“Australopithecus afarensis”: A composite species

In response to a critique byFerguson (1989),Leonard (1991) reiterates most of his original arguments for supporting “Australopithecus afarensis”Johanson, White, andCoppens, 1978 as a single species. He disregards the principle of morphological equivalence by comparing the dental metrics and morphology of a hominid with those of species of the Pongidae, which do not correspond with the degree of variation in hominids, instead of with those of species of the Hominidae. He fails to refute clear evidence that the range of variation of dental metrics and morphology in “A. afarensis” exceeds that seen in species of the Hominidae. On the basis of extreme variation, “A. afarensis” is, therefore, interpreted as representing a composite species.     

The extracellular matrix of lip wounds in fetal, neonatal and adult mice.

Wound healing in the fetus occurs rapidly, by a regenerative process and without an inflammatory response, resulting in complete restitution of normal tissue function. By contrast, in the adult, wounds heal with scar formation, which may impair function and inhibit further growth. The cellular mechanisms underlying these differing forms of wound healing are unknown but the extracellular matrix (ECM), through its effects on cell function, may play a key role. We have studied the ECM in upper lip wounds of adult, neonatal and fetal mice at days 14, 16 and 18 of gestation. The spatial and temporal distribution of collagen types I, III, IV, V and VI, fibronectin, tenascin, laminin, chondroitin and heparan sulphates were examined immunohistochemically. Results from the fetal groups were essentially similar whilst there were distinct differences between fetus, neonate and adult. Fibronectin was present at the surface of the wound in all groups at 1 h post-wounding. Tenascin was also present at the wound surface but the time at which it was first present differed between fetus (1 h), neonate (12 h) and adult (24 h). The time of first appearance paralleled the rate of wound healing which was most rapid in the fetus and slowest in the adult. Tenascin inhibits the cell adhesion effect of fibronectin and during development the appearance of tenascin correlates with the initiation of cell migration. During wound healing the appearance of tenascin preceded cell migration and the rapid closure of fetal wounds may be due to the early appearance of tenascin in the wound. Collagen types I, III, IV, V and VI were present in all three wound groups but the timing and pattern of collagen deposition differed, with restoration of the normal collagen pattern in the fetus and a scar pattern in the adult. This confirms that lack of scarring in fetal wounds is due to the organisation of collagen within the wound and not simply lack of collagen formation. The distribution of chondroitin sulphate differed between normal fetal and adult tissues and between fetal and adult wounds. Its presence in the fetal wound may alter collagen fibril formation. No inflammatory response was seen in the fetal wounds. The differences in the ECM of fetal and adult wounds suggests that it may be possible to alter the adult wound so that it heals by a fetal-like process without scar formation, loss of tissue function or restriction of growth.     

Functional reconstitution of the cardiac sarcoplasmic reticulum Ca2(+)-ATPase with phospholamban in phospholipid vesicles

The Ca2(+)-ATPase in cardiac sarcoplasmic reticulum (SR) is under regulation by phospholamban, an oligomeric proteolipid. To determine the molecular mechanism by which phospholamban regulates the Ca2(+)-ATPase, a reconstitution system was developed, using a freeze-thaw sonication procedure. The best rates of Ca2+ uptake (700 nmol/min/mg reconstituted vesicles compared with 800 nmol/min/mg SR vesicles) were observed when cholate and phosphatidylcholine were used at a ratio of cholate/phosphatidylcholine/Ca2(+)-ATPase of 2:80:1. The EC50 values for Ca2+ were 0.05 microM for both Ca2+ uptake and Ca2(+)-ATPase activity in the reconstituted vesicles compared with 0.63 microM Ca2+ in native SR vesicles. Inclusion of phospholamban in the reconstituted vesicles was associated with a significant inhibition of the initial rates of Ca2+ uptake at pCa 6.0. However, phosphorylation of phospholamban by the catalytic subunit of the cAMP-dependent protein kinase reversed the inhibitory effect on the Ca2+ pump. Similar findings were observed when a peptide, corresponding to amino acids 1-25 of phospholamban, was used. These findings indicate that phospholamban is an inhibitor of the Ca2(+)-ATPase in cardiac SR and phosphorylation of phospholamban relieves this inhibition. The mechanism by which phospholamban inhibits the Ca2+ pump is unknown, but our findings with the synthetic peptide suggest that a direct interaction between the Ca2(+)-ATPase and the hydrophilic portion of phospholamban may be one of the mechanisms for regulation.     

Determination of 35S-aminoacyl-transfer ribonucleic acid specific radioactivity in small tissue samples

Rate determination of protein synthesis utilizing tracer amino acid incorporation requires accurate assessment of the specific radioactivity of the labeled precursor aminoacyl-tRNA pool. Previously published methods presumably useful for the measurement of any aminoacyl-tRNA were unsuccessful when applied to [³⁵S]methionine, due to the unique chemical properties of this amino acid. Herein we describe modifications of these methods necessary for the measurement of ³⁵S-aminoacyl-tRNA specific radioactivity from small tissue samples incubated in the presence of [³⁵S]methionine. The use of [³⁵S]methionine of high specific radioactivity enables analysis of the methionyl-tRNA from less than 100 mg of tissue. Conditions for optimal recovery of ³⁵S-labeled dansyl-amino acid derivatives are presented and possible applications of this method are discussed.     

Dissolved Hydrocarbons and Related Microflora in a Fjordal Seaport: Sources, Sinks, Concentrations, and Kinetics

The continuous addition of toluene as a solute of treated ballast water from oil tankers into a well-defined estuary facilitated the study of the dynamics of dissolved hydrocarbon metabolism in seawater. Most rates of toluene oxidation were in the range of 1 to 30 pg/liter per h at 0.5 μg of toluene per liter. Near the ballast water injection point, a layer of warm ballast water, rich in bacteria, that was trapped below the less-dense fresh surface water was located. Toluene residence times were approximately 2 weeks in this layer, 2 years elsewhere in Port Valdez, and 2 decades in the surface water of a more oceanic receiving estuary adjacent. Mixing was adequate for a steady-state treatment which showed that 98% of the toluene was flushed from Port Valdez before metabolism and gave a steady-state concentration of 0.18 μg/liter. Total bacterial biomass from direct counts and organism size data was usually near 0.1 mg/liter, but ranged up to 0.8 mg/liter in the bacteria-rich layer. The origin of bacteria in this layer was traced to growth in oil tanker ballast during shipments. The biomass of toluene oxidizers in water samples was estimated from the average affinity of pure-culture isolates for toluene (28 liters per g of cells per h) and observed toluene oxidation kinetics. Values ranged from nearly all of the total bacterial biomass within the bacteria-rich layer down to 0.2% at points far removed. Because the population of toluene oxidizers was large with respect to the amount of toluene consumed and because water from a nearby nonpolluted estuary was equally active in facilitating toluene metabolism, we searched for an additional hydrocarbon source. It was found that terpenes could be washed from spruce trees by simulated rainfall, which suggested that riparian conifers provide an additional and significant hydrocarbon source to seawater.     

Differential biosynthesis of polyunsaturated fatty acids by Tetrahymena supplemented with ergosterol.

Tetrahymena grown with foreign sterols such as ergosterol incorporate them into cellular membranes at the expense of the native compound, tetrahymanol. It is shown that cells grown with ergosterol have a lessened capacity to produce the polyunsaturated linoleic and gamma-linolenic acids from [14C]oleic acid. However, the same cells have normal capacities to introduce double bonds at C-6 into linoleate, alpha-linolenate, or cis-vaccenate. Thus, a presumed 12-desaturase is inhibited in the presence of ergosterol, while desaturation at C-6 is unaffected.     

Ultrastructural studies on the sporulation of oocysts of Toxoplasma gondii. II. Formation of the sporocyst and structure of the sporocyst wall

The ultrastructural changes observed during sporocyst formation and the structure of the sporocyst wall was examined in oocysts which had been allowed to sporulate for between 12 and 48 hours at 27 degrees C. As the spherical sporoblast developed into the sporocyst the cytoplasmic mass became ellipsoidal in shape although no change was noted in the organelle compliment, which cosisted of two nuclei plus a number of polysaccharide granules, lipid globules, mitochondria, Golgi bodies, and some rough endoplasmic reticulum. The sporocyst wall consisted of a thin outer layer (15-20 nm) which was formed from two limiting membranes of the sporoblast and an inner layer (40-50 nm) which was comprised of four curved plates. This inner layer was formed under the outer layer and, although no specific cytoplasmic organelle disappeared with its formation, some unit membranes were observed close to the plasmalemma during its formation. Each curved plate has a marginal swelling and an interposing strip of material is present between the margins of adjacent plates. The plates are joined to the interposing strip by a thin band of osmiophilic material. In oblique and tangential sections through the plates two types of cross banding were observed which differed in periodicity.