bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Unilateral Blockage of a Pronephric Duct upon the Development of the Pronephroi in Triturus helveticus
Authors: Fox H. 
Published: April 2021

ABSTRACT
Larvae of Triton helveticus, 20 days after the pronephric duct on one side has been blocked at the caudal bud stage, do not differ from controls in total length or nose-to-cloacal length. The unblocked functional pronephros of the other side shows significantly higher mean values for the following measurements when compared with control pronephroi in sham-operated animals: antero-posterior length, nuclear population, total volume of cells, total volume of lumina, overall volume of the pronephros, internal surface area of tubules, calculated individual cell volume, and antero-posterior length of the posterior nephrostome base. The blocked pronephros also shows significantly higher values than controls in all these measurements, except that it is the anterior nephrostome base and not the posterior which significantly increases in antero-posterior length, and that the calculated individual cell volume significantly falls. The glomus adjacent to the functional pronephros and that adjacent to the blocked pronephros do not differ significantly in size and shape. Both groups show a significant superiority in mean total volume over the controls. The pronephric duct of the functional pronephros, when its partner is blocked, is expanded along its length, like the duct of the remaining pronephros when a larva has undergone unilateral pronephrectomy. The remainder of the duct behind the lesion of the blocked pronephros is degenerate, and has a flattened reduced lumen like the duct remaining when its ipsilateral pronephros has been extirpated. There is no evidence that a blocked pronephros in situ exercises any inhibition on growth of its functional partner. In compensatory growth local intra-tubular tension may be an important influence.
The cellular effect of 5-bromodeoxyuridine on the mammalian embryo
Authors: Bannigan John , Langman Jan 
Published: April 2021

ABSTRACTIt is well known that 5-bromodeoxyuridine (BUdR) when injected into pregnant animals may cause exencephaly, cleft palate, and limb abnormalities. Similarly, it is well established that the drug when added to a culture medium may prevent differentiation of embryonic cell systems without affecting cell division or cell viability. The goal of our experiments was to examine whether the congenital malformations resulting from BUdR treatment were due to lack of differentiation of certain cell lines or were due to other mechanisms. The effects of BUdR on proliferating and differentiating cells in the 12-day mouse embryo were therefore examined and special attention was given to the proliferating cells of the rhombic lip which give rise to the Purkinje cells.When the embryos were treated with BUdR the mitotic index of the neuroepithelium of the rhombic lip doubled in value 3 h after treatment and remained high until 24 h later. By using the colchicine index it was calculated that the mitotic duration in the BUdR-treated embryos lasted at least 2 h and that in the control embryos less than 1 h. When the cell generation time in the BUdR treated animals was calculated the length of the S-phase was increased by about 50%. It was thus concluded that BUdR caused an increase in the duration of the S-phase and mitosis, together making the cell cycle 5 h longer than normal.Eighteen hours after treatment many neuroepithelial cells became degenerative. By radioautography it was demonstrated that the degenerating cells were in their second DNA-synthetic phase following BUdR injection and that cells which incorporated BUdR and were differentiating into neurons were not affected. By injecting [3H]BUdR it was found that many cells which incorporated the analogue were able to leave the proliferative population after their first cell division. They migrated to the periphery where they developed into apparently normal Purkinje cells. The additive effects of cell death and retardation of the cell cycle caused a 15% deficit of Purkinje cells in the postnatal cerebellum but the BUdR did not interfere with their differentiation. Thus, contrary to the BUdR effect on cultures of embryonic cells, in vivo the drug causes cell death and a delay in the cell cycle time. Our experiments therefore seem to indicate that the congenital malformations caused by BUdR in the mammalian embryo are caused by cell death and growth retardation rather than by interference with the process of differentiation.
Autoradiographic study of macromolecular synthesis in the fusion epithelium of the developing rat primary palatein vitro
Authors: Figueroa Alvaro A. , Pratt Robert M. 
Published: April 2021

ABSTRACTThe facial processes involved in primary palate formation undergo epithelial fusion in a manner morphologically analogous to that observed during secondary palate formation. We have used whole embryo culture to analyze the synthesis of macromolecules (DNA, protein, glycoprotein) in the primary palate, based on the incorporation of various labeled precursors. The results of this study demonstrate that changes in the synthesis of macromolecules occur during the fusion of the facial processes, which resemble those previously reported to occur during secondary palate development. These changes include cessation of DNA synthesis in cells in a restricted zone of the epithelium, concomitant with maintenance of glycoprotein synthesis. These findings indicate that the molecular events underlying the development of the primary and secondary palate may be similar.
Selection of appropriate medial branch of the optic tract by fibres of ventral retinal origin during development and in regeneration: An autoradiographic study inXenopus
Authors: Straznicky C. , Gaze R. M. , Horder T. J. 
Published: April 2021

ABSTRACTThe formation of the branches of the optic tract has been studied with the use of [3H]-proline autoradiography, during development and during regeneration of the optic nerve in Xenopus with one compound ventral (VV) eye made by the embryonic fusion of two ventral eye fragments.The formation of the optic pathway was abnormal in that the lateral branch failed to develop, suggesting that fibres from a VV retina selectively entered the tectum via the medial branch during development. Three months after section of the optic nerve of a VV eye, regenerated fibres were present both in the contralateral and ipsilateral tecta. On the ipsilateral side regenerated fibres entered the tectum via the medial branch only. Retinal fibres entered the contralateral tectum through both branches in some animals and through the medial branch only in others.It is concluded that mechanical factors alone are insufficient to explain the phenomenon of selection of the appropriate medial branch by fibres of ventral retinal origin either during development or in regeneration. Some form of fibre-substrate interaction seems to be necessary; and this ability of fibres from a VV eye to take the path appropriate for ventral retina argues strongly that the VV eye is not a regulated system in terms of cell specificities.
Cell number in relation to primary pattern formation in the embryo of Xenopus laevis: I. The cell cycle during new pattern formation in response to implanted organizers
Authors: Cooke Jonathan 
Published: April 2021

ABSTRACT
Results are presented which offer strong evidence that extensive alteration of the fates of embryonic Xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. The experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of gastrulation. Within each set two embryos, an unoperated control and a sham-operated embryo whose own dorsal-lip (organizer) cells had been replaced with an equivalent graft, were developing normally. The third, experimental embryo had received an organizer implant to replace an equivalent number of cells from its ventral marginal zone, and was thus developing two axial mesodermal patterns of differentiation in relation to two dorsal midlines, the extra pattern embracing much host tissue. Mitotic index was also determined, in specific regions and throughout the mesoderm, in similar sets of embryos but at mid-gastrula stages.
The conclusions are justified by the results of a control investigation which show that there is normally no difference in cell cycle time along the presumptive dorso-ventral mesodermal, dimension, during the interval between time of operations and the determination of patterm The lack of any enhancement of mesodermal cell number in late embryos with dual axia patterns, or intervening enhancement of mitotic index in younger operated embryos, thus suggests that new patterns may be determined in the Xenopus gastrula without generation of extra cells.
The results are discussed in relation to recent ideas about pattern formation, and the concepts of morphallaxis and epimorphosis.
Enzyme analysis of mouse extra-embryonic tissues
Authors: Sherman Michael I. , Atienza-Samols Sui Bi 
Published: April 2021

ABSTRACTWe have separated for enzyme analysis the following layers that surround the conceptus at midgestation: decidua, trophoblast, parietal endoderm (including Reichert’s membrane), visceral endoderm, yolk-sac mesoderm and amnion. Measurement of several catabolic enzyme activities )N-acetyl-β,D-hexosaminidase, β-glucuronidase, alkaline and acid phosphatases and non-specific esterases) in these tissues indicates that they are biochemically distinct, perhaps reflecting the different functions that they perform in providing the embryo proper with a desirable environment for differentiation and development. Our studies also provide an example of how visceral endoderm cells can effectively block passage of maternal macromolecules (in this case a serum esterase) in the fetal circulation. Finally, since there is often difficulty in distinguishing among early embryonic and extra-embryonic cell types produced in teratocarcinoma cultures, we have considered how our observations might be of use in this respect, particularly in discriminating between visceral and parietal endoderm.
Investigation of the lethal yellowAy/Ayembryo using mouse chimaeras
Authors: Papaioannou Virginia , Gardner Richard L. 
Published: April 2021

ABSTRACTChimaeric combinations of normal and mutant embryonic tissues were used to investigate the lethal effect of the yellow gene. The homozygous mutant embryos could not be identified before implantation. Therefore, embryos from both intercross matings and control backcross matings were used to provide inner cell masses (ICMs) for injection into genetically marked blastocysts of the CFLP random-bred stock. All conceptuses obtained from reimplanted blastocysts were analysed at mid-gestation for the presence of donor isozyme of glucose phosphate isomerase. A similar proportion of chimaeras were found in the experimental and control series, indicating rescue of the lethal Ay/Ay ICM tissue. The reciprocal experiment also produced a similar proportion of chimaeras but there was a 25 % postimplantational loss of injected embryos evidenced by empty decidual swellings. The results suggest that the yellow mutation primarily affects the trophectoderm which cannot be rescued by a normal ICM, whereas Ay/Ay ICM is capable of survival in a chimaera at least until mid-gestation.
Genetical Studies on the Skeleton of the Mouse1 : XXII. The Development of Danforth’s Short-tail
Authors: Grüneberg Hans 
Published: April 2021

ABSTRACT
An embryological investigation of the semi-dominant gene for Danforth’s short-tail in the mouse shows that, contrary to the results of earlier investigations, the syndrome can be understood as a unitary system dependent on a single root cause. The effects of the gene are similar in heterozygotes and homozygotes, but more extreme in the latter. The most fundamental anomaly probably resides in the primitive streak. This gives rise to a structurally abnormal notochord with a reduced calibre. The abnormality of the notochord increases in intensity in a cranio-caudal direction. At a somewhat later stage the notochord disintegrates all along its length. The process starts in the cervical region where it is also most complete. As a direct result of the disintegration of the notochord there is a reduction of the nuclei pulposi of the intervertebral disks and a reduction of the centra of the vertebrae, particularly in the cervical region; the dens epistrophei is virtually absent, and as a result of this anomaly, an atypical but fully functional horse-shoe articulation is formed between the first two cervical vertebrae with yet more remote effects on neighbouring muscles. The abnormality of the notochord is responsible for regressive processes (cell pyknosis) which at a later stage lead to the loss of part or the whole of the tail. The abnormality of the notochord is also responsible for a considerable reduction of the cloaca and the tail-gut. The cloaca is too small for the development of a urorectal septum and hence persists; the shrinkage of the cloaca also leads to a (? secondary) separation from the cloacal membrane; this results in absence of the bladder, urethra, and genital papilla. Finally, there is an arrest or delay in the establishment of contact between the reduced cloaca and the Wolffian ducts; it is suggested that this may interfere with the growth of the ureter buds and thus, in turn, lead to the absence of the metanephros. Further minor effects of the Sd gene include right-to-left connexions between paraxial mesoderm or somites in the tail, a slight effect on the ventral ectodermal ridge of the tail, and a statistical effect on the metoptic roots of the ala orbitalis of the presphenoid. All these effects are clearly secondary, but the mechanism of the last two of them is not understood in detail.
The Conversion of Yolk into Cytoplasm in the Chick Blastoderm as shown by Electron Microscopy
Authors: Bellairs Ruth 
Published: April 2021

ABSTRACTThree main types of yolk drop are present in the area pellucida of the chick blastoderm. They have been given the names ‘complex yolk drop’, ‘type A yolk drop’, and ‘type B yolk drop’. Together they have been called secondary yolk to distinguish them from the extra-embryonic or primary yolk. It is concluded that the complex yolk drops are early stages in the conversion of yolk. They contain granular material which resembles that found in the primary yolk. Type A drops are present in the complex yolk drops and appear to be formed from the granular material. Type B drops, mitochondria, vacuoles, and membranes are also found within the complex drops. The membranes around the complex drops appear to break down, releasing the contents of the yolk drops into the cell. Most type A drops appear to become converted into a number of circular, or possibly tubular, bodies. These are believed to be predominantly lipoproteins. It is concluded that the membrane around each type A drop breaks down and these circular bodies are then released into the cytoplasm where they may contribute to the endoplasmic reticulum. Other type A drops are composed of numbers of micro-particles. They closely resemble the cytoplasmic micro-particles and may become part of them. Evidence is presented for considering these micro-particles to be precursors of ribonucleoproteins. The type B drops persist in the cytoplasm after the complex drops and the type A drops have almost completely disappeared. Evidence is presented for considering them to be fatty drops. Primary yolk from the hen’s egg has also been examined.
Type-specific Morphogenesis of Cartilages developed from Dissociated Limb and Scleral Mesenchymein vitro1
Authors: Weiss Paul , Moscona Aron 
Published: April 2021

ABSTRACTThe emergence of definite organ and tissue structure during development implies that the component units—cells and intercellular materials—assume patterned space relations. These reveal themselves in geometric features of position, proportions, orientation, grouping, alignment, and so on. The ordering processes involved are variously referred to as ‘organization’, ‘differentiation’, ‘morphogenesis’, ‘field action’, and the like. Such terms, while useful as identifying labels for the respective problems, are largely lacking in concrete operational meaning. To realize this, one need only consider how little is known about the practical devices and tools by which any given product of development is achieved. The study of the ‘biotechnology’ of developmental mechanisms has indeed been lagging behind the preoccupation with general principles.
Teratogenic Effects of Trypan Blue on Hamster Embryos1
Authors: Ferm Vergil H. 
Published: April 2021

ABSTRACT
Little information is available in the literature on the susceptibility of the hamster embryo to teratogens. Desoxycorticosterone acetate apparently has some teratogenic activity (Tedford & Risely, 1950), but the degree and type of abnormality produced by this agent in the hamster have not been recorded. Orsini (1952) has described naturally-occurring urogenital anomalies which appear in females of a piebald strain of the golden hamster.
On Regeneration after the Amputation of Abnormal Structures
Authors: Newth D. R. 
Published: April 2021

ABSTRACT
Supernumerary limbs induced in the flank of larvae of Triturus helveticus by homoplastic grafts of nasal placode are frequently abnormal in structure. Some are highly polydactylous, others hypodactylous, and yet others are mere protuberances whose character as limbs cannot be assumed from their appearance in vivo. The amputation of such induced formations at a level close to the flank of the larva is usually followed by regeneration. The regenerates so formed are, in most cases, more nearly normal in structure than the original inductions they are replacing. A second amputation and regeneration may completely restore normality. The possibility of explaining these results in terms of the known peculiarities of supernumerary induced limbs is discussed.
The Origin of the Acoustic Ganglion in the Sheep
Authors: Batten E. H. 
Published: April 2021

ABSTRACTThe acoustic ganglion arises from placodal cells which detach from the otic vesicle between the 6 ·0-mm. and 14·0-mm. stages. The accepted view that it develops from a common ‘acustico-facial’ neural crest is rejected. The initial rudiment of the acoustic ganglion is a mass of detached placodal cells which lies at the base of the vesicle and is distinctly separated from the facial crest by a zone of mesenchyme. After the 8·0-mm. stage the detachment and migration of placodal cells becomes more vigorous and the enlarging acoustic ganglion becomes secondarily apposed to the geniculate ganglion. Nevertheless, these ganglia retain their separate identity through cytological differences which rest on the fact that the young neuroblasts are already present in the geniculate ganglion before a distinct acoustic rudiment is evident. This contrast wanes gradually after the 11·0-mm. stage when the placodal cells begin to differentiate into acoustic neuroblasts. It is concluded that the acoustic ganglion arises exclusively from placodal cells and the participation of facial crest cells in the root portion, if it occurs at all, is probably negligible. The definitive vestibular ganglion is derived from the pars superior together with the lateral zone of the pars inferior in which the earliest neuroblasts appear. The definitive cochlear ganglion begins to develop rather later and arises from the remaining medial zone of the pars inferior with the addition of further diffuse placodal contributions from the base of the vesicle.
Skeletal Regeneration in Amphibians
Authors: Goss R. J. 
Published: April 2021

ABSTRACT
In order to investigate the replacement of skeletal elements in the Amphibia, bones were removed from the extremities of anuran tadpoles, and larval and adult urodeles. Following the extirpation of tibiae from the hind limbs of R. pipiens tadpoles, skeletal regeneration occurred in only a few of the smaller legs. Ulnae removed from the forelimbs of adult T. viridescens were not replaced even when the bone had been previously fractured or when it was replaced by blastema tissue from amputated arms. Cartilaginous skeletal regeneration did occur, however, after extirpation of ulnae from the forelimbs of larval A. maculatura. Likewise, ulnae removed from young forelimb regenerates of adult Triturus were regularly reconstituted, but as such regenerates grew older the percentage of ulna replacement progressively diminished. In view of these results, it is concluded that in order for skeletal regeneration to occur the extirpated structure must be cartilaginous, and it must be removed from a limb otherwise capable of regeneration after amputation. This, together with the evidence that skeletal regeneration, like total limb regeneration, is dependent upon adequate innervation, substantiates the contention that these two phenomena are different manifestations of the same process. It is suggested that the absence of skeletal regeneration is dependent upon the developmental state of surrounding tissues, such that in larval or recently regenerated urodele limbs sufficient potential chondroblasts persist after skeletal extirpation to ensure replacement, while in adult limbs chondrogenic cells, being restricted to the periosteum, are nearly all removed with the bone.
Supplemented eggshell restores calcium transport in chorioallantoic membrane of cultured shell-less chick embryos
Authors: Tuan Rocky S. 
Published: April 2021

ABSTRACT
It was previously reported (Tuan, 1980a) that the development-specific expression of calcium transport and related functions in the chick embryonic chorioallantoic membrane (CAM) requires the continuous presence of the eggshell, the calcium source of the embryo. To further understand the mechanism of action of the eggshell on the CAM functions, this study reports the effects of eggshell supplementation on chick embryos maintained in shell-less cultures. The cultured embryos were able to accumulate and utilize the exogenous shell calcium, applied directly onto the CAM, for skeletal formation. In the region of the CAM directly adhering to the added shell, calcium transport activity, calcium-binding protein (CaBP) activity, and vitamin K-dependent y-glutamyl carboxylase activity were significantly restored. These results strongly suggest that the proximity of shell calcium may regulate expression of calcium transport and related functions in the chick embryonic CAM.