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Biomedical subjects

J F Fallon

Publications and source records attributed to J F Fallon.

At least 73 records · Page 4Linked to original sources
PubMed1984

Cell death in cultured dorsal and ventral chick wing bud epithelia.

We have examined the fate of cultured stage 20 and 25 dorsal and ventral wing bud epithelia and have found evidence that the requirements of apical ectodermal ridge and nonridge limb ectoderms for in vitro survival are different. As previously reported for the apical ectodermal ridge (Boutin and Fallon, '84), dorsal and ventral ectoderms were extensively necrotic after 12 hours of culture in serum-containing medium. The survival of dorsal and ventral limb epithelia at 18 hours was not improved by a collagen substratum, 10% Nuserum, epidermal growth factor, nerve growth factor, multiplication-stimulating activity, insulin, or insulin, transferrin, and selenium. This is in contrast to our observations on the ridge which remains vital for at least 24 hours in insulin or insulin, transferrin, and selenium.

Animals↗
PubMed1984

Evidence that the ectoderm is the affected germ layer in the wingless mutant chick embryo.

We grafted normal flank ectoderm to the denuded presumptive wing bud mesoderm of stages 14-15 wingless embryos. When this was done, the wingless wing bud mesoderm was capable of inducing a ridge in the grafted ectoderm, maintaining that ridge, and growing out to form a wing. However, when stage 17-18 wingless wing bud mesoderm was combined with a normal leg bud ectodermal jacket, the recombinant bud failed to grow out to form a wing (Zwilling, '56a; and this report). When normal ectoderm was first grafted to a wingless host at stages 14-15, and the resulting stage 18 wing bud was removed and then the mesoderm recombined with a normal ectodermal jacket, the double recombinant bud could form a distally complete wing. However, these wings had some deficiencies compared to similar double recombinants made with normal mesoderm. These results show, first, that the ectoderm is affected by the wingless gene and, second, that there may be a prelimb bud stage interaction between wingless ectoderm and mesoderm such that, by stage 17, the wingless mesoderm becomes defective as a result of the ectodermally expressed mutation. Deficiencies in wingless mesoderm double recombinants indicate that the mesoderm may be sensitive to manipulation, possibly because the ectoderm has affected the mesoderm to some extent before stage 14. We believe it is not possible to determine the affected germ layer in wingless after the limb bud arises. However, after using the prelimb bud recombinant technique which we have designed, it becomes apparent that the ectoderm is affected by the wingless gene.

Animals↗
PubMed1984

An analysis of the fate of the chick wing bud apical ectodermal ridge in culture.

Stages 20 and 25 chick apical ectodermal ridge have been cultured in nutrient medium containing fetal bovine serum and the tissues have been examined for dying cells at 0, 6, 12, 18, and 24 hr. By 12 hr, an average of 43% of the cells were dying. By 24 hr, stage 20 ridge had lost its integrity and stage 25 ridge contained an average of 50% dying cells. These results are in agreement with the observations of R. L. Searls and E. Zwilling (1964, Dev. Biol. 9, 38-55) on isolated stage 20 ridge. In subsequent experiments, ridge ectoderm was cultured in serum-containing medium to which insulin (5 micrograms/ml), transferrin (5 micrograms/ml), and selenium (5 ng/ml) or insulin (5 micrograms/ml) had been added. Under these conditions the ectoderms remained viable even after 24 hr in vitro.

Animals↗
PubMed1984

Development of the lateral motor column in the limbless mutant chick embryo.

This is a report on the development of the lateral motor column (LMC) in the limbless mutant chick embryo. The limbless mutant was used to study the effects of the absence of a periphery on the developing nervous system. The limbless mutant provides a unique opportunity to compare the effects on the LMC of deletion of a limb caused by the genotype with those seen following surgical removal of the limb primordium. Cell counts of the total number of motoneurons in the LMC at both the brachial and lumbar levels were done in a large series of limbless embryos and on their normal siblings. In normal embryos, a substantial loss of LMC motoneurons was observed during the course of normal development. At the brachial level, 54% of the initial LMC cell population was lost between day 6 and day 18. At the lumbar level, 40% of the initial population was lost between the 6th and 12th days of development with no further loss through day 18. An even more massive cell loss was observed in the limbless mutant LMC at both brachial and lumbar spinal cord levels between day 5 and day 12. This resulted in the elimination of at least 85% of the motoneurons that were initially present in the limbless LMC. Our data demonstrate that the effects of peripheral deprivation on LMC development in the limbless mutant are similar to those seen following surgical removal of the periphery. The initial production of motoneurons and assembly of the LMC did not appear to be significantly affected by the mutation, while the subsequent degeneration of LMC motoneurons is greatly accelerated and increased in comparison to the normal.

Animals↗
PubMed1984

The stages of flank ectoderm capable of responding to ridge induction in the chick embryo.

Reports on the stages when chick flank ectoderm can respond to ridge induction are contradictory. Different results have been obtained using presumptive wing or leg bud mesoderm as the inducing tissue with flank ectoderm as the responding tissue. In addition, although incomplete outgrowths have been obtained from recombinants with stage-19 flank ectoderm in a small percentage of cases, no complete outgrowths have been obtained from recombinants with ectoderm older than stage 18. We reinvestigated when chick flank ectoderm can respond to ridge induction and promote outgrowth of complete limbs. To do this, we combined flank ectoderm with in situ chick presumptive wing bud mesoderm using a pre-limb bud recombinant technique. When presumptive wing bud ectoderm was removed from the host and not replaced, wing development was suppressed. When host ectoderm was replaced with stage-15 through -18 chick flank ectoderm, limbs grew out in all cases; 86.4% of these recombinant limbs were distally complete. Stage-19 flank ectoderm formed a ridge and promoted limb outgrowth in 80.9% of recombinants; 52.9% of these were distally complete limbs. Recombinants made by grafting early stage-20 (40-somite donor) flank ectoderm to stage-15 hosts resulted in outgrowths in 60% of the cases and 33.3% of these were distally complete. Graft ectoderm from older donors did not respond to inductive mesoderm. Our results demonstrate that chick flank ectoderm from stage-15 through early stage-20 donors can respond to inductive signals from presumptive wing bud mesoderm to form an apical ridge. This ridge can promote outgrowth of distally complete wings in a substantial proportion of recombinants. This is two stages beyond when the ability to promote outgrowth of distally complete wings appeared to be lost using other methods.

Animals↗
PubMed1984

Development of the apical ectodermal ridge in the chick wing bud.

Histological examination of the stage-18 to stage-23 chick wing bud apex revealed the following. Initially, the wing bud was covered by a cuboidal to columnar epithelium with an overlying periderm. Thickening of the apical ectoderm was not obvious until late stage 18 (36 pairs of somites), after the appearance of the wing bud. At late stage 18, cells of the inner layer of ectoderm had elongated slightly along an axis perpendicular to the epithelial-mesenchymal interface. Well-defined apical ectodermal ridge morphology, i.e., pseudostratified columnar epithelium with an overlying periderm, was not apparent until stage 20. Subsequently the ridge lengthened along the anteroposterior perimeter of the wing bud. We demonstrated histologically that the apical ectodermal ridge of the wing bud was asymmetric with respect to the anteroposterior axis, in that there was more ridge associated with posterior mesoderm. Other observations include the spatial and temporal location of a groove in the base of the thickest part of the ridge. The groove can be correlated with the specification of distal wing elements. The groove was first seen at stage 20 and became more prominent through stage 23. An anteroposterior progression of ectodermal cell death was also observed. This began at late stage 18 and continued through each of the stages examined.

Animals↗
PubMed1983

External malformations in chick embryos following concomitant administration of methylxanthines and beta-adrenomimetic agents: 1. Gross pathologic features.

The objectives of this report are to document external malformations observed in chick embryos following concomitant administration of methylxanthines (caffeine, theophylline) and beta-adrenomimetic agents (isoproterenol, epinephrine) and to suggest reasonable explanations for the anomalies. Administration of caffeine or theophylline alone (2.5-5.0 mg/egg) retarded growth in a dose-dependent fashion. Doses of 5.0 mg caffeine and theophylline produced beak malformations in 4.9% and 57.1% of embryos, respectively. Limb malformations, seen in low frequency (3.6% in 56 embryos) after administration of 1 microgram isoproterenol, were not seen in 224 methylxanthine-treated embryos. Structural defects following coadministration of methylxanthines and beta-adrenomimetics were frequently observed in limbs (primarily lower limbs with predilection for left-sided oligodactyly) and beak. Other findings included limb hematomas, hygromas in the nuchal region, and prominent generalized edema. The most dramatic effects observed in this study were those induced by concomitant administration of 2.5 mg caffeine and 1 microgram isoproterenol. This combination produced at least one of the embryopathies listed above in 87.9% of treated embryos and frequently induced beak (24.2%) and lower limb defects (75.8%) in addition to nuchal hygromas (9.1%). Similar severe malformations were observed following administration of 3.8 mg theophylline with 1 microgram epinephrine. Embryos that died within 12-48 hours following drug insult demonstrated marked cardiac dilation, apparently due to congestive heart failure. The results of this study suggest that methylxanthines and beta-adrenomimetic agents are synergistic in their action in the developing chick. Doses of alpha-adrenomimetic agents that were used in this study were not synergistic with methylxanthines. Increased intracellular cyclic adenosine monophosphate (AMP) is offered as an explanation for digital anomalies due to inhibition of proximodistal development of limbs. Increased intracellular cyclic AMP may also explain limb hypoplasia and loss of intermediate limb structures as a result of inhibited mitosis and/or necrosis of embryonic tissue.

Abnormalities, Drug-Induced↗
PubMed1982

The proximodistal determination of skeletal parts in the developing chick leg.

Currently the chick leg bud or its components are being used extensively to study questions in development. Although fate maps of the leg, similar to that developed by Saunders (1948) for the wing, have been available (Hampé, 1957 a, 1959), no study of the proximodistal sequence of the specification of leg structures exists. Such a sequence developed for the wing by removal of the apical ectodermal ridge at successive stages (Saunders, 1948; Summerbell, 1974), has proven useful to the study of wing development. In this paper, we present a similar proximodistal sequence for the chick leg including the same developmental stage range as that of the wing sequence.

Animals↗
PubMed1982

Normal anterior pattern formation after barrier placement in the chick leg: further evidence on the action of polarizing zone.

Impermeable barriers were inserted into the stage-20 to -21 leg bud to test whether or not such an interruption of diffusion of the proposed morphogen from the polarizing zone would result in failure of leg elements to develop anterior to the barrier. Tantalum foil was placed at somite levels 30/31 or mid-31 through the dorsoventral extent of the leg bud separating anterior from posterior mesoderm and ectodermal ridge. In the resulting legs, structures developed anterior to the level of the barrier. For example, legs with foil at the 30-/31-somite level developed digits 1 and 2. We conclude that either the barrier is not an effective block of diffusion of polarizing zone morphogen or that the influence of the polarizing zone is not required for determination of leg structures at these stages.

Animals↗
PubMed1982

Control of pattern formation in urodele limb ontogeny: a review and a hypothesis.

From a review of the literature, the hypothesis is advanced that the forelimb region of the urodele embryo acquires its transverse axial polarity and pattern by the action of posterior and dorsal polarizing regions. The anterior-posterior and dorsal-ventral axes are determined simultaneously and their determination is a prerequisite for proximal-distal outgrowth. Outgrowth of the limb bud is accompanied by the generation, between proximal and distal boundaries, of a set of positional values specifying proximal-distal axial polarity and pattern. The proximal boundary is the initial positional value carried by the cells of the limb area. The distal boundary is imposed upon the outermost layer of limb disc cells by the overlying ectoderm.

Ambystoma↗
PubMed1980

Pattern regulation and the origin of extra parts following axial misalignments in the urodele limb bud.

Pattern regulation following axial misalignments in the stage-38+to stage-40 urodele limb bud was studied on one newt and two salamander species. Grafts of the distal tip of the limb bud were made to the stump of a host limb bud from which a similar piece had been removed. The grafts were positioned with either their anteroposterior, dorsoventral, or both of these axes reversed with respect to the host axes. Mirror-imaged duplications, positioned posteriorly or both anteriorly and posteriorly, occurred nearly all (96%) of the time when the anteroposterior axis was reversed. Dorsoventral axial misalignment rarely promoted the generation of mirror-imaged duplication (8%) but did affect the organization along the anteroposterior axis by causing a serial repetition of either digit 2 or digit 3. Regulation, therefore, does not always occur along each axis independently of the others. Consistent with the data derived from reversing individual axes, most of the duplications which occurred when both axes were reversed were in the anteroposterior plane. Some were in the dorsoventral plane, and a few had intermediate positions. Of these duplications a few were neither right not left hands, rather they were of mixed handedness with a change in the dorsoventral polarity from the anterior border to the posterior border. Whether extra parts which result from axial misalignments arise from the graft, the host, or both the graft and the host was investigated using heteroplastic grafts and grafts exchanged between triploid and diploid axolotls. Duplications were found to have cellular contributions from both the graft and the host. In some cases on source would dominate but usually both made a substantial contribution. The diploid-triploid material suggests that a considerable mixing of host and graft cells may occur in duplications. Additionally, some digits of the graft sequence of digits can be derived from host tissue. The extra digit in those hands displaying a serial repetition was derived from host tissue in some cases and graft tissue in other cases.

Ambystoma↗
PubMed1978

Evidence of a role for cell death in the disappearance of the embryonic human tail.

The development and disappearance of the human tail between stages 14 and 22 were studied using scanning and transmission electron microscopy, supravital staining and light microscopy. The tail is a prominent feature of the human embryo during stage 14 and is composed of paired somites, mesenchyme and extensions of the neural tube, notochord and gut. The tail grows with the embryo through early stage 17 when it extends more than a millimeter from the trunk. Overgrowth by the trunk at the base of the tail may account for the loss of part of its length during late stage 17 and stage 18. However, during stage 17 cells begin to die in all structures throughout the tail. Cell death continues in the succeeding stages reaching massive numbers by stages 18 and 19, and the tail becomes less and less prominent with developmental time. Most of the dead cells are phagocytosed. The debris-laden macrophages appear to migrate from the tail to the body. By late stage 21 or early stage 22 there is no free tail. We conclude that cell death has a major role in the destruction of tail structures and the concurrent loss of the human tail.

Cell Survival↗
PubMed1978

Identification and distribution of gap junctions in the mesoderm of the developing chick limb bud.

Sub-ridge, core, anterior and posterior borders of mesoderm were dissected from stages 22-24 chick wing buds to investigate whether structures for intercellular coupling develop between mesenchymal cells. Fine structure was examined using techniques of transmission electron microscopy, freeze-fracture and scanning electron microscopy. Gap (communicating) junctions which were observed between mesenchymal cells of all limb bud regions were distributed between apposed cell bodies, points of contact between cell processes and other cell bodies, and between contacting tips of slender cell projections. In addition particularly in the the subridge region, filopodia were observed to extend through the intercellular matrix to contact other cells several micrometers distant. The observations reported in this paper show that mesodermal cells throughout the limb have the structural capability for electrotonic and metabolic coupling during a critical period of morphogenesis in the avian limb. Whether intercellular signals which are thought to be transmitted through gap junctions are active in normal limb development remains to be investigated.

Animals↗