bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developmental analysis of the homoeotic mutationbithoraxoidofDrosophila melanogaster
Authors: Kerridge Stephen , Sang James H. 
Published: April 2021

ABSTRACTThe homoeotic transformations caused by bxd are described in detail. The anterior histoblast nests of the first abdominal segment are missing, and are replaced by one or two leg discs ventrally. Mainly anterior compartment patterns are found in the ectopic, abdominal legs of adult flies. However, cell lineage analyses show that both anterior and posterior polyclones are established early in the development of these ectopic legs, but the posterior polyclone is smaller. Cells of the anterior polyclone may regulate later in development to adjust for this and form pattern elements normally derived from the posterior polyclone. In addition, experiments show that bxd+ is required by the second larval instar stage, and possibly as early as the blastoderm stage.
Pattern re-establishment – transplantation and regeneration of the leg in the cricket Teleogryllus commodus (Walker)
Authors: Biggin Robert J. 
Published: April 2021

ABSTRACT
Regeneration and grafting experiments were carried out on the prothoracic leg of the cricket Teleogrylhts commodus (Walker) to examine the precision with which surface cuticular structures and internal epidermal derivatives are reformed. By comparing regenerated and grafted limbs with normal limbs it was found that the three-dimensional structure of epidermal derivatives is not restored. This is despite the fact that regenerated and grafted limbs appear similar in their external morphology to normal limbs. The implication of these results are discussed in the context of theories of pattern formation.
Ultrastructural and histochemical observations in the developing iris musculature in the chick
Authors: Narayanan Y. , Narayanan C. H. 
Published: April 2021

ABSTRACT
Irises from chick embryos and from 2- and 3-week-old chicks were studied using ultrastructural and histochemical methods in order to clarify the relationship between cell loss in the ciliary ganglion and the establishment of permanent peripheral connections between the ciliary neurons and the iris muscle. The iris muscle undergoes morphological and biochemical differentiation between 11 and 13 days of incubation. This period coincides with the critical period in the development of the ciliary ganglion when massive cell degeneration occurs. During this period, the iris develops typical sarcomeric structure, with AChE activity in the nuclear envelope, Golgi, and the ‘T’ system. At 15 days of incubation AChE activity is found localized in discrete areas on the muscle fiber, forming specific neuromuscular junctions. Between 13 and 15 days of incubation, there is a shift in the localization of AChE activity in the iris muscle, from the sarcoplasmic structures to the junctional membranes.
Few synaptic terminals are observed in the iris musculature prior to 11 days of incubation. There is a marked increase in the number of synaptic terminals between 11 and 13 days of incubation which also coincides with the period of cell loss in the ciliary ganglion. The establishment of neuromuscular junctions at 15 days of incubation corresponds with the period when the number of neurons in the ciliary ganglion has attained the adult level. The time table of the events described above, leads us to conclude that during development only those neurons in the ciliary ganglion which make peripheral contacts survive, and only such contacts differentiate into mature neuromuscular junctions on the iris muscle. This will imply that neurons which are doomed to die, although they may send out fibers to the periphery, do not make peripheral contacts before death.
Mouse egg ribosomes: evidence for storage in lattices
Authors: Bachvarova R. , Leon V. De , Spiegelman I. 
Published: April 2021

ABSTRACT
The ribosomes of mouse ova were labeled by exposure of growing ovarian oocytes to [3H]uridine. The ribosomes of ova lysed and dispersed in hypotonic medium were contained in particles with an unusually low buoyant density in CsCl density gradients. These particles sedimented at 9000g or less, and electron microscopy of the pellet revealed ribosome-like particles embedded in a fibrillar network. These results indicate that the ribosomes are present in a proteinaceous superstructure, probably the lattices seen in situ by transmission electron microscopy.
Formation of the retina-lamina projection of the cockroach: no evidence for neuronal specificity
Authors: Nowel Mark S. 
Published: April 2021

ABSTRACT
There is a topographical mapping of neural elements onto the lamina neuropile of the optic lobe of the cockroach, such that adjacent ommatidia project to adjacent points (optic cartridges) in the lamina neuropile. Postembryonic growth of the compound eye occurs by addition of new ommatidia to its growing margin. Retinula axons grow from the newly formed ommatidia to the lamina. By transplantation experiments in which the position or the orientation of retinal material is altered, it is shown that retinula axons do not make connections in the lamina with respect to their old position and orientation, but rather, in keeping with their new situations, apparently maintaining a retinotopic mapping upon the optic lobe.
Postembryonic growth of the compound eye of the cockroach
Authors: Nowel Mark S. 
Published: April 2021

ABSTRACT
The postembryonic growth of the compound eye of the cockroach Periplaneta americana involves increases in the size of the individual ommatidia as well as a 35-fold increase in the number of ommatidia. These ommatidia are added to the anterior, dorsal, and ventral margins of the eye by means of an almost continuous process of cell division in the proliferation zone in these margins. This proliferation phase is followed by a process of maturation of bundles of ‘pre-ommatidial’ cells into mature ommatidia, a process which involves further cell division. Processes involved in compound-eye development are investigated by eye margin grafting, histological techniques and cell proliferation studies.
An experimental study on neural crest migration in Barbus conchonius (Cyprinidae, Teleostei), with special reference to the origin of the enteroendocrine cells
Authors: Lamers C. H. J. , Rombout J. W. H. M. , Timmermans L. P. M. 
Published: April 2021

ABSTRACT
A neural crest transplantation technique is described for fish. As in other classes of vertebrates, two pathways of neural crest migration can be distinguished: a lateroventral pathway between somites and ectoderm, and a medioventral pathway between somites and neural tube/notochord. In this paper evidence is presented for a neural crest origin of spinal ganglion cells and pigment cells, and indication for such an origin is obtained for sympathetic and enteric ganglion cells and for cells that are probably homologues to adrenomedullary and paraganglion cells in the future kidney area. The destiny of neural crest cells near the developing lateral-line sense organs is discussed. When grafted into the yolk, neural crest cells or neural tube cells appear to differentiate into ‘periblast cells’; this suggests a highly activating influence of the yolk. Many neural crest cells are found around the urinary ducts and, when grafted below the notochord, even within the urinary duct epithelium. These neural crest cells do not invade the gut epithelium, even when grafted adjacent to the developing gut. Consequently enteroendocrine cells in fish are not likely to have a trunk- or rhombencephalic neural crest origin. Another possible origin of these cells will be proposed.
Mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in Xenopus laevis oocytes
Authors: Marinos E. , Billett F. S. 
Published: April 2021

ABSTRACT
An estimate has been made of the numbers of mitochondria in the mitochondrial cloud (Balbiani body) of Xenopus laevis oocytes ranging in size from 50 to 250 μm. The mito-chondrial number is expressed in terms of a ‘standard’ organelle measuring 2 μm in length and 0·2 μm in diameter and is derived by measurements on electron micrographs of sections through the cloud. It is found that the amount of mitochondrial material rises very rapidly as the oocyte grows in size. At the time the cloud disperses, in oocytes of about 300μm in diameter, it is estimated that there are the equivalent of over 500000 mitochondria in each cell. The rate of increase is very similar to the rate of accumulation of mitochondrial DNA during the same period of growth.
Using a polarographic technique the specific activity of cytochrome oxidase and succinic dehydrogenase was determined in mitochondrial fractions isolated from oocytes over a size range of 80–1200μm in diameter. Although the specific activity of succinic dehydrogenase remains constant that of cytochrome oxidase falls sharply during the period when the mitochondria are replicating rapidly, i.e. up to about 300μm diameter. In larger oocytes the specific activity of enzymes appears to remain constant but increasing contamination of the isolated mitochondrial fraction does not allow conclusions to be drawn from the enzyme loading of the mitochondria once they have dispersed from the cloud.
The results are discussed in relation to the possibility that mitochondrial replication preceeds, or at least outpaces, mitochondrial differentiation during the course of oogenesis.
Control of maintenance and anteroposterior skeletal differentiation of the anterior mesenchyme of the chick wing bud by its posterior margin (the ZPA)
Authors: Hinchllffe J. R. , Gumpel-Pinot M. 
Published: April 2021

ABSTRACT
If the posterior half of the chick wing bud (stages 17–22) is excised, the anterior half which normally forms humerus (part), radius and digit 2, forms only a single skeletal element, either humerus or humerus fused with reduced radius. Beginning at 18 h after operation, and continuing to 48 h the anterior and distal mesenchyme in such anterior halves becomes necrotic and the AER regresses. By contrast, if the anterior half of the chick wing bud (stages 17-22) is excised, the posterior half develops as in the normal bud, and forms humerus (part), ulna and digits 3, 4 and 5. Such posterior halves develop no more mesenchymal necrosis than the normal contralateral wing buds and the AER remains healthy. Further, if the excision of the posterior part is made in such a way as to leave in place a part of the zone of polarising activity (ZPA), a normal wing with complete skeleton is formed. Thus in order to survive and differentiate, the anterior part of the wing bud needs a factor supplied by the posterior part containing the ZPA. These results support the view that the ZPA plays a role in controlling the anteroposterior differentiation of the normal wing bud.
Pattern formation along the anteroposterior axis of the chick wing: the increase in width following a polarizing region graft and the effect of X-irradiation
Authors: Smith J. C. , Wolpert L. 
Published: April 2021

ABSTRACT
A study is made of the widening of the chick limb bud that occurs after a graft of an additional polarizing region. Such buds are about 50% wider than controls, after 36 h. By contrast, growth along the proximodistal axis is unaffected. This widening is reduced by treating the host embryo with 10 Gy X-irradiation and the altered pattern of digits is consistent with a diffusible morphogen model for the specification of positional information along the anteroposterior axis.
Experiments on Anuran limb buds and their significance for principles of vertebrate limb development
Authors: Maden M. 
Published: April 2021

ABSTRACT
A standard set of six experiments performed on the limb buds of two species of Anurans - Rana temporaria and Xenopus laevis - are described. The experiments are limb-bud amputation, distal to proximal shifts, proximal to distal shifts, inversion of the dorsoventral axis inversion of the anteroposterior axis and inversion of both axes. The results are compared to those previously reported for Urodeles and chicks to determine whether any principles of vertebrate limb development can be formulated. It appears that the proximodistal axis becomes increasingly mosaic from the Urodeles through Anurans to chicks. In the transverse axes however, there is much more uniformity of behaviour in the production of supernumerary limbs. The relation between the type of limb development (regulative or mosaic) and the subsequent regenerative powers of the adult limb is discussed.
Significance of cell-to-cell contacts for the directional movement of neural crest cells within a hydrated collagen lattice
Authors: Davis Edward M. , Trinkaus J. P. 
Published: April 2021

ABSTRACTNeural tubes whose neural crest had just begun migration were isolated from stage-14 chick embryos, cleaned with 0·1% trypsin, and cultured in transparent hydrated collagen lattices (HCL) in an effort to stimulate in part the three-dimensional environment through which neural crest cells migrate in situ, in the embryo. The concentration of collagen in the lattices varied from 50 μ g/ml to 390 μ g/ml. The mode of movement and contact behaviour of neural crest cells migrating from the neural tube under these conditions were recorded directly with time-lapse cinemicrography. Both their shape and their rate of translocation were dependent on the concentration of collagen in the HCL. In low concentrations (50 μ g/ ml to 105 μ g/ml), neural crest cells have elongate spindle shapes and translocate at an average rate of 1 μ m/min, whereas in high concentrations (190μ g/ml to 390μ g/ml), their shape is rounded, and they translocate at an average rate of only 0·5 μ m/min. Neural crest cells migrate from neural tubes in these preparations principally in loose clusters, with a few single cells in the lead. The cells in these groups display leading-to-trailing edge adhesions and form tongues or streams of cells directed away from the neural tube. The paths of migration of both individual cells and groups of cells are aligned with the collagen fibrils of the HCL, which radiate from the neural tube. The classical visible characteristic of contact inhibition of movement, change in direction of cell movement after contact with other cells, was not observed; neither the rate of translocation nor the time spent migrating away from the tube is dependent on the number of contacts between cells. It is concluded that the directional movement of neural crest cells in HCL cultures does not depend on contact inhibition of movement.
Muscle nerve branches do not develop in chick wings devoid of muscle
Authors: Lewis Julian , Chevallier Alain , Kieny Madeleine , Wolpert Lewis 
Published: April 2021

ABSTRACT
If the somitic mesoderm of a 2-day chick embryo is destroyed by X-irradiation, the adjacent limb develops with a normal pattern of connective tissues, but is devoid of muscle. The innervation of muscleless wings produced in this way was examined in silver-stained whole mounts, fixed 3 to 8 days later. The main nerve trunks and their cutaneous branches developed normally; but the nerve branches which in a normal limb would lead to individual muscles were generally absent. In almost all those exceptional cases where muscle nerve branches were present, muscle was found to be present also, despite the X-irradiation. Where there was no muscle, the muscle nerve branches apparently did not even begin to form. As a control for side effects of the X-irradiation, wing buds were grafted from normal to irradiated embryos and vice-versa, and again analysed for their innervation. The results confirmed that the absence of muscle nerve branches was due to the absence of muscle cells in the limb. Thus
(1) the routes taken through a limb by the main mixed nerve trunks and by their cutaneous branches are determined by the connective tissues, and not by any mechanisms requiring muscle cells; but (2) muscle cells are necessary to provoke the formation of the side branches leading to the sites of individual muscles.
Influence of the entoderm on mesodermal expansion in the area vasculosa of the chick
Authors: Augustine J. M. 
Published: April 2021

ABSTRACT
To determine whether expansion of the splanchnic mesoderm of the area vasculosa is influenced by the entodermal substratum on which it occurs, entoderm was separated from a small area of splanchnic mesoderm. The splanchnic mesoderm then contracted and thickened, decreasing to 7 % of its original area in 16 h. By then entoderm had reattached to most of it, and it expanded, reaching 11 % of its original area by 24 h. It was concluded that attachment to entoderm may be required for expansion of the splanchnic mesoderm, but the small amount of expansion obtained made this conclusion tentative.
For technical reasons subsequent investigation was done on mesodermal transplants, which attached to the host’s entoderm in 6 h, by which time they had contracted to 15% of their original area. They then expanded, reaching 30% by 16 h and 49% by 24 h. The onset of their expansion was also accompanied by the formation of connexions between their blood vessels and those of the host, and by the resumption of blood flow in them. To see whether their expansion was due to resumption of blood flow or to attachment to entoderm, other transplants were made in which the middle one-third was separated from the host’s entoderm by a piece of Millipore filter. This portion failed to expand although it became connected to the host’s blood vessels and flow of blood resumed in it, while the two lateral thirds, which regained attachment to entoderm, expanded. Transplants were also rotated so that their splanchnic mesoderm attached to ectoderm instead of entoderm. These transplants also formed connexions with the host’s vessels and blood flow resumed in them, but they expanded only slightly compared to non-rotated controls, in which the splanchnic mesoderm attached to entoderm.
It was concluded that while flow of blood undoubtedly promotes splanchnic mesodermal expansion as others have shown, attachment of the splanchnic mesoderm to entoderm is also important, and without it the promotive effect of blood flow does not occur. Evidence was also obtained that attachment to entoderm maintains the thinness of the splanchnic mesoderm, and that a vascular growth stimulus may be produced by the unvascularized entoderm distal to the mesoderm.
Evidence for regulation of growth, size and pattern in the developing chick limb bud
Authors: Summerbell Dennis 
Published: April 2021

ABSTRACT
This paper examines the hypothesis that the developing chick limb bud has mechanisms for regulating the control of growth, size and pattern. The tests included: surgical removal of selected parts of the limb field, X-irradiation, temperature shock and the manipulation of known limb organizer regions (removal of the apical ectodermal ridge, or the addition of an extra zone of polarizing activity). The results strongly support the idea that there are regulatory mechanisms controlling both the pattern and the size of the limb and suggest that they involve regulation of the growth rate via control of cell division throughout the embryonic period. Possible mechanisms are discussed.
The effect of removing posterior apical ectodermal ridge of the chick wing and leg on pattern formation
Authors: Rowe Donene A. , Fallon John F. 
Published: April 2021

ABSTRACT
Recent experiments, in which barriers were inserted between anterior and posterior tissues of the chick wing bud, resulted in deletion of structures anterior to the barrier (Summerbell, 1979). From these data it was concluded that blockage of morphogen from the polarizing zone by the barrier resulted in the observed failure of specification of anterior structures. We suggest an alternative interpretation, viz. the interruption of the apical ridge by the barrier caused the deletions. This hypothesis was tested by removal of increasing lengths of ridge. This was done beginning at either the anterior or posterior junction of the wing bud with the body wall and proceeding posteriorly or anteriorly, respectively, to each half-somite level between 16/17 and 19/20. With removal of progressively greater lengths of anterior ridge, more anterior limb elements failed to develop. These data were used to construct a map of the ridge responsible for each digit. To test our hypothesis we removed posterior sections of apical ridge, as described above. Removal of posterior ridge to a level which was expected to allow outgrowth of digits anterior to the level of removal resulted in wings without digits in the majority of cases. An exception occurred when ridge posterior to the mid-19 somite level was removed. In almost half of these cases digits 2 and 3 did develop. In most cases the retention of only a half-somite piece of ridge with all other ridge removed, also resulted in deletion of all digits. Again the exception occurred when ridge posterior to somite level mid-19 and anterior to level 18/19 was removed, leaving only that ridge between somite level 18/19 and mid-19. In many of these cases digit 3 did develop. We conclude from these data that, in the wing bud, ridge anterior to the mid-19 somite level must be connected to more posterior ridge to function.
The leg ridge does not exhibit the asymmetrical, low anterior, high posterior configuration, which appears in the wing. Because the leg ridge is symmetrically high anteriorly and posteriorly, we questioned whether or not leg would also require a continuity between anterior and posterior ridge for anterior ridge to function. It did not. When posterior ridge was removed, structures developed under remaining anterior ridge and the elements which developed were complementary to those which developed after anterior ridge removal to the same somite level. Those leg elements, which failed to develop, were truncated at the appropriate proximodistal levels as indicated by the fate map we have constructed for the leg.
The data reported here do not rule out a role for the polarizing zone in specification of anterior structures. It is apparent that posterior ridge removal in the wing results in loss of structures anterior to the removal. However, this is not true for the leg.
Cellular contacts between hindbrain and prospective ear during inductive interaction in the axolotl embryo
Authors: Model Pat G. , Jarrett Lonny S. , Bonazzoli Robin 
Published: April 2021

ABSTRACT
In the amphibian embryo, beginning in the late neurula and continuing through midtailbud stages, the developing medulla exerts an inductive influence on the prospective ear, effecting its determination. Fine structural analysis of the region of closest apposition between the two tissues in the axolotl (Ambystoma mexicanum) reveals that during this period, there is a significant increase in the surface area of the apposed cells through the projection of long finger-like processes that traverse the medulla–ear interspace and the appearance of many focal contacts between the two cell types. These contacts are small, varying in diameter from 10–30 nm and they exhibit the septilaminar appearance and 2–4 nm intercellular cleft characteristic of gap junctions. Once the ear has been determined, both the cell processes and the focal junctions between apposed cells virtually disappear.
We suggest that the projection of processes from the surfaces of the apposed cells enhances the opportunity for cell interaction through the formation of very small gap junctions and that the junctions could provide the structural substrate for direct communication between medulla and ear during their inductive interaction.