Relationship between enamel formation and eruption rate in rat mandibular incisors

Summary The relationship between the formation of dental enamel and tooth eruption was investigated. Rat mandibular incisor eruption rate was accelerated by maintaining incisors out of occlusion. Rate of eruption, enamel thickness, secretory zone length and matrix breakdown were measured. Eruption rate increased by 120% in experimental teeth but enamel secretion increased by only 90%. There were no obvious differences between control and experimental teeth in final enamel thickness or in the molecular weight distribution of the enamel matrix proteins.     

Primary teeth in Anura are nonpedicellate and bladed

1. Scanning electron microscop of the dentition of four anuran species (Discoglossus pictus, Bombina orientalis, Rana cyanophlyctis, Rana temporaria) revealed that at least the primary teeth, which are established during metamorphosis, are more or less bicuspid, bladed and nonpedicel-late. Juveniles and adults, however, have pedicellate teeth. 2. Thus, regardin the pedicellate condition, the sequence of stages in tooth development of Anura und Urodela show some similarities, although the primary teeth of urodeles develop already before metamorphosis.     

Differential regulation of TIMP-1, -2, and -3 mRNA and protein expressions during mouse incisor development

Tissue inhibitors of metalloproteinases (TIMPs) possess multiple functions, in addition to their matrix metalloproteinase (MMP) inhibitory activity. The continuously growing incisor of mouse possesses a stem cell compartment at the apical end of the epithelium (the apical loop) and thus provides an excellent tool to analyze the mechanisms of organogenesis and cytodifferentiation. To understand the functions of TIMPs in tooth development, we have analyzed the gene expression and protein localization of TIMP-1, -2, and -3 during mouse incisor development, from embryonic day 13 (E13) to postnatal day 3 (P3). TIMP-1 was present on the basement membrane during early developmental stages. At P2, TIMP-1 was strongly detected along the apical loop, transiently disappeared from the basement membrane in the cytodifferentiation zone, and later reappeared at the distal end of functional ameloblasts. Expression of TIMP-2 protein was restricted to the outer part of the apical loop throughout the examined stages. At P2, TIMP-2 was present on the basement membrane at the outer part of the apical loop. The dental follicle also expressed Timp-2, and the corresponding protein was abundant within the extracellular matrix. Timp-3 mRNA was highly expressed in the mesenchyme surrounding the apical loop. During matrix formation, Timp-3 was expressed by subodontoblasts, and the protein was detected in this layer and between odontoblasts. Distinct temporal and spatial expression patterns of TIMPs suggest divergent functions of these factors in incisor organogenesis. This work was supported by INSERM, CNRS, ARC, French Ministry of Research (ACI), Japanese Ministry of Education, Culture, Sports, Science, and Technology, and Niigata University Research Projects.     

Patterns of dental wear and the role of the canine in Cercopithecinae.

The importance of dental wear patterns in understanding masticatory functions in primates has long been appreciated. However, studies of wear patterns among populations of nonhuman primates are few. The purpose of this investigation is to establish the developmental aspects of dental wear in the Cercopithecinae and to describe certain relevant morphological traits. Studies were made of dental casts from 200 primate specimens of Macaca nemestrina, Macaca mulatta, and Papio cynocephalus. These casts were taken at four-month intervals, beginning at two years of age and continuing over a period of six to seven years. The wear pattern starts with the rounding and eventual flattening of the protoconid and protocone of the erupted first molars. Once this stage is reached, the hypoconid and metaconid of the mandibular, and the hypocone and paracone of the maxillary molars are rounded and eventually flattened. This pattern is maintained until the cusp tips are removed and the dentin exposed, however, the entoconid and metacone are not subjected to significant wear at this stage. Analysis of these dental casts and museum specimens has provided data on the development of dental wear during the maturation of these primates. The distribution of forces acting upon the teeth produce diagnostic patterns of wear, which provide evidence of the force location and magnitude. In examining the data, the hypothesis of canine guidance and its limitation of mandibular motion was evaluated. Specimens whose canines were removed demonstrate that the canines play no significant role in the development or maintenance of dental wear planes.     

Spire index and preferred surface orientation in some land snails

Fourteen species of land snails have been tested for their preference for surfaces at 0, 90 or 180 degrees under laboratory conditions. They range from high-spired (height/breadth = 4.1) to discoidal forms (height/breadth = 0.4). There is a positive association of spire height with tendency to adopt the 90 degree surface. Species of intermediate (globular) shape show less specificity for a particular surface than high- or low-spired species. The exception is Helix aspersa , which behaves more like one of the high-spired species than like one of its similarly shaped relatives. The differences in preference will help to reduce interaction between co-existing species in the field.     

Dorsoventral patterning of the C. elegans postembryonic mesoderm requires both LIN-12/Notch and TGFbeta signaling

The heparin binding molecules MK and HB-GAM are involved in the regulation of growth and differentiation of many tissues and organs. Here we analyzed the expression of MK and HB-GAM in the developing mouse incisors, which are continuously growing organs with a stem cell compartment. Overlapping but distinct expression patterns for MK and HB-GAM were observed during all stages of incisor development (initiation, morphogenesis, cytodifferentiation). Both proteins were detected in the enamel knot, a transient epithelial signaling structure that is important for tooth morphogenesis, and the cervical loop where the stem cell niche is located. The functions of MK and HB-GAM were studied in dental explants and organotypic cultures in vitro. In mesenchymal explants, MK stimulated HB-GAM expression and, vice-versa, HB-GAM upregulated MK expression, thus indicating a regulatory loop between these proteins. BMP and FGF molecules also activated expression of both cytokines in mesenchyme. The proliferative effects of MK and HB-GAM varied according to the mesenchymal or epithelial origin of the tissue. Growth, cytodifferentiation and mineralization were inhibited in incisor germs cultured in the presence of MK neutralizing antibodies. These results demonstrate that MK and HB-GAM are involved in stem cells maintenance, cytodifferentiation and mineralization processes during mouse incisor development.     

Light interception and radiation use efficiency of okra and normal leaf cotton isolines

Okra-leaf cotton (Gossypium hirsutum L.) types have been reputed to produce equal or higher amounts of lint yield than normal-leaf types, while intercepting less or similar amounts of radiation. In this field study, okra- and normal-leaf cotton isolines were compared for their efficiency to produce dry matter utilizing intercepted radiation. At three weeks after first flower, the two leaf-shape isolines produced similar amounts of dry matter, with the okra-leaf type partitioning a larger fraction to fruiting organs. However, at the end of the season no differences in lint yield, yield components and fiber-quality properties were recorded between the two isolines. Fractional light interception throughout the period of the study was greater for the normal-leaf type compared to the okra-leaf type. The okra-leaf isoline utilized intercepted radiation more efficiently to produce dry matter. Values of radiation use efficiency were estimated at 1.897 and 2.636 g MJ⁻¹ of intercepted photosynthetically active radiation for the normal- and okra-leaf types, respectively. Growth chamber studies revealed similar single leaf carbon exchange rates, therefore radiation use efficiency differences between the leaf shape isolines could be attributed to light interception characteristics.     

Cycling efficiency and pedalling frequency in road cyclists

The purpose of this study was to determine the influence of pedalling rate on cycling efficiency in road cyclists. Seven competitive road cyclists participated in the study. Four separate experimental sessions were used to determine oxygen uptake (VO(2)) and carbon dioxide output (VCO(2)) at six exercise intensities that elicited a VO(2) equivalent to 54, 63, 73, 80, 87 and 93% of maximum VO(2) (VO(2max)). Exercise intensities were administered in random order, separated by rest periods of 3-5 min; four pedalling frequencies (60, 80, 100 and 120 rpm) were randomly tested per intensity. The oxygen cost of cycling was always lower when the exercise was performed at 60 rpm. At each exercise intensity, VO(2) showed a parabolic dependence on pedalling rate (r = 0.99-1, all P < 0.01) with a curvature that flattened as intensity increased. Likewise, the relationship between power output and gross efficiency (GE) was also best fitted to a parabola (r = 0.94-1, all P < 0.05). Regardless of pedalling rate, GE improved with increasing exercise intensity (P < 0.001). Conversely, GE worsened with pedalling rate (P < 0.001). Interestingly, the effect of pedalling cadence on GE decreased as a linear function of power output (r = 0.98, n = 6, P < 0.001). Similar delta efficiency (DE) values were obtained regardless of pedalling rate [21.5 (0.8), 22.3 (1.2), 22.6 (0.6) and 23.9 (1.0)%, for the 60, 80, 100 and 120 rpm, mean (SEM) respectively]. However, in contrast to GE, DE increased as a linear function of pedalling rate (r = 0.98, P < 0.05). The rate at which pulmonary ventilation increased was accentuated for the highest pedalling rate (P < 0.05), even after accounting for differences in exercise intensity and VO(2) (P < 0.05). Pedalling rate per se did not have any influence on heart rate which, in turn, increased linearly with VO(2). These results may help us to understand why competitive cyclists often pedal at cadences of 90-105 rpm to sustain a high power output during prolonged exercise.     

Adaptation to hard-object feeding in sea otters and hominins

The large, bunodont postcanine teeth in living sea otters (Enhydra lutris) have been likened to those of certain fossil hominins, particularly the ’robust’ australopiths (genus Paranthropus). We examine this evolutionary convergence by conducting fracture experiments on extracted molar teeth of sea otters and modern humans (Homo sapiens) to determine how load-bearing capacity relates to tooth morphology and enamel material properties. In situ optical microscopy and x-ray imaging during simulated occlusal loading reveal the nature of the fracture patterns. Explicit fracture relations are used to analyze the data and to extrapolate the results from humans to earlier hominins. It is shown that the molar teeth of sea otters have considerably thinner enamel than those of humans, making sea otter molars more susceptible to certain kinds of fractures. At the same time, the base diameter of sea otter first molars is larger, diminishing the fracture susceptibility in a compensatory manner. We also conduct nanoindentation tests to map out elastic modulus and hardness of sea otter and human molars through a section thickness, and microindentation tests to measure toughness. We find that while sea otter enamel is just as stiff elastically as human enamel, it is a little softer and tougher. The role of these material factors in the capacity of dentition to resist fracture and deformation is considered. From such comparisons, we argue that early hominin species like Paranthropus most likely consumed hard food objects with substantially higher biting forces than those exerted by modern humans.     

Human adaptation and energetic efficiency

A lack of consensus on the general adaptive significance of energetic efficiency can be shown to exist in ecology and anthropology. After briefly reviewing key studies in optimal foraging theory and ecological anthropology, a model is presented which includes the following elements: (1) an equation of adaptive success with reproductive fitness, within an optimality framework; (2) a definition of energy limitation consistent with this framework; (3) a distinction between efficiency of energy capture and efficiency of energy use in achieving other goals; (4) a multiple definition of energetic efficiency that distinguishes purely energetic measures (output/input) from rate measures (energy captured per unit time); (5) the inclusion of time budgeting as a primary adaptive constraint; (6) a quantitative demonstration that increased output/input ratios do not consistently predict an increase in net energy captured, and are poor measures where time is a constraint. The general conclusion is that where energy is limiting, increased efficiency in the rate of energy capture will be adaptive because more net energy will be made available; where energy is not limiting, an increased net capture rate may still confer increased adaptive success, since time and labor energy are freed from energy-capture activities and can be devoted to achieving other adaptive goals. But while energetic efficiency, properly defined, is shown to have general adaptive significance in all cases where time or energy are constraints, considerations of adaptive optimality preclude the general equation of energetic efficiency and adaptive success.     

The quantum efficiency of photosynthesis in macroalgae and submerged angiosperms

Summary Photon absorption and photosynthesis under conditions of light limitation were determined in six temperate marine macroalgae and eight submerged angiosperms. Photon absorption and photosynthetic efficiency based on incident light increased in proportion to chlorophyll density per area and approached saturation at the highest densities (300 mg chlorophyll m^–2) encountered. Absorption and photosynthetic efficiency were higher in brown and red algae than in green algae and angiosperms for the same chlorophyll density because of absorption by accessory pigments. Among thin macroalgae and submerged angiosperms chlorophyll variations directly influence light absorption and photosynthesis, whereas terrestrial leaves have chlorophyll in excess and thus there is only a minor influence of pigment variability on light-limited photosynthesis. The quantum efficiency of photosynthesis averaged 0.062±0.019 (±SD) mol O₂ mol^–1 photons absorbed for macroalgae and, significantly less, 0.049±0.016 mol O₂ mol^–1 photons for submerged angiosperms. Of the measurements 80% were between 0.037 and 0.079 mol O₂ mol^–1 photons. The results are lower than values given in the literature for unicellular algae and terrestrial C₃ species at around 0.1 mol O₂ mol^–1 photons, but resemble values for other marine macroalgae and terrestrial C₄ species. The reason for these differences remains unknown, but may be sought for in differential operation of cyclic photophosphorylation and photorespiration.     

Transpiration efficiency of three Mediterranean annual pasture species and wheat

Attempts to improve water use efficiency in regions with Mediterranean climates generally focus on increasing plant transpiration relative to evaporation from the soil and increasing transpiration efficiency. Our aim was to determine if transpiration efficiency differs among key species occurring in annual pastures in southern Australia. Two glasshouse experiments were conducted with three key pasture species, subterranean clover (Trifolium subterraneum L.), capeweed [Arctotheca calendula (L.) Levyns] and annual ryegrass (Lolium rigidum Gaudin), and wheat (Triticum aestivum L.). Transpiration efficiency was assessed at the levels of␣whole-plant biomass and water use (W), leaf gas exchange measurements of the ratio of CO₂ assimilation to leaf conductance to water vapour (A/g), and carbon isotope discrimination (Δ) in leaf tissue. In addition, Δ was measured on shoots of the three pasture species growing together in the field. In the glasshouse studies, annual ryegrass had a consistently higher transpiration efficiency than subterranean clover or capeweed by all methods of measurement. Subterranean clover and capeweed had similar transpiration efficiencies by all three methods of measurement. Wheat had W values similar to ryegrass but A/g and Δ values similar to subterranean clover or capeweed. The high W of annual ryegrass seems to be related to a conservative leaf gas exchange behaviour, with lower assimilation and conductance but higher A/g than for the other species. In contrast to the glasshouse results, the three pasture species had similar Δ values when growing together in mixed-species swards in the field. Reasons for these differing responses between glasshouse and field-grown plants are discussed in terms of the implications for improving the transpiration efficiency of mixed-species annual pasture communities in the field. Received: 6 March 1997 / Accepted: 23 December 1997     

Metabolite production and growth efficiency

The capacity to sustain the large fluxes of carbon and energy required for rapid metabolite production appears to be inversely related to the growth efficiency of micro-organisms. From an overall energetic point of view three main classes of metabolite may be distinguished. These are not discrete categories, as the energetics of biosynthesis will depend on the precise biochemical pathways used and the nature of the starting feed stock(s). (1) for metabolites like exopolysaccharides both the oxidation state and the specific rate of production appear to be inversely related to the growth efficiency of the producing organism. Maximum rates of production are favored when carbon and energy flux are integrated, and alteration of this balance may negatively effect production rates. (2) The production of metabolites like organic acids and some secondary metabolites results in the net production of reducing equivalents and/or ATP. It is thought that the capacity of the organism to dissipate this product associated energy limits its capacity for rapid production. (3) For metabolites like biosurfactants and certain secondary metabolites that are composed of moieties of significantly different oxidation states production from a single carbon source is unfavorable and considerable improvements in specific production rate and final broth concentration may be achieved if mixed carbon sources are used. By careful selection of production organism and starting feedstock(s) it may be possible to tailor the production, such that the adverse physiological consequences of metabolite overproduction on the production organism are minimized.     

The trade-off between tooth strength and tooth penetration: predicting optimal shape of canine teeth

We investigate the shape of canine teeth under the assumption that the tooth's morphology is optimized by the evolutionary trade-off to minimize breakage and maximize ease of the penetration of prey. A series of experiments using artificial teeth to puncture the hides of a deer Odocoileus virginianus and pig Sus scrofa domesticus were conducted to establish the relationships between the tooth shape and the force needed to puncture the hide. The shapes of these teeth were also used in a beam theory analysis to calculate the strength of the teeth. Because the relative costs of puncturing and breakage were not known, a complete prediction of tooth shape was not possible. Instead, we used two independent measures of tooth shape: aspect ratio (total tooth length/tooth width at base) and rate of taper along the shank of the tooth. We quantified rate of taper in several species of felids, and by assuming this was the optimal design, we determined the relative costs of breakage and puncturing that would produce such a taper. Then, we used the relative costs to predict the aspect ratio of the optimum tooth. The average predicted value is about 2.5, very close to the average value in extant species of cats.     

Neandertal energetics and foraging efficiency

Mechanical interpretations of Neandertal skeletal robusticity suggest extremely high activity levels compared to modern humans. Such activity patterns imply high energy requirements; yet it has been argued that Neandertals were also inefficient foragers. The present study addresses this apparent conflict by estimating energy needs in Neandertals and then evaluating those estimates in the context of energetic and foraging data compiled for contemporary human foragers and nonhuman primates. Energy demands for Neandertals were determined by first predicting basal metabolic rates (BMR) from body weight estimates using human standards developed by the World Health Organization [FAO/WHO/UNU (1985) Energy and Protein Requirements. Report of the Joint FAO/WHO/UNU Export Committee, Geneva: WHO]. Total daily energy expenditure (kcal/day) was then estimated assuming high levels of physical activity (i.e., 2--3 x BMR), comparable to those observed among subsistence-level populations today. These estimates of energy requirements (ranging from 3000--5500 kcal/day) were then used to determine Neandertal foraging efficiency assuming (1) minimal survival-level foraging returns, and (2) daily foraging times longer than those observed among any contemporary foraging group and comparable to a nonhuman primate. Even with these extremely conservative parameters, estimates of Neandertal foraging efficiency (approximately 800--1150 kcal/h foraged) were comparable to those observed among living hunter-gatherers. These results indicate that if Neandertals did have heavy activity levels, as implied by their skeletal robusticity, they would have required foraging efficiencies within the range observed among modern groups. Thus, Neandertals could have been either highly active or poor foragers, but they could not have been both.     

小鳞鱼箴的维持日粮与转换效率

1998年 8月在一个养虾场蓄水池利用网箱进行了小鳞鱼箴维持日粮与转换效率的研究 .小鳞鱼箴生长率(GR)与日粮 (DR)的关系可表示为GR =14 0 .37DR -2 4.0 3 ;食物转换效率和能量转换效率分别为 13 .96 %和16 .12 % .从生长率和特定生长率计算的小鳞鱼箴维持日粮分别为体重的 17.12 %和 2 0 .39% ,表明从生长率和特定生长率计算维持日粮可能会导致不同的结果 .当日粮水平低于 3 .30 %时 ,小鳞鱼箴生长表现异常 ,意味着它可能利用了网采浮游动物以外的其它食物源 .     

Effects of additives on efficiency and specificity of ligase detection reaction

Ligase detection reaction (LDR) is adaptable to a wide variety of applications ranging from scientific research to clinical diagnosis, especially in the field of nucleotide polymorphism discrimination and analysis. Efficiency and specificity of LDR are the most two important characteristics that influence its application. To improve the specificity or efficiency of ligase, optimization of the design of LDR probes and the reaction of LDR were investigated previously by most researchers. But the effects of additives on LDR have not been reported. In this study, the effects of additives (DMSO, Tween-20, glycerol, formamide, and PEG-6000) on LDR efficiency and specificity were investigated. The results showed that all of these compounds, except for Tween-20, could improve the specificity of LDR. PEG-6000 was proved to be the best additive among the five tested with an optimal concentration of 5% at which the highest yield was obtained with a relatively improved specificity.     

Photosynthetic efficiency and nitrogen distribution under different nitrogen management and relationship with physiological N-use efficiency in three rice genotypes

Nitrogen fertilization strategies were widely adopted to enhance grain production and improve nitrogen utilization in rice all over the world. For fertilization timing strategy, ear fertilization was usually employed in recent years. For fertilization amount strategy, nitrogen fertilization would continually increase to meet the demands of increasing people for food. However, under heavy ear fertilization as well as great nitrogen amount (NA), physiological N-use efficiency (PE, defined as grain production per unit nitrogen uptake by plants) decreased. Under three NA and two ratios of fertilization given during ear development period to total NA (ear fertilization distribution ratio, EFDR), net photosynthetic rate (Pn), Pn to nitrogen content per unit area (photosynthetic N-use efficiency, Pn/N), nitrogen accumulation in plant tissues and PE of three rice (Oryza sativaL.) genotypes, Jinyou 253, Liangyoupeijiu and Baguixiang were screened in the first and second seasons in 2002 so as to understand the fluctuation patterns of Pn/N and nitrogen distribution in leaf blades under great NA & EFDR and relationship with PE in rice. Results showed that under greater NA & EFDR, Pn in flag leaves at heading and plant nitrogen accumulation at maturity always increased and PE & Pn/N always decreased in spite of increased grain production. Rice distributed more nitrogen in leaf blade under greater NA and EFDR. PE indicated significantly (P<0.05) positive relationship with Pn/N and negative relationship with nitrogen distribution ratio in leaf blades at heading and maturity, and no association with Pn in two growing seasons. Results suggested that low PE in rice under great NA and heavy ear fertilization is associated to more nitrogen distribution in leaf blades and decreases in photosynthetic efficiency.     

Energetic constraints and foraging efficiency

Previous research considers foraging options that differ interms of their gross rate of gain b and rate of energy expenditurec. This research argues that maximizing efficiency b/c willmaximize net energetic gain when there is an upper limit onthe amount of energy that can be assimilated. This analysisdoes not include the expenditure during the time for which theanimal is unable to forage because of this constraint. Whenthis expenditure is included, maximizing efficiency is no longeroptimal. Instead the best feeding option is the one with thehighest value of b/(c – c₁), where c, is the metabolicrate when the animal is not foraging.