Migration of human and mouse primordial germ cells and colonization of the developing ovary: an ultrastructural and cytochemical study

This review is an account of the origin and migratory events of primordial germ cells until their settlement in the gonad before sexual differentiation in the human as well as mice. In this context, the morphodynamic characteristics of the migration of the primordial germ cells, the macromolecular characteristics of the extracellular matrix of the migratory pathway, and the factors involved in the germ cell guidance have been analyzed and discussed in the light of recent advances in this field, by means of immunocytochemical procedures. The events prior to gonadal morphogenesis and the origin of the somatic cell content of the human gonadal primordium have been also analyzed. In particular, evidences are presented showing that cells derived from the coelomic epithelium and mesenchyme are at the origin of the somatic components of the gonadal primordium, and that a mesonephric cell contribution to the generation of somatic cell components of the genital ridge in humans should be discarded due to the morphological stability of the different nephric structures during the period preceding the sexual differentiation of the gonad.     

Photoreceptor cells in the Xenopus retina

This review summarizes our present state of knowledge about spectrally different photoreceptor cell types in the Xenopus retina. The classification of the photoreceptors was based on morphology, combined with immunolabelling with various anti-visual pigment antibodies and other molecular probes on semithin sections and retinal wholemounts. The majority of photoreceptors is represented by rods. Altogether 97-98% of the total rod population consists of the principal ("red") rods that are selectively labeled by N-terminal specific anti-bovine rhodopsin monoclonal antibodies (mAbs) and are maximally sensitive to green light. The other, rare, blue-sensitive rod type ("green rod") is thinner, not stained by these antibodies but binds C-terminal specific anti-rhodopsin mAbs. The major representatives of the cones are red-sensitive and consist of a morphologically heterogeneous group comprising both (principal and accessory) members of double cones, as well as large single cones. Outer segments in this group are selectively labeled by mAb COS-1, specific to the L/M group of cone visual pigments. Another, relatively rare cone type is similar in size, but slightly smaller than the large single cone and is not labeled by mAb COS-1. This cone type is assumed to have a blue-sensitive cone visual pigment. The third, least abundant, and immunocytochemically distinct cone type is a small single (miniature) cone, which binds mAb OS-2 relatively strongly, and anti-rhodopsin mAbs 4B4 and 1D4 weakly. By exclusion, this small single cone may be identical with the UV-sensitive cone. Further studies are needed, however, to identify the color sensitivity of the latter two cone types.     

Role of alkyl moieties in the antiwear and antioxidant performance of alkyl phosphorodithioates

Phosphorodithioate derivatives having different alkyl substitu‐ents have been synthesised, while keeping the core phosphorus‐sulphur moiety intact. The change in antiwear, extreme‐pressure, and antioxidant properties with the variation in sub‐stituents at oxygen and at sulphur linkages in the phosphorodithioates has been studied. The role of the heteroatoms with regard to the alkyl substituents has been examined. The experimental data show that the chemical structure of an additive influences its physicochemical and tribological properties.     

Detection of haemoglobin in red cells of Xenopus laevis by immunofluorescent double labelling

Red cells from metamorphosing Xenopus laevis were treated with a fluorescein-conjugated guinea-pig antibody to Xenopus tadpole haemoglobin, a rabbit antibody to Xenopus adult haemoglobin, and a rhodamine-conjugated goat anti-rabbit globulin antibody. The presence of both red and green fluorescence in some cells indicated that at metamorphosis a proportion of the red cells contained both adult and tadpole haemoglobins.     

Symphony of rhythms in the Xenopus laevis retina

The photoreceptor layer in the retina of Xenopus laevis harbors a circadian clock. Many molecular components known to drive the molecular clock in other organisms have been identified in Xenopus, such as XClock, Xper2, and Xcrys, demonstrating phylogenetic conservation. This model system displays a wide array of rhythms, including melatonin release, ERG rhythms, and retinomotor movements, suggesting that the ocular clock is important for proper retinal function. A flow-through culture system allows measurements of retinal rhythms such as melatonin release in vitro over time from a single eyecup. This system is suited for pharmacological perturbations of the clock, and has led to important observations regarding the circadian control of melatonin release, the roles of light and dopamine as entraining agents, and the circadian mechanisms regulating retinomotor movements. The development of a transgenic technique in Xenopus allows precise and reliable molecular perturbations. Since it is possible to follow rhythms in eyecups obtained from adults or tadpoles, the combination of the flow-through culture system and the transgenic technique leads to the fast generation of transgenic tadpoles to monitor the effects of molecular perturbations on the clock.     

From egg to pole cells: ultrastructural aspects of early cleavage and germ cell determination in insects.

Insect eggs are giant and very complex cells covered by an extremely resistant shell. Both the egg cell and surrounding eggshell express anteroposterior and ventrodorsal polarity. The molecular and cytoplasmic organization of both axes originates during oogenesis and leads to the production of an ooplasmic system which consists of euplasm and deutoplasm (yolk) and contains a nucleus as well as extranuclear determinants of maternal origin. Both are part of the store of information for early embryogenesis. In addition, the deutoplasm serves as raw material and early nutrient supply for building the embryo. The insect egg cell, which is arrested in the first maturation division when released from the ovary during oviposition, will be activated by different stimuli among different species to complete meiosis and start embryogenesis. The zygote nucleus undergoes a number of synchronous mitotic divisions leading to cleavage energids which initially form a syncytial blastoderm and subsequently the cellular blastoderm. In many insects, prior to blastoderm formation, polar granules (or oosome material) are incorporated in a single cell or a small number of cells which bud off at the posterior pole. These so called pole cells give rise to the primordial germ cells. Therefore, polar granules or the oosome material mark the germ line, and while structural counterparts of determinants of body pattern formation have so far not been found, the polar granules or oosome serve as an autonomous ooplasmic determinant for the pole or germ cells. Anteroposterior body polarity can arise independent of the germ plasm.     

Confocal microscopy and 3-D reconstruction of the cytoskeleton of Xenopus oocytes

Xenopus oocytes contain a complex cytoskeleton composed of three filament systems: (1) microtubules, composed of tubulin and at least three different microtubule-associated proteins (XMAPs); (2) microfilaments composed of actin and associated proteins; and (3) intermediate filaments, composed of keratins. For the past several years, we have used confocal immunofluorescence microscopy to characterize the organization of the oocyte cytoskeleton throughout the course of oogenesis. Together with computer-assisted reconstruction of the oocyte in three dimensions, confocal microscopy gives an unprecedented view of the assembly and reorganization of the cytoskeleton during oocyte growth and differentiation. Results of these studies, combined with the effects of cytoskeletal inhibitors, suggest that organization of the cytoskeleton in Xenopus oocytes is dependent upon a hierarchy of interactions between microtubules, microfilaments, and keratin filaments. This article presents a gallery of confocal images and 3-D reconstructions depicting the assembly and organization of the oocyte cytoskeleton during stages 0-VI of oogenesis, a discussion of the mechanisms that might regulate cytoskeletal organization during oogenesis, and speculates on the potential roles of the oocyte cytoskeleton during oogenesis and axis formation.     

Photoreceptor classes and transmission at the photoreceptor synapse in the retina of the clawed frog, Xenopus laevis

The photoreceptor population in Xenopus consists of a green-sensitive rod (lambda(max) = 523 nm), a blue-sensitive rod (lambda(max) = 445 nm) and three classes of cone. The largest cone is red-sensitive (lambda(max) = 611 nm). The intermediate cone is presumed to be blue-sensitive based on physiological criteria, whereas the miniature cone may be UV-sensitive. Horizontal cells (HC) are of two sorts: axon-bearing and axonless. The axon-bearing HC is of the luminosity type and probably contacts all types of photoreceptor. The axonless HC is of the chromaticity type and contacts only intermediate (blue) cones and at least one type of rod. During development dendrites of HCs and bipolar neurons penetrate photoreceptor bases. A progressive maturation of HC and bipolar synapses with rods and cones occurs between tadpoles stages 37/8 and 46. Neighboring rods and cones are joined by gap junctions. During this same period, the outer segments are laid down and photopigments synthesized. A linear relation was found between the quantum capturing ability of the rod and its absolute threshold. Mature rods of the Xenopus retina release glutamate in a calcium-dependent manner. Glutamate release was found to be a linear function of calcium influx through L-type calcium channels. Both types of HC possess ionotropic glutamate receptors of the AMPA subtype.     

Measurements of the diameters of the great arteries and semi-lunar valves of chick and mouse embryos

The great arteries of embryos are small channels of a complex three-dimensional arrangement. Measurements of their diameters, as required for understanding cardiovascular morphogenesis and the genesis of malformations, cannot be performed in two-dimensional histological sections. We present and evaluate a quick and simple method for performing highly significant and objective measurements of the diameters of blood vessels in vertebrate embryos and used this method for providing statistics of the diameter of the semi-lunar valves and the lumina of the great arteries of early chick and mouse foetus. We employed the high-resolution episcopic microscopy technique for generating volume data and three-dimensional computer models of the arterial trees of 30 chick embryos (Hamburger Hamilton stage 34), 30 mouse embryos of the OF1 strain harvested on 14.5 dpc, 30 embryos of the OF1 strain harvested on 15.5 dpc and 28 mouse embryos of the PARKES strain harvested on 14.5 dpc. The three-dimensional models (voxel size 2 μm × 2 μm × 2 μm and 3 μm × 3 μm × 3 μm) were used for defining virtual resection planes perpendicular to the longitudinal axis of the blood vessels at comparable positions. In these planes, we measured the lumen areas and the lumen perimeters. We also calculated the lumen diameter and the true lumen area from the perimeter and present statistical analysis. Finally, we evaluate and discuss the reliability and reproducibility of our method and present all measurements in a form that minimizes the influence of specimen size variation, specimen processing and data generation methods.     

原油及生油岩中甾烷和萜烷的质谱特征及鉴定

本文报道我们近几年来利用色质联用仪对原油及生油岩中生物标志物（甾烷、萜烷）的定性分析鉴定。     

N-50/200型单列卧式五级活塞式压缩机检修

N-50／200型单列卧式五级活塞式压缩机检修的内容多，过程复杂、要求高，介绍了该类压缩机的检修项目及检修的方法。     

大蒜中大蒜素等含硫化合物的GC/MS法测定

对大蒜中的有效成分———大蒜素进行提取,并利用气相色谱-质谱联用仪对大蒜中的大蒜素进行测定。确定大蒜素的成分主要包含二烯丙基一硫醚,二烯丙基二硫醚,二烯丙基三硫醚等在内的多种含硫化合物。     

光固化快速成形中待支撑区域识别技术研究

从实现的角度出发,以支撑设计规则为分类原则,对待支撑区域进行了分类。在对零件的STL格式表示和其几何特征的相互关系研究的基础上,介绍了基于STL模型的三维待支撑区域特征识别的数据结构设计和实现技术,最后,给出三维待支撑区域特征识别的完整算法及其应用实例。     

Identification of the unbalance distribution in flexible rotors

This paper presents a new method for estimating unbalance distributions of flexible shafts and constant eccentricities of rigid disks based on the transfer matrix method for analyzing the steady-state responses of rotor-bearing systems, in which the transfer matrix of a flexible shaft is derived in a continuous sense with any spatial unbalance distribution. Rotary inertia, gyroscopic and transverse-shear effects are also included. When deflections and deflection angles of one free end are measurable, the unbalance distribution of shafts and disks can be estimated under operating conditions by the proposed method. The main advantage of this identification technique is that only the state vector of the one free end of the rotating shaft need to be measured. Justification of the method is presented by numerical simulations.     

Effects of vitamin A deficiency on the inter-Sertoli cell tight junctions and on the germ cell population.

When 20-day-old rats are placed on a vitamin A deficient diet (VAD) for a period of 10 weeks, the seminiferous tubules are found to contain only Sertoli cells, a few residual A0, A1 spermatogonia, and preleptotene spermatocytes (PL). The type A1 spermatogonia and PL spermatocytes are arrested in their G2 phase. In VAD rats type A2-A4, intermediate (In) and B spermatogonia and all types of spermatocytes (except PL spermatocytes) and spermatids are eliminated from the seminiferous tubules. Two questions were raised in this investigation: 1) Is there, in VAD rats, any correlation between a breakdown of the blood-testis barrier (e.g., Sertoli cell tight junctions) and germ cell loss? 2) Is the disappearance of most germinal cells due to their degeneration during spermatogenesis or to a maturation depletion process resulting from an arrest of spermatogenesis at the spermatogonial stage? To investigate these questions four groups of male Sprague-Dawley rats (20-days old) were fed a VAD diet for 7 to 12 weeks. The testes were fixed by perfusion with 2.5% glutaraldehyde in 0.1 M sodium cacodylate containing 2% lanthanum nitrate, an electron opaque tracer used to test the patency of Sertoli cell tight junctions. The lanthanum permeated the intercellular space of the basal compartment but was arrested by normal inter-Sertoli cell tight junctions. The seminiferous epithelium showed numerous degenerating germ cells, some being internalized by Sertoli cells as membrane-bound phagosomes.(ABSTRACT TRUNCATED AT 250 WORDS)     

FX1N-40MR型PLC在卧式镗床控制系统的应用

分析了三菱公司的FX1N-40MR型PLC在卧式镗床上的电气改造应用,给出了电气控制的软、硬件的设计。实践证明,采用先进的PLC取代传统的继电器控制,提高了卧式镗床的电气安全性和工作可靠性,说明PLC在传统制造行业是大有作为的。     

Identification of molecules in the kidney utilizing immunocytochemistry

Immunocytochemistry of the kidney is a unique method to integrate physiology, biochemistry, and molecular biology with morphology. Both mono- and polyclonal antibody reagents are useful and each has advantages and disadvantages. Specificity with low background is of the greatest importance. Tissue preparation techniques depend on the antigen being studied as well as the methodology to be used. Pre- and postembedding techniques combined with visualization with peroxidase reaction products or with particulate markers such as ferritin and gold must be chosen for each individual circumstance to be studied. Important applications in the kidney have included studies of glomerular antigens, specific transport proteins, and segment-specific antigens of unknown specificity. Future utilization of this technique with new molecular probes will greatly enhance our knowledge of the biology of the kidney.