The information transmitted at final position in visually triggered forearm movements

Visually triggered forearm movements were analyzed by an Information Theory approach. Human subjects made smooth movements which were characterized by moderate speeds, ranging about 100 degrees per second, by continuity in the position and velocity traces, and attainment of final average EMG levels before completion of the movement. We calculated the information transmitted by final position, biceps EMG, triceps EMG, and the ratio of the EMGs. The results were: (1) The information transmitted by final joint angle increased with number of targets but gradually levelled off. The maximum value was slightly over 3 bits, corresponding to an equivalent number of less than nine independent arm positions for a single movement. (2) The information transmitted by the ratio of the EMGs exceeds that transmitted by the biceps or triceps alone. (3) A previous theoretical prediction based on a spring model (Sakitt, 1980a) gives a moderately good fit to the experimental EMG ratio as a function of final position over a large range of angles. Our results lend consistency to two ideas about the nature of visually triggered forearm movements. First, our finding about the EMG ratio suggests that the basic motor program for final position is probably in terms of relative allocation of innervations, rather than looking up individual values. Second, single movements of this kind transmit surprisingly little information. If this is the case, it suggests that very fine accuracy is not achieved by a single program but requires feedback in order to program and execute additional movement.Laboratoire de Physiologie Neurosensorielle, CNRS, Paris, France     

Replicon size and mean rate of DNA synthesis in rye (Secale cereale L. cv. Petkus Spring)

Chromosomal DNA replication was investigated in root meristem cells of Secale cereale L. cv. Petkus Spring using DNA fibre auto-radiography. At 23 ° the mean rate of replication, per single replicon fork, was 12.1 m/h. Replicon size was between 20–25 m. These results are compared with corresponding measurements for other angiosperm species.     

Genetics of microcystless mutants of polysphondylium pallidum

Mutants were selected that are incapable of differentiating microcysts, a resting stage formed in response to high osmotic conditions. In the selection procedure amebae that failed to encyst were removed by flotation in 46% Percoll. Genetic crosses among 15 mutant strains were made by means of the macrocyst sexual cycle. Eleven of the strains mapped to three loci. Mutations at two of these loci (cysA and cysB) produced no observable alteration in the aggregation-fruiting pathway, although one set of strains altered at the cysA locus carried defects at a second unlinked site which blocked aggregation. The single strain that defined the third locus (cysC) is aggregateless. These results confirm the conclusion that there are several genes whose function is essential to microcyst development and is exclusive to this pathway. It remains uncertain whether there are other genes whose action is crucial to both encystment and to aggregation/fruiting.     

Identification of a prominent 85-kDa cAMP-dependent phosphoprotein associated with late G1 phase in mitogen-stimulated B lymphocytes

In order to elucidate late regulatory events which may be involved in the onset of S phase in B lymphocytes, we studied the effect of anti-Ig on phosphorylation of soluble proteins at late G1 phase. Stimulation of murine splenic B lymphocytes with anti-Ig and other mitogens for 18 h was found to be associated with a major increase in phosphorylation of an 85 kDa/pI approximately 5.3 cytosolic protein, conversely, stimulation of the cells with non-mitogenic stimuli did not induce the phosphorylation of pp85. The increase in phosphorylation of pp85 could not be detected after 30 min, was barely detectable after 6 h, but was very prominent after 18 h of stimulation with anti-Ig. Thus, the increase in phosphorylation of pp85 is not an early signal but is rather correlated with the late G1 phase. pp85 could not be detected in the nuclei of either control or stimulated cells. Stimulation of B cells for 30 min with forskolin induced the phosphorylation of pp85, while phorbol ester did not have any effect. The phosphorylation of pp85 was induced by the catalytic subunit of cAMP protein kinase. Comparison of the phosphopeptide map of pp85 phosphorylated by anti-Ig in intact cells to the phosphopeptide map phosphorylated by forskolin or by the catalytic subunit of cAMP protein kinase, showed a striking similarity indicating that cAMP protein kinase may be involved in phosphorylation of pp85 in mitogen-stimulated cells. An increase in intracellular cAMP levels at late G1 phase was found in B cells stimulated by mitogens. These results implicate an important role for cAMP-dependent phosphorylation events, specifically the phosphorylation of pp85/pI 5.3, at late G1 phase during the cell cycle.     

N-glycosylation is required for human CD2 immunoadhesion functions.

The T-lymphocyte glycoprotein receptor, CD2, mediates cell-cell adhesion by binding to the surface molecule CD58 (LFA-3) on many cell types including antigen presenting cells. Two domains comprise the CD2 extracellular segment, with all adhesion functions localized to the amino-terminal domain that contains a single N-glycosylation site at Asn65. We have defined an important role for the N-linked glycans attached to Asn65 of this domain in mediating CD2-CD58 interactions and also characterize its N-glycotype structure. Analysis of deglycosylated soluble recombinant CD2 as well as a mutant transmembrane CD2 molecule containing a single Asn65-Gln65 substitution demonstrates that neither deglycosylated CD2 nor the mutant CD2 transmembrane receptor binds CD58 or monoclonal antibodies directed at native CD2 adhesion domain epitopes. Electrospray ionization-mass spectrometry demonstrates that high mannose oligosaccharides ((Man)nGlcNAc2, n = 5-9) are the only N-glycotypes occupying Asn65 when soluble CD2 is expressed in Chinese hamster ovary cells. Based on a model of human CD2 secondary structure, we propose that N-glycosylation is required for stabilizing domain 1 in the human receptor. Thus, N-glycosylation is essential for human CD2 adhesion functions.     

Methane oxidation by methanotrophs and its effects on the phosphate flux over the sediment-water interface in a eutrophic lake

The effect of methane oxidation in aerobic sediment on oxygen consumption and phosphate flux was investigated in diffusion chambers. The diffusion chambers consisted of two compartments separated by a Teflon membrane. In the upper chamber a thin sediment layer was present and the lower chamber was continuously flushed with gas. The hydrophobic membrane allowed for diffusion of gases from the lower chamber through the sediment layer toward the headspace of the upper chamber. In experiments with a methane oxidation rate of 9.8 mmol m^–2 day^–1, the oxygen consumption rate increased by a factor of two compared with controls without methane oxidation (8.6 vs 17.7 mmol m^–2 day^–1). Methane oxidation significantly decreased oxygen penetration depth (2.5–4.0 vs 1.0–2.0 mm). However, despite the shrinkage of the oxidized microlayer, no differences were found in phosphate flux across the sediment water interface. Batch experiments with standard additions of methane revealed that the growth of methanotrophic bacteria contributes to the phosphate uptake of aerobic sediment. From the batch experiments a molar ratio of carbon to phosphate of 45 mol:mol was calculated for the growth of methanotrophs. Results suggest that a decrease in chemical phosphate adsorption caused by a decrease in the oxygen penetration depth could be compensated for entirely by the growth of methanotrophic bacteria. Send offprint requests to: A.J.C. Sinke