Biomedical subjects

B K Hall

Publications and source records attributed to B K Hall.

At least 73 records · Page 4Linked to original sources

PubMed1990

Evolutionary issues in craniofacial biology.

This overview discusses evolution in the context of craniofacial development and developmental processes. It begins with a discussion of the origins of the craniofacial tissues in the dentine and bone of the dermal denticles of the Ordovician jawless vertebrates, followed by a brief discussion of the mechanisms responsible for the evolution of the jaws and the origin of vertebrate dentition. Then the unique neural crest cell origin of the craniofacial skeletogenic and odontogenic tissues is discussed with emphasis on the constancy of rostrocaudal polarization of the skeletogenic cranial neural crest. Given this constancy, the variation in the craniofacial region that occurs across the vertebrates must arise because of epigenetic interactions that evoke the differentiation of craniofacial tissues. These are discussed in the context of epigenetic cascades of epithelial-mesenchymal interactions and how such epigenetic control has itself evolved. Although several mechanisms are considered, emphasis is placed on variation of the timing of development processes (heterochrony).

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PubMed1990

Reciprocal interactions between epithelium, mesenchyme, and epidermal growth factor (EGF) in the regulation of mandibular mitotic activity in the embryonic chick.

Mandibular epithelia and mesenchyme from chick embryos of Hamburger and Hamilton (H.H.) stage 18-25 were cultured intact, in isolation, or in recombinations in the presence or absence of 5-40 ng/ml epidermal growth factor (EGF). 3H-thymidine labelling demonstrated that mesenchyme influenced epithelial mitotic activity and vice versa. EGF can substitute for the epithelial effect. The stimulation of mesenchymal proliferation by H.H. 18 and 22 epithelia correlated with high levels of epithelial proliferation. Epithelial proliferation was low at H.H. 25 and unaffected by mesenchyme or by EGF. Epithelial stimulation of mesenchymal proliferation began earlier (H.H. 18) than did mesenchymal stimulation of epithelial proliferation (H.H. 22); i.e., within the ages tested, the epithelium initiated these reciprocal mitogenic interactions. That epithelial dependence on mesenchyme coincided with epithelial bone-evoking properties, suggested a) that mesenchyme promotes or maintains epithelial bone-promoting activity and b) that the critical differentiative influence of epithelium on mesenchyme is a mitogenic one. The temporal correlation between a sharp decline in mesenchymal proliferation and termination of the osteogenic epithelial-mesenchymal interaction at H.H. 25 further supports a connection between epithelial maintenance of mesenchymal proliferation and epithelial evocation of osteogenesis.

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PubMed1990

Lack of either chondrocyte hypertrophy or osteogenesis in Meckel's cartilage of the embryonic chick exposed to epithelia and to thyroxine in vitro.

Osteogenesis was not initiated when Meckel's cartilages from embryonic chicks of Hamburger and Hamilton (H. H.) stages 38 and 39 were recombined with mandibular epithelia obtained from embryos of H. H. stage 22 (a stage when an epithelial-mesenchymal interaction elicits osteogenesis from mandibular mesenchyme) and grafted to the chorioallantoic membranes of host embryos for 7 to 21 days. Failure of osteogenesis was not because the cartilage inhibited or blocked the osteogenesis-initiating capabilities of mandibular epithelium for mandibular epithelia could still elicit osteogenesis when removed from Meckel's cartilages and recombined with mandibular mesenchyme. Chondrocyte hypertrophy is associated with osteogenesis in other cartilages, including Meckel's cartilage from rodent embryos. However, Meckel's cartilages from chick embryos of H. H. stages 34, 38, and 39 failed to hypertrophy when cultured in the presence of 7.5 nM thyroxine (3,3',5-triiodo-L-thyroxine), although H. H. stage 28 tibial chondrocytes cocultured with Meckel's cartilage did hypertrophy. Therefore, avian Meckelian chondrocytes fail to hypertrophy or to produce osteoprogenitor cells in response to stimuli known to evoke these events in other skeletal cells.

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PubMed1989

Morphological integration in the cranium during anuran metamorphosis.

We examined the role of thyroid hormone in mediating morphological integration between cranial cartilage and bone during anuran metamorphosis. Exogenous T3 applied to premetamorphic tadpoles (Bombina orientalis) via intracranial implants of plastic micropellets precociously induced typical metamorphic changes in both tissues, but also dissociated the relative timing of developmental events between them. Morphological integration between the two primary cranial tissues is achieved in part by each tissue responding independently to endocrine factors and does not reflect a tight developmental coupling between them.

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PubMed1989

Developmental processes, developmental sequences and early vertebrate phylogeny.

(1) We have put forth the position that evolutionary sequences can be deduced by an analysis of fundamental developmental sequences. Such sequences are highly conserved within a group and 'contain steps which are necessary to achieve a developmental fate'. The premise of our work then, is that such fundamental sequences do not arise de novo time and time again but can be traced back through their evolutionary history in organisms which contain portions of the sequence. (2) These highly conserved developmental sequences are in fact developmental constraints to evolution in as much as natural selection has not been able to discard them, but rather has utilized them in achieving evolutionary change. (3) We have demonstrated the ability to use developmental data by producing an evolutionary sequence for the origin of the vertebrates using the processes of neuralization and cephalization, the latter due primarily to the influences of the neural crest and epidermal placodes. The evolutionary sequence created, while not novel in structure, is distinct in that it was created solely by following a developmental sequence that is highly conserved among the vertebrates. The sequence is: (a) Chordamesoderm differentiates from the surrounding mesoderm and induces an overlying neural tube. (b) Through the influence of neuralizing morphogens, the neural tube differentiates into anterior (fore-, mid- and hindbrain) and posterior (spinal cord) parts. Cephalization has begun. (c) Cephalization proceeds via the development of two new populations of embryonic cells, the neural crest, a derivative of the neural epithelium and the epidermal placodes, derivatives of the ectoderm immediately adjacent to the neural tube. These two populations contribute significantly to the subsequent development of the vertebrate head including the skeleton, connective tissues, cranial nerve and sensory organs. Sequence (a) occurs in the most primitive protochordates and is one of the differences between the chordates and deuterostome invertebrates. Sequence (b) occurred next leading to a protochordate with a differentiated central nervous system, but lacking most vertebrate head structures. Sequence (c) signalled the beginning of the true vertebrates or branchiates (after the branchial arches which all 'vertebrates' share) since the production of a neurocranium, viscerocranium, cephalic armour, teeth and cranial peripheral ganglia was only possible with the acquisition of this developmental step.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1989

Growth of the clavicle and development of clavicular secondary cartilage in the embryonic mouse.

Whether secondary cartilage develops in the mammalian clavicle has been a matter of controversy. This study documents, in the embryonic mouse: (a) the onset of clavicular osteogenesis at 14 days of gestation (Theiler stage 22); (b) the appearance of secondary cartilage at 16 days of gestation (Theiler stage 24) and its persistence as a prominent cartilage until 18 days of gestation; (c) that the relative growth rate of the clavicle is much higher (0.097 mg/g body weight/day) between 16 and 17 days of gestation than at later ages (mean of 0.005 mg/g/day between 17 days of gestation and 4 days postnatally), and (d) that secondary cartilage failed to form in clavicles from 15-day-old embryos maintained in vitro. We conclude that secondary cartilage is a feature of the developing mouse clavicle, that it arises when the relative growth rate of the clavicle is highest, and that the most likely stimulus for differentiation of this cartilage is mechanical, muscle-based and associated with rapid relative clavicular growth.

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PubMed1989

Chondrogenesis of mandibular mesenchyme from the embryonic chick is inhibited by mandibular epithelium and by epidermal growth factor.

This study documents the role of mandibular epithelium and epidermal growth factor (EGF) in the initiation, maturation and maintenance of Meckel's cartilage using percent 3H-thymidine-labelled cells as an index of proliferative activity and distribution of labelled cells, chondrocyte size and relative amount of extracellular matrix as indices of chondrogenesis. Mandibular mesenchyme from embryos of H.H. stages 18, 22, 25 was cultured for 2 to 10 days (a) unseparated from mandibular epithelium, (b) in isolation, or (c) after recombination with mandibular epithelium in the presence or absence of 5-40 ng/ml EGF. Epithelium delayed both initiation of chondrogenesis and maturation of already formed cartilage. The 3H-thymidine-labelling index was reduced in cartilage that differentiated in the presence of mandibular epithelium. Epithelium influenced the timing of mesenchymal differentiation (a) by delaying cytodifferentiation through prolonging high levels of proliferation, and (b) by directly affecting differentiation itself. EGF, especially at 10-20 ng/ml, affected both proliferation of mesenchyme and chondrogenesis in mesenchyme cultured with or without epithelium. All observed effects of epithelium on intact tissues could be duplicated by exposing isolated mesenchyme to EGF at 10 ng/ml, i.e. a role for EGF in chondrogenesis is suggested.

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PubMed1989

In vitro reformation of the perichondrium from perichondrial-free Meckel's cartilages of the embryonic chick.

Perichondria were removed from Meckel's cartilages of chick embryos of Hamburger and Hamilton stages 34, 38, or 39 (8, 12, or 13 days of incubation) and cultured, either at the air-medium interface or submerged, under standard organ culture conditions, for 7 to 21 days. Meckel's cartilages formed a new fibrous perichondrium by the 10th day of culture. Perichondria both formed earlier and were thicker in those cartilages cultured at the air-medium interface than in those cultured submerged. Histological and ultrastructural analysis indicated that the outermost layer of Meckelian chondrocytes dedifferentiated into fibrous cells to form the new fibrous perichondrium; i.e., the fibrous perichondrium can arise from superficial chondrocytes.

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PubMed1988

Ultrastructure of the osteogenesis of acellular vertebral bone in the Japanese medaka, Oryzias latipes (Teleostei, Cyprinidontidae).

An ultrastructural study by transmission electron microscopy (TEM) of the vertebrae of embryonic, larval, juvenile and mature medaka shows that each vertebra consists of a core of notochordal cells surrounded by a sheath of bone. The vertebral bone lacks either fully or partially embedded cells in the matrix throughout development. Bone matrix is secreted by a layer of cells that lies over the outer surface of the vertebral bone. During the early stages of osteogenesis, these cells secrete bone matrix all around themselves. However, because of the gradual flow of the newly synthesized bone matrix through intercellular spaces, matrix-producing cells do not become trapped in their own secretion. In later stages of osteogenesis, these cells secrete matrix only toward the already-deposited bone. This polarized matrix secretion allows the osteoblasts to stay always on the bone surface and never to become trapped in the matrix as osteocytes.

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PubMed1988

Skull development during anuran metamorphosis: I. Early development of the first three bones to form--the exoccipital, the parasphenoid, and the frontoparietal.

In anuran amphibians, cranial bones typically first form at metamorphosis when they rapidly invest or replace the cartilaginous larval skull. We describe early development of the first three bones to form in the Oriental fire-bellied toad, Bombina orientalis--the parasphenoid, the frontoparietal, and the exoccipital--based on examination of serial sections. Each of these bones is fully differentiated by Gosner stage 31 (hindlimb in paddle stage) during premetamorphosis. This is at least six Gosner developmental stages before they are first visible in whole-mount preparations at the beginning of prometamorphosis. Thus, developmental events that precede and mediate the initial differentiation of these cranial osteogenic sites occur very early in metamorphosis--a period generally considered to lack significant morphological change. Subsequent development of these centers at later stages primarily reflects cell proliferation and calcified matrix deposition, possibly in response to increased circulating levels of thyroid hormone which are characteristic of later metamorphic stages. Interspecific differences in the timing of cranial ossification may reflect one or both of these phases of bone development. These results may qualify the use of whole-mount preparations for inferring the sequence and absolute timing of cranial ossification in amphibians.

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PubMed1988

Role of the neural crest in development of the cartilaginous cranial and visceral skeleton of the medaka, Oryzias latipes (Teleostei).

Neural crestectomies were performed on neurula stage medaka embryos to remove neural crest with tungsten needles from one of five anteriorly located zones. The embryos were allowed to develop to stage 35 (immediately posthatching) larvae, then cleared and stained for cartilage. An analysis of changes to the head skeletons indicated that most of the anterior neurocranium and the entire viscerocranium received neural crest contributions during development. The elements involved included; the lamina orbitonasalis of the nasal capsule, the trabeculae, Meckels' cartilage and the quadrate of the lower jaw, the pterygoid process, the orbital cartilages and the epiphyseals of the neurocranial roof, as well as all the elements of the hyoid and branchial arches. By further analysis of only those neural crest ablations which produced alterations to the head skeleton, the neural crest cells which contributed to the development of each element were mapped. They originated principally, from one of three regions; the mesencephalon (second most anterior zone removed, number II), the preotic rhombencephalon (zone III), or the postotic rhombencephalon (zone IV). Neural crest from the level of the prosencephalon (zone I) was not chondrogenic nor was neural crest from the fifth region (zone V) which extended beyond the 5th to about the 8th or 10th somite and marked the anterior end of trunk neural crest. The data are discussed and are found to be consistent with the results from other vertebrates and support the central role of the neural crest in the development and evolution of the vertebrate head skeleton.

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PubMed1988

Skull development during anuran metamorphosis. II. Role of thyroid hormone in osteogenesis.

We examined the role of thyroid hormone (TH) in mediating cranial ossification during metamorphosis in the Oriental fire-bellied toad, Bombina orientalis. Exogenous T3 (3,3',5-triiodo-L-thyronine) was administered in three treatment dosages (0.025, 0.25, and 2.5 micrograms) plus a control dosage via plastic micropellets implanted within the dermis of tadpoles of three Gosner developmental stages: 28/29, 30/31, 32/33. Tadpoles were recovered after 2, 4, 6, and 8 d, and scored for the presence of three bones - median parasphenoid and paired frontoparietals and exoccipitals--as seen in cleared-and-stained, whole-mount preparations. T3 induced precocious ossification in both a stage-dependent and a dosage-dependent manner; stage dependence corresponded precisely with the degree of osteogenic differentiation at the time of hormone administration. Precocious ossification thus was due to the T3-promoted growth and calcified matrix deposition of these centers. Differential TH sensitivity among osteogenic sites may underlie both the temporal cranial ossification sequences characteristic of metamorphosing amphibians as well as sequence differences commonly observed among taxa.

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PubMed1988

The organ culture and grafting of lamprey cartilage and teeth.

Cartilage from larval (ammocoetes) and adult (prespawning upstream migrant) lamprey was successfully maintained both when cultured in vitro or grafted in vivo (on the chorioallantoic membrane (CAM) of host chick embryos). In addition teeth from adult lamprey were successfully cultured in vitro. Cartilages were cultured in supplemented Lebovitz's l15 medium at 15 and 20 degrees C for periods of up to 56 d and in supplemented BGJb medium at 37 degrees C for periods of up to 14 d. Cartilages were also grafted onto the CAM for up to 16 d. Both the cultured and grafted cartilages retained their structural and cellular integrity as verified histologically. The viability of the cartilage, even after extended culture periods, was demonstrated ultrastructurally by the presence of chondrocytes displaying abundant rough endoplasmic reticulum, mitochondria, and Golgi apparatii with associated vesicles. In addition the cartilages were shown to be metabolically active in vitro by the incorporation of radioactive sulfur into the matrix. Some cell outgrowth from other tissues, such as connective tissue, muscle, and gill when left adjacent to the cartilage, occurred over time in cultures. No cell outgrowth was observed in CAM-grafted tissue nor was there any invasion of the agnathan tissue by chorioallantoic blood vessels. Teeth cultured in L15-supplemented media for up to 14 d at either 15 or 20 degrees C retained their structural and cellular integrity as observed histologically, with no apparent cell outgrowth. With the successful culture of these tissues, their development, biochemistry, and physiology, potentially of great importance in understanding early vertebrate evolution, can be better understood.

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PubMed1988

Mechanism of adaptation in the mandibular condyle of the mouse. An organ culture study.

The cranial base and whole mandible of 7-day-old mice were cultured for 1 or 2 weeks in a novel organ culture system that provided an articulating movement for the temporomandibular joints. The mandibles were articulating either in a closed or in an open position to simulate the in vivo mouth-breathing pattern. The reactions of the condylar processes were followed macroscopically and microscopically after osteoid or von Kossa staining. After 1 week of culture, small differences were found in the shape of the condylar processes between the two groups. After 2 weeks, significantly increased growth was observed superiorly in those condyles which had been working in a closed position and posteriorly in the condyles which had been working in an open position. Histologic analysis revealed that after 1 week calcification had proceeded faster in the posterior aspect of the condyles in the mandibles which had been working in a closed position as compared to the mandibles which had been working in an open position, and the difference was even more marked after 2 weeks. In the latter condyles calcification had proceeded markedly in the anterosuperior aspect. Osteoid staining showed that perichondrial mesenchymal cells had differentiated into osteoblasts in the posterior aspect of the condyles in those mandibles which had been working in a closed position. This led to a ceasing of expansive growth in the posterior aspect and thus to a more upwardly directed condylar growth. In mandibles which had been working in the open position to simulate the mouth-breathing pattern in vivo, chondrogenesis and thus expansive growth continued in the posterior aspect, leading to a more posteriorly directed condylar growth.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1988

Patterning of connective tissues in the head: discussion report.

The three papers presented by Noden, Thorogood and Lumsden in this session encompassed the connective tissues as broadly defined, i.e. soft (fibrous) connective tissue, cartilage, bone, muscle and the dental tissues, enamel and dentine, and utilized a variety of experimental techniques on both avian and mammalian embryos to explore specificity and patterning of the vertebrate head. Whether similar developmental processes pattern homologous structures in different Vertebrate classes (Amphibia, Aves, Mammalia) was discussed with reference to patterning of the cranial musculature, chondrocranium and dental tissues. A number of challenging ideas emerged during this session. Does the premigratory neural crest consist of a homogenous population of totipotent cells or of subpopulations of bi- or tripotential cells? Is fundamental patterning of the head an early embryonic event, perhaps specified during primary embryonic induction or the consequence of neuroepithelial folding, brain growth, inductive interactions and/or spatially and temporally distributed extracellular matrix products? Can the fact that mesoderm and angioblasts do not display distinctive patterning that relates to their particular embryologic origins be extrapolated to patterning in general? How does the documentation of an odontogenic trunk neural crest in mammals affect our theories of how patterning mechanisms arose or were modified during vertebrate evolution?

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PubMed1988

Organ culture providing an articulating function for the temporomandibular joint.

Cranial bases of 5 days old mice along with the temporomandibular joints and the whole mandibles were maintained in organ culture for one, two or three weeks. A device consisting of an electric motor rotating a bar with three magnets was developed for providing an articulating function for the temporomandibular joints. The tissue samples were attached to the end of a lever arm inside a container and a piece of iron was fixed to the other end of the lever arm to allow it to be lifted magnetically every 45 seconds. This movement pressed the other end of the lever arm downwards, submerging the tissues in the medium. As the anterior end of the mandible was attached to a wire above the tissues with a silk thread while the rest of the tissue sample moved downwards, a rotating movement was produced in the mandibular joint. Control mandibles were cultured without any such movement in the temporomandibular joints. The reactions in the condyles were studied macroscopically after alizarin red injections and microscopically with haematoxylin and eosin, alcian blue, osteoid and von Kossa stains. The condylar processes had increased 0.6 mm in length in functional organ culture, 0.4 mm more than the sham-cultured condyles. Osteoid formation was more marked in the latter and calcification had proceeded closer to the superior surface of the cartilage than in the condyles cultured with articulatory function. The organ culture system developed here obviously resembles the situation in vivo more closely than do previously available organ culture systems and is the first in which it has been possible to provide the function necessary for maintaining growth. The system also seems suitable for culturing organs in which tissue size has previously been a limiting factor.

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PubMed1987

The development of acellularity of the vertebral bone of the Japanese medaka, Oryzias latipes (Teleostei; Cyprinidontidae).

Among vertebrates, some teleosts are unique in having bone which lacks osteocytes embedded in the matrix. The fate of cells that secrete the matrix of these acellular bones has not been investigated thoroughly. Histological and fluorescent microscopic analysis of the vertebral bone of Oryzias latipes demonstrated that acellularity is not a secondary appearance of an early cellular bone during ontogeny. Vertebral bone is devoid of cells embedded in the matrix throughout development. Cells that secrete bone matrix do not become trapped in their own secretion. Instead, they always remain as a surface layer over the outer surface of the bone. Fluorescent microscopic visualization of tetracycline injected into growing fish demonstrated that bone was only deposited by osteoblasts lining the outer surface of the bone; no deposition of bone took place on the inner surface.

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PubMed1987

Sodium fluoride as an initiator of osteogenesis from embryonic mesenchyme in vitro.

Sodium fluoride, which preferentially and rapidly becomes incorporated into bone, is a potent stimulator of bone formation. As such, it has been used to increase total bone mass in patients suffering from osteoporosis. How NaF stimulates bone formation is little understood. Farley et al. (Science 222:330-332, 1983) demonstrated that NaF has a direct effect on proliferation and bone-forming activity of isolated bone cells and of bones exposed to NaF in vitro, that is, NaF stimulates ongoing osteogenesis. In this study, we ask whether NaF can allow preosteogenic embryonic mesenchymal cells to undergo their initial differentiation into osteoblasts and to deposit bone matrix. The mesenchymal cells were from mandibular mesenchyme from embryonic chicks. Mesenchyme from the mandibular arches has to undergo a tissue interaction with mandibular arch epithelium until 4 1/2 days of incubation before osteogenesis can be initiated. Therefore, mandibular arch mesenchyme from younger embryos (3 1/2-4 days), enzymatically freed from its epithelium, was used to provide a source of uninduced preosteogenic cells. Mesenchyme was cultured in the presence or absence of NaF (10(-5) M) in both serum-free and serum-supplemented medium. Osteogenesis was only initiated when NaF was present and only in the presence of serum. Mesenchyme from older embryos that failed to undergo osteogenesis in serum-free medium did form bone in the presence of NaF. It is concluded that preosteogenic embryonic mesenchyme can be stimulated by NaF to differentiate into osteoblasts and to deposit bone matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

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