Morphology of spines and spine joint in the crown-of-thorns starfish Acanthaster planci (Echinodermata,Asteroida)

Summary Morphology and movement of the spines of Acanthaster planci were studied. All surfaces of the animal are covered with spines. The spines on the aboral surface are cylindrical with sharp tips. The spines on the oral surface are flat; they bend over to cover the mouth and the ambulacral grooves when these soft parts are stimulated. Those on the side of the animal make a barrier of crossed spines. Thus the structure and movement of the spines are well-adapted for defense.The junction between the primary aboral spine and its pedicel makes a movable joint. The ultrastructure of the connective tissue at the joint was studied. The connective tissue is mainly composed of collagen fibers. Presumed neurosecretory cells with processes which are filled with electron-dense granules of 0.2 m diameter were found between collagen fibers. Muscle fibers are mainly found in the connective tissue at the central holes. These observations support the view that the joint connective tissue has catch properties.     

A new class of rapidly developing mutants in Dictyostelium discoideum: implications for cyclic AMP metabolism and cell differentiation

Rapidly developing (rde) mutants of Dictyostelium discoideum, in which cells precociously differentiated into stalk and spore cells without normal morphogenesis, were investigated genetically and biochemically. Genetic complementation tests demonstrated that the 16 rde mutants isolated could be classified into at least two groups (groups A and C) and that the first described rde mutant FR17 (D. R. Sonneborn, G. J. White, and M. Sussman, 1963, Dev. Biol. 7, 79-93) belongs to group A. Morphological studies revealed several differences in development and final morphology between group A and group C mutants. In group A mutants, the time required for cell differentiation from vegetative cells to aggregation competent cells is reduced, whereas the time required for spore and stalk cell differentiation following the completion of aggregation is shortened in group C mutants. This suggests that group C mutants represent a new class of rde mutants and that there exist at least two mechanisms involved in regulating the timing of development in D. discoideum. Measurements of cell-associated and extracellular phosphodiesterase activities, and intracellular and total cAMP levels revealed that cAMP metabolism in both groups is significantly altered during development. Group A mutants showed precocious and excessive production of phosphodiesterase and cAMP during the entire course of development; intracellular cAMP levels in group C mutants were extremely low, and spore and stalk cell differentiation occurred without an apparent increase in these levels. Thus, while cAMP metabolism is abnormal in all the rde mutants studied, there exist several distinct types of derangement, not necessarily involving the overproduction of cAMP.     

Dichroism of bacteriochlorophyll in cells of the photosynthetic bacterium Rhodopseudomonas palustris

1. The dichroism was measured at varied wavelengths of polarized light in “intact” cells of Rhodopseudomonas palustris and in films of air-dried lamellar fragments of the bacterium.     

Chain conformation of copoly(γ-methyl D,L-glutamate)

Copolymers of γ-methyl D - and L -glutamates with various D /L ratios were prepared. Infrared absorption spectra of solid films were measured and sums of right- and left-handed helix contents were determined from intensities of amide V bands. Farultraviolet absorption spectra and optical rotatory dispersion of these copolymers in solutions are used to ascertain their helical character. Chain conformations of DL -copolypeptides are discussed.     

Activation of phospholipase C by the agonist U46619 is inhibited by cromakalim-induced hyperpolarization in porcine coronary artery.

We measured inositol 1,4,5-trisphosphate (IP3) production, intracellular calcium concentration ([Ca2+]i) and force of contraction induced by a thromboxane A2 analogue U46619 in porcine coronary artery to elucidate the relaxant effect of a K+ channel opener cromakalim. Cromakalim (10 microM) significantly inhibited the production of IP3, Ca2+ release from intracellular stores and contraction induced by 300 nM U46619. The inhibitory effect of cromakalim on IP3 was blocked by a K+ channel blocker tetrabutylammonium (TBA, 3 mM) and counteracted by 20 mM KCl-induced depolarization. These results suggest that the hyperpolarization of the plasma membrane by cromakalim inhibits the activation of phospholipase via the stimulation of the thromboxane A2 receptor to result in vasodilation.     

SFA-1, a novel cellular gene induced by human T-cell leukemia virus type 1, is a member of the transmembrane 4 superfamily.

A novel cellular gene termed SFA-1 was isolated by differential hybridization of a cDNA library, using probes obtained from an adult T-cell leukemia cell line in comparison with probes obtained from normal CD4+ T cells and the MOLT-4 cell line. The mRNA of the SFA-1 gene is approximately 1.6 kb in size and encodes a protein of 253 amino acids, containing four putative transmembrane domains, a number of cysteine residues, and one potential N-glycosylation site in a major hydrophilic region between the third and fourth transmembrane domains. Expression of the SFA-1 gene was either absent or present at a low level in lymphoid cells but was up-regulated after transformation by human T-cell leukemia virus type 1 and transactivated by Tax. SFA-1 was broadly expressed in many human cell types and conserved in different species. Computer-aided comparison showed that SFA-1 had significant sequence homology and common structural features with members of the transmembrane 4 superfamily. SFA-1 antigen was detected as a 29-kDa membrane protein by immunoblotting, using anti-SFA-1 monoclonal antibody.     

Comparison of muscle force,muscle endurance,and electromyogram activity during an expedition at high altitude

Handgrip force (HF), maximal pinch force (MF), muscle endurance (ME), and the median power frequency (MdPF) of the activity shown in the electromyogram (EMG) were studied at various altitudes in eight normal healthy subjects. MF and ME were measured between the index finger and thumb, and all measurements were obtained at altitudes ranging from 610 to 4860 m during an expedition in the Qinghai Plateau in China. With the change in altitude HF, ME, and MF showed no significant change. Compared to the MdPF at 2260 m on ascent, the MdPF at other altitudes showed a significant decrease (P<0.01). Thus, we conclude that muscle performance (HF, MF, and ME) was not affected by the environment at high altitude. However, MdPF was affected and the mean MdPF at 610 m after the expedition did not recover to initial values of MdPF. We suggest these results may have been affected by fatigue and chronic exposure to the hypobaric hypoxic environment, since the members of the expedition party expressed feelings of sluggishness and fatigue after the expedition.