摘要:

AbstractFollowing removal of the lens through the cornea, early stages of lens regeneration from the dorsal riris of the adult newt,Notophthalmus viridescens, were studied using light and electron microscopic observations on sectioned, plastic‐embedded irises. Specimens were fixed in Karnovsky's fixative every 2 days from 0 to 12 and 15 days after lentectomy. Infiltration of the iris epithelium by macrophages and their phagocytosis of melanosomes and small fragments of iris epithelial cells were observed. These macrophages were characterized by coarse nuclear chromatin, numerous mitochondria, free ribosomes, granular endoplasmic reticulum, Golgi complexes, vesicles, lysosomes, and phagosomes containing ingested melanosomes. Lamellipodia of varying length projected from their surface. Most of the cells lying on or close to the posterior surface of the iris could be identified as macrophages by these criteria. During this period, there was enlargement of the intercellular spaces within the iris epithelium. The iris epithelial cells near the margin of the pupil elongated, lost their melanin pgigment and some associated cytoplasm, and acquired abundant free polyribosomes to form a lens vesicle of depigmented cell

ISSN:0002-9106    

DOI:10.1002/aja.1001880402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe lens was removed from both eyes of adult newts(Notophthalmus viridescens), and the eyes were fixed in Karnovsky's fixative every 2 days 0–20 days after operation. Anterior half‐eyes were prepared by standard procedures for scanning electron microscopy of the surface. Before fixation, the posterior iris surface was cleaned of adhering vitreous mechanically with forceps or by treatment with bovine testicular hyaluronidase or with hyaluronidase and collagenase. Some specimens were cryofractured in buffer or ethanol transverse to the mid‐dorsal iris, and the fractured surface viewed with scanning electron microscopy (SEM).Cells with various combinations of ridges, blebs, filopodia, and lamellipodia were observed adhering to the posterior surface of the iris by 6 days after lentectomy. These cells, which exhibited the surface characteristics of macrophages, became more numerous in specimens fixed after longer intervals. Invasion of the iris epithelium was observed in a cryofractured specimen. After observations with SEM, selected specimens were embedded in plastic and sectioned for study with transmission electron microscopy (TEM). The cells on the iris surface had the cytological characteristics of macrophages, and other macrophages were located within the iris epithelium. In specimens fixed 16 or more days after lentectomy, a bulging lens vesicle was regenerating from the dorsal pupillary margin of the iris. Macrophages were absent or few on the surface of this developing lens but remained scattered over the adjoining iris.Roles that might be played by these macrophages during the transdifferentiation of iris epithelium into lens are disc

ISSN:0002-9106    

DOI:10.1002/aja.1001880403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe differentiation of brown adipocyte precursor cells was studied in interscapular brown adipose tissue of adult mice by electron microscopy. Different stages of cell differentiation were characterized in situ. Previous autoradiographic studies suggested that interstitial cells represent the precursor cells of fully differentiated brown adipocytes. The present observations provide morphological evidence for a progressive differentiation of interstitial stem cells into mature brown adipocytes. Four typical stages of development were identified: (1) interstitial cells, (2) protoadipocytes, (3) preadipocytes, and (4) mature brown adipocytes. Interstitial stem cells were small spindle shaped cells, situated between brown adipocytes and characterized by a high nuclear‐cytoplasmic ratio, the scarcity of organelles, and the absence of lipid inclusions. Protoadipocytes resembled interstitial cells except that they contained a few tiny lipid droplets in their cytoplasm. Preadipocytes had a larger cytoplasm enclosing many mitochondria and lipid droplets; the smooth endoplasmic reticulum was well developed surrounding the lipid droplets, and was closely associated with the mitochondria. Preadipocytes had the typical structure of growing cells, developing long cytoplasmic processes between and around blood capillaries. Mature brown adipocytes represented the final stage of differentiation. Almost all their cellular volume was occupied by lipid droplets and numerous mitochondria with very dense cristae. Brown adipocytes were also characterized by a tight association with blood capillaries, as expected from metabolically active cells requiring oxygen and substrates. These observations provide direct ultrastructural evidence for a progressive differentiation of interstitial cells into brown adipocytes with a continuum of intermediate cellular type

ISSN:0002-9106    

DOI:10.1002/aja.1001880404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractErythrocytes extravasated into the sinuses of the rat mesenteric lymph nodes as a result of short‐term clamping of the portal vein were, although autologous, phagocytized markedly by the lymph node macrophages at 1 hr after reopening of the vein. The erythrophagosomes formed in the macrophages were exposed three dimensionally by the cellular matrix maceration method and observed with a high‐resolution scaning electron microscope. These results were compared to those obtained by conventional transmission electron microscopy. The process of degradation of an erythrocyte took about 6 hr. Coated pits were formed on the erythrophagosomal membrane at the early stage, and the erythrophagosomes were degraded by two different pathways: (1) the degradative pathway by invaginations of the phagosomal membrane, through which the erythrophagosome shrank and broke into secondary lysosomes, and (2) the hemolytic degradative pathway, by which it lost its content and formed a gh

ISSN:0002-9106    

DOI:10.1002/aja.1001880405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractRemarkable differences among various membranes of bone cells became evident by examination of freeze‐fracture replicas. In osteoclasts, three types of intramembranous particles (IMPs) were identified based on their size and shape: two sizes of isolated globular particles (8 and 12 nm in diameter) and rod‐shaped, linear aggregates (8 × 30 nm in dimension). Furthermore, the density and distribution pattern of these IMPs enabled us to distinguish three different domains of membranes of osteoclasts including reffled border, clear zone, and basolateral regions, as were also observed in thin sections. The highest density of IMPs was 3,500‐4,000/μm2in the ruffled border membrane, and these IMPs included linear aggregates among the usual globular particles. Linear aggregated particles were also observed in the membrane of cytoplasmic vesicles in the vicinity of the ruffled border region, but not in this membrane in other bone cells. In attached osteoclasts, the distribution pattersn and densities of IMPs in each ruffled‐finger and ‐plate were extremely variable, from closely to the loosely packed membrane particles. Focal aggregates of membrane particles were also frequently encountered. An important outcome of the present study was the finding that the presence of linear aggregated particles proved to be an additional criterion for distinguishing membrane domains in freeze‐replicas of osteoclasts. The surface of the clear zone membrane was not smooth in profile, but revealed a number of eminences that were almost free of particles. Basolateral membranes exhibited a particle density of 2,400/μm2. Globular particles were homogeneously scattered in random fashion on their exposed fracture faces. In some cases, aggregates of IMPs on the basolateral membranes were encountered. In comparison with the ruffled fingers, microprojections from the basolateral surface showed a lesser density of IMPs and were devoid of rod‐shaped or linear aggregated particles. Differences between osteoblasts and osteocytes were apparent in the density and the size of IMPs. The membranes of osteoblasts and osteocytes contained the same types of globular particles as seen in osteoclasts. Various sizes of gap junctions were located only on basolateral membranes of the osteoblasts. In contrast, no cellular junctions were observed between osteoclasts and any oth

ISSN:0002-9106    

DOI:10.1002/aja.1001880406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis study concerns techniques used in experimental cranial growth research: roentgen cephalometry, roentgen stereophotogrammetry, and gross measurements (osteometry). A comparison of the precision of these methods has not been found in the literature. Computation of technical errors is fundamental to the sound evaluation of registered findings, and such a presentation must be obligatory in all biometric reports. We compared the measurement error of roentgen cophalometric and osteometric data with that obtained by roentgen stereophotogrammetry (RSA). RSA demonstrates a superior replicability, and this technique gives possibilities for kinematic and volumetric determinations simultaneously with distance evaluation. Roentgen cephalometry has the advantage of enabling distance and angular measurements between any well‐defined skeletal points or lines. This technique, preferably after implantation of bone markers, is a reliable alternative, but optimal results necessitates calculations of the magnification factor for each bone segment involved. Direct osteometry does not contribute additional information, but problems of image magnification are omitted. Preferably, one individual should perform all measurements regardless of the method used. Growth rates and values calculated by one technique cannot be directly transformed to some other approach. In all probability, assessments of distance changes would gain substantially by using one technical approach consistently throughout actual age intervals. The least variable measurements of sutural growth are made for sutures growing primarily in one plane and with substantial growth rates. One must realize that differences among studies may be due to the limitations of, in particular, the cephalometric and osteometric technique

ISSN:0002-9106    

DOI:10.1002/aja.1001880407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEpidermal growth factor (EGF) stimulates the growth of various tissues and, therefore, EGF receptor expression in fetal tissues may play a key role in organogenesis. We have examined immunohistochemically the ontogeny and localization of the EGF receptor in the fetal mouse palate during in vivo and in vitro palatogenesis using the anti‐human EGF receptor rabbit antibody. Immunoreactive products against the EGF receptor were observed in the palatal tissue examined on days 12, 13, and 14 of gestation. On days 12 and 13, the immunoreactive products were predominantly positive on the oral and medial edge epithelia but were minimal on the epithelium of the vertical shelf. The EGF receptor immunoreactivity was less intense in the posterior palate as compared with the midpalatal region. In the fusing palate of day 14 fetuses, the cells forming the midline epithelial seam were continuously positive for EGF‐R immunoreactivity. The mesenchyme of palatal shelves also showed regional heterogeneity and temporal sequence in EGF receptor expression. The localization of the EGF receptor in fetal mouse palates cultured in a serumless medium generally simulated that observed in v

ISSN:0002-9106    

DOI:10.1002/aja.1001880408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractProtein‐carbohydrate recognition may be involved in an array of molecular interactions on the cellular and subcellular levels. To gain insight into the role of proteins in this type of interaction, surgically removed specimens of human endomyocardial tissue were processed for histochemical and biochemical analysis. The inherent capacity of these sections to bind individual sugar moieties, which are constituents of the carbohydrate part of cellular glycoconjugates, was assessed using a panel of biotinylated neoglycoproteins according to a standardized procedure. Together with appropriate controls, it primarily allowed localization of endogenous lectins. Differences in lectin expression were observed between layers of endocardial tissue, myocardial cell constituents, connective‐tissue elements, and vascular structures. The endocardium proved to be positive with β‐galactoside‐bearing probes; with neoglycoproteins carrying β‐xylosides, α‐fucosides, and galactose‐6‐phosphate moieties; and with probes containing a carboxyl group within the carbohydrate structure, namely sialic acid and glucuronic acid. In contrast, only fucose‐and maltose‐specific receptors were apparent in the elastic layers of the endocardium. Aside from ascertaining the specificity of the protein‐carbohydrate interaction by controls, i.e., lack of binding of the probe in the presence of the unlabelled neoglycoprotein and lack of binding of the labelled sugar‐free carrier protein, respective sugar receptors were isolated from heart extracts by using histochemically effective carbohydrates as immobilized affinity ligand. Moreover, affinity chromatography using immobilized lactose as affinity ligand as well as the use of polyclonal antibodies against the predominant β‐galactoside‐specific lectin of heart demonstrated that the lactose‐specific neoglycoprotein binding was due to this lectin. Remarkably, the labelled endogenous lectin, preferred to plant lecins for detecting ligands of the endogenous lectin, localized ligands in tissue parts where the lectin itself was detected glycohistochemically as well as immunohistologically. This demonstration of receptor‐ligand presence in the same system is a further step toward functional assignment of the recorded protein‐carbohydrate interaction. Overall, the observed patterns of lectin expression may serve as a guideline to elucidate the precise physiological relevance of lectins and to analyze

ISSN:0002-9106    

DOI:10.1002/aja.1001880409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of short‐and longterm stimulation of glycogen synthesis elicited by dexamethasone were studied by light (LM) and electron (EM) microscopic radioautography (RAG) and biochemical analysis. Adrenalectomized rats were fasted overnight and pretreated for short‐ (3 hr) or long‐term (14 hr) periods with dexamethasone prior to intravenous injection of tracer doses of3H‐galactose. Analysis of LM‐RAGs from short‐term rats revealed that about equal percentages (44%) of hepatocytes became heavily or lightly labeled cells increased slightly 6 hr after labeling, and unlabeled glycogen became apparent in some hepatocytes. The percentage of heavily labeled cells had decreased somewhat 12 hr after labeling, and more unlabeled glycogen was evident. In the long‐term rats 1 hr after labeling, a higher percentage of heavily labeled cells (76%) was observed compared to short‐term rats, and most glycogen was labeled. In spite of the high amount of labeling seen initially, the percentage of heavily labeled hepatocytes had decreased considerably to 55% by 12 hr after injection; and sparsely labeled and unlabeled glycogen was prevalent. The EM‐RAGs of both short‐ and long‐term rats were similar. Silver grains were associated with glycogen patches 1 hr after labeling; 12 hr after labeling, the glycogen patches had enlarged; and label, where present, was dispersed over the enlarged glycogen clumps. Analysis of DPM/mg tissue corroborated the observed decrease in label 12 hr after adminstration in the long‐term animals. The loss of label observed 12 hr after injection in the long‐term pretreated rats suggests that turnover of glycogen occurred during this interval despite the net accumulation of glycogen that was visible morphologically and evident fro

ISSN:0002-9106    

DOI:10.1002/aja.1001880410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractEmbryonic testes grafted in the extraembryonic coelom of 3‐day‐old genetically female chick embryos may induce total and definitive reversal of gonadal sex differentiation. In this experimental condition, the left gonad becomes a testis instead of an ovary. This makes it possible to compare testicular and ovarian morphogenesis in animals having the same genetic sex and to discount what is due to differences in the genetic determination between male and female.The morphogenesis of such testes is marked by a disappearance of the cortical germinal epithelium. The medullary sex cords keep a narrow lumen instead of becoming large lacunae. The germ cells remain few in the sex cords and do not become meiotic. Furthermore, interstitial cell development is known to be very slow. As a consequence the gross size of the gonad is much smaller than that of an ovary. All these morphogenetic phenomena are unlike those observed during normal ovarian differentiation and evidence an inhibiting influence of the grafted testes. Since inhibition and masculinization are concomittant, inhibition appears to be the mechanism responsible for gonadal sex reversal.The extraembryonic situation of the grafted testes and their relation with the embryo only via the blood stream demonstrates the role of a secreted substance or substances still to be exactly identified. Previous data suggest that this could be the anti‐Müllerian‐hormone (AMH).Furthermore, previous and present results show that testis differentiation can be actively induced in a bird. This does not agree with the hypothesis that the gonads of the homogametic sex, i.e., the testes in birds, do not need any inducer in order to differentiate.The similarity between chronological and structural events of morphogenesis in experimentally induced and normal testes suggests that both result from the same inhibitory m

ISSN:0002-9106    

DOI:10.1002/aja.1001880411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY