摘要:

AbstractBackground: In the hope of understanding how chromosomes condense at mitosis, we took advantage of a subdivision of the cell cycle into 11 stages to examine the changes in DNA taking place during the stages preceding the emergence of metaphase chromosomes.Methods: To identify DNA changes, pieces of mouse duodenum were fixed in formaldehyde, and sections of the rapidly dividing cells of the crypts were stained by the osmium‐ammine method, which is specific for the detection of DNA in the electron microscope.Results: Throughout the cell cycle, DNA is present in nucleofilaments composed of rows of 11‐nm‐wide nucleosomes. At stage I, during which the DNA‐synthesizing or S phase of the cell cycle begins, some of the nucleofilaments are compacted in the heterochromatin accumulations associated with nuclear envelope and nucleoli, while the others are scattered in the nucleoplasm where they appear either “free” or “attached” to the heterochromatin. This DNA distribution is similar to that observed in the noncycling cells examined. After the beginning of the S phase, “free” nucleofilaments are seen to assemble into structures composed of compacted nucleofilaments and referred to as “aggregates”; these make their appearance at stage II and increase in size through stage III up to the end of S during stage IV. Meanwhile, the heterochromatin associated with nuclear envelope and nucleoli expands toward the nucleoplasm in the form of protrusions referred to as “bulges,” which gradually enlarge during stages III and IV, while the heterochromatin shrinks and eventually vanishes. On average, a total of 1,171 aggregates and bulges are formed in the nucleus during the S phase. At the apparition of stage V, which corresponds approximately to prophase, aggregates and bulges are rapidly gathered into an average of 288 spheroidal bodies referred to as “chromomeres.” These are connected to one another by nucleofilamentous bridges in such a way as to be lined up in rows. The formation of rows of chromomeres represents in the electron microscope the prophasic condensation observed in the light microscope. Finally, during stage VIa, which corresponds to prometaphase, the chromomeres approach one another within each row, make contact, and coalesce to become the 40 chromosomes of the mouse, which during stage VIb are organized in the equatorial plate of metaphase.Conclusions: The condensation of metaphase chromosomes occurs in three main steps. The first and longest takes place during the S phase, as nucleofilaments are assembled into aggregates, while the heterochromatin give rise to bulges. The brief second step occurs toward the beginning of prophase, when the numerous aggregates and bulges are congregated into a limited number of chromomeres, which are lined up in rows. The third step takes place during the brief prometaphase, when the chromomeres of a row coalesce into a mitotic chr

ISSN:0003-276X    

DOI:10.1002/ar.1092420402

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: Since it has been found that new chromatin structures make their appearance in the nucleus during the DNA‐synthesizing or S phase of the cell cycle, the question arises as to how these structures are related to the nascent DNA.Methods: DNA‐containing structures were detected in sections of mouse duodenal crypt cells by the DNA‐specific osmium‐ammine procedure. In the same sections, the nascent or newly‐replicated DNA was localized during stages I–IV of the cell cycle (corresponding to four successive parts of the S phase) by immunogold labeling of the DNA precursor bromodeoxyuridine (BrdU) in mice sacrificed 10 min after its injection. Moreover, the fate of the nascent DNA with time was traced up to 6 hr after the injection. (The nomenclature of the DNA‐containing structures is that proposed by El‐Alfy et al., 1995.)Results: Ten minutes after BrdU injection, the gold particles indicative of nascent DNA are associated with discrete nucleofilaments scattered in the nucleoplasm, but not with the compacted nucleofilaments making up the heterochromatin or the new S phase structures named “aggregates.” The gold‐particle‐associated discrete nucleofilaments are classified into three types: a) The “free” nucleofilaments have been given this name, since they appear to be independent of heterochromatin and aggregates; nearly all gold particles are over these at stage I; but the numbers of particles over them decreases from stage I to IV. b) The “aggregate‐attached” nucleofilaments project from the surface of the aggregates; the number of particles over these is high at stages II and III but decreases at stage IV. c) The “heterochromatin‐attached” nucleofilaments project from the surface of the heterochromatin; the number of particles over these increases from stage II to IV.By 1 hr after BrdU injection, gold particles can be over loose clumps of nucleofilaments at stages I and II, but are mostly over small aggregates at stage II, midsized aggregates and small heterochromatin‐associated “bulges” at stage III and large aggregates and large bulges at stage IV. By 2–6 hr, virtually all particles are over aggregates and bulges, frequently deep within them.Conclusions: The distribution of the gold particles at 10 min reveals that DNA is synthesized in discrete nucleofilaments that are “free” or “aggregate‐attached” or “heterochromatin‐attached.” In contrast, by one and especially two hours, the gold particles are present over aggregates and bulges, indicating that, after discrete nucleofilaments acquire nascent DNA, they are displaced to become part of these structures. More precisely, the aggregates arise from the repeated addition of replicated portions of “free” nucleofilaments, while the bulges arise from the repeated addition of replicated portions, of “heterochromatin‐attached” nucleofilaments. Aggregates and bulges are the two initial building stones fro

ISSN:0003-276X    

DOI:10.1002/ar.1092420403

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: The pectoralis muscle of the chicken contains fast‐twitch glycolytic fibers, which during development undergo a transformation in their myosin heavy chain (MyHC) content from embryonic to a neonatal to an adult isoform (Bandman et al., 1990). Little, however, is known of MyHC expression within the ends of these or other muscle fibers. Here we test the hypothesis that the tapered ends of mature skeletal muscle fibers contain a less mature MyHC isoform than that typically found throughout their lengths.Methods: We apply an ammoniacal silver histological stain for endomysium and monoclonal antibodies against neonatal and adult MyHCs of chicken pectoralis to transverse serial sections of pectoralis from five mature chickens. The “lesser fiber diameters” of populations of fibers from each bird are also measured.Results: Most (∼81.8%) of the small (20μm) diameter fibers contain the neonatal MyHC. Following these smaller fibers through serial sections, we show that they are the tapered ends of the larger fibers. Whereas neonatal MyHC is restricted to the tapered fiber ends, adult MyHC is present throughout the entire lengths of all fibers. We also demonstrate acetylcholinesterase (AChE) activity at some of these fiber ends.Conclusions: We postulate that longitudinal growth of myofibrils in adult muscle is characterized by the sequential expression of MyHC isoforms similar to that observed in rapidly growing muscle and that the presence of the neurotransmitter hydrolase AChE at the tapered fiber ends may be related to the retention of neonatal MyHC. © 1995 Wiley

ISSN:0003-276X    

DOI:10.1002/ar.1092420404

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: In carnivores, the supporting organ of the epiglottis is usually called “epiglottic cartilage” (EC) although it is composed of elastic cartilage and unilocular fat storing cells. We studied the cat's EC in order to decide whether these fat storing cells are true adipocytes or fat storing (dedifferentiated) chondrocytes.Methods: ECs were studied in cat embryos at gestation days 40 and 60, in newborn, postnatal, and adult cats. We used classical staining methods, immunohistochemistry, and transmission electron microscopy to identify the different kinds of tissues contributing to the EC and to follow their differentiation.Results: The cat's EC was defined by a layer of coarse collagen fibers representing atunica albuginea. This tunica covered irregularly formed and irregularly sized areas of elastic cartilage, fibrous cartilage, myxoid tissue, and lobules of unilocular fat cells. All these tissues showed regular morphology. Adipocytes were provided with continuous basal laminae and fat lobules were well supplied with capillaries. Alcianophilia of ground substance was observed in all tissue components but was strongest in elastic cartilage. Most islets of elastic cartilage adhered to thetunica albugineaof the EC at one surface and were connected to the opposite surface by coarse strands of connective tissue traversing the organ. Intercalated areas of fibrous cartilage contained fuchsinophilic collagen bundles. Myxoid tissue was characterized by stellate cells in alcianophilic ground substance with intermingled fuchsinophilic bundles. All kinds of supporting tissues combined with each other without clear demarcation. Immunohistochemistry revealed strong reactivity for S‐100 of chondrocytes, myxoid cells, and fat cells. Chondrocytes and myxoid cells also stained for glial fibrillary acidic protein, neurofilament protein 200, and neuron specific enolase. During development, condensation of mesenchymal cells indicated the blastema of the EC at gestation day 40. At day 60, delicate collagen fibrils indicated the futuretunica albuginea, faint alcianophilia was noted in the ground substance, and multilocular fat cells were scattered throughout the blastema. At birth, alcianophilia was moderate and multilocular fat cells were numerous. Three weeks after birth, single and grouped unilocular fat cells were seen, alcianophilia of ground substance was prominent, and former blastema cells presented as ramified myxoid cells. Eight weeks after birth, the EC primarily consisted of myxoid tissue, but the first islets of cartilage were seen in the center of myxoid areas. Unilocular fat cells already formed lobules.Conclusions: These results show that in the cat EC a) differentiation of adipocytes precedes differentiation of all the other tissue components, and b) differentiation of myxoid tissue precedes differentiation of cartilage. It is concluded that myxoid tissue may serve as a precursor of fibrous and elastic cartilage. © 1995 Wiley‐L

ISSN:0003-276X    

DOI:10.1002/ar.1092420405

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: The m. supraspinatus stabilizes the shoulder joint to bear the body weight, and the m. infraspinatus assists in extension and flexion of the joint in sheep. Postural muscles have many SO myofibers, whereas locomotory muscles have numerous fast‐twitch myofibers. In sheep the distribution of myofiber types within the two muscles, necessary for a better understanding of postural function, remains to be clarified.Methods: Muscle samples were removed from the whole transverse sections of the dorsal, middle, and ventral compartments of the m. supraspinatus and m. infraspinatus of sheep. Myofibers were classified into FG, FOG, SO‐1, and SO‐2 myofibers by histochemical methods.Results: The distribution of SO myofibers changed more greatly in the m. supraspinatus (15.0–99.1%) than in the m. infraspinatus (24.5–62.3%). SO myofibers were concentrated markedly in the caudal and deep regions near the spine and fossa of the scapula in the m. supraspinatus and distributed more in the medial part than in the lateral part in the m. infraspinatus. Such changes were caused by increases in percentage of SO‐2 myofibers and not SO‐1 myofibers. The craniolateral regions of the m. supraspinatus and the caudolateral regions of the m. infraspinatus had many fast‐twitch (FOG plus FG) myofibers suited for rapid extension and flexion of the shoulder joint.Conclusions: The m. supraspinatus has the compartmentalized, deep, and caudal regions occupied by SO myofibers, which seem to be specialized for maintenance of the joint extension. The medial region of the m. infraspinatus may assist in the joint stabilization. © 1995

ISSN:0003-276X    

DOI:10.1002/ar.1092420406

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: Elephants are an important and isolated order. Their kidneys need substantial investigation and hitherto have not been portrayed even by a pyelogram.Methods: Pyelograms and injection of vessels with colored acrylic emulsions were done initially. Dissection was under fiberoptics using a dissecting microscope with frequent measurements. Special areas were cut for microscopy (light and electron) and photography. Glomerular counts were done by macerating weighed pieces of cortex and later finding the cortical fraction of the renal parenchyma.Results: The elephant kidney is devoid of dorsoventral symmetry. It is composed of 8 ± 2 lobes separated by fine interlobar septa. There is no reduction of lobes with maturity. The pelvis bifurcates at the sinus into primary branches or infundibula which dispatch a secondary branch or infundibulum into every lobe. Interlobar arteries and veins, nerves, fat, and connective tissue generally accompany every secondary infundibulum into its lobe. A major branch of the renal artery may perforate the renal capsule and course to the cortico‐medullary (C‐M) border independently of the secondary infundibulum to that lobe.The number of glomeruli per kidney is approximately 15 × 106. In adults the glomerular mass is 4.9 ± 0.5% of the renal parenchyma and 6.7 ± 0.3% of the cortex. Areae cribrosae occur generally at low papillae. They are the outlets of numerous terminal collecting ducts which may be accompanied by a tubus maximus (T.M.) A T.M. of diameter 1.6 mm and length 10 mm may act as the only substitute for an area cribrosa.Wide anastomoses between the two main renal veins occur within the renal sinus. Intralobar arteries and veins often course right through the outer medulla to and from, respectively, the C‐M border.Conclusions: Anatomically, an elephant's kidneys appear to be able to concentrate urine only moderately. Their kidneys tend to resemble those of the manatee but not of the dugong. © 1995 Wiley

ISSN:0003-276X    

DOI:10.1002/ar.1092420407

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: In the present study, principal cells of the intermediate zone of the epididymis, an area situated between the initial segment and proximal caput, were observed to present morphological features distinct from those of principal cells of other regions.Methods: The epididymides of adult rats were fixed by perfusion with glutaraldehyde and embedded in Epon. Administration of fluid phase tracers was performed in the case of several animals. Localization of anti‐SGP‐2 and anti‐immobilin antibodies in conjunction with light (LM) and electron (EM) microscope immunocytochemistry was also performed.Results: In the LM and EM, the most distinctive feature of many principal cells of this zone was the presence of apically located vacuoles referred to as giant endosomes due to their large size and because they readily incorporated tracers introduced into the lumen of the epididymal duct and were acid phosphatase‐negative, Giant endosomes, containing electron‐dense granular patches, appeared to form by the progressive fusion of small, medium, and large endosomes. In the supranuclear region, multivesicular bodies (MVBs) and lysosomes were present. Although smaller in size than the giant endosomes, MVBs and lysosomes contained the electron‐dense patches. It is suggested from morphological images that giant endosomes fragment into smaller units corresponding to MVBs which gradually transform into lysosomes. Experiments using anti‐SGP‐2 and anti‐immobilin antibodies revealed gold particles over the Golgi apparatus and secretory vesicles (150–300 nm) of principal cells of this zone as well as the luminal contents indicative of secretion of these proteins. Interestingly, giant endosomes were also immunolabeled with both antibodies as were stereocilia, coated pits and vesicles, and endosomes of various sizes; lysosomes were minimally labeled. These results suggest that principal cells of the intermediate zone endocytose as well as secrete SGP‐2 and immobilin. The internalized SGP‐2 and immobilin may correspond to that secreted further upstream and that, possibly due to their short half‐life and terminated function, are removed from the lumen of the duct. Principal cells of this zone secrete these proteins possibly to replenish that lost by endocytosis.Conclusions: Principal cells of the intermediate zone contain giant endosomes. The presence of such large structures suggests that the early events in endocytosis is a slower process in principal cells of this zone as compared to other regions. The fact that these cells both secrete and endocytose SGP‐2 and immobilin adds to the complexity of our understanding of how principal cells function along the length of the epididy

ISSN:0003-276X    

DOI:10.1002/ar.1092420408

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: Pulmonary lymphatics are critical to clearing lung fluid. Although their structure can be shown with light and transmission electron microscopy, scanning electron microscopy of their casts can better show their number, size, shape, distribution, and degree of filling. This technique has identified four forms of lung lymphatics, but these forms have not been fully evaluated by tissue microscopy. A most important site of pulmonary edema formation, the pulmonary capillary, is just upstream from small veins which have focal, smooth muscle tufts termedvenous sphincters. Because of their constricting potential, these sphincters may control lung perfusion and cause edema.Methods: With light and transmission electron microscopy of tissue and scanning electron microscopy of casts, the lymphatic forms were explored in relation to the tissue anatomy in rats without pulmonary edema and with mild‐to‐moderate edema caused by extended vascular rinsing.Results: The edematous lungs had increased sacculo‐tubular lymphatics adjacent to the venous sphincters. These lymphatics were in the adventitial connective tissue and were partially endothelialized. As lymphatics became more tubular their endothelium became more complete. Collagen fibers traversed the lumen of these lymphatics even where endothelial cells were present and caused the lines on the surface of the lymphatic casts. Overlapping endothelial cells caused clefts on the casts.Conclusions: Scanning electron microscopy of lymphatic casts better defines their ultrastructure and shows the spatial relationship of veins and their sphincters to venous lymphatics. Sphincter contraction may influence pulmonary lymph production which could affect other aspects of regional lung perfusion. © 1995 Wiley‐L

ISSN:0003-276X    

DOI:10.1002/ar.1092420409

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: Interendothelial tight junctions and gap junctions have been described in large blood vessels and in cultures of endothelium derived from large blood vessels. Transfer of microinjected smallmolecular weight tracers between adjacent endothelial cells also has been demonstrated indicating the presence of gap junctional interendothelial communication. Similar transfer of tracers is evident between microvessel endothelial cells in culture and in microvessels in situ. However, gap junctions have not been detectable by electron microscopy of intact capillary systems. This may be due to limited sampling available in diffuse capillary systems and a small area of overlap between adjacent endothelial membranes.Methods: Thin slices of the parallel, tightly packed capillary bed of the eel rete mirabile were cryofixed and prepared for conventional TEM by freeze substitution. Other samples were freeze‐fractured and replicated for examination of endothelial junctional components.Results: A novel tight‐gap junctional complex between rete capillary endothelial cells is described. In freeze‐fracture replicas of the membrane P face, rows of gap junction subunits are flanked on either side by linear depressions representing grooves previously occupied by tight junctional strands that partition to the E face. In thin sections, the junctions appear in profile as short lengths of closely apposed membranes characteristic of gap junctions.Conclusions: The tight junctional components imply a barrier to paracellular transport across the capillary wall between the endothelial cells. The gap junctional component may provide a mechanism for communication between endothelial cells along the length of the vessel wall. © 1995 Wiley‐L

ISSN:0003-276X    

DOI:10.1002/ar.1092420410

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

年代:1995

数据来源: WILEY

摘要:

AbstractBackground: When examining the left atrial appendage by transesophageal echocardiography, differences in size and shape of the left atrial appendage are to be observed. The study was carried out with the aim of investigating the morphology of the left atrial appendage and to find associations with pathologic cardiac findings.Methods and results: In 220 cases (106 female, 114 male, mean age 72 ± 13 years) a cast of the left atrial appendage was made after the post mortem examination by using synthetic resin. In 198 cases an ECG was available (sinus rhythm n = 143, atrial fibrillation n = 55). The casts were described in respect to course and ramifications of the principal axis. The casts were measured concerning orifice diameters, outline, and volume. Most frequently (42%) the course of the principal axis was angulated below 100°. More than five ramifications of the principal axis were found in 56% of the casts. The volume ranged from 770–19,270 mm3(mean 5,220 ± 3,041). When comparing the clinical and autopsy‐data of the patients with the morphology of the casts, associations could be found between the volume of the casts and atrial fibrillation (7,060 mm3as compared to 4,645 mm3in sinus rhythm,P<0.01), left ventricular hypertrophy (5,740 mm3as compared to 4,639 mm3without hypertrophy,P<0.01), myocardial scars (5,923 mm3as compared to 4,891 mm3without scars,P<0.05), closed foramen ovale (5,515 mm3as compared to 4,037 mm3with patent foramen ovale,P<0.01), and left atrial appendage thrombi (8,566 mm3as compared to 5,027 mm3without thrombi,P<0.01).Conclusion: Left atrial appendages are formations greatly varying in volume and shape. This variability should be considered when interpreting images of the left atrial appendage, and in particular when diagnosing thrombi. © 1995 Wiley‐

ISSN:0003-276X    

DOI:10.1002/ar.1092420411

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

年代:1995

数据来源: WILEY