Hippocampal overexpression of Down syndrome cell adhesion molecule in amyloid precursor protein transgenic mice.

Down syndrome cell adhesion molecule (DSCAM) is located within the Down syndrome critical region of chromosome 21. DSCAM is a broadly expressed neurodevelopmental protein involved in synaptogenesis, neurite outgrowth, and axon guidance. We previously demonstrated DSCAM overexpression in the cortex of amyloid precursor protein (APP) transgenic mice, suggesting possible regulatory interactions between APP and DSCAM. APP mice exhibit deficits in hippocampus-dependent learning and memory. In this preliminary study, we examined age-related changes in DSCAM expression within the hippocampus in 16 APP transgenic mice (1, 3, 6 and 12 months old). Hippocampus-dependent spatial memory was assessed in APP mice and age-matched wild type littermates (WTs) using the Morris water maze (MWM). The cellular distribution of hippocampal DSCAM and total expression at both mRNA and protein levels were measured by immunohistochemistry, qRT-PCR, and western blotting, respectively. APP mice exhibited spatial memory deficits in the MWM. Intense DSCAM immunoreactivity was observed in the dentate gyrus granule cell layer and hippocampal stratum pyramidale. Total hippocampal DSCAM mRNA and protein expression levels were substantially higher in APP mice than WTs at 1 and 3 months of age. Expression decreased with age in both groups but remained higher in APP mice. DSCAM is overexpressed in the hippocampus over the first 12 months of life in APP mice, but especially during maturation to adulthood. In conclusion, these results suggest an association between DSCAM and APP mice, which is characterized by neuropathology and behavioral deficits. These results provide some clues for future studies on the role of DSCAM overexpression in the precocious cognitive decline observed in APP transgenic mice.

Characterization of novel nitrate reductase-deficient mutants for transgenic Dunaliella salina systems.

The aim of the present study was to isolate and characterize novel nitrate reductase (NR)-deficient mutants, which may be useful for the transgenic manipulation of Dunaliella salina. Three NR-deficient mutants of D. salina, J-1, J-2, and J-3, were successfully isolated by screening for chlorate resistance after chemical mutagenesis with ethylnitrosourea. NR activity was not detected in the mutants and the expression of NR mRNA was significantly decreased. Growth analysis of D. salina strains grown in media containing different nitrogen sources revealed that these mutants were capable of utilizing nitrite and urea, but not nitrate as a nitrogen source, indicating that these mutants are indeed NR-deficient. Mutation analysis of NR cDNA sequences revealed that there were 11 point mutations shared by the J-1, J-2, and J-3 mutants. Furthermore, the results of the functional complementation experiment showed that NR activity of transformant T-1 derived from J-1 was recovered to 48.1 % of that of the wild-type D. salina. The findings of the present study indicate that nitrate may be used as a selective agent rather than antibiotics or herbicides for the isolated NR-deficient mutants in future transgenic D. salina systems.

Natural variation of rice blast resistance gene Pi-d2.

Studying natural variation in rice resistance genes of cultivated and wild rice relatives can predict resistance stability to rice blast fungus. In the present study, the protein coding regions of the rice R gene Pi-d2 in 35 rice accessions, including Oryza sativa L. subsp. indica Kato (Aus), indica (IND), temperate japonica (TEJ), tropical japonica (TRJ), aromatic (ARO); subgroups of Oryza sativa; 6 accessions of wild rice varieties; O. nivara; and O. rufipogon were analyzed. A total of 13 nucleotide differences were found in the open reading frames (ORFs) of Pi-d2. Translation of these ORFs revealed 9 variants; 3 were novel Pi-d2 variants. Variants H2 and H5 were identified in accessions of cultivated rice and O. nivara, H1, H3, H4, H6, and H8 were only identified in cultivated rice. H2 and H5 were the common types of IND and O. nivara, H8 was the common type of TRJ and AUS, H6 was the specific type of AUS, and H3 was the specific type of ARO. H7 and H9 were specific haplotypes of O. nivara and O. rufipogon, respectively. These findings demonstrate that Pi-d2 variants are useful indicators for each subgroup, and Pi-d2 is an ancient gene that predates speciation of rice subgroups.