Immunocytochemical detection of triphosphoinositide in vestibular hair cells

Triphosphoinositide (TPI), an aminoglycoside receptor and a possible regulator of cationic permeation through its ability to bind with Ca++, was localized by the protein-A gold technique in vestibular sensory epithelia using an antibody highly specific to TPI. TPI was detected on the stereocilia, kinocilia, and cuticular plate of hair cells, and in the reticular membrane of supporting cells. The cilia of hair cells are damaged by aminoglycosides at a relatively early stage of toxicity. Ca++-regulated bioactivity in this area is probably involved.     

Structural analysis and specific expression of microsomal cytochrome P-450(M-1) mRNA in male rat livers

cDNA clones for the P-450(M-1) mRNA, which exhibits a male-specific expression in rat livers, were isolated by using synthetic oligonucleotides as the probes. Sequence analysis of the cDNAs showed that P-450(M-1) mRNA contains 1,853 nucleotides in addition to a poly(A) chain, and a single open reading frame of 1,500 nucleotides encodes a polypeptide of 500 amino acids with a Mr = 57,187. The predicted NH2-terminal sequence of 30 amino acids agrees well with that of the purified protein determined by Edman degradation, and the predicted primary structure included all the partial sequences of six internal peptides of P-450(M-1) obtained by the proteolytic digestion and a conserved amino acid sequence containing a putative heme-binding cysteine, proximate to the COOH terminus of the molecules. P-450(M-1) showed relatively high sequence similarity with P-450b (Fujii-Kuriyama, Y., Mizukami, Y., Kawajiri, K., Sogawa, K., and Muramatsu, M. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 2793-2797) (52% similarity), P-450-3b (Ozols, J., Heinemann, F. S., and Johnson, E. F. (1985) J. Biol. Chem. 260, 5427-5434) (64%), P-450-1 (Tukey, R. H., Okino, S., Barnes, H., Griffin, K. J., and Johnson, E. F. (1985) J. Biol. Chem. 260, 13347-13354) (74%), P-450PBc1 (Leighton, J. K., DeBrunner-Vossbrinck, B. A., and Kemper, B. (1984) Biochemistry 23, 4598-4603) (71%), while its sequence similarity with 3-methylcholanthrene-inducible P-450c and P-450d is rather low. Consequently, P-450(M-1) could be structurally classified into the phenobarbital-inducible type of P-450 gene family. RNA blot analysis using a synthetic oligonucleotide specific for P-450(M-1) revealed that P-450(M-1) mRNA was expressed exclusively in the livers of mature male rats in a sex-specific manner, but not in other tissues so far examined.     

Deoxyribonucleoside triphosphate imbalance. 5-Fluorodeoxyuridine-induced DNA double strand breaks in mouse FM3A cells and the mechanism of cell death

The mechanism of cytotoxic action of 5-fluorodeoxyuridine (FdUrd) in mouse FM3A cells was investigated. We observed the FdUrd-induced imbalance of intracellular deoxyribonucleoside triphosphate (dNTP) pools and subsequent double strand breaks in mature DNA, accompanied by cell death. The imbalance of dNTP pools was maximal at 8 h after 1 microM FdUrd treatment; a depletion of dTTP and dGTP pools and an increase in the dATP pool were observed. The addition of FdUrd in culture medium induced strand breaks in DNA, giving rise to a 90 S peak by alkaline sucrose gradient sedimentation. The loss of cell viability and colony-forming ability occurred at about 10 h. DNA double strand breaks as measured by the neutral elution method were also observed in FdUrd-treated cells about 10 h after the addition. These results lead us to propose that DNA double strand breaks play an important role in the mechanism of FdUrd-mediated cell death. A comparison of the ratio of single and double strand breaks induced by FdUrd to that observed following radiation suggested that FdUrd produced double strand breaks exclusively. Cycloheximide inhibited both the production of DNA double strand breaks and the FdUrd-induced cell death. An activity that can induce DNA double strand breaks was detected in the lysate of FdUrd-treated FM3A cells but not in the untreated cells. This suggests that FdUrd induces the cellular DNA double strand breaking activity. The FdUrd-induced DNA strand breaks and cell death appear to occur in the S phase. Our results indicate that imbalance of the dNTP pools is a trigger for double strand DNA break and cell death.     

A transgenic class I antigen is recognized as self and functions as a restriction element

The function of a transgenic Dd class I molecule in the induction of immunologic tolerance to major histocompatibility complex antigens and in directing major histocompatibility complex restriction in C57BL/6 mice were investigated. All of the transgenic Dd mouse strains were found to be tolerant for the Dd antigen. Spleen cells from transgenic mice were immunocompetent but consistently failed to generate an anti-Dd cytotoxic T lymphocyte response in vitro, and skin grafts between transgenic Dd mice were not rejected. These data suggests that the Dd antigen was recognized as a self molecule. In addition, the transgenic Dd mice generated antigen-specific Dd-restricted cytotoxic T lymphocyte, indicating that the Dd antigen also functioned as a restriction element for antigen recognition. These observations demonstrate the usefulness of the transgenic mouse system for studying class I antigen expression and function.     

Assignment of the prealbumin (PALB) gene (familial amyloidotic polyneuropathy) to human chromosome region 18q11.2–q12.1

Summary The assignment of the human prealbumin (PALB) gene to chromosome region 18q11–q12.1 has been achieved using a human genomic probe in the study of human-mouse somatic cell hybrids and by in situ hybridization. Because familial amyloidotic polyneuropathy was reported previously to be due to a mutation in prealbumin, it can be inferred that the gene for this disorder also maps to 18q11.2–q12.1.