ALS). FUS is an RNA-binding protein that is normally localized in the nucleus, but is mislocalized to the cytoplasm in ALS, and comprises cytoplasmic inclusions in ALS-affected areas. However, it is still unknown whether the neurodegeneration that occurs in ALS is caused by the loss of FUS nuclear function, or by the gain of toxic function due to cytoplasmic FUS aggregation. Cabeza (Caz) is a Drosophila orthologue of human FUS. Here, we generated Drosophila models with Caz knockdown, and investigated their phenotypes. In wild-type Drosophila, Caz was strongly expressed in the central nervous system of larvae and adults. Caz did not colocalize with a presynaptic marker, suggesting that Caz physiologically functions in neuronal cell bodies and/or their axons. Fly models with neuron-specific Caz knockdown exhibited reduced climbing ability in adulthood and anatomical defects in presynaptic terminals of motoneurons in third instar larvae. Our results demonstrated that decreased expression of Drosophila Caz is sufficient to cause degeneration of motoneurons and locomotive disability in the absence of abnormal cytoplasmic Caz aggregates, suggesting that the pathogenic mechanism underlying FUS-related ALS should be ascribed more to the loss of physiological FUS functions in the nucleus than to the toxicity of cytoplasmic FUS aggregates. Since the Caz-knockdown Drosophila model we presented recapitulates key features of human ALS, it would be a suitable animal model for the screening of genes and chemicals that might modify the pathogenic processes that lead to the degeneration of motoneurons in ALS.     

A splice variant of Arabidopsis mitogen-activated protein kinase and its regulatory function in the MKK6–MPK13 pathway

Alternative splicing (AS) generates multiple forms of proteins. A role for AS in the plant mitogen-activated protein kinase (MAPK) cascade has not been clarified. In this study, we analyzed expression of 20 Arabidopsis MAPK genes by RT-PCR and found five that generate splice variants. The MPK13 gene, with six exons and five introns, generates at least three splice variants, one in which complete splicing of five introns occurs (MPK13 Full), and ones in which the 4th and 5th introns are retained (MPK13 I4 and I5). Translation products of the splice variants MPK13 Full and I4, were found in Arabidopsis tissues by Western blot. Yeast two-hybrid analysis and protein kinase assays of recombinant proteins showed that neither I4 nor I5 interacted with upstream MAPKKs, and neither had protein kinase activity. However, MPK13 I4 protein enhanced the MKK6-dependent activation of MPK13 Full, indicating the possibility of an additional mechanism to regulate the MAPK cascade by AS.     

Urine calcium concentrations in bullfrog tadpoles kept in tap water or high calcium environment, with special reference to ultimobranchialectomy

1. Urine calcium concentrations were determined in intact and ultimobranchialectomized bullfrog tadpoles kept in tap water (Ca: 8.5 and 19.7 mg/100 ml), urine calcium levels did not show significant increases. 3. In ultimobranchialectomized tadpoles, hypercalciuria concomitant with the rise in serum calcium levels in recognized under both conditions of high calcium water and tap water. 4. It was suggested that in bullfrog tadpoles ultimobranchial glands do not exert effective influences on the renal handling of calcium.     

Changes in expansin activity and cell wall susceptibility to expansin action during cessation of internodal elongation in floating rice

We investigated the involvement of expansin action in determining the growth rate of internodes of floating rice (Oryza sativa L.). Floating rice stem segments in which rapid internodal elongation had been induced by submergence for 2 days were exposed to air or kept in submergence for 2 more days. Both treatments reduced the elongation rate of the internodes, and the degree of reduction was much greater in air-exposed stem segments than in continually submerged segments. These rates of internodal elongation were correlated with acid-induced cell wall extensibility and cell wall susceptibility to expansins in the cell elongation zone of the internodes, but not with extractable expansin activity. These results suggest that the reduced growth rate of internodes must be due, at least in part, to the decrease in acid-induced cell wall extensibility, which can be modulated through changes in the cell wall susceptibility to expansins rather than through expansin activity. Analysis of the cell wall composition of the internodes showed that the cellulosic and noncellulosic polysaccharide contents increased in response to exposure to air, but they remained almost constant under continued submergence although the cell wall susceptibility to expansins gradually declined even under continued submergence. The content of xylose in noncellulosic neutral sugars in the cell walls of internodes was closely and negatively correlated with changes in the susceptibility of the walls to expansins. These results suggest that the deposition of xylose-rich polysaccharides into the cell walls may be related to a decrease in acid-induced cell wall extensibility in floating rice internodes through the modulation of cell wall susceptibility to expansins.