A re-evaluation of the cytology of cat Pacinian corpuscles

Summary The ultrastructure of cat mesenteric Pacinian corpuscles in cross and longitudinal sections has been examined. The terminal ends of lamellar cells of the inner core have been identified in longitudinal sections through the proximal portion of the inner core. These terminal bulbous expansions contain characteristic concentric membranes of rough endoplasmic reticulum and in some cases masses of oval membranous inclusions. The central axon as seen in cross section is oval in profile, having X-(short) and Y-(long) axes, and each axonal face is characterized by specializations of the axolemma. At the X-axis, the inner lamellae of the inner core tightly abut a smooth axolemma, with no intervening connective tissue matrix, in a manner reminiscent of a neuroepithelium. The axolemma of the Y-axis has numerous axonal spines (microspikes) that project into the cleft in the inner core. The extent of the axolemma having axonal spines can only be appreciated in longitudinal sections. The clefts contain a specialized connective tissue with elastic and collagen fibrils. The connective tissue compartment of fibers and matrix separating individual inner core lamellae is unique, in that it contains extremely thin collagen fibrils measuring approximately 15 nm in diameter. The diameter of collagen fibrils increases as the cleft is approached. Here the fibrils resemble typical endoneural collagen.     

Role of cell displacement, cell division, and fragment size in pattern formation during embryonic retinal regeneration in Xenopus

Studies on the regenerating vertebrate retina provide, for the first time, a detailed view of how cells respond to removal of 2/3 of the eyebud, how their displacements, new juxtapositions, and extra mitotic activity correlate with stable changes in the retinotectal projection. They provide insight into how retinal ganglion cells encode "position", and how they use this information to form specific neural connectivity patterns.     

The genotoxicity of a variety of aniline derivatives in a DNA repair test with primary cultured rat hepatocytes

The genotoxicity of a variety of aniline derivatives was examined by a DNA repair test with rat hepatocytes. Out of 37 aniline derivatives, 6 chemicals, i.e., 2,4,6-trimethylaniline (mesidine), 2,4-xylidine, 3,5-diaminobenzoic acid, 3,4-diaminochlorobenzene, 2-chloro-4-methylaniline and 4-chloro-N-methylaniline, elicited positive DNA repair responses. The results are in agreement with the bacterial mutagenicities with or without norharman of these compounds. Positive compounds of unknown carcinogenicity in the present assay, i.e., 3,5-diaminobenzoic acid, 2-chloro-4-methylaniline and 4-chloro-N-methylaniline are suspected of being potentially carcinogenic.     

Sequence-specific DNA recognition by basic peptides.

A chiral template with C2 symmetry has been used for modeling a dimeric interface of DNA binding protein. An oligopeptide derived from the basic region of MyoD, a recently described "helix-loop-helix" class of DNA binding protein, has been tethered to the template. Among the four models which differ in chirality and polarity with respect to the arrangement of two subunits, only one dimer model with right-handed and C-terminus to C-terminus arrangement of the peptide subunits binds DNA containing native MyoD binding sequence.     

Structure of the Bombyx mori fibroin light-chain-encoding gene: upstream sequence elements common to the light and heavy chain.

Two overlapping genomic clones containing the fibroin light-chain (Fib-L)-encoding gene (Fib-L) were obtained from the cosmid library of the silkworm, Bombyx mori J-139, by hybridization with the Fib-L cDNA clone. Sequencing of the 14.6-kb region revealed that Fib-L was 13472 bp long containing seven exons, and that the gene contained a large first intron which occupied about 60% of the gene. Comparison of restriction patterns of the J-139 Fib-L with those of eight other B. mori breeds producing normal-level fibroin demonstrated that considerable restriction-fragment length polymorphisms were present in regions containing the first intron and the 3′-flanking sequence. However, sizes of the Fib-L mRNA and the Fib-L polypeptide were very similar among the nine breeds tested, suggesting that the exon sequences and the splice signals were all well conserved. 5′-Flanking regions of Fib-L and the fibroin heavy-chain (Fib-H)-encoding gene (Fib-H) compared in this study contained three 18-30-bp sequences of high similarity and many 8-10-bp common elements, six of which coincided with the binding sites of homeodomain proteins. Gel retardation assays with the nuclear extracts of the posterior and middle silk glands suggested that protein factors present in the posterior silk-gland nuclei could bind to a set of those common upstream elements.     

The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

Summary Two laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.     

SV40 T-antigen is required for maintenance of immortal growth in SV40-transformed human fibroblasts.

Two lines of immortal human fibroblasts were isolated following transfection of TIG-3 cells with plasmid DNA, pMT-1ODtsA, that contained SV40 early gene with a deletion in replication origin and ts mutation in coding sequence for T-antigen. These cells continued proliferation at 34 degrees C, over 565 population doubling level (PDL) which is far over the limited division potential of untransformed normal TIG-3 of 70-80 PDL. When the culture temperature was shifted to 40 degrees C after 70 PDL, they ceased proliferation immediately. One of these immortal clones, SVts8, lost its ts phenotype after retransformation with wtT-antigen gene. These results indicated that the function of intact T-antigen is required for maintenance of immortal proliferation, at least in one of the SV40 transformed immortal clones.     

Retinoic acid promotes proliferation and chondrogenesis in the distal mesodermal cells of chick limb bud

Distal and proximal mesoderm of chick limb bud was respectively dissociated and cultured in the medium containing various concentrations of retinoic acid (RA). At low concentrations (5-50 ng/ml), RA promoted proliferation and chondrogenesis in the distal mesodermal cells. The distal cells of stage 20-24 limb buds were responsive to RA, although those of stages 25-27 were unresponsive. Both the cells of anterior and posterior regions of the distal mesoderm were responsive to RA, while the cells of proximal mesoderm were unresponsive. At higher concentrations, the growth-promoting effect of RA was reduced and chondrogenesis in the distal cells was rather inhibited. These results were discussed in relation to the role of RA as the morphogen in normal limb development and experimental duplicate formation.     

Oxidation and esterification of geometrical and positional isomers of octadecenoic acids in perfused rat liver

The metabolic fate of the geometrical isomers of 6-, 9-, and 11-octadecenoic acids was studied in isolated perfused rat livers. Although the ketogenicities of these monounsaturated fatty acids generally decreased as the double bond was moved away from the carboxyl group, a dependence on the geometrical difference was found only for 9-octadecenoate, the rate being significantly lower in the cis-isomer. Very low density lipoprotein lipid secretion was distinctly and specifically decreased when trans-9-octadecenoic acid was perfused, but no such difference was observed with other isomers. Various trans-isomers were actively incorporated into the hepatic lipids and secreted apparently at the expense of preexisting endogenous cis-octadecenoate. The trans-isomers were all incorporated exclusively at the 1-position of hepatic phosphatidylcholine. Concentrations of the cis-octadecenoate in the glycerolipids secreted and remaining in the liver were characteristically modified depending on the location of the ethylenic bond of the cis-octadecenoate. Thus, both the location of the double bond in the acyl-chain and the geometrical configuration specifically influence the rate of oxidation and esterification of octadecenoic acid in perfused rat liver.     

Genotoxicity of carcinogenic N-nitrosopropylamine derivatives in the hepatocyte primary culture/DNA-repair test

The genotoxicity of N-nitrosodipropylamine, 8 of its oxidized derivatives and N-nitroso-2,6-dimethylmorpholine was examined in the hepatocyte primary culture (HPC)/DNA repair test. Nine N-nitrosamines which are known to be carcinogenic and mutagenic were clearly positive in the HPC/DNA-repair test. N-Nitroso(2,3-dihydroxypropyl) (2-hydroxypropyl)amine did not elicit DNA repair, but showed a borderline mutagenic response in the Salmonella/microsome test. Thus, the HPC/DNA-repair test displays a comparable capacity to the bacterial mutagenesis test for detecting the genotoxic effects of this class of carcinogens.