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Biomedical subjects

M W Ferguson

Publications and source records attributed to M W Ferguson.

At least 109 records · Page 6Linked to original sources
PubMed1990

Size-dependent pigmentation-pattern formation in embryos of Alligator mississippiensis: time of initiation of pattern generation mechanism.

The pigmentation pattern of Alligator mississippiensis was examined. The number of white stripes on the dorsal side of embryos (stages 21-28) and hatchlings from eggs incubated at 30 degrees C (100% females) and 33 degrees C (100% males) was recorded. Total length, nape-rump length and tail length were recorded for each embryo and hatchling. The number of white stripes was affected by incubation temperature but not sex; hatchlings incubated at 33 degrees C had two more white stripes than those at 30 degrees C, despite being the same length. Five female hatchlings produced at 33 degrees C by manipulation of the temperature, had the same number of stripes as males that developed under the same incubation temperatures. The appearance of the pigmentation was accelerated in embryos incubated at 33 degrees C, occurring eight days earlier than at 30 degrees C. At the time just before the first signs of pigment deposition, embryos from 33 degrees C were longer than those at 30 degrees C. If the stripe formation is size dependent this explains why hatchlings at 33 degrees C have more stripes than hatchlings from 30 degrees C. The mechanism that produces the stripe patterns is unknown. We describe key elements a pattern formation mechanism must possess to produce such stripes and suggest a possible mechanism, based on cell movement driven by chemotaxis. We apply the mathematical model to dorsal patterning on A. mississippiensis. We show how length at pattern formation is the prime factor in determining stripe number and how the pattern can be formed in the observed anterior-posterior sequence. We present numerical simulations and show that the qualitative behaviour is consistent with the experimental results.

Alligators and Crocodiles↗
PubMed1990

Development of the dentition in Alligator mississippiensis: upper jaw dental and craniofacial development in embryos, hatchlings, and young juveniles, with a comparison to lower jaw development.

Development of the upper dentition in Alligator mississippiensis was investigated using a close series of accurately staged and aged embryos, hatchlings, and young juveniles up to 11 days posthatching, as well as some young and old adult specimens. Studies from scanning electron microscopy, light microscopy, acetate and computer reconstructions, radiography and macroscopy were combined to elucidate the details of embryonic dental development, tooth initiation pattern, dentitional growth, and erupted functional dentition. The results were compared with those from the lower jaw and related to the development of other craniofacial structures. Approximately 17 early teeth in each jaw half develop as surface teeth, of which 13 project for 1 to 12 days before sinking into the mesenchyme. The first three teeth initiate directly from the oral epithelium at Ferguson stages 14-15 (days 15-19 after egg laying), before there is any local trace of dental lamina formation. All other teeth develop from a dental prolamina or lamina; and with progressive lamina development, submerged teeth initiate from the aboral end leading to the formation of replacement teeth. All teeth form dentin matrix, but 12 early teeth do not form enamel. Approximately 20 embryonic teeth are resorbed, 6 are transitional, and 42 function for longer periods after hatching. The embryonic tooth initiation pattern (illustrated by defining a tooth position formula) does not support the previous models of Odontostichi, Zahnreihen, and Tooth Families, each of which postulates perfect regularity. Up to three interstitial tooth positions develop between sites of primary tooth initiation, and families with up to five generations at hatching are at first arbitrarily defined.

Alligators and Crocodiles↗
PubMed1990

Cancellous bone resorption in the proximal ilium of the ovariectomized rat.

Bone histomorphometry was performed on the proximal ilium of mature Sprague-Dawley rats following ovariectomy, and these rats were compared with sham-operated controls. Bone volume per unit tissue volume (BV/TV), osteoid surface, and the depth and extent of eroded cavities were measured in animals killed at intervals after operation. The rate of bone loss and the mean osteoid surface in the proximal ilium of the ovariectomized rats was significantly greater than that of the control rats over a 210-day postoperative period. The eroded surface and mean trabecular thickness in the proximal ilium of the ovariectomized rats were not significantly different from that of the control rats, and therefore failed to explain the difference in the rate of bone loss. The distribution of the depths of trabecular eroded cavities in the ilium of ovariectomized rats was different from that in the control rats. The loss of trabecular bone mass in the proximal ilium of ovariectomized, mature rats appeared due to increased activity of individual osteoclasts, rather than to increased osteoclast numbers and thinning of trabeculae.

Animals↗
PubMed1990

Fine structure of the organic matrix remaining in the mature cap enameloid in Halichoeres poecilopterus, teleost.

Crystals and the organic matrix in both the enameloid and the maturation stage in this teleost fish were viewed by scanning and transmission electron microscopy. For transmission electron microscopy, specimens were demineralized by basic chromium (III) sulphate or phosphotungstic acid. Large numbers of defined compartments, thought to represent the outline of enameloid crystals, were seen in the outer layer of mature cap enameloid after this demineralization. However, the compartments were both less numerous and less well defined in the inner layer. These compartments suggest the existence of an organic enameloid matrix, which may correspond to the enamelins in mammalian enamel. As these defined compartments occurred in the areas of the tooth where large enameloid crystals were present, it is possible that the organic matrix constituting these compartments is involved in the production of large crystals.

Animals↗
PubMed1990

The rate of incisor dentine calcification and of mandibular growth in the molar region of the ovariectomized rat.

In 14 ovariectomized and 15 control rats, killed at intervals over a 117-day period, the height of the mandible in the molar region was determined radiographically. Mandibular height was significantly related to time after operation in both groups, but their rate of mandibular growth was not significantly different. In a separate study, the rate of dentine formation in the right mandibular incisor of 9 ovariectomized and 10 control rats was calculated from the distance between two fluorescent labels injected at known time intervals. The rate of dentine apposition was measured at 117 and 201 days after ovariectomy. In both groups, the distance between the fluorescent labels was significantly correlated with the time interval between the injections. There was no significant difference between the rate of dentine calcification in either group. Transient changes in dentine apposition may have occurred post-ovariectomy which would be undetected at either 117 or 201 days after operation. There was thus no evidence for an effect of ovariectomy on either the rate of mandibular growth or dentine apposition.

Animals↗
PubMed1990

Studies in fetal wound healing, VI. Second and early third trimester fetal wounds demonstrate rapid collagen deposition without scar formation.

The mechanisms that underlie the lack of scarring in fetal wounds are unknown, but probably relate to the control of collagen fibrillogenesis. The role of collagen in the fetal wound matrix is controversial, and several wound implant models have been used to evaluate collagen deposition in fetal wounds. Unfortunately, these models create an artificial wound environment and may thereby affect the results. In order to study fetal wound collagen deposition in linear wounds without artificially altering the wound environment, we applied a highly sensitive immunohistochemical technique that uses antibodies to collagen types I, III, IV, and VI. We found that collagen was deposited in fetal wounds much more rapidly than in adult wounds. Wound collagen deposition occurred in a normal dermal and mesenchymal pattern in second and early third trimester fetal lambs. These findings are consistent with the observation that the fetus heals rapidly and without scar formation. In contrast, wounds in late gestation fetal lambs showed some evidence of scar formation. Further studies may suggest ways to alter the adult wound so that it heals in a fetal manner.

Animals↗
PubMed1990

Tenascin distribution in the normal human breast is altered during the menstrual cycle and in carcinoma.

Tenascin is a novel extracellular matrix glycoprotein which appears to have a major role in tissue development. Previous studies have stated that tenascin is absent from the normal human, rat and mouse breast, its distribution being restricted to embryonic and malignant mammary tissues. No previous studies have investigated tenascin distribution as a function of the normal menstrual cycle. Therefore this study addresses the cyclical appearance of tenascin in the normal breast and associated changes in distribution in preinvasive cancer (carcinoma-in-situ) and invasive infiltrating ductal carcinoma. Tenascin is present in the normal human adult mammary gland, principally in the basement membrane, sub-basement-membrane zone and delimiting layer of fibroblasts around the ductules. Both the distribution and quantity of tenascin change during the menstrual cycle. In carcinoma-in-situ (preinvasive cancer) tenascin is present in the attenuated basement membrane/sub-basement-membrane zone around the expanded ductules and in small amounts in the stroma. In infiltrating ductal carcinoma, tenascin is absent from the remnants of the basement membrane and sub-basement-membrane zone but greatly increased in the adjacent intralobular and interlobular stroma. Therefore, if tenascin is used as a basement membrane/sub-basement-membrane marker for distinguishing carcinoma-in-situ from invasive ductal carcinoma, the time of the menstrual cycle is of importance in interpreting the biopsy appearance. This study suggests that the optimal time for biopsy is between weeks 3 and 4 of the cycle, to avoid confusion between the normal low levels of tenascin (due to hormonal status) and those due to microinvasive disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Determination of ultrasonic velocity in human enamel and dentine.

Acoustic velocity data have been obtained preparatory to investigation of high frequency ultrasound as a non-invasive imaging technique for dental hard tissues and their pathology. In vitro studies were conducted on extracted human permanent teeth. Pulse-echo ultrasound of 18 MHz centre frequency and approx. 150 ns pulse duration successfully detected the front and back surfaces of 0.45-1.07 mm thick sections of enamel and of dentine. Water was used as the coupling agent. The oscilloscope traces of the echoes from pure enamel and pure dentine were similar. The longitudinal ultrasonic velocities for pure enamel and dentine were experimentally determined for a number of teeth in different planes of section. For enamel in longitudinal and transverse sections, the mean ultrasonic velocities were 6150 +/- 140 and 6500 +/- 190 m/s respectively. For dentine in longitudinal section, the mean ultrasonic velocity was 4050 +/- 30 m/s.

Dental Enamel↗
PubMed1989

Biocompatibility testing of a posterior composite and dental cements using a new organ culture model.

Mandibular first molars from day 14 and 17 mouse embryos were cultured in vitro for 7 days in chemically defined Pratt's medium in a submerged culture system. Ameloblast and odontoblast polarization and morphogenesis occurred in the control tooth germs. Discs of Occlusin, Silicate, ChemFil, IRM and Dycal were exposed to the culture system as either fresh material, leached discs (by pre-incubation in media) or the leachate from the incubated discs. Their effects on dental differentiation were assessed histologically. Day 17 tooth germs were slightly more sensitive to the effects of the exogenous agents than day 14 tooth germs. In general, silicate and ChemFil were toxic, IRM was slightly less toxic and the major effect was from the leachate. Dycal was toxic but most of this effect resulted from pH changes in the leachate. Occlusin was the most biocompatible material tested. Only a very mild adverse effect was detected, and this appeared to be caused by an agent (not a pH change) released into the leachate.

Aluminum Silicates↗
PubMed1989

Studies in fetal wound healing: III. Early deposition of fibronectin distinguishes fetal from adult wound healing.

Wound healing in the fetus proceeds through a series of steps that differ in the fetus and the adult. At each phase of this complex process, there is signaling between the tissue cells and the wound microenvironment, signals that are mediated by and through the extracellular matrix. We postulate that these signals occur earlier in fetal wounds, resulting in more rapid repair. To investigate this, we compared the first 24 hours of wound healing in the rabbit fetus and adult, using antibodies against key extracellular matrix macromolecular components: laminin, fibronectin, and type-specific collagens I, III, IV, and V. Fibronectin was the first matrix component to be deposited, and was visualized as early as four hours after fetal wounding and 12 hours after adult wounding. There was no evidence of new laminin or collagen deposition in either the fetal or adult wounds at any time point examined. The early deposition of fibronectin, a matrix adhesion molecule that provides a scaffolding for epithelial migration, may underlie the rapid reepithelialization observed in fetal wounds.

Animals↗
PubMed1989

Compositional changes in the rat femur following ovariectomy.

Ovariectomy has been shown to produce osteoporosis in the femur of the rat. 11-month-old Sprague-Dawley rats were either ovariectomized or given a sham operation. The loss of calcium in the femur of the rats was compared with two indices of osteoporosis, the ponderal index and the femur score. The calcium content was more closely associated with the femur score (r = 0.5, p = 0.0064) than with the ponderal index (r = -0.367, p = 0.05). An accelerated rate of fat deposition in the ovariectomized rat femur reduced the femur weight loss, which resulted in a barely significant association of calcium content with the ponderal index.

Animals↗
PubMed1988

Environmental regulation of sex determination in reptiles.

The various patterns of environmental sex determination in squamates, chelonians and crocodilians are described. High temperatures produce males in lizards and crocodiles but females in chelonians. Original experiments on the effects of incubation at 30 degrees C (100% females) or 33 degrees C (100% males) on development in Alligator mississippiensis are described. These include an investigation of the effect of exposing embryos briefly to a different incubation temperature on the sex ratio at hatching, and a study of the effects of 30 degrees C and 33 degrees C on growth and development of alligator embryos and gonads. A 7-day pulse of one temperature on the background of another was insufficient to alter the sex ratio dramatically. Incubation at 33 degrees C increased the rate of growth and development of alligator embryos. In particular, differentiation of the gonad at 33 degrees C was enhanced compared with 30 degrees C. A hypothesis is developed to explain the mechanism of temperature-dependent sex determination (TSD) in crocodilians. The processes of primary sex differentiation are considered to involve exposure to a dose of some male-determining factor during a specific quantum of developmental time during early incubation. The gene that encodes for the male-determining factor is considered to have an optimum temperature (33 degrees C). Any change in the temperature affects the expression of this gene and affects the dose or quantum embryos are exposed to. In these cases there is production of females by default. The phylogenetic implications of TSD for crocodilians, and reptiles in particular, are related to the life history of the animal from conception to sexual maturity. Those animals that develop under optimal conditions grow fastest and largest and become male. A general association between the size of an animal and its sex is proposed for several types of vertebrate.

Animals↗
PubMed1988

Histological evidence of fusion between the posterior palatal shelves and the floor of the mouth in Alligator mississippiensis.

Unlike the anterior four-fifths of the secondary palatal shelves the posterior one-fifth grows vertically downward along the side of the tongue and unites with the floor of the mouth. This feature appears to be unique to alligators, and may be important in the development of the basihyal valve. The valve seals off the mouth from the nasal cavities, pharynx and larynx, and thus allows simultaneous breathing and capturing of prey while in the aquatic environment. This developmental feature may enhance the survival value of the species.

Alligators and Crocodiles↗
PubMed1988

Palate development.

In all vertebrates, the secondary palate arises as bilateral outgrowths from the maxillary processes. In birds and most reptiles, these palatal shelves grow initially horizontally, but do not fuse with each other resulting in physiological cleft palate. In crocodilians, shelf fusion occurs resulting in an intact secondary palate. Mammalian palatal shelves initially grow vertically down the side of the tongue, but elevate at a precise time to a horizontal position above the dorsum of the tongue and fuse with each other to form an intact palate. Palatal shelf-elevation is the result of an intrinsic shelf elevating force, chiefly generated by the progressive accumulation and hydration of hyaluronic acid. In all vertebrates the nasal epithelium differentiates into pseudostratified ciliated columnar cells and the oral epithelia differentiates into stratified squamous cells, but the medial edge epithelial (MEE) phenotype differs in different groups. In mammals, the MEE of opposing shelves adhere to each other to form an epithelial seam which then disrupts by cell death and cell migration into the mesenchyme accompanied by an epitheliomesenchymal transformation. In birds, the MEE keratinize resulting in cleft palate whereas, in alligators, the MEE migrate onto the nasal aspect of the palate. In all vertebrates, this regional, temporal and species-specific epithelial differentiation is specified by the underlying mesenchyme. Signalling of this interaction is complex but involves both extracellular matrix and soluble factors e.g. minor collagen types, tenascin, EGF, TGF alpha, TGF beta, PDGF, FGF. These soluble growth factors have a biphasic effect: directly on the epithelia and on the mesenchyme where they stimulate or inhibit cell division and synthesis of specific extracellular matrix molecules. The extracellular matrix molecules (and bound growth factors) synthesized by the mesenchymal cells may then directly affect the epithelium. These signals cause differential gene expression via second messenger systems e.g. cAMP, cGMP, Ca2+, pH, pI etc. Molecular markers for nasal, medial and oral epithelial cell differentiation include the types of cytokeratin intermediate filaments and specific cell surface molecules recognized by monoclonal antibodies: the genes for such molecules are probably expressed in response to mesenchymal signals. Using such an approach, it is possible to go from a morphological description of palate development to a cellular analysis of the mechanisms involved and then to identification of candidate genes that may be important for screening and diagnosis of cleft palate.

Animals↗
PubMed1988

Mesenchymal influences on epithelial differentiation in developing systems.

Mesenchyme tissue: cells, matrix and soluble factors, influence the morphogenesis, proliferation and differentiation of a variety of embryonic epithelia, e.g. in the tooth, skin, mammary and salivary glands. Mesenchyme derivatives also 'maintain' adult epithelia, e.g. the local proliferation rate and cytokeratin composition of oral mucosa. Abnormalities in such epithelial-mesenchymal interactions lead to a variety of pathologies such as premalignant lesions, e.g. leukoplakia, tumours and psoriasis, whilst therapeutic manipulation of such interactions can prevent the exfoliation of dental implants. In all of these systems it is critical to understand, at the cellular and molecular levels, how the mesenchyme signals to the epithelium and how the latter processes and responds to such signals. We have investigated such questions using the developing embryonic palate both as a model system and as an important organ: failure of mesenchymal signalling leads to the common and distressing birth defect of cleft palate. Bilateral palatal shelves arise from the maxillary processes of embryonic day 11 (E11) mice, grow initially vertically down the sides of the tongue, elevate on E13.8 to a horizontal position above the dorsum of the tongue and fuse with each other in the midline on E14. The medial edge epithelia of each shelf fuse with each other to form a midline epithelial seam, suprabasal cells die, and the basal (stem) cells synthesize extracellular matrix molecules and turn into mesenchymal cells. Simultaneously the oral epithelia differentiate into stratified squamous cells and the nasal epithelia into pseudostratified ciliated columnar cells. Oral, medial and nasal epithelial differentiation is specified by the underlying mesenchyme in vivo and in vitro. Signalling involves a bifurcating action of a combination of soluble growth factors e.g. TGF-alpha, TGF-beta, PDGF and FGF on palatal epithelia and mesenchyme. These factors stimulate the synthesis of specific extracellular matrix molecules by palate mesenchyme cells, and the appearance of receptors for such molecules on epithelial cells. In this way, a combination of mesenchymal soluble factors and extracellular matrix molecules direct palatal epithelial differentiation. These signals act on epithelial basal (stem) cells, causing them to synthesize unique proteins, which may direct subsequent differentiation of daughter cells. In the most extreme example, namely the medial edge epithelia, these signals result in the basal epithelial cells transforming into mesenchymal cells, thus demonstrating that they are indeed multipotential stem cells.

Animals↗
PubMed1988

Immunocytochemical localisation of tenascin during the development of scleral papillae and scleral ossicles in the embryonic chick.

We have used a polyclonal antibody against tenascin (a 240 kDa extracellular matrix glycoprotein) and indirect immunofluorescence to investigate the distribution of tenascin in cryostat sections of the chick sclera during the six stages of scleral papilla development (Murray, 1943) and formation of membrane bone anlagen (mesenchymal condensations between 6-12 days of incubation - HH Stage 29-37). At Stages 1 and 2, when the papilla was a slight thickening in the conjunctival epithelium and mesenchymal condensation formation was initiated, tenascin was sparse in the sclera. At Stage 3, when the papilla had an epithelial mass intruding into the mesenchyme, there was an accumulation of tenascin fibrils along the subsurface of the papilla with fibrils extending from this region into the mesenchymal condensation. Interestingly, tenascin was sparse between papillae and between mesenchymal condensations. The Stage 4 papilla had a similar localisation of tenascin fibrils and in addition fine arborizing fibrils of tenascin were observed within the basal epithelia of the papilla adjacent to the epithelial-mesenchymal interface (which suggested that the fibrils infiltrated through the basement membrane region). The Stage 5 and 6 papillae had a column of vertical tenascin fibrils extending from the subsurface of the papilla to the interior mesenchyme corresponding exactly to the location of the mesenchymal condensation which was then forming the anlage of the ossicle in a flat bed about 100 microns from the conjunctival surface. The column of tenascin disappeared as the osteoid appeared in the ossicular bed on the 12th day of incubation but a dense accumulation of tenascin remained along the subsurface of the papilla. With the exception of tenascin fluorescence in the basal region of the Stage 4 papilla, tenascin fibrils were not observed in the other stages of papilla development in the epithelium covering areas between the mesenchymal condensation. This restricted distribution of tenascin may be important in the morphogenesis of scleral papillae and scleral ossicles.

Animals↗