Molecular Mechanisms of Translation Initiation in Mammals Studied by in vitroReconstruction of Initiation Complexes

Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field.     

Sex differences in leg dexterity are not present in elite athletes

We studied whether the time-varying forces that control unstable foot–ground interactions provide insight into the neural control of dynamic leg function. Twenty elite (10 F, 26.4 ± 3.5 yrs) and 20 recreational (10 F, 24.8 ± 2.4 yrs) athletes used an isolated leg to maximally compress a slender spring designed to buckle at low forces while seated. The foot forces during the compression at the edge of instability quantify the maximal sensorimotor ability to control dynamic foot–ground interactions. Using the nonlinear analysis technique of attractor reconstruction, we characterized the spatial (interquartile range IQR) and geometric (trajectory length TL, volume V, and sum of edge lengths SE) features of the dynamical behavior of those force time series. ANOVA confirmed the already published effect of sex, and a new effect of athletic ability, respectively, in TL (p = 0.014 and p < 0.001), IQR (p = 0.008 and p < 0.001), V (p = 0.034 and p = 0.002), and SE (p = 0.033 and p < 0.001). Further analysis revealed that, for recreational athletes, females exhibited weaker corrective actions and greater stochasticity than males as per their greater mean values of TL (p = 0.003), IQR (p = 0.018), V (p = 0.017), and SE (p = 0.025). Importantly, sex differences disappeared in elite athletes. These results provide an empirical link between sex, athletic ability, and nonlinear dynamical control. This is a first step in understanding the sensorimotor mechanisms for control of unstable foot–ground interactions. Given that females suffer a greater incidence of non-contact knee ligament injuries, these non-invasive and practical metrics of leg dexterity may be both indicators of athletic ability, and predictors of risk of injury.     

Three-dimensional ultrastructure and quantitative analysis of the human Sertoli cell nucleolus

The nucleolus of the human Sertoli cell displays a spontaneous segregation of its components and has only one or 2 large fibrillar centers. The 3-dimensional reconstruction and quantitative analysis of its components was undertaken using a Quantimet 900 image analysis system in order to define the spatial relationships between the dense fibrillar component and the fibrillar center and especially to investigate whether threads of dense fibrillar component exist independently, without being linked to a fibrillar center. Our 3D reconstructions demonstrated that the dense fibrillar threads or sheets were never independent of fibrillar centers. These structures belonged to a continuous network that joined the layer of dense fibrils surrounding the fibrillar center. When the nucleolus contained 2 different-sized fibrillar centers, quantitative analysis showed that there was a proportional relationship between the volume of the dense fibrillar component and the volume of the fibrillar center. These data, compared with those previously obtained by means of autoradiographic techniques, suggest that the rDNA-containing chromatin passes through the fibrillar center and unwinds from there into the dense fibrillar component.     

Quantitative cytology of the alfalfa generative cell and its relation to male plastid inheritance patterns in three genotypes

Summary Studies utilizing restriction analysis of plastid DNA, as well as those employing chlorophyll-deficient mutants, have shown a high frequency of paternal plastid transmission in alfalfa. Recent research has also shown that plastid inheritance patterns among alfalfa genotypes and are under genetic control. In a previous study we were unable to detect any correlations between qualitative, three-dimensional ultrastructure of generative cells and male plastid transmission strength in certain genotypes. In the present study we used serial ultrathin sectioning, computerized reconstruction and quantitation, and stereology to further analyze generative cells within mature pollen. Measurements included volumes and surface areas of cells, nuclei, and organelles, as well as organelle number and distribution. Three genotypes were investigated, one that is a strong transmitter of male plastids (genotype 301), one that is a weaker transmitter of male plastids (genotype 7W), and a third that is an even weaker male plastid transmitter (genotype MS-5). Our results show that genotype MS-5 has significantly fewer plastids/generative cell than either of the other genotypes, which may account for it being a relatively poor transmitter of male plastids. However, plastid number does not explain known differences in male plastid inheritance between genotypes 301 and 7W, since plastid number does not differ significantly between these two genotypes. Regarding the other features of generative cells measured in this study, no consistent correlations were found that might account for differences in male plastid inheritance patterns between genotypes. Plastid distribution is equal in each end of the spindle-shaped generative cell in all genotypes studied. Similar relative results were found with regard to mitochondria within generative cells; however, comparative genetic data are not available on mitochondrial transmission patterns in alfalfa genotypes.     

Quantitative ultrastructural analysis of barley sperm

Summary Complete serial ultrathin sections of seven sperm pairs, computer-assisted measurements of cell, nuclear and organelle surface areas and volumes, and three-dimensional imagery were used to demonstrate that a process of cytoplasm and organelle elimination occurs during sperm maturation in barley. The number of mitochondria per sperm cell is reduced by 50%; sperm cell surface area and volume are reduced by 30% and 51% respectively. Mean volume and surface area per mitochondrion are significantly less in mature sperms. No examples of mitochondrial fusion or degeneration were observed within sperm cells. These data, along with observations of plasma membrane apposition and vesiculation within cytoplasmic extensions containing mitochondria, support the proposition that cytoplasm and organelle loss results primarily from the formation of cytoplasmic projections that are subsequently discarded from the sperm cell body. Comparisons of the quantitative data, including the number of mitochondria, indicate that differences between sperm cells of a pair are absent to very slight. Spatial organization within the pollen grain is such that the mature sperms, as well as the sperms and vegetative nucleus, are not in close proximity.     

Three-dimensional structure of a regular surface layer from Pseudomonas acidovorans

The regular surface layer of Pseudomonas acidovorans was investigated by computer processing of a series of tilted view electron micrographs, and a reconstruction of the three-dimensional structure was obtained. The pattern is tetragonal and consists of massive identical subunits, block-like in face-view, which interlock loosely in a simple cobblestone pattern. The square unit cell has a lattice constant of 11 nm. The surface layer pattern of P. acidovorans appears to be more dependent on the underlying membrane for maintaining its integrity than those so far studied in other bacteria.     

组胺H2受体拮抗剂对骨髓造血重建的影响

用组胺H_2受体拮抗剂(甲氰咪胍或呋喃硝胺)处理正常和亚致死量γ-射线照射小鼠,探讨正常体内造血和再生骨髓中造血重建与组胺受体的关系。发现非毒性剂量的甲氰咪胍对正常小鼠骨髓多能造血干细胞(CFU-s)无抑制作用,但可抑制小鼠体内粒单系祖细胞(CFU-GM)的生长和亚致死量照射后CFU-s产率的恢复。组胺可能与骨髓的再生有关,组胺H_2受体拮抗剂可抑制骨髓的造血重建。