大黄鱼精子的超微结构

大黄鱼的精子由头产和尾部两部分组成。头部结构较为独特,其腹侧有一较大的细胞核,背部有中心粒复合体。头部的后端是袖套。细胞核的腹面稍向外突出背面则稍向内凹。细胞核中的染以质浓缩成致密的团块状。团块状的染色质之间分布着松散的纤维状染色质。植入窝位于细胞核的背部表面,由细胞核背面向内凹陷而成,呈一沟状,其走向与精子的长轴平行。     

Expression patterns of fork head and goosecoid homologues in the mollusc Patella vulgata supports the ancestry of the anterior mesendoderm across Bilateria

We have characterised orthologues of the genes fork head and goosecoid in the gastropod Patella vulgata. In this species, the anterior-posterior (AP) axis is determined just before gastrulation, and leads to the specification of two mesodermal components on each side of the presumptive endoderm, one anterior (ectomesoderm), and one posterior (endomesoderm). Both fork head and goosecoid are expressed from the time the AP axis is specified, up to the end of gastrulation. fork head mRNA is detected in the whole endoderm, as well as in the anterior mesoderm, whereas goosecoid is only expressed anteriorly, in the three germ layers. The two genes are thus coexpressed in the anterior mesoderm, suggesting the latter's homology with vertebrate prechordal mesoderm. In addition, since prechordal plate is known to belong to an anterior, so called "head organiser", and since its inductive role is dependent on the function of the vertebrate fork head and goosecoid orthologues, we further suggest that the anterior mesoderm may also have a role in anterior inductive patterning in Spiralia. Finally, we propose that a mode of axial development involving two organisers, one anterior and one posterior, is ancestral to the Bilateria, and that both organisers evolved from the single head organiser of a putative hydra-like ancestor.     

Rücken‐WNT für die Primärachse der Tiere

Axis formation in animals The last common ancestor of Cnidaria and Bilateria likely used the WNT/β‐Catenin pathway in a regionalized fashion to establish its primary, anterior‐posterior axis. Unexpectedly, the morphological head of Cnidaria corresponds to the rear end of Bilateria. Moreover, annelids use the WNT/β‐Catenin system for early, local and binary decisions, and insects developed a completely unrelated pathway. They use Bicoid (Drosophila) – or Hunchback/Orthodenticle (Tribolium) – to control axis formation. Nevertheless, WNT functions are essential during the segmentation phase in insects and in ancestral insects as well as in other arthropods during formation of posterior structures. In summary, the WNT/β‐Catenin system is an essential part of the molecular tool kit, which helped to establish the unique features of animals.     

Clonal analysis of epiblast fate during germ layer formation in the mouse embryo.

The fate of cells in the epiblast at prestreak and early primitive streak stages has been studied by injecting horseradish peroxidase (HRP) into single cells in situ of 6.7-day mouse embryos and identifying the labelled descendants at midstreak to neural plate stages after one day of culture. Ectoderm was composed of descendants of epiblast progenitors that had been located in the embryonic axis anterior to the primitive streak. Embryonic mesoderm was derived from all areas of the epiblast except the distal tip and the adjacent region anterior to it: the most anterior mesoderm cells originated posteriorly, traversing the primitive streak early; labelled cells in the posterior part of the streak at the neural plate stage were derived from extreme anterior axial and paraxial epiblast progenitors; head process cells were derived from epiblast at or near the anterior end of the primitive streak. Endoderm descendants were most frequently derived from a region that included, but extended beyond, the region producing the head process: descendants of epiblast were present in endoderm by the midstreak stage, as well as at later stages. Yolk sac and amnion mesoderm developed from posterolateral and posterior epiblast. The resulting fate map is essentially the same as those of the chick and urodele and indicates that, despite geometrical differences, topological fate relationships are conserved among these vertebrates. Clonal descendants were not necessarily confined to a single germ layer or to extraembryonic mesoderm, indicating that these lineages are not separated at the beginning of gastrulation. The embryonic axis lengthened up to the neural plate stage by (1) elongation of the primitive streak through progressive incorporation of the expanding lateral and initially more anterior regions of epiblast and, (2) expansion of the region of epiblast immediately cranial to the anterior end of the primitive streak. The population doubling time of labelled cells was 7.5 h; a calculated 43% were in, or had completed, a 4th cell cycle, and no statistically significant regional differences in the number of descendants were found. This clonal analysis also showed that (1) growth in the epiblast was noncoherent and in most regions anisotropic and directed towards the primitive streak and (2) the midline did not act as a barrier to clonal spread, either in the epiblast in the anterior half of the axis or in the primitive streak. These results taken together with the fate map indicate that, while individual cells in the epiblast sheet behave independently with respect to their neighbours, morphogenetic movement during germ layer formation is coordinated in the population as a whole.     

Mesodermal cell migration during Xenopus gastrulation

The adhesive glycoprotein fibronectin (FN), which is a component of the network of extracellular matrix fibrils on the inner surface of the blastocoel roof (BCR), has been proposed to play a major role in directing mesodermal cell migration during amphibian gastrulation. In the first part of this paper, the adhesion of Xenopus mesodermal cells to FN in vitro is examined. Cells from several mesoderm regions, which differ in developmental fate and morphogenetic activity, are able to bind specifically to the RGD cell-binding site of FN. Dorsal mesodermal cell adhesion to FN varies along the anterior-posterior (a-p) axis: adhesion is strongest in the anterior head mesoderm, and gradually decreases posteriorly. This a-p gradient of mesodermal adhesiveness to FN does not change during mesodermal involution, and is reflected in the morphology of mesodermal explants on FN. An a-p strip of mesoderm develops a spreading, leading anterior margin and a compact, retracting posterior end, thus moving slowly and directionally over the FN substrate at about 0.8 micron/min. Although dissociated cells from all levels of the dorsal mesodermal axis adhere to FN, only the anterior, leading prospective head mesoderm cells migrate as single cells on a FN substrate in vitro. Locomotion by means of lamelliform protrusions occurs at an average rate of about 1.5 micron/min. Cells of the more posterior axial mesoderm merely shift position at random without substantial net translocation, and preinvolution mesoderm cells are completely stationary. On the BCR, the in vivo substrate for mesodermal cell migration, dissociated prospective head mesoderm cells spread and migrate as on FN in vitro, at 2.2 microns/min. In the presence of an RGD peptide which inhibits cell-FN interaction, cells remain globular and do not spread. They are still motile, but change direction frequently, which leads to less efficient net translocation. Apparently, interaction with the RGD cell-binding site of FN and concomitant spreading of head mesoderm cells is required for the stabilization of cell locomotion. In contrast to the directional migration of the mesoderm cell population toward the animal pole in the embryo, the pathways of dissociated cells on the BCR are randomly oriented. Coherent explants of migratory mesoderm do not move at all on the BCR, although they translocate on FN in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)     

水螅异常极性体轴的形成及矫正进程的观察

目的:如何建立和维持体轴是一个基本的发育生物学问题,而淡水水螅是适合进行形态发生和个体发育调控机制研究的重要模式生物。本文观察了大乳头水螅异常极性体轴的形成及矫正进程,初步探讨水螅极性体轴的维持和调控机制。方法:先切取水螅的整个头部,再获得带二根触手的口区组织。通过ABTS细胞化学染色法检测水螅基盘分子标志物过氧化物酶的表达,判别水螅基盘组织(水螅足区的末端)是否形成。结果:从40块口区组织再生得到的水螅个体中有1例极性体轴发育异常的个体,其身体两端均发育成头区,且两端的头区均具有捕食能力。随后水螅其中一端头区的触手逐渐萎缩、退化,最终该端头区转化成具有吸附能力的基盘组织。结论:水螅组织的再生涉及极性体轴的重建,而一些特殊因素可能造成临时性的水螅极性体轴调控紊乱。本研究表明水螅具备自我矫正异常极性体轴的能力。另外,本研究结果显示水螅触手可以萎缩直至退化,该现象涉及的细胞学过程可能是非常复杂的,有可能涉及到触手细胞的凋亡转化过程,也可能是触手的高度分化细胞仍然具备去分化能力、去分化后再转移到身体其他地方,其具体机制值得进一步探究。     

What are the roles of retinoids,other morphogens,and Hox genes in setting up the vertebrate body axis?

This article is concerned with the roles of retinoids and other known anterior–posterior morphogens in setting up the embryonic vertebrate anterior–posterior axis. The discussion is restricted to the very earliest events in setting up the anterior–posterior axis (from blastula to tailbud stages in Xenopus embryos). In these earliest developmental stages, morphogen concentration gradients are not relevant for setting up this axis. It emerges that at these stages, the core patterning mechanism is timing: BMP‐anti BMP mediated time space translation that regulates Hox temporal and spatial collinearities and Hox‐Hox auto‐ and cross‐ regulation. The known anterior–posterior morphogens and signaling pathways––retinoids, FGF's, Cdx, Wnts, Gdf11 and others––interact with this core mechanism at and after space–time defined “decision points,” leading to the separation of distinct axial domains. There are also other roles for signaling pathways. Besides the Hox regulated hindbrain/trunk part of the axis, there is a rostral part (including the anterior part of the head and the extreme anterior domain [EAD]) that appears to be regulated by additional mechanisms. Key aspects of anterior–posterior axial patterning, including: the nature of different phases in early patterning and in the whole process; the specificities of Hox action and of intercellular signaling; and the mechanisms of Hox temporal and spatial collinearities, are discussed in relation to the facts and hypotheses proposed above.     

Behavioral plasticity and central regeneration of locomotor reflexes in the freshwater oligochaete, Lumbriculus variegatus. II: Ablation studies

Abstract. After 8–10 segments of posterior ventral nerve cord were ablated in Lumbriculus variegatus , touch-evoked locomotor responses were evident both in segments anterior and posterior to the ablation site. However, responses in these two regions were independent and uncoupled. During recovery, four outcomes were observed at the ablation site: (Group 1) recovery of normal functions with no growth of new segments; (Group 2) formation of a laterally protruding, multi-segmented, ectopic head; (Group 3) formation of a laterally protruding, amorphous, and multi-segmented outgrowth; and (Group 4) segmental autotomy. In Groups 1 and 2, touch-evoked swimming and body reversal were studied. In addition, sensory fields and conduction properties of giant nerve fibers were examined near the ablation site. In some Group 1 worms, clear-cut behavioral and electrical signs of recovery and reconnection were seen by 3 d after ablation. By 8 d, all worms had recovered and exhibited response patterns comparable to those of normal worms. In Group 2 worms, with an ectopic head, segments posterior to the ablation (together with those in the ectopic head), exhibited touch-evoked swimming and body reversal responses resembling those of a complete worm. Segments anterior to the ectopic head were independently capable of locomotor responses. Medial and lateral giant fiber sensory fields in worms with ectopic heads reflected a pattern expected for two worms. Thus, through apparent morphallactic reorganization, a medial giant fiber sensory field emerged which included the ectopic head and 10–15 adjacent posterior segments. In contrast, electrical recordings showed longitudinal through-conduction of giant fiber spikes, across the ablation site. Histological examination revealed that the giant nerve fibers in the ectopic head were complexly interconnected with those in the main body axis.     

Axis formation in half blastoderms of the chick: Stage at separation and the relative positions of fused halves influence axis development

The blastoderm of the avian embryo acts during the early stages of development as an integrative system programmed to form a single embryonic axis. Isolated parts of the blastoderm are known to each form an axis, owing to the system's properties. In the work reported here, the regulative capability of the right and left halves of chick blastoderms to form an embryonic axis was examined systematically at different stages. This revealed a progressive change in the developing blastoderm. After early separation, the axis in each half will form at some distance from the blastoderm's original midline, while with late separation the axis will form next to the original midline and may even lack one row of somites at the medial rim. Since development stops in culture after about 2 days, axis development after early separation ceases before somites are formed, whereas after late separation somites and brain vesicles can develop. In addition, an attempt was made to learn whether the two halves of blastoderm, when shifted along the midline and then reunited in staggered fashion, act as a single or two separate embryonic fields. When reunion of the right and left halves was achieved so that the posterior end of one half was adjoining the posterior area pellucida region of the other half, a single embryonic axis developed. When, on the other hand, the shift was larger so that the posterior end was fused to the central area pellucida of the other half, two separated embryonic axes developed.     

MITOSIS, CELL WALL AND FLAGELLA SYNTHESIS IN SYNCHRONIZED CULTURES OF THE PRASINOPHYTE, SCHERFFELIA DUBIA

Cell division occurs within the parental cell wall, yielding two progeny cells. Since Scherffelia dubia sheds all four flagella prior to cell division, the maturing progeny cells must regenerate new cell walls and flagella during and/or after cytokinesis. To better understand these processes, we have synchronized cell division in cultures of S. dubia and observed all stages of mitosis, cytokinesis, and progeny cell maturation, including flagella and cell wall formation, via DAPI staining of fixed cells, DIC microscopy of live cells embedded in agarose and standard TEM. Microscopical observations revealed the following sequence of events: 1) Golgi stacks divide during late interphase and immediately begin producing theca scales; 2) deflagellation and release of the parental cell wall from the plasma membrane occurs during early prophase; 3) synthesis of theca and flagella scales within the Golgi and/or scale reticulum continues throughout mitosis; 4) during cytokinesis, a coalescence of vesicles containing theca scales at the posterior end of the cell results in a cleavage furrow slightly diagonal to the cells' longitudinal axis (40 min); 5) post-mitotic nascent basal body formation and flagella elongation at the inherited basal bodies (and later at the mature nascent basal bodies) occurs concurrently with continued cell wall synthesis; 6) the cleavage furrow rotates into a transverse position (35 min); 7) reorientation of the nuclei results in a "head to tail" orientation of the maturing progeny cells; and 8) matured progeny cells emerge from the posterior end of the parental theca not before 8 hrs after the onset of mitosis.     

鲤鱼精子超微结构的研究

鲤鱼精子由头部,中片和尾部组成,头部的细胞核卵形,染色质致密。核中有些小空隙,空中的电子致密物质存在。中片紧连在核的后端。中片由中心粒复合体和袖套组成。中心粒复合体位于核后植入窝中,袖套一侧肥厚,一侧狭窄,袖套中有线粒体和囊泡。囊泡有二类,一类含有电子致密物质;另一类无电子致密物质。近袖套内膜处的细胞质中还存在着与内膜平行的膜,精子尾部从袖套腔中伸出。尾部的轴丝与基体相接。尾部的近核端多有许多囊泡     

Ultrastructure and morphology of spermatozoa in Chinese sturgeon (Acipenser sinensis Gray 1835) using scanning and transmission electron microscopy

The Chinese sturgeon (Acipenser sinensis Gray 1835) is an endangered anadromous sturgeon inhabiting the Yangtze River in China. In this study, the ultrastructure and morphology of spermatozoa was studied using transmission and scanning electron microscopy with a cryo-holder. The spermatozoon consisted of an elongated head with a distinct acrosome and nucleus region, a midpiece and a flagellum. The mean length of the head and midpiece, the flagellum and total length of spermatozoon were 4.48, 33.3 and 37.8 microm, respectively. The nucleus was an elongated trapezoid shape with anterior (acrosome) end narrower than the posterior. Granular material and an actin filament were observed within the anterior acrosome. Three to five endonuclear canals were present. The midpiece was eudipleural along its longitudinal axis. Compared to other sturgeon species, the data from the present study suggest a more recent evolutionary linkage between Chinese sturgeon and white sturgeon (Acipenser transmontanus Richardson 1836).     

Polarization of eggs and embryos: some common principles

Embryonic development depends on the establishment of polarities which define the axial characteristics of the body. In a small number of cases such as the embryo of the fly drosophila, developmental axes are established well before fertilization while in other organisms such as the nematode worm C. elegans these axes are set up only after fertilization. In most organisms the egg posesses a primary (A-V, Animal-Vegetal) axis acquired during oogenesis which participates in the establishment of the embryonic axes. Such is the case for the eggs of ascidians or the frog Xenopus whose AV axes are remodelled by sperm entry to yield the embryonic axes. Embryos of different species thus acquire an anterior end and a posterior end (Antero-Posterior, A-P axis), dorsal and ventral sides (D-V axis) and then a left and a right side.     

A linear canal-otolith interaction model to describe the human vestibulo-ocular reflex

A control systems model of the vestibulo-ocular reflex (VOR) originally derived for yaw rotation about an eccentric axis (Crane et al. 1997) was applied to data collected during ambulation and dynamic posturography. The model incorporates a linear summation of an otolith response due to head translation scaled by target distance, adding to a semi-circular canal response that depends only on angular head rotation. The results of the model were compared with human experimental data by supplying head angular velocity as determined by magnetic search coil recording as the input for the canal branch of the model and supplying linear acceleration as determined by flux gate magnetometer measurements of otolith position. The model was fit to data by determining otolith weighting that enabled the model to best fit the data. We fit to the model experimental data from normal subjects who were: standing quietly, walking, running, or making active sinusoidal head movements. We also fit data obtained during dynamic posturography tasks of: standing on a platform sliding in a horizontal plane at 0.2 Hz, standing directly on a platform tilting at 0.1 Hz, and standing on the tilting platform buffered by a 5-cm thick foam rubber cushion. Each task was done with the subject attending a target approximately 500, 100, or 50 cm distant, both in light and darkness. The model accurately predicted the observed VOR response during each test. Greater otolith weighting was required for near targets for nearly all activities, consistent with weights for the otolith component found in previous studies employing imposed rotations. The only exceptions were for vertical axis motion during standing, sliding, and tilting when the platform was buffered with foam rubber. In the horizontal axis, the model always fit near target data better with a higher otolith component. Otolith weights were similar with the target visible and in darkness. The model predicts eye movement during both passive whole-body rotation and free head movement in space implying that the VOR is controlled by a similar mechanism during both situations. Factors such as vision, proprioception, and efference copy that are available during head free motion but not during whole-body rotation are probably not important to gaze stabilization during ambulation and postural stabilizing movement. The linearity of the canal-otolith interaction was tested by re-analysis of the whole body rotation data on which the model is based (Crane et al. 1997). Normalized otolith-mediated gain enhancement was determined for each axis of rotation. This analysis uncovered minor non-linearities in the canal-otolith interaction at frequencies above 1.6 Hz and when the axis of rotation was posterior to the head. Received: 11 March 1998 / Received in revised form: 1 March 1999     

Axial progenitors with extensive potency are localised to the mouse chordoneural hinge

Elongation of the mouse anteroposterior axis depends on a small population of progenitors initially located in the primitive streak and later in the tail bud. Gene expression and lineage tracing have shown that there are many features common to these progenitor tissues throughout axial elongation. However, the identity and location of the progenitors is unclear. We show by lineage tracing that the descendants of 8.5 d.p.c. node and anterior primitive streak which remain in the tail bud are located in distinct territories: (1) ventral node descendants are located in the widened posterior end of the notochord; and (2) descendants of anterior streak are located in both the tail bud mesoderm, and in the posterior end of the neurectoderm. We show that cells from the posterior neurectoderm are fated to give rise to mesoderm even after posterior neuropore closure. The posterior end of the notochord, together with the ventral neurectoderm above it, is thus topologically equivalent to the chordoneural hinge region defined in Xenopus and chick. A stem cell model has been proposed for progenitors of two of the axial tissues, the myotome and spinal cord. Because it was possible that labelled cells in the tail bud represented stem cells, tail bud mesoderm and chordoneural hinge were grafted to 8.5 d.p.c. primitive streak to compare their developmental potency. This revealed that cells from the bulk of the tail bud mesoderm are disadvantaged in such heterochronic grafts from incorporating into the axis and even when they do so, they tend to contribute to short stretches of somites suggesting that tail bud mesoderm is restricted in potency. By contrast, cells from the chordoneural hinge of up to 12.5 d.p.c. embryos contribute efficiently to regions of the axis formed after grafting to 8.5 d.p.c. embryos, and also repopulate the tail bud. These cells were additionally capable of serial passage through three successive generations of embryos in culture without apparent loss of potency. This potential for self-renewal in chordoneural hinge cells strongly suggests that stem cells are located in this region.     

Cell fate, morphogenetic movement and population kinetics of embryonic endoderm at the time of germ layer formation in the mouse

The fate of the embryonic endoderm (generally called visceral embryonic endoderm) of prestreak and early primitive streak stages of the mouse embryo was studied in vitro by microinjecting horseradish peroxidase into single axial endoderm cells of 6.7-day-old embryos and tracing the labelled descendants either through gastrulation (1 day of culture) or to early somite stages (2 days of culture). Descendants of endoderm cells from the anterior half of the axis were found at the extreme cranial end of the embryo after 1 day and in the visceral yolk sac endoderm after 2 days, i.e. they were displaced anteriorly and anterolaterally. Descendants of cells originating over and near the anterior end of the early primitive streak, i.e. posterior to the distal tip of the egg cylinder, were found after 1 day over the entire embryonic axis and after 2 days in the embryonic endoderm at the anterior intestinal portal, in the foregut, along the trunk and postnodally, as well as anteriorly and posteriorly in the visceral yolk sac. Endoderm covering the posterior half of the early primitive streak contributed to postnodal endoderm after 1 day (at the late streak stage) and mainly to posterior visceral yolk sac endoderm after 2 days. Clonal descendants of axial endoderm were located after 2 days either over the embryo or in the yolk sac; the few exceptions spanned the caudal end of the embryo and the posterior yolk sac. The clonal analysis also showed that the endoderm layer along the posterior half of the axis of prestreak- and early-streak-stage embryos is heterogeneous in its germ layer fate. Whereas the germ layer location of descendants from anterior sites did not differ after 1 day from that expected from the initial controls (approx. 90% exclusively in endoderm), only 62% of the successfully injected posterior sites resulted in labelled cells exclusively in endoderm; the remainder contributed partially or entirely to ectoderm and mesoderm. This loss from the endoderm layer was compensated by posterior-derived cells that remained in endoderm having more surviving descendants (8.4 h population doubling time) than did anterior-derived cells (10.5 h population doubling time). There was no indication of cell death at the prestreak and early streak stages; at least 93% of the cells were proliferating and more than half of the total axial population were in, or had completed, a third cell cycle after 22 h culture.(ABSTRACT TRUNCATED AT 400 WORDS)     

Defining ATPase activity in functionally different parts of the body of the cestode Bothriocephalus scorpii

Data on the distribution of ATP-activity (A) along the longitudinal axis of the body of Bothriocephalus scorpii are given. A has been shown to decrease from the head to the posterior parts of the body. However, A has been noted to increase a little on the part of the body where mature eggs are thrown out.     

Residual strains in porcine and canine trachea

Residual strains exist in canine and porcine tracheas. They are revealed by cutting the trachea first perpendicular to its axis into rings, then radially into sectors. Each sector is characterized by an opening angle which is defined as the angle subtended between two radii joining the middle point of the inner wall to the tips of the inner wall. The trachea being non-axisymmetric, the opening angle depends on the position of the radial cut. The trachea being also nonuniform in the axial direction, the opening angle varies along the length of the trachea. In the dog, the opening angle of the trachea cut at the anterior position (cartilaginous) is about 100 degrees at the larynx; it increases fairly linearly to 180 degrees midway down the trachea; then increases slowly to about 200 degrees at the lower end where the trachea bifurcates into the main bronchi. Dog trachea cut in the posterior (muscular) position have an opening angle of about 50 degrees at the larynx, which increases to about 70 degrees three-quarters of the way down the trachea, then drops to 60 degrees at the lower end. In the pig, the opening angle of the trachea is much smaller, the values at anterior and posterior cuts are similar (without significant difference), and their mean value decreases from about 15 degrees at the laryngeal end to about 5 degrees at the lower end. These species and regional differences are discussed in relation to tracheal geometry and structure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Wnt3 signaling in the epiblast is required for proper orientation of the anteroposterior axis

The establishment of anteroposterior (AP) polarity in the early mouse epiblast is crucial for the initiation of gastrulation and the subsequent formation of the embryonic (head to tail) axis. The localization of anterior and posterior determining genes to the appropriate region of the embryo is a dynamic process that underlies this early polarity. Several studies indicate that morphological and molecular markers which define the early AP axis are first aligned along the short axis of the elliptical egg cylinder. Subsequently, just prior to the time of primitive streak formation, a conformational change in the embryo realigns these markers with the long axis. We demonstrate that embryos lacking the signaling factor Wnt3 exhibit defects in this axial realignment. In addition, chimeric analyses and conditional removal of Wnt3 activity reveal that Wnt3 expression in the epiblast is required for induction of the primitive streak and mesoderm whereas activity in the posterior visceral endoderm is dispensable.