Tangential cell migration during layer formation of chick optic tectum

The laminated structure of the optic tectum is formed by radial and tangential cell migration during development. Studies of developing chick optic tectum have revealed two streams of tangential cell migration in the middle and superficial layers, which have distinctive origins, migratory paths, modes of migration, and destinations. We will review the process of the two types of tangential migrations, in order to elucidate their roles in the formation of the optic tectum layers.     

Characterization of translucent segments observed in an smbA mutant of Escherichia coli

Abstract The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22°C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrastt microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22°C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.     

The occurrence of a premature form of egg-specific protein in vitellogenic follicles ofBombyx mori

Summary Analysis of yolk proteins of the silkworm,Bombyx mori, by SDS-polyacrylamide gel electrophoresis and immunoblotting showed that there was a developmental change in subunit composition of egg-specific protein; egg-specific protein consisting of 72 kDa subunits alone (premature form) was found in vitellogenic follicles, whereas the protein in mature eggs was composed of 72 kDa and 64 kDa subunits (mature form). The premature form of egg-specific protein was purified from young ovaries to homogeneity using a high performance liquid chromatography system. The purified protein had an apparent molecular mass of 225 kDa which could not be distinguished from that of the mature form. By circular dichroism analysis, both egg-specific proteins were estimated to have about 30% -helix and 20% -sheet, but the mature form showed a relatively rigid conformation in the aromatic region. The premature egg-specific protein purified from vitellogenic ovaries, consisted of three 72 kDa subunits, whereas mature egg-specific protein was composed of two 72 kDa subunits and one 64 kDa subunit. All of these subunits showed the same immunoreactivity towards antiserum raised against the mature form. An identical NH₂-terminal amino acid sequence was found in both 72 kDa polypeptides and 64 kDa polypeptide for the initial 10 amino acids.Abbreviations SDS sodium dodecyl sulfate - PMSF phenylmethylsulfonyl fluoride - PAGE polyacrylamide gel electrophoresis - HPLC high performance liquid chromatography - ESP egg-specific protein - Vtn vitellin     

On periodic responses of a mathematical neuron model

The periodic responses of a mathematical neuron model, when periodically varying input stimuli are applied to the model, are investigated. An explicit representation of periodic responses is obtained. It is shown that a periodic response as a 0–1 string is a uniform string. That is, the 1's of the 0–1 string are distributed uniformly in the string.     

Distinct effects of different low temperatures on the induction of NAD-sorbitol dehydrogenase activity in diapause eggs of the silkworm,Bombyx mori

Summary Diapause eggs of the silkworm, Bombyx mori, exposed to 5°C and 0.5°C from 2 or 30 days after oviposition, were examined for changes in contents of glycogen, sorbitol and glycerol. Cold acclimation did not alter the profile of accumulation of sorbitol from that in eggs kept continuously at 25°C. However, acclimation at 5°C resulted in conversion of sorbitol to glycogen, while acclimation at 0.5°C was not accompanied by the utilization of sorbitol. NAD-sorbitol dehydrogenase (NAD-SDH; EC 1.1.1.14) activity was examined in the cold-acclimated eggs. The activity was induced by acclimation at 5°C but not at 0.5°C. Incubation at 0.5°C suppressed any further increase in the activity that had been induced. Temperature-directed changes in NAD-SDH activity paralleled those in sorbitol content. Hatching of the diapause eggs was monitored after cold acclimation for various periods of time and subsequent transfer to 25°C. Incubation at 0.5°C was less effective than 5°C at breaking diapause. The time required for the eggs to hatch in synchrony after acclimation at 5°C coincided with that required for the induction of NAD-SDH activity. These results show that different effects result from acclimation at 5°C and near 0°C with respect to the control of NAD-SDH activity, that utilization of sorbitol is controlled by NAD-SDH activity, and that induction of this activity is temperature-dependent. Furthermore, induction of NAD-SDH activity is involved in the termination of diapause in B. mori.Abbreviations DH diapause hormone - NAD nicotinamide-adenine-dinucleotide - NAD-SDH NAD-sorbitol-dehydrogenase     

Expression of NADH-Dependent Glutamate Synthase in Response to the Supply of Nitrogen in Rice Cells in Suspension Culture

The effects of inorganic and organic nitrogen on the levelsof mRNA for NADH-dependent glutamate synthase (GOGAT) and theprotein were examined in rice cells in suspension culture. Asupply of NH⁺₄, NO^-₃, glutamine, or asparagine induced the accumulationof the protein and mRNA, but levels of mRNA for ferredoxin-GOGATwere hardly affected. ¹Present address: P.C. Center Wakuya-cho, Toda-gun, Miyagi,Japan.     

Initiation of Cyclin B Degradation by the 26S Proteasome upon Egg Activation

Immediately before the transition from metaphase to anaphase, the protein kinase activity of maturation or M-phase promoting factor (MPF) is inactivated by a mechanism that involves the degradation of its regulatory subunit, cyclin B. The availability of biologically active goldfish cyclin B produced in Escherichia coli and purified goldfish proteasomes (a nonlysosomal large protease) has allowed the role of proteasomes in the regulation of cyclin degradation to be examined for the first time. The 26S, but not the 20S proteasome, digested recombinant 49-kD cyclin B at lysine 57 (K57), producing a 42-kD truncated form. The 42-kD cyclin was also produced by the digestion of native cyclin B forming a complex with cdc2, a catalytic subunit of MPF, and a fragment transiently appeared during cyclin degradation when eggs were released from metaphase II arrest by egg activation. Mutant cyclin at K57 was resistant to both digestion by the 26S proteasome and degradation at metaphase/anaphase transition in Xenopus egg extracts. The results of this study indicate that the destruction of cyclin B is initiated by the ATP-dependent and ubiquitin-independent proteolytic activity of 26S proteasome through the first cutting in the NH₂ terminus of cyclin (at K57 in the case of goldfish cyclin B). We also surmise that this cut allows the cyclin to be ubiquitinated for further destruction by ubiquitin-dependent activity of the 26S proteasome that leads to MPF inactivation.     

Properties of a DNA-dependent ATPase from rat mitochondria.

A DNA-dependent ATPase has been highly purified from rat liver mitochondria and characterized. The enzyme catalyzes the hydrolysis of ATP or dATP in the presence of single-stranded DNA cofactor and a divalent cation. The Km values for ATP and dATP are 0.15 mM and 0.35 mM, respectively. The enzyme activity is highly sensitive to N-ethylmaleimide. The sedimentation coefficient of the enzyme is 8.3 S in a glycerol gradient. From this and data on Sephadex G-200 gel filtration, the molecular weight of the native enzyme was calculated to be about 190,000. All the natural single-stranded DNAs tested were equally effective for the ATPase activity, but synthetic deoxyhomopolymer poly(dC) was found to be more effective than natural single-stranded DNAs. Synthetic and natural RNAs had no effect on the activity.