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Biomedical subjects

M A England

Publications and source records attributed to M A England.

At least 19 recordsLinked to original sources
PubMed1999

Programmed cell death and the morphogenesis of the hindbrain roof plate in the chick embryo.

The spatial and temporal distribution of apoptosis in the dorsal midline of the developing chick hindbrain was examined in relation to the development of the neuroepithelium and neural crest using scanning and transmission electron microscopy, immunocytochemistry and in situ hybridization. The pattern of TUNEL labeling and Slug expression in the dorsal midline at stages 10 and 11 differed from that at stages 12-15. At stages 10 and 11, TUNEL labeling and Slug expression were observed in the dorsal part of location II of rhombomere 1/2 (i.e., between the surface ectoderm and the neuroepithelium), but from stage 12 onward, they were observed in both the dorsal and ventral parts of location II. The implication is that whereas apoptosis may be restricted to a subpopulation of the early migrating neural crest at stages 10 and 11, it presumably occurs in subpopulations of both neural crest and neuroepithelial cells from stage 12 onward. Furthermore, as judged by the pattern of TUNEL labeling and Slug expression in r3 and r5, apoptosis in these two rhombomeres likely occurs in subpopulations of both neural crest and neuroepithelial cells. The eminence present in location I of r1/r2 between stages 10 and 12 consisted of both neural crest and neuroepithelial cells. These cells gradually underwent apoptosis until stage 12, when the eminence disappeared in most embryos. The formation of the inner (neuroepithelial) aspect of the hindbrain roof plate involved both cell migration from adjacent neuroepithelium and an alteration in the shapes of the cells, such that cells with flattened surfaces eventually lined the roof plate. During these processes, some of the neuroepithelial cells underwent apoptosis (i.e., in location IV). The results of this study thus demonstrate that subpopulations of both neuroepithelial and neural crest cells may be involved in programmed cell death in the hindbrain. Additionally, apoptosis in the hindbrain contributes significantly to morphogenetic thinning during roof plate formation.

Animals↗
PubMed1998

Neural fold fusion in the cranial region of the chick embryo.

Cranial neural fold fusion in the chick embryo is known to commence in the midbrain region before progressing cranially and caudally to involve the fore- and hindbrain regions, respectively. The two epithelial layers at the tips of the neural folds that participate in fusion are the surface ectoderm and the neuroepithelium. We have examined and compared cranial neural fold fusion in both layers, and our results show that fusion of the neuroepithelial component of the neural folds, unlike that of the surface ectoderm, starts in the caudal portion of the forebrain. Second, contrary to the widely accepted opinion, we have demonstrated that in the hindbrain region, fusion of the neuroepithelial component of the neural folds does not occur. Soon after neural fold apposition, a neuroepithelial eminence appears in rhombomeres 1 and 2, and this, together with other neuroepithelial cells in the dorsal midline of the hindbrain, undergoes massive apoptosis. The absence of neuroepithelial fusion in the hindbrain may be due to the presence of massive apoptosis among neuroepithelial cells that should have participated in the fusion process. The events described above may predispose the hindbrain to the development of neural tube defects. The appearance of cranial neural crest cells in the midline during their migration may enhance the fusion of the surface ectodermal portion of the neural folds.

Animals↗
PubMed1998

Surface ectodermal wound healing in the chick embryo.

Wound healing has been studied in the surface ectoderm overlying the midbrain region of stages 16-20 chick embryos by light microscopy, scanning and transmission electron microscopy, and immunofluorescent techniques. The embryos were divided into 6 groups, i.e. stages 16-17 for groups I, V and VI, and stages 19-20 for groups II, III and IV. For groups I and II embryos, a longitudinal incision about 0.6 mm was made close to the dorsal midline and the embryos incubated for varying periods of time up to 24 h. To determine the role of actin in the process of healing, selected groups I and II embryos were stained with FITC phalloidin and the wound margins examined using a confocal microscope. Wounds of all embryos in group I and about 20% in group II healed completely within 24 h of reincubation. The process of healing involved a change in the shapes of the ectodermal cells at the wound ends. This appeared as a zipping-up of the wound from both ends. In about 80% of group II embryos where healing did not occur, wound gaping was marked. Intense actin staining (actin cable) was observed at the wound margins of groups I and II embryos suggesting that the actin purse-string mechanism may play a role during wound healing in this epithelial model. The role of tension in wound healing was also determined by placing 2 secondary wounds about 0.5-0.7 mm long close to, and at right angles to the ends of the primary wound in groups III and V embryos. The procedure decreased the tension within the ectodermal cells at the wound ends. Groups IV and VI embryos served as controls for groups III and V embryos, respectively. Healing of both primary and secondary wounds after reduction of tension was rapid. Most primary wounds in group V embryos healed completely within 3 h of reincubation and the rate of reepithelialisation after the reduction of tension was about 160% more than that in group VI (control) embryos. Similarly, most primary wounds in group III embryos were almost closed within 6 h of reincubation. Here, the rate of reepithelialisation was 80 % more than that in group IV (controls). Thus tension is an important factor in wound healing in this model.

Animals↗
PubMed1996

The effect of embryonic cerebrospinal fluid pressure and morphogenetic brain expansion on wound healing in the midbrain of the chick embryo.

The role of increased cerebrospinal fluid pressure and morphogenetic brain expansion on midbrain wound healing was studied in chick embryos at stages 16-22. The embryos were divided into six groups as follows: group I (stages 16/17), group II (stages 18/19), group III (stages 20-22), group IV (stages 18/19), group V (stages 20-22) and group VI (stages 18/19). The mid-brains of embryos of groups I-III were wounded and the embryos re-incubated for varying periods up to 24 h. The neuroepithelial wounds of all group-I embryos healed completely within 24 h. However, complete healing was observed in only 25% of wounds in group II and 11.4% in group III by 24 h. To reduce cerebrospinal fluid pressure and thus slow down brain expansion, longitudinal wounds (about 0.8 mm long) were made in the hindbrain roof plate of group-IV and group-V embryos, and puncture wounds (0.1 mm in diameter) also in the hindbrain roof plate of group-VI embryos. This allowed cerebrospinal fluid to escape prior to wounding the midbrain. There was a significant increase in the proportion of group-IV and group-V embryos with completely healed midbrain neuroepithelial wounds (77.3% and 28.6% respectively). However, a comparison between groups II and VI embryos yielded no statistically significant difference in healing. Thus, increasing cerebrospinal fluid pressure and brain expansion adversely affect midbrain neuroepithelial wound healing.

Animals↗
PubMed1994

Human cumulus cell complexes studied in vitro by light microscopy and scanning electron microscopy.

Various researchers describe the morphology of cumulus cells (CC) in vitro, but few have investigated their behaviour on plastic. Knowledge concerning the behaviour of human CC could be useful in improving the success of in vitro fertilisation procedures. This study aimed to describe the morphology and behaviour of CC in vitro and to investigate movement on a collagen-coated substrate. Following collection some cumulus were mechanically dissected from those surrounding the oocyte. Cumulus aggregates were cultured over 24 h using Earle's medium supplemented with 8% albumin. Substrata were plastic coverslips coated with collagens I, IV, or mixed collagens. Cumulus cultured over corresponding time periods on uncoated coverslips served as controls. Specimens were fixed and prepared for scanning electron microscopy. Over 24 h the controls began exhibiting the morphological features associated with cell movement: cell surface protrusions changed from blebs to microridges, lamellipodia and leading lamellae; cell shape altered from rounded and upright, to flattened. Extracellular matrix (ECM) transformed from a thick, sheet-like substance to a thin, fibrous material. By 24 h, cells contacting ECM remained rounded showing few features of movement. Collagens enhanced attachment of CC as a monolayer on the substrate. Cell morphology varied according to the collagen type used. On mixed collagens, cells attached rapidly, appearing to be predominantly non-motile. On collagen type I there was less attachment of cells but increased motility. On collagen type IV there was decreased attachment and the cells remained spherical. In conclusion, collagens enhance the settling of cumulus cells on a plastic substrate and the cells exhibit some specificity in attaching to collagens.

Adult↗
PubMed1994

The fusion of ossification centres in the cartilaginous and membranous parts of the occipital squama in human fetuses.

The process of fusion of the ossification centres in the occipital squama is described in human fetal skulls. During the 3rd fetal month, irregular ossification centres appear in the membranous tissue behind the cartilaginous supraoccipital bone plate. The centres rapidly develop to form a meshwork of bony trabeculae which cover the external surface of the supraoccipital plate and then fuse with the primary interparietal part along its lateral edges. In the 4th fetal month, similar irregular ossification centres appear on the internal surface of the supraoccipital plate. After the 5th month, these ossification centres fuse with the root of the secondary interparietal part in the midline. They occasionally fuse with the lateral portion of the primary interparietal part in the early 5th month. These show that the external and internal surfaces of the supraoccipital part are covered with a thin sheet of bone ossified in membrane, which is periosteal ossification, while the main portion of this part develops in cartilage.

Female↗
PubMed1993

Isolation of chick primordial germ cells from stages 4-8 embryos.

Chick embryo primordial germ cells (PGCs) stages 4-8 were manually isolated for the first time from the late hypoblast layer. They were confirmed to be PGCs by periodic acid-Schiff (PAS) staining and examination by scanning electron microscopy (SEM). They were subsequently introduced onto a variety of artificial substrata. On two dimensional substrata, the cells change from a spherical shape covered with numerous microvilli to a rounded cell with a "skirt" of cytoplasm. Eventually a process projects from one side of the smooth cell. On a three dimensional substrate the PGCs change from a spherical shape covered with numerous microvilli to a smooth surfaced cell with a long single process. It is concluded that the PGCs which are originally spherical in situ in stage 4 alter their morphology both in vivo during their migration and in vitro studies.

Animals↗
PubMed1993

Natural wound formation: endodermal responses in experimental primary neural induction in the chick embryo.

Natural wound formation in experimental primary neural induction has been studied by SEM and in paraffin wax sections in embryos from 0 minutes to 10 hours of re-incubation. Stage 4 host and graft embryos were removed from hen's eggs and mounted as for New culture. Graft Hensen's nodes were transplanted into "pockets" created in the host area pellucida and re-incubated for up to 10 hours. Initially the cut edges of the graft establish contact with the host ectoderm layer. After 4 hours the cut edges of the graft move from the host ectoderm to the host endoderm layer. Several small openings form in the host endoderm over the graft tissue. By 6 hours, these openings join to form a single natural wound through which the underlying graft is exposed to the external environment. At 8 hours the graft forms a head-fold and neural folds are evident. During 8 to 10 hours of re-incubation the edges of the graft which attach to the edges of the host endoderm meet in the midline and close the opening in the host endoderm; simultaneously, the graft forms a neural tube. The endodermal wounds form by cell re-arrangement and by a minor contribution from cell loss.

Animals↗
PubMed1993

Migration of lacZ positive cells from the tibialis anterior to the extensor digitorum longus muscle of the X-linked muscular dystrophic (mdx) mouse.

C2 mouse myogenic cells carrying the lacZ gene coding for beta-galactosidase (beta-gal) were injected into the tibialis anterior muscle of dystrophin-deficient mdx mice. Introduced cells were shown to have been incorporated into fibres of the injected muscle by virtue of the colocalization of beta-gal and dystrophin within them. Synthetic Nuclepore membrane inserted between the injected tibialis anterior and adjacent extensor digitorum longus muscle permitted the visualization of cells migrating between the two muscles through the pores of the membrane. Although the exact nature of the cells passing through the Nuclepore could not be determined by this method, they were thought to include implanted myogenic cells. Evidence for this was gained by the presence of beta-gal/dystrophin positive fibres within the extensor digitorum longus. Incorporation of cells into the adjacent extensor digitorum longus was greater in animals where this muscle had been autografted by the cutting and resuturing of the distal tendon. Autografted extensor digitorum longi differed from those which had not been subject to this procedure, by undergoing extensive fibre degeneration followed by regeneration, and further by the stripping of their surrounding epimysial covering. Implanted cells substantially participated in extensor digitorum longus fibre formation in these mice, up to 31% of their fibres 3 weeks after implantation coexpressing both the introduced lacZ gene product and the dystrophin gene product, the latter not normally expressed within the fibres of this myopathic recipient.

Acid Phosphatase↗
PubMed1993

Primordial germ cells in the primitive streak stages chick embryo as studied by scanning electron microscopy.

Chick embryo primordial germ cells (PGCs) at stages 4-8 were localised in the late hypoblast layer. PAS staining confirmed their distribution in a large arc at the anterior border of the area pellucida/area opaca. By scanning electron microscopy the PGCs were seen as spherical cells within the late hypoblast layer. Individual cells separated from this layer and collected in groups of 2-10 in shallow pockets in the hypoblast layer prior to their migration. The pockets containing PGCs were clearly visible by light and scanning electron microscopy and demarcated the germinal ridge at stages 4-8.

Animals↗
PubMed1992

Studies on wound healing in the neuroepithelium of the chick embryo.

Wound healing has been studied by light microscopy, SEM, and TEM in the neuroepithelium of the early neurula (stages 6 and 8) and advanced neurula (stages 10 and 12) chick embryos. Healing involves two major events: (1) apposition of the wound edges and (2) restitution of the neuroepithelium at the wound site (i.e., restoration of the epithelial integrity of neuroepithelium). Apposition of the wound edges occurs within the first 15 minutes of re-incubation and involves the entire length of the wound. The main event during restoration is a change in the shapes of the rounded cells to elongated forms (i.e., spindle, wedge, and inverted wedge shapes). Wounds of younger embryos heal faster than those of older ones.

Animals↗
PubMed1987

Effects of antimitotic drugs on the morphological features of PC12 cells in culture--a light and EM study.

PC12 cells were grown in monolayer cultures either as untreated controls or treated with (1) NGF, (2) mitomycin C/BUdR, or (3) a combination of NGF and mitomycin C/BUdR. The cells from these four groups were processed for scanning and transmission electron microscopy and for fluorescence histochemistry. With scanning electron microscopy, the control and mitomycin C/BUdR treated cells showed the presence of very small extensions for attachment, and numerous fine processes on the cell surface, while the NGF treated cells and cells treated with the combination exhibited many large processes that were even longer with the combination treatment. The combination treatment also inhibited cell growth completely. Fluorescence histochemical studies revealed strong fluorescence in the perikarya of cells from all the four groups. Transmission electron microscopic studies showed that the cells in all the four groups contained many chromaffin-type granules in addition to the presence of other cellular organelles. The neurites in the NGF group and the combination treatment also contained these granules and well-defined microtubules. Therefore, antimitotic agents inhibit PC12 cell growth without affecting important cellular parameters.

Adrenal Gland Neoplasms↗
PubMed1986

The migration of amphibian primordial germ cells in the chick embryo.

A fibrous band of extracellular materials on the chick embryo area pellucida/area opaca border is a preferential migratory pathway for chick embryo primordial germ cells (PGC). This band contains fibronectin, collagen Type I and sulphated glycosaminoglycans. It is known that PGCs from Xenopus laevis interact with fibronectin as they undergo migration in the embryo from their site of origin to the gonads. To establish whether this pathway is species specific in chick embryos it was decided to transplant PGC from Xenopus laevis embryos stage 48 on to chick embryos stage 4 fibrous band. Their rapid migration on this extracellular matrix and their subsequent re-orientation of the basement membrane has been studied by scanning electron microscopy.

Animals↗
PubMed1986

Scanning electron microscopical and histochemical study of the endoderm in the early chick embryo.

The endoderm of gastrulating chick embryos shows regional variations in cell shape and size. These were studied by scanning electron microscopy, histochemistry and immunofluorescence. Particular attention was given to the distribution of the cytoskeleton. Four zones of differing morphology were observed. The changing size and shape of these zones could be correlated with the entry of the definitive endoblast through the primitive streak, displacing existing primary hypoblast to the edges of the area pellucida. Endodermal cells were shown to have a well organised cytoskeleton. The cytoskeletons of individual cells were linked to give a cytoskeletal network extending across the endoderm as a whole.

Animals↗
PubMed1982

The developing ferret palate--a scanning electron microscope study: I. Primary palate and secondary palatal shelves.

Palatogenesis was studied in the ferret (Mustela putorius) from day 27 to day 29 of gestation. At day 27 the primary palate is present as a flattened shield area, and the two secondary palatal shelves are directed at 45 degrees to the horizontal plane, passing downward on the lateral sides of the tongue, which occupies the space between them. By day 28 the primary palate is bulging convexly in the oral cavity, and the secondary palatal shelves have elevated and are in contact in the midline. Finally, at day 29 the primary palate and nasal septum are in contact with the two secondary palatal shelves. During fusion of the secondary palatal shelves, no structures (leading edges or filopedia) associated with cell movement were apparent. It is suggested there are two stages of secondary palate formation in the ferret; an initial contacting of the secondary palatal shelves with the production of cell debris, and further midline movement of the shelves and cell migration out of the epithelial seam.

Animals↗
PubMed1981

Applications of the SEM to the analysis of morphogenetic events.

Scanning electron microscopy (SEM) is a valuable tool for the analysis of morphogenetic events. The role of extracellular materials in primary neural induction in the early stage 5 chick embryo may be analysed by SEM as well as by histochemical techniques. During primary neural induction, extracellular materials in the early stage 5 chick embryo form a fan-shaped region on the ectoderm anterior to Hensen's node. Fibronectin and sulphated glycosaminoglycans are present anterior to Hensen's node on the ventral ectoderm layer. It is proposed that the fanshape of extracellular materials has a dual function; as a chemical substrate to form close contacts between the inducing cells and the target ectoderm cells, and to serve as a contact guidance system of the pre-notochordal cells.

Animals↗
PubMed1981

Timed study of experimental primary neural induction.

Experimental primary neural induction was studied by transmission electron microscopy and compared with normal primary neural induction studies. A change was observed in the ectoderm cytoplasm and the ribosomes formed polysomes in the same way as previously described in normal induction.

Animals↗