Origin of glutaminyl-tRNA synthetase: An example of palimpsest?

Sequence data and evolutionary arguments suggest that a similarity may exist between the C-terminal end of glutaminyl-tRNA synthetase (GlnRS) and the catalytic domain of glutamine amidotransferases (GATs). If true, this would seem to imply that the amidation reaction of the Glu-tRNA^GIn complex was the evolutionary precursor of the direct tRNA^GIn aminoacylation pathway. Since the C-terminal end of GlnRS does not now have an important functional role, it can be concluded that this sequence contains vestiges that lead us to believe that it represents a palimpsest. This sequence still conserves the remains of the evolutionary transition: amidation reaction aminoacylation reaction. This may be important in deciding which mechanism gave origin to the genetic code organization. These observations, together with results obtained by Gatti and Tzagoloff [J. Mol. Biol. (1991) 218: 557–568], lead to the hypothesis that the class I aminoacyl-tRNA synthetases (ARSs) may be homologous to the GATs of the trpG subfamily, while the class Il ARSs may be homologous to the GATs of the purF subfamily. Overall, this seems to point to the existence of an intimate evolutionary link between the proteins involved in the primitive metabolism and aminoacyl-tRNA synthetases.     

Paranthropus boisei: An example of evolutionary stasis?

Of the presently recognised early hominid species, Paranthropus boisei is one of the better known from the fossil record and arguably the most distinctive; the latter interpretation rests on the numbers of apparently derived characters it incorporates. The species as traditionally diagnosed is distributed across approximately one million years and is presently confined to samples from East African sites. The hypodigm has been examined for evidence of intraspecific phyletic evolution, with particular emphasis on the areas best represented in the fossil record, namely the teeth and mandible. The results of this examination of 55 mandibular and dental variables, which uses the Γ test statistic for the detection of trend, and nonparametric spline regression (Loess regression) for investigating pattern and rate of temporal change, show that within Paranthropus boisei sensu stricto most evidence of temporally related morphological trends relates to the morphology of the P₄ crown. There is little or no evidence of any tendency to increase in overall size through time. Fossils from the Omo Shungura Formation and West Turkana which have been recovered from a time period earlier than the P. boisei sensu stricto hypodigm resemble the latter taxon in some features, but differ from it in aspects of cranial morphology. There is insufficient fossil evidence of the earlier taxon to tell whether it changes through time, but when trends of 47 mandibular and dental variables are assessed across the combined East African “robust” australopithecine sample, there is evidence for a relatively abrupt change around 2.2–2.3 Myr in approximately 25% of the dental and mandibular remains. Some of these changes correspond with the temporal trends within P. boisei sensu stricto, but others, such as mandible height, do not. If the earlier material is ancestral to P. boisei sensu stricto, evidence from the teeth and jaws is consistent with a punctuated origin for the latter taxon. © 1994 Wiley-Liss, Inc.     

Flowering phenology: An example of relaxation of natural selection?

Flowering phenology has normally been viewed as fundamental to a plant species' reproductive ecology. Researchers in the field have emphasized the adaptive importance of flowering at a particular time relative to other individuals in the population, or other species in the community. An alternative view, however, is that flowering phenology is a trait that may not be under strong selection, and this may have allowed some variation to appear in populations by chance.     

Are spontaneous activity and supraspinal control co-responsible for functional development of the generator of embryonic motility?

The effect of chronic administration of phenobarbital (from the 4th to the 16th day of incubation) combined with chronic spinal decentralization (decapitation at stage 11-13) on the development of spontaneous motor activity (recorded on the 17th day of incubation) was studied in 4 to 17-day-old chick embryos. 1. Combination of the two experimental treatments led to summation of their negative effect on development; spontaneous motor activity fell to 15.2% of the control value (to 26.9% after the isolated administration of phenobarbital and to 30.5% after isolated decapitation). 2. Metrazol activation of motor activity (100 mg/kg egg weight) after combination of the two factors was relatively no different from the results after their isolated use. 3. The acute administration of GABA (100 mg/kg e.w.) likewise induced relatively the same depression of spontaneous motility as after isolated chronic decapitation and the isolated chronic administration of phenobarbital. The results confirm the hypothesis of the significance of spontaneous activity of the spinal motoneurones for their survival and their actual functional development during the embryonic period.     

Are geriatric units needed for elderly patients with hip fractures?

To assess the need for a multidisciplinary geriatric unit in the treatment of elderly patients with hip fractures, we reviewed the charts of all patients aged 60 years or older who were treated for hip fractures in five hospitals in Hamilton, Ont., between August 1982 and September 1983. We hypothesized that discharge to a different location from that before admission would indicate reduced functional status and classified the reasons for a change in residence as poor patient motivation, need for rehabilitation, compromised ambulation, postoperative complications and inevitable deterioration. We believed that geriatric care would be most beneficial to those in the first three groups. Of the 327 patients with hip fractures 40 (12%) died before discharge. Of the 287 surviving patients 149 (52%) had been discharged by 4 weeks, and only 29 (10%) remained in hospital by 12 weeks. Of the 287, 44 (15%) were discharged to a different location from that before admission: in 75% the cause appeared to be inevitable deterioration (57%) or postoperative complications (18%). The remaining 25% needed rehabilitation and were all sent to appropriate facilities. None of the patients with ambulation problems or poor motivation required an increased level of care. We could not show a need for geriatric care in our population; possible explanations are discussed.     

Are mu-opioid receptor polymorphisms important for clinical opioid therapy?

Mutations in the mu-opioid receptor--the primary site of action of opioid analgesics--are candidates for the variability of clinical opioid effects. This has been substantiated by recent advances in genetic research. A common mu-opioid receptor polymorphism was associated with higher demands for alfentanil or morphine for pain relief. It also decreased the potency of morphine for pupil constriction and experimental analgesia, but its molecular mechanisms are unclear. Another opioid receptor mutation greatly impaired receptor signalling in vitro, but is very rare. The accumulated evidence provides a solid basis for continuing research that should address the underlying molecular mechanisms and the role and benefits of OPRM1 genotyping for clinical pain therapy.     

Are mitochondria a spontaneous and permanent source of reactive oxygen species?

The bioenergetic properties of mitochondria in combination with the high turnover rate of dioxygen qualify these organelles for the formation of reactive oxygen species (ROS). The assumption that mitochondria are the major intracellular source of ROS was essentially based on in vitro experiments with isolated mitochondria. The transfer of these data to the living cell may, however, be incorrect. Artefacts due to the preparation procedure or inadequate detection methods of ROS may lead to false positive results. Inhomogeneous results were found to be due to an interaction of the detection system with components of the respiratory chain which could be avoided by a recently developed non-invasive method. One of the most critical electron transfer steps in the respiratory chain is the electron bifurcation from ubiquinol to the cytochrome bc(1) complex. This electron bifurcation requires the free mobility of the head domain of the Rieske iron-sulfur protein. Inhibition of electron bifurcation by antimycin A causes leakage of single electrons to oxygen which results in the release of ROS. Hindrance of electron bifurcation was also observed following alterations of the physical state of membrane phospholipids in which the cytochrome bc(1) complex is inserted. Irrespective of whether the fluidity of the membrane was elevated or decreased, electron flow rates to the Rieske iron-sulfur protein were drastically reduced. Concomitantly superoxide radicals were released from these mitochondria, strongly suggesting the involvement of the ubiquinol/cytochrome bc(1) redox couple in this process.     

Are current textbooks good enough for physiology education? For example, the ECL cells are missing

Current textbooks are believed to provide an updated knowledge. Medical students usually read the textbooks but not the literature that contain the original research articles and reviews. Here, we examined the gap between the current textbooks and literature with the enterochromaffin-like (ECL) cells as an example. A total of 70 textbooks that were published for medical education during the last 10 yr was examined. The literature has been searched mainly from the Internet. We found that most textbooks (59 of 70) fail to mention the ECL cells. Due to the lack of information on the ECL cells, the mechanisms behind gastric acid secretion are described variously from book to book. However, up to the year 2000, 574 research articles and reviews have been published on the various aspects of the ECL cells. The role of the ECL cells in the regulation of the acid secretion has been well demonstrated for more than 20 years. The fact that the textbooks are out of date cannot be explained by the time required to write and publish them. Therefore, we question whether or not the current textbooks are good enough for physiology education and suggest both teachers and students read not only the textbooks, but also utilize the other sources such as the Internet to find and fill the gaps between the textbooks and literature. This is one of the approaches of problem-based learning.     

Are gap junctions necessary for cell-to-cell coupling of smooth muscle?: An update.

Earlier, it was questioned whether gap junctions (GJs) were necessary for cell-cell communication in smooth muscle, and GJs were not seen in some smooth muscles. We reexamined this question in the myometrium and in intestinal smooth muscle, in light of current knowledge of the presence and function of GJs. In the uterus, numerous studies show that an increase in GJ number is associated with the onset of delivery and is required for effective parturition. In all cases, this increase in GJ number and the changes in uterine contractility were correlated with increased electrical and metabolic coupling. Evidence for the much smaller, but detectable, degree of electrical coupling in the preterm uterus is explained by the small (but again detectable) number of GJs present. In the intestine, GJs are readily detected in the circular muscle layer but have not been described in the adjacent longitudinal layer. While our immunohistochemical studies failed to detect GJs in the longitudinal layer, this may not be adequate to prove their absence. Therefore, current knowledge of GJ number and function is adequate to explain cell-cell coupling in the uterus. Although it remains uncertain whether GJs are absent from the longitudinal muscle of the intestine, there is no definitive evidence that cell-cell coupling can occur by means other than GJs.     

Are blue-green algae a suitable food for zooplankton? An overview

One of the reasons suggested to explain the dominance of blue-greens in eutrophic lakes is that they are not used as food by zooplankton; and even when ingested, they are poorly utilized.

An increase in herbivores might be the expected result of biomanipulation of the aquatic food chain. This attempt at controlling the algae population is, however, destined to fail if zooplankton do not also utilize blue-greens as food. In this respect, a series of in-lake experimental results indicates that after the food chain has been biomanipulated, there is a decrease in blue-green density in periods when there is an increase in herbivores. Is this only an accidental result or are the two facts interrelated; in other words, can the decrease in the density of blue-greens be attributed to the increased use of them by zooplankton herbivores?

The suitability of blue-greens as food for zooplankton has been widely investigated by many authors with contrasting and inconclusive results. Two main factors seem to play important role in determining their suitability as food: the biochemical properties of the different species, or even different strains of the same species; and the shape and size of the colonies.

In particular, biochemical properties can result in toxic effects on zooplankton, while size and shape may strongly interfere with filtering, thus reducing the possibility of gathering food.

     

Analysis of hemoglobin oxygen equilibrium curves. Are unique solutions possible?

As a hemoglobin tetramer is oxygenated, it converts from a form with low ligand affinity to a high-affinity structure. This allosteric transition occurs in partially liganded molecules, typically after two or three ligands are bound. As a result of the co-operative nature of the process, the populations of the partially liganded forms are low. The relative proportions and precise properties of these intermediate substrates are therefore difficult to measure and are subject to controversy. The problem is compounded by compensating effects; for example, over-estimation of the oxygen affinity of triply liganded forms will result in under-estimation of the proportion of these species. Specifically, published values for the oxygen affinity of the triply liganded species vary for identical conditions by a factor of more than 6. In analyses based on the highest affinity values, the triply liganded species virtually disappears. However, this affinity is usually calculated from the last few per cent of the oxygenation curve, and this part of the curve is extremely sensitive to the normalization of the data. We conclude that unique solutions for the ligand affinity and substrate populations may be impossible to achieve, and that unusual mechanisms based on particular combinations of parameters, therefore, should be viewed with caution.     

Are animals capable of Bayesian updating? An empirical review

Numerous behavioral models assume individuals combine knowledge in the form of a prior distribution with current sample information using Bayesian updating to estimate the quality of environmental parameters. I examine this assumption by reviewing 11 empirical studies. Six studies compared observed behavior to predictions of Bayesian and non-Bayesian models, while five studies manipulated prior distributions directly and observed how such manipulations altered behavior. Eight species of birds, three mammals, one fish and one insect exhibited behavior consistent with Bayesian updating models; one studied bird species failed to show evidence of Bayesian updating. Most studies examined how individuals estimated food patch quality but two investigated mating decisions. These studies suggest a variety of animals in different ecological contexts behave in manners consistent with predictions of Bayesian updating models. Future work on decision-making should focus on understanding how animals learn prior distributions and on decision-making in additional ecological contexts.     

Reproductive segregation among the Barbus intermedius complex of Lake Tana,Ethiopia. An example of intralacustrine speciation?

Reproductive segregation among the large barbs Barbus intermedius complex, Cyprinidae , of Lake Tana, Ethiopia, was investigated in the mouths and upstream reaches of rivers tributary to the lake, during the spawning seasons of 1993 and 1994. The percentage of running fish of four Barbus morphotypes [Acute (Ac), Bigmouth big-eye (Be), Intermedius (In), and Shorthead (Sh)] peaks with the highest water level of the lake. Large differences are apparent in the minimum fork length of running fish among morphotypes [c. 12 cm for male Sh and 28 cm for male Bigmouth small-eye (Se)]. Significant differences occur in temporal, but especially in spatial patterns of the relative abundance of running morphotypes, when the lake is compared with the four major river mouths and their upstream reaches. These different relative abundances are clearest among Ac, Be, In, Sh and Troutlike (Tr). Also, the absence from the rivers of some morphotypes that are usually abundant in the lake itself [Barbel (Ba), Dark (Da), Lip (Li), and Zurki (Zu)], and the abundant presence in the rivers of Tr, rare in the lake, strengthen the hypothesis that spatial and/or temporal spawning segregation is present among the morphotypes. There are indications that Bighead (Bh) and Zu spawn in the lake itself, while other morphotypes were only found running in or near rivers. Combined with the morphological, ecological, and genetic differences, these data suggest the existence of several Barbus species, forming a unique species flock, which probably evolved within the lake. The presence of several, instead of one Barbus species complicates management of sustainable fisheries and protection of the lake's biodiversity. Present results show the importance of the rivers for Barbus reproduction and stress the urgent need for careful management of fishing activities in spawning times and areas.     

Are captive tortoises a reservoir for conservation? An assessment of genealogical affiliation of captive Gopherus agassizii to local, wild populations

The conservation of tortoises poses a unique situation because several threatened species are commonly kept as pets within their native ranges. Thus, there is potential for captive populations to be a reservoir for repatriation efforts. We assess the utility of captive populations of the threatened Agassiz’s desert tortoise (Gopherus agassizii) for recovery efforts based on genetic affinity to local areas. We collected samples from 130 captive desert tortoises from three desert communities: two in California (Ridgecrest and Joshua Tree) and the Desert Tortoise Conservation Center (Las Vegas) in Nevada. We tested all samples for 25 short tandem repeats and sequenced 1,109 bp of the mitochondrial genome. We compared captive genotypes to a database of 1,258 Gopherus samples, including 657 wild caught G. agassizii spanning the full range of the species. We conducted population assignment tests to determine the genetic origins of the captive individuals. For our total sample set, only 44 % of captive individuals were assigned to local populations based on genetic units derived from the reference database. One individual from Joshua Tree, California, was identified as being a Morafka’s desert tortoise, G. morafkai, a cryptic species which is not native to the Mojave Desert. Our data suggest that captive desert tortoises kept within the native range of G. agassizii cannot be presumed to have a genealogical affiliation to wild tortoises in their geographic proximity. Precautions should be taken before considering the release of captive tortoises into the wild as a management tool for recovery.