bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amphibian pronephric duct morphogenesis: segregation, cell rearrangement and directed migration of theAmbystomaduct rudiment
Authors: Poole T. J. , Steinberg M. S. 
Published: April 2021

ABSTRACTThe axolotl pronephric duct rudiment is readily accessible to both SEM observation and surgical manipulation. The rudiment segregates from the dorsal part of the lateral mesoderm and then extends caudally along the ventrolateral border of the segmenting somites, eventually contacting the cloacal wall. The marked thinning of the rudiment which accompanies this migration is paralleled by a corresponding reduction in cell number across the duct’s diameter and by caudad translocation and elongation of vital dye marks applied to the duct mesoderm. Duct extension thus involves appreciable cell rearrangement. The morphology of duct mesoderm and its substratum (somite and lateral mesoderm) suggests that active locomotion of cells near its tip marshals the duct’s caudad elongation. Filopodia and small focal areas of intercellular contact may mediate the adhesions between duct cells which must be broken and reformed as the cells rearrange.
Positional signalling along the anteroposterior axis of the chick wing. The effect of multiple polarizing region grafts
Authors: Wolpert L. , Hornbruch Amata 
Published: April 2021

ABSTRACTWe have proposed that positional information along the anteroposterior axis is specified by a signal from the polarizing region and that position may be specified by the concentration of a diffusible morphogen. While this model can account for a variety of results it is now clear that a model based on intercalation by growth of positional values can do the same. The distinction between the two models lies in whether a grafted polarizing region can alter existing positional values and in the distance over which it exerts its influence. The two models make different predictions as to the effect of grafting two polarizing regions. The intercalation model predicts that this effect will be the sum of two single grafts, whereas the morphogen model predicts different results depending on how close together the two polarizing regions are placed. The pattern of digits following grafts of two polarizing regions show that it is sensitive to the distance between the grafts and consistent with a model based on long-range interaction, such as a diffusible morphogen.
The control of growth and the development of pattern across the anteroposterior axis of the chick limb bud
Authors: Summerbell Dennis 
Published: April 2021

ABSTRACTTwo grafts of zone of polarizing activity (ZPA) were made to host limb buds. The grafts define the width of the shared responding field lying between them. They cause a change in the growth pattern of the bud so that there is an increase in the width of the tissue between the grafts. Concurrently they redefine (respecify) cell states in the responding tissue so as to cause formation of a mirror-image reduplicate hand between them. The number and type of digits formed depends on the initial distance between the grafts.The results suggest that the initial presumptive hand field is very small (∼ 300μm), that it is not a classical morphallactic system, and that it is able to regulate its growth pattern. A point-source diffusion model is presented.
Spatiotemporal patterns of fibronectin distribution during embryonic development I. Chick limbs
Authors: Melnick Michael , Jaskoll Tina , Brownell Anna G. , MacDougall Mary , Bessem Conny , Slavkin Harold C. 
Published: April 2021

ABSTRACTIt has been suggested that an extracellular matrix - and cell surface - associated glycoprotein, fibronectin, plays a role in the positioning of cells in morphogenesis and in the maintenance of orderly tissue organization. In the present study the appearance and distribution of fibronectin during in ovo chick limb development has been investigated by indirect immunofluorescence techniques in H.H. stages 20–30. Fibronectin is not detectable until just prior to the transition from the morphogenetic to the cytodifferentiation phase of development. Beginning at H.H. stage 25, successive nonrandom patterns of fibronectin detection and distribution, which resemble the subsequent cartilaginous elements, precede overt chondrogenesis as detected by Alcian blue staining. This corresponds to the onset of the cytodifferentiation phase of limb development. As the accumulation of acidic proteoglycan increases in the cartilage matrix and the mesenchymal cells become more round in appearance, the presence of detectable fibronectin decreases and is ultimately seen only in the perichondria and basement membrane. However, predigestion of developed cartilage tissue with testicular hyaluronidase, prior to fibronectin staining, indicated that fibronectin remains a major constituent of cartilage matrix and is apparently masked by cartilagespecific proteoglycans. This study of chick limb development is consistent with the hypothesis that fibronectin may be a molecule that facilitates the spatial organization of cartilaginous primordia cytodifferentiation.
The effect of delay on the expression of thet6/t6genotype
Authors: Nadijcka Mary , Morris Marie , Hillman Nina 
Published: April 2021

ABSTRACTIn vivo, t 6 /t 6 embryos are developmentally arrested between gestation days 5·5 (short-egg-cylinder stage) and 6·75 (long-egg-cylinder stage). In the present series of studies we used both in vivo and in vitro blastocyst delay followed by in vitro outgrowth to determine whether the r°/7c lethality is time- or stage-specific. The results show that the t6/t6 genome is expressed differently in vivo and in vitro and that the in vitro expression of the homozygous t6 genome differs with different methods of effecting developmental delay. Although delay increases the life span of t6/t6 embryos it does not alter the stage of lethality. One method used to effect delay (ovariectomy) causes the t6/t6 embryos to remain as blastocysts for a significantly longer period of time than their wild-type littermates when placed into outgrowth medium. This distinction provides a unique method for obtaining a sample composed entirely of t6/t6 embryos at a stage prior to the lethal period.
X-chromosome activity in foetal germ cells of the mouse
Authors: Monk Marilyn , McLaren Anne 
Published: April 2021

ABSTRACTA cycle of inactivation and reactivation of one X chromosome in the female (XX) germ line is shown by analysis of gene dosage effects on activity of an X-linked enzyme. The ratio of activities of the X-linked enzyme HPRT and an autosomal enzyme APRT are determined in XX and XY germ cells from embryonic gonads from the 12th to the 17th day of pregnancy. Mitotic stages of XX and XY germ cells on the 12th day have similar HPRT: APRT ratios, but on the 13th day the ratios are significantly higher in XX than XY germ cells. As the XX germ cells enter meiosis they show a marked increase in HPRT:APRT ratio which is primarily due to a rise in X-linked HPRT activity. Comparisons are made with XO germ cells on the 12th and 14th day. On the 12th day, XO do not differ from XX and XY germ cells, suggesting that only one X chromosome is active in XX germ cells at this stage. On the 14th day, on the other hand, the HPRT:APRT ratios in XO and XY germ cells are similar but in XX germ cells the ratio is significantly higher. The twofold difference between the ratio in XX and XO germ cells suggests that by this stage both X chromosomes are active in XX germ cells. The subsequent large increase of the ratio in XX relative to XY germ cells is thought to reflect their differing cell states.
In vitrostudies of mouse embryos bearing mutations in the T complex: effects of culture in suboptimal medium upont6/t6and normal embryos
Authors: Pai Anna C. , Wudl Linda R. , Sherman Michael I. 
Published: April 2021

ABSTRACTWe have compared the behaviour of normal and t6/ t6 embryos in PCMF, a suboptimal ‘delay’ medium which arrests normal development. Morphologically, the two types of embryos are indistinguishable in this medium. Although β -glucuronidase activity in embryos does not rise as quickly in delay medium as in cNCTC, a nutritive medium, the rate of increase is similar in t6/t6 and normal embryos. We conclude from these observations that the lethality of r®/r® embryos is not a consequence of their reaching a given absolute age. Together with previous studies, our data suggest that embryo lethality correlates more closely with metabolic state than with morphological stage.Blastocysts maintained in PCMF are unable to give rise to trophoblast outgrowths but do so upon transfer into cNCTC medium. When a mixture of fourth-day t6/ t6 and normal embryos are transferred to cNCTC medium after lengthy pre-incubation periods in PCMF, trophoblast outgrowth is initiated from both types of embryos at approximately the same time. However, when embryos are removed from the genital tract on the second or third day of gestation, t6/ t6 embryos are slower to produce trophoblast outgrowths than are normal embryos upon transfer from PCMF to cNCTC medium. Although the reason for this differenial behaviour is not yet clear, it is hypothesized that some product(s) required for the outgrowth process is (are) more unstable in third-day t6/ t6 embryos than in normal third-day embryos or fourth-day t6/ t6 embryos.Our ability to separate t6/ t6 from normal embryos by their delayed initiation of trophoblast outgrowth provides us with a convenient way to identify, and to isolate for analysis, enriched populations of homozygous mutant embryos prior to the time at which they show gross morphological abnormalities.
Development of a sensory afferent projection in the grasshopper embryo:I. Growth of peripheral pioneer axons within the central nervous system
Authors: Shankland Marty 
Published: April 2021

ABSTRACTThe grasshopper’s cereal nerve is established early in embryogenesis by an identified pair of peripheral neurons called the cereal pioneers. Like the peripheral pioneer neurons in other insect appendages, these two cells send their axons from the periphery to the rudimentary CNS and thus lay the foundation for a nerve that will later be followed by a large number of sensory axons. In this paper, cobalt fills of the primordial cereal nerve were used to characterize the disposition of these peripheral pioneer axons within the embryonic CNS. The pioneer axons stained by this technique terminate in ellipsoidal growth cones which have filopodia radiating from the leading edge and a single long terminal filament pointing along the path the axon is taking. The growing axons also bear filopodia along their sides, but these structures disappear as the cells mature. The pioneer axons of the cereal nerve make an abrupt turn where they first enter the ganglion rudiment and join the axons of the primary longitudinal tract. The pioneers then grow along this tract for several hundred microns without forming secondary growth cones or branches. This prolonged absence of central arborization distinguishes the peripheral pioneer axons from the axons of later-arising epidermal sensory neurons.
Development of a sensory afferent projection in the grasshopper embryo:II. Growth and branching of peripheral sensory axons within the central nervous system
Authors: Shankland Marty 
Published: April 2021

ABSTRACTThe morphogenesis of several types of sensory axon branching patterns has been described by cobalt filling the cereal nerve of the grasshopper embryo at a series of different stages in development, thus staining the earliest sensory axons as they grow through the CNS. This embryonic sensory projection contains all five types of cereal afferents seen in the adult, and no new sensory tracts are added during postembryonic life. When the embryonic sensory axons first follow their pioneer axons into the neuropil they choose pathways which are characteristic of the adult sensory tracts. Since the afferents follow these paths without sending collaterals into the other tracts, it appears that the growing axon chooses its specific pathway without extensive exploration of alternative routes. Likewise, nearly all of the branches which arise from the embryonic sensory axons remain within the eventual domain characteristic of each cell type. This precise, determinate pattern of initial growth implies that the sensory axons are guided through the neuropil and achieve their final branching patterns with a minimum of overgrowth and pruning. The fact that initial growth is so precise also suggests that the parameters which guide the growing axon may help to determine its eventual pattern of synaptic connectivity by limiting its physical access to large portions of the neuropil which contain potentially compatible synaptic partner cells. Two different types of neurons may be supplying the sensory afferents with guidance cues: (i) Although most of the cereal sensory axons diverge from the cereal pioneer axons within the CNS, some sensory afferents continue to follow the pioneers through several ganglia, (ii) In the adult, a large number of the cereal sensory axons form a hollow shell of arborization around the main dendrite of an identified synaptic target cell, the Medial Giant Interneuron (MGI). This structure, the interneuron dendrite and the shell of sensory arbor, is called the cereal glomerulus. Since the MGI’s dendrite is already present at the stage when the first sensory axons enter the CNS, interactions between these cells could serve to guide the glomerular sensory axons away from the pioneers into their future tracts.
Early erythropoiesis in foetal rat bone marrow: evidence for a liver-to-bone marrow relay
Authors: Nagel M. D. , Nagel J. , Jacquot R. 
Published: April 2021

ABSTRACTErythropoietic activity of foetal rat femoral marrow was examined during the last four days of intra-uterine life. Insignificant at day 18, it develops slowly thereafter until birth. In the non-suckled neonate (not older than two hours), it appears notably enhanced. In order to test the potential of the foetal marrow to develop precocious or increased erythropoiesis, the activity of the erythropoietic organ predominant at this time, the liver, was altered by modifying the level of circulating corticosteroids which govern its function. Maturation and involution of the hepatic erythron were prevented by corticosteroid deprivation of the foetus (maternal adrenalectomy and foetal hypophysectomy). Precocious maturation and exhaustion of the hepatic erythron was induced by submitting foetuses to corticosteroids excess from day 14. Both corticosteroid deprivation and excess increase the erythropoietic activity of the femoral marrow. This activity can reach and even exceed by day 20 of intrauterine life that in neonatal marrow. Foetal hepatic erythron misfunction can therefore initiate and stimulate bone marrow erythropoiesis. The study of circulating red blood cells demonstrates that: (1) anaemia initiates medullary erythropoietic activity; (2) this anaemia is largely corrected by the bone marrow. The regulatory mechanism is presumably erythropoietin mediated.
Cytoskeletal coordination and intercellular signalling during metazoan embryogenesis
Authors: Tucker J. B. 
Published: April 2021

ABSTRACTThis article draws attention to certain recently discovered features of cell surface organization and cytoskeletal deployment that may be revealing a new basis for intercellular signalling during metazoan embryogenesis. It is a signal mode that could coordinate many aspects of ‘Entwicklungsmechanik’ by spatiotemporal integration of the cytoskeletal/motor network throughout developing tissues. Evidence that this is achieved by ‘intercellular cytoskeletal/ plasma membrane connecting systems’ which coordinate the spatial organization of microtubules, microfilaments, and intermediate filaments in developing animal tissues is critically examined. It is argued that this system does operate but that it is not used to transmit positional information in embryonic fields. However, it probably responds to such information and might play an important part in establishing field boundaries during the very earliest stages of embryogenesis.Certain aspects of cell surface organization in contemporary protozoans reveal ways in which the Protozoa could have been pre-adapted for the employment of cytoskeletal/cell surface signalling during the advent of multicellularity. In marked contrast, such signalling does not appear to be exploited during plant morphogenesis. The extent to which cytoskeletal organization might be coordinated in sister cells by transmission of spatial instructions during cell division in both animal and plant tissues is also considered.
Sex differentiation in bilaterally allophenic animals produced by cloning of two bipartite male/female chimaeras ofLineus sanguineus
Authors: Sivaradjam S. , Bierne J. 
Published: April 2021

ABSTRACTTwo bipartite chimaeras were constructed in Lineus sanguineus by grafting the lateral halves from a phenotypically dark-brown male onto the anatomically complementary halves from a phenotypically light-brown female. Regeneration of a large number of pieces transected from these two bilaterally allogeneic chimaeras produced two clones of bilaterally allophenic nemertines (♂/ ♀ and ♀/ ♂).Sex differentiation in the cloned worms started with a transitory stage of gonad developmental autonomy, termed the primary gynandromorphous state; at this stage there were young testes in the originally male lateral halves and juvenile ovaries in the originally female ones, the only abnormality then was that the ovarian development was more advanced than the testicular development relative to those in male and female controls. Then, unilateral sex reversal occurred, with feminization of the testes, i.e. oogenesis took the place of spermatogenesis in the many male gonads located in either the right or the left side of allophenic worms according to the symmetry patterns of the two clones. Finally, when the gonads reached maturity, both sides of allophenic L. sanguineus contained only ovaries with ripe oocytes.The complete feminization of these allophenic worms and the previously observed masculinization of ‘heterosexual’ chimaeras in L. ruber suggest that a diffusible factor controls gonadal differentiation in worms of the prevailing sex, which is the female sex in L. sanguineus and the male sex in L. ruber.
Transfilter evidence for a zone of polarizing activity participating in limb morphogenesis
Authors: Kaprio Eero A. 
Published: April 2021

ABSTRACTBarriers were inserted into stage-20 HH chick embryo wing buds to separate the zone of polarizing activity from the anterior two-thirds of the wing bud with its overlying apical ectodermal ridge. Half of the barrier length projected out of the wing bud at insertion. Sham-operated wing buds developed only occasionally into wings with cartilage deletions. After insertion of an impermeable membrane (Cellophane), the typical wing skeleton contained only a humerus and a radius. In order to differentiate between diffusion, cell contact and cell penetration, Nuclepore filters with pore sizes of 0·05μm, 1·0 μm and 8 ·0 μm, respectively, were inserted. The typical wing skeleton after Nuclepore filter insertion was one with post-axial deletions. None, however, developed with complete distal deletions as after Cellophane. Deletions in the wing skeletons after Nuclepore insertion were the least with 1·0μm filters and the most with 8·0 μm filteis. Elevation of the apical ectodermal ridge was noted until 18 h after the insertions. In none of the groups did the ridge flatten. The results suggest that the zone of polarizing activity does have a role in normal limb morphogenesis. The mechanism by which its morphogen spreads is diffusion rather than being mediated via cell contacts.
How axons grow down theXenopusoptic nerve
Authors: Fawcett J. W. 
Published: April 2021

ABSTRACTRetinotectal fibres from different parts of the retina have been filled with Horse Radish Peroxidase (HRP). During their course down the nerve their ordering decays, but it is reestablished at the chiasma, except for nasal fibres which remain relatively disordered. The consequences of this for development are discussed.
An experimental study of the relation of cardiac jelly to the shape of the early chick embryonic heart
Authors: Nakamura Atsuyo , Manasek Francis J. 
Published: April 2021

ABSTRACTThe structural roles of cardiac jelly components were examined in the early developing chick embryonic heart. Cardiac jelly matrix components were enzymically removed in situ by injecting nanogram quantities of enzymes directly into the cardiac jelly. Injection of ovine testicular hyaluronidase caused shrinkage and the heart became flaccid, but overall heart shape did not change. These responses were the result of enzymatic removal of glycosaminoglycan sugar moieties and were not due to lumenal collapse. Although purified collagenase did not cause any noticeable change, enzymes with non-specific proteolytic activity induced marked cardiac shape changes. In such hearts the dorsal mesocardium opened completely, and the myocardium as well as splanchnic mesoderm of foregut detached from their substrata and the entire heart region swelled. Consequently the shape of the heart was altered completely. These results suggested that in the normal condition the myocardial envelope was under an internal pressure due to the presence of glycosaminoglycans in the cardiac jelly space, and that some matrical non-collagenous protein components were essential to control the internal pressure. Therefore it is suggested that the internal pressure of cardiac jelly may be the direct driving force for the looping process and protein components of cardiac jelly may be important in directing the force for the morphogenetic process.
Effects of concanavalin A on developing ganglion cells in the retina of chick embryos
Authors: Meller K. 
Published: April 2021

ABSTRACTThe administration of concanavalin A (Con A) (50−200 μg/egg) to chick embryos between the third and the seventh day of incubation has the following effects on the retina:Con A causes the degeneration of a large number of ganglion cells and consequently the layer that should be formed by these cells is not present or is constituted only by a small number of ganglion cells. The lectin seems to be effective only when it is administered during the postmitotic phase of the ganglion cells. The degenerated cells are phagocytosed by the Müller cells in a manner similar to that occurring during the natural cell death in normal retinal development. The differentiation of other retinal elements (photoreceptors, bipolar, amacrine and Muller cells) is not affected by the lectin administration. The administration of Con A in later stages of development, even at ten times higher dosages (2000 μg/egg), fails to affect retinal neurogenesis.It is suggested that Con A binding to receptor sites of the cell membrane affects the distribution or mobility of surface components producing an alteration in the mechanism by which the developing cells regulate positional information during retinal neurogenesis.