Cleavage of bacteriophage phi 80 CI repressor by RecA protein

We have purified the CI repressor protein of bacteriophage phi 80. Its N-terminal amino acid sequence and its amino acid composition agree with those predicted from the nucleotide sequence of the cI gene. The phi 80 CI repressor was cleaved at a Cys-Gly bond by the wildtype RecA protein in the presence of single-stranded DNA and ATP or its analogues. This cleavage site is different from other repressors such as LexA, lambda CI and P22 C2, which were cleaved at an Ala-Gly bond. The phi 80 CI repressor was cleaved at the same site by the RecA430 protein, but was not cleaved by the RecA1 protein. This effect of the bacterial recA mutations on cleavage is consistent with the fact that prophage phi 80 in recA430 cells can be induced by irradiation with ultraviolet light, while the prophage in recA1 cells cannot.     

Combined study of 1H-magnetic resonance imaging and depth-selected, EKG-gated 31P-magnetic resonance spectroscopy of the heart in vivo

NMR is useful for both 1H-magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We undertook to combine these two merits of NMR for in vivo characterization of living rat heart in wide bore (9 cm) superconducting magnet under high magnetic field (6.4 Tesla). Spatial resolution of 1H-MRI attained 0.1 mm by spin warp method. Then, depth-selected, EKG-gated 31P-MRS was performed, adjusting the detection area to cover the heart that was identified by the preceding 1H-MRI. Three evidences that 31P-SMR signal chiefly originated from the heart without cross talk of adjacent organs indicated that combination of 1H-MRI and in vivo 31P-MRS under high magnetic field in whole animal is promising for more accurate evaluation of cardiac muscle metabolism.     

Orthogonal microvillus pattern in the eighth rhabdomere of the rock crab Grapsus

Summary The eighth retinular cell (R 8) of Grapsus lacks cytoplasmic pigment granules and basically resembles those previously known in the ghost crab Ocypode and the mysid Praunus. Distally located, R 8 comprises four lobes inserted between the outer ends of the seven regular retinular cells (R 1–R 7). A thin cytoplasmic bridge connects these lobes. One lobe adjacent to R 1 contains the nucleus of R 8 and gives rise proximally to the cell's axon. The short distal eighth rhabdomere consists of microvilli (mvl) protruding axially from all four lobes. Similar R 8's were found also in two other crab families and in two other genera of mysids.In Grapsus the eighth rhabdomere is extraordinary in possessing mvl oriented in two orthogonal directions parallel to the mvl of R 1–R 7. The distal 20% of the rhabdom consists of mvl originating exclusively from R 8. These appear in somewhat irregular bands and are alternately oriented parallel to the animal's vertical or horizontal axis. More proximally the retinula contains eleven sectors but the rhabdom still comprises bands of alternating mvl with those from R 8 joined respectively by the rhabdomeres of R 1, 4, and 5 (horizontal) and R 2, 3, 6 and 7 (vertical). The rest of the rhabdom shows typical decapod organization with seven interdigitating rhabdomeres.This research has been aided by grants from the United States Public Health Service (5 RO1 EY 00405) and the National Geographic Society. The authors are grateful to Mabelita Campbell for her helpful assistance.     

Actin paracrystal in the acrosome of newt sperm

When a newt sperm-head was treated with trypsin and DNase, an arrow-like thin rod was revealed. This rod presumably corresponds to the ‘perforatorium’ described by Picheral [1, 2] in Pleurodele sperm. It consisted of one apical and one caudal part. In the apical part there appeared to be an envelope with a 530 Å structural repeat, inside which coursed a filament bundle, presumably identical with that in the caudal part. In the caudal part, a characteristic filament bundle, quite similar to the paracrystal of rabbit skeletal actin [3], was observed after extensive treatment with trypsin. The optical diffraction pattern of this bundle indicates that it has the same helical symmetry as that of rabbit skeletal actin [4] but slightly different from that of the acrosomal process of Limulus sperm [5]. The diffraction pattern frequently has a strong meridional reflection at about (27 Å)⁻¹, which is usually observed only with low intensity in the actin paracrystals. This fact suggests that the structural unit in the bundle has a shape considerably different from that of the usual G-actin.     

The origin and development of retinal pigment cells and melanophores analyzed by Xenopus black-white chimeras

At the 16 cell stage, three kinds of borealis–laevis and eight kinds of laevis–laevis chimeric embryos were produced by replacing a particular blastomere of albino embryos of Xenopus laevis with that of wild-type embryos of X. borealis or X. laevis , and then leaving the embryos to develop into frogs.
In the borealis–laevis chimera frogs, we found that all the melanized cells (retinal pigment cells and melanophores) were derived from a transplanted wild-type blastomere with a nuclear marker of X. borealis and that all the albino-mutant cells derived from the host did not become melanized. Thus, retinal pigment cells and melanophores differentiated according to their own genotype. We then examined the origin of these two types of cells, using melanin as a cell-marker in the borealis–laevis and laevis–laevis chimeras.
Retinal pigment cells derive from A1 (dorso-animal) and A2 (latero-animal) blastomeres. A1 of one side contributes to retinal pigment cells in both eyes. Though the blastomeres of one side contribute to the formation of bilateral melanophores, the major contribution is to melanophores of the same side. A1, A2 and V2 (latero-vegetal) form the anterior part of the neural fold, and A2 and V2 contribute to melanophores of the head region. The most anterior part of the neural fold derived from A1 does not make a significant contribution to melanophores. Though V2 is a vegetal blastomere, it forms the anterior part of the neural fold by upward movement against the downward movement for gastrulation. A3 forms the middle and posterior parts of the neural fold and contributes to melanophores of the trunk and hindlimbs. Melanophores of hindlimbs also come from A2, A4 and V2. It is to be noted that A4 contributes to melanophores of hindlimbs, despite no apparent contribution to the neural fold.
Development of the retinal pigment cells and melanophores is discussed from the point of pigmentation patterns of the chimeras.     

Fatty acid compositions of arthropod and cephalopod photoreceptors: interspecific,seasonal and developmental studies

Fatty acid compositions of the compound eyes of insects (soldier-bug, Hemiptera, and silk moth, Lepidoptera), crustaceans (crayfish and grapsid crab, Decapoda) and inner and outer segments of visual cells of a squid (Cephalopoda, Mollusca) were analyzed by gaschromatography for interspecific comparison. Fatty acid compositions showed great variation among species. In insect compound eyes, 16:0 and 18:0 were the main saturated fatty acids, and 18:1 was the dominant unsaturated fatty acid. Silk moth eyes contained, in addition, considerable amounts of 18:2 and 20:5. In crustacean compound eyes, the main saturated fatty acids were 16:0 and 18:0, and 14:0 (5.0%) was only detected in grapsid crabs; the main unsaturated fatty acids were 20:4, 20:5 and 22:6. Both whole eyes and rhabdom fraction of crayfish showed similar profiles of fatty acid compositions. Both inner and outer segments of squid retinae were characterized by high amounts of unsaturated fatty acids, especially 22:6. Compound eyes of grapsid crabs were used for the experiments on seasonal changes of fatty acid compositions. UFA/SFA ratios (weight in % of unsaturated fatty acids saturated fatty acids) were lowest (1.0) in July and highest (2.5) in March, and unsaturation indexes (average number of double bonds per molecule) were lowest (1.5) in July and highest (2.3) in March. Fatty acids 18:0 and 20:1 showed a significant correlation with the changes of seasonal temperature. Fatty acid analysis of the developing compound eyes of silk moths during the pupal stage revealed that eicosapentanoic acid (20:5) increased remarkably in parallel with the development of photoreceptive membranes, the rhabdoms. This suggests that eicosapentaenoic acid may play an important role in formation and function of rhabdoms.     

Inhibition of apoptosis by the actin-regulatory protein gelsolin.

Gelsolin is an actin-regulatory protein that modulates actin assembly and disassembly, and is believed to regulate cell motility in vivo through modulation of the actin network. In addition to its actin-regulatory function, gelsolin has also been proposed to affect cell growth. Our present experiments have tested the possible involvement of gelsolin in the regulation of apoptosis, which is significantly affected by growth. When overexpressed in Jurkat cells, gelsolin strongly inhibited apoptosis induced by anti-Fas antibody, C2-ceramide or dexamethasone, without changing the F-actin morphology or the levels of Fas or Bcl-2 family proteins. Upon the induction of apoptosis, an increase in CPP32(-like) protease activity was observed in the control vector transfectants, while it was strongly suppressed in the gelsolin transfectants. Pro-CPP32 protein, an inactive form of CPP32 protease, remained uncleaved by anti-Fas treatment in the gelsolin transfectants, indicating that gelsolin blocks upstream of this protease. The tetrapeptide inhibitor of CPP32(-like) proteases strongly inhibited Fas-mediated apoptosis, but only partially suppressed both C2-ceramide- and dexamethasone-induced apoptosis. These data suggest that the critical target responsible for the execution of apoptosis may exist upstream of CPP32(-like) proteases in Jurkat cells and that gelsolin acts on this target to inhibit the apoptotic cell death program.     

Occurrence of viable photoautotrophic picoplankton in the aphotic zone of Lake Biwa, Japan

The distribution and abundance of photoautotrophic picoplankton(PPP. Synechococcus group) in the aphotic bottom sediments ofLake Biwa were investigated by direct counting and viable counting(most probable number, MPN) methods. In the surface layer ofbottom sediments (0–1 cm). where large PPP blooms occurredin the past 5 years, >10⁵ cells cm^–3 of PPP were foundto be viable throughout the year. Furthermore, the density ofPPP deposited on the sediment surface (0–0.1 cm) was oneorder of magnitude higher (MPN = 1.3 x 10⁶ cells cm^–3.direct count = 9.9 x 10⁶ cells cm^–3) than that of bulkedsurface sediments (0–1 cm). Even in the deeper layer (13–14cm) of bottom mud, viable PPP were still found (10¹ cells cm^–1.In winter, viable PPP in the aphotic bottom sediments were 10⁴–10⁵times greater per Unit volume than those in the euphotic lakewater. Since the aphotic bottom sediments have high levels ofPPP, as well as high growth potential (high ratio of viablecount/total direct count), they are likely to seed PPP bloomsin the North Basin of Lake Biwa.     

Proliferating cells in histiocytic necrotizing lymphadenitis.

The phenotypes of proliferating cells in histiocytic necrotizing lymphadenitis (HNL) were examined. The affected areas consisted mainly of CD 8-positive (suppressor/cytotoxic T-cells) and CD 4-positive (helper/inducer T-cells) in association with some CD 15-positive cells (monocytes). A marker of proliferating cells (Ki-67) and monoclonal antibodies for determining the phenotypes of cells (CD 4, CD 8, CD 15) in the affected areas were applied using a double-staining method. Ki-67-positive proliferating cells were mainly CD 8-positive. A few CD 4-positive cells and rare CD 15-positive cells were also Ki-67-positive. The percentage of CD 8-positive cells increased gradually over time and the ratio of CD 8-positive to proliferating cells did not decrease throughout the observation period of 6 weeks. These results suggest that the proliferation of CD 8-positive T-cells together with the accumulation of CD 4- and CD 15-positive cells is the main phenomenon occurring in HNL.