Embryonic and post-embryonic development of the parietal and visceral peritoneum in white mice]

Light and electron microscopy were used in order to investigate histogenesis of the parietal and visceral peritoneum of white mice in embryonic and postembryonic periods of development. Four periods were distinguished, during which gradual differentiation of the primordium material into tissue structures (mesothelium and the connective tissue) of the peritoneum were observed. Asynchronous differentiation of the mesothelium as well as certain correlation in the degree of differentiation of mesothelial and mesenchymal cells took place at all stages of the embryonic and postembryonic development. More differentiated cells of prolonged shape were predominant in the mesenchyma even at early stages (11 days) in those portions where the lining of the secondary cavity of the body resembled mesothelim in its structure.     

Reactive growth of the mesothelium of the parietal leaf of the peritoneum]

In the process of reparative regeneration of the mesothelium caused by suturing of a portion of the jugular vein into the peritoneum defect the inflammatory mesothelial growings are formed. They have different configuration, consist only of the mesotheliumor the connective tissue covered with the mesothelium and are observed from the 4th day till 3 months after operation, being always faced to the abdominal cavity. The capacity of mesothelial cells to high mitotic activity and wedging out from the layer underlies the formation of posttraumatic structures of the mesothelium.     

A morphologic and histochemical study of the mesentery in the guinea pig

The guinea pig mesentery is a uniform, continuous, thin (18 micron) sheet of connective tissue covered by a single layer of flattened mesothelial cells on both surfaces. Tight and gap junctions provide for cell-to-cell adhesion among mesothelial cells. These cells possess numerous micropinocytotic vesicles; a conspicuous basal lamina separates the mesothelium from the underlying connective tissue. Most of the material found between the two serous coverings consisted of a three-dimensional meshwork of abundant collagenous fibers intermingled with a sparse net of very thin (0.4 micron) elastic fibers. Two distinct populations of collagen fibrils are segregated into different compartments of the mesentery. One population is formed of thick (56 nm) fibrils which associate to form closely packed fibers. The second population, composed of loosely arranged thin (38 nm) fibrils which do not become assembled into fibers, is found underlying the basal lamina that separates the mesothelium from the connective tissue. These observations strongly suggest that the mesentery contains both collagens type I and type III. The guinea pig mesentery contains 6.8 mg of sulfated glycosaminoglycans/g dry weight. Most of these glycosaminoglycans (78%) were identified as dermatan sulfate, whilst the rest (22%) corresponded to heparan sulfate.     

Maternal topoisomerase II alpha, not topoisomerase II beta, enables embryonic development of zebrafish top2a -/- mutants

Background

Determining the type and source of cells involved in regenerative processes has been one of the most important goals of researchers in the field of regeneration biology. We have previously used several cellular markers to characterize the cells involved in the regeneration of the intestine in the sea cucumber Holothuria glaberrima.

Results

We have now obtained a monoclonal antibody that labels the mesothelium; the outer layer of the gut wall composed of peritoneocytes and myocytes. Using this antibody we studied the role of this tissue layer in the early stages of intestinal regeneration. We have now shown that the mesothelial cells of the mesentery, specifically the muscle component, undergo dedifferentiation from very early on in the regeneration process. Cell proliferation, on the other hand, increases much later, and mainly takes place in the mesothelium or coelomic epithelium of the regenerating intestinal rudiment. Moreover, we have found that the formation of the intestinal rudiment involves a novel regenerative mechanism where epithelial cells ingress into the connective tissue and acquire mesenchymal phenotypes.

Conclusions

Our results strongly suggest that the dedifferentiating mesothelium provides the initial source of cells for the formation of the intestinal rudiment. At later stages, cell proliferation supplies additional cells necessary for the increase in size of the regenerate. Our data also shows that the mechanism of epithelial to mesenchymal transition provides many of the connective tissue cells found in the regenerating intestine. These results present some new and important information as to the cellular basis of organ regeneration and in particular to the process of regeneration of visceral organs.     

Equivalent radius of paracellular "pores" of the mesothelium.

Diffusional permeability (P) to water (P(w)), Cl(-) (P(Cl(-))), and mannitol (P(man)) was determined in specimens of rabbit parietal pericardium without and with phospholipids added on the luminal side, as previously done with sucrose and Na(+). P to the above-mentioned molecules and to Na(+) (P(Na(+))) was also determined after mesothelium was scraped away from specimens. P(w), P(Cl(-)), P(Na(+)), and P(man) of connective tissue were the following (x10(-5) cm/s): 73.1 +/- 7.3 (SE), 59.5 +/- 4.5, 41.7 +/- 3.4, and 23.4 +/- 2.4, respectively. From these and corresponding data on integer pericardium, P(w), P(Cl(-)), P(Na(+)), and P(man) of mesothelium were computed. They were the following: 206, 17.9, 9.52, and 3.93, and 90.2, 14.4, 4.34, and 1.75 x 10(-5) cm/s without and with phospholipids, respectively. As previously found for P to sucrose, P to solutes is smaller in mesothelium than in connective tissue, although the latter is approximately 35-fold thicker; instead, P(w) is higher in mesothelium, suggesting marked water diffusion through cell membrane. Equivalent radius of paracellular "pores" of mesothelium was computed with two approaches, disregarding P(w). The former, a graphical analysis on a P-molecular radius diagram, yielded 6.0 and 1.7 nm without and with phospholipids, respectively. The latter, on the basis of P(man), P to sucrose, and function for restricted diffusion, yielded 7.8 and 1. 1 nm, respectively.     

Ultrastructure of the somatic portion of the gonads in asteroids,with emphasis on flagellated-collar cells and nutrient transport

Somatic portions of gonads in two phanerozonian sea-stars, Ctenodiscus crispatus and Hippasteria phrygiana, were similar in all aspects of gross structure and histology seen previously in both forcipulate and spinulosan asteroids. For the first time, detailed ultrastructural observations have been made of cells and tissues that reveal several features believed to be of universal occurrence in the gonads of asteroids. These include flagellated-collar cells in the visceral peritoneum and other coelomically derived epithelia, muscular-flagellated-collar cells in the visceral peritoneum and genital coelomic (perihaemal) sinus, the digestion of collagen fibers by cells in the connective tissue layer, and the intimate relationship of the genital haemal sinus and the entire germinal epithelium. Structural and functional compartmentalization are discussed in relation to major activities of the gonad throughout the annual reproductive cycle. The distinctive ultrastructure and current generation of flagellated-collar cells found in the visceral peritoneum are analyzed relative to their role in nutrient transport to gonadal tissues. The single flagellum of each flagellated-collar cell beats in coordination with those on neighboring cells to produce extremely rapid, oriented currents of coelomic fluid. The form of beating in an individual flagellum is planar, and the resulting synchronized activity of many adjacent flagella is non-metachronal; both of these characteristic aspects of current production have, thus far, been encountered together only in the Echinodermata. Flagellated-collar cells are efficient in generating currents which mix contents of the coelomic fluid, and they can presumably supply themselves with nutrients. It is concluded that nutrients so obtained are generally not passed through the wall of the gonad to the germinal epithelium and, as a result, have little to do with nutrition of somatic and germinal cells of the germinal epithelium. Alternatively, well-developed genital portions of the haemal system of the sea-star are advanced as the major channels supplying nutrients to germinal epithelia during gametogenesis.     

Location and identification of the collagen found in the 14.5-d rat embryo visceral yolk sac

The collagens associated with 14.5-d rat visceral yolk sacs were localized and identified by a variety of procedures. Morphological examination showed that both the visceral epithelium and mesothelium rested upon thin basement membranes, whereas the majority of the extracellular matrix consisted of a stroma containing occasional cells and abundant banded fibrils. Immunohistochemistry at the electron microscope level showed that the basement membranes specifically cross- reacted with antibodies directed against mouse basement membrane components, whereas the stroma specifically cross-reacted with antibodies directed against rat type I collagen. Extractions of acellular visceral yolk sacs and subsequent analyses showed that type I collagen components were prevalent. Furthermore, in vitro biosynthetic studies showed only the presence of type I procollagen components (or their conversion products) and alpha-fetoprotein. These findings, taken together with our previous studies on the 14.5-d rat parietal yolk sac, provide us with protein markers for studying the origin of cells in rat parietovisceral yolk sac carcinomas.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Ultrastructural aspects of and observations on the permeability of the rat mesentery to colloidal iron

In works already published, it was made clear that many researches were interested in the absorption phenomena, permeability and structure of the visceral mesothelial tissue. Attention was concentrated on the mesentery and observations were made using the application of lanthanum nitrate and osmium-amine. The penetration of lanthanum nitrate is impeded by the basement membrane situated between the connective and mesothelial tissues. The heavy salt moves through and not between the mesothelial cells by passive diffusion. No reaction was observed in general with osmium-amine, with the exception of a few cases. In those instances, the osmium-amine reacted not only in the outer surface of the mesentery, but also penetrated with no visible reaction all the way to the connective tissue where it was detected in the elastic layer. In this paper, the colloidal iron was employed using different techniques, and depositions were detected in the surface of the mesentery, in the mesothelial cells and also in the connective tissue. A final conclusion that the permeability of different layers of tissues is of great variety and has a definite capacity for selectivity is suggested.     

Organization of cell junctions in the peritoneal mesothelium

Intercellular junctions in the mesothelium of the visceral (mesentery and omentum), and parietal (diaphragm, pre-aortic, and iliac region) peritoneum were examined in rats and mice by using freeze-cleaved preparations. In addition to usual intercellular junctions (cell body junctions), special junctions are found between cell processes and the surface of the neighboring cell (cell process junctions). Cell body junctions are provided with tight junctions and communicating (gap) junctions. The former consist of one to two junctional strands which show a characteristic staggered arrangement, and focal discontinuities. In cell process junctions, the strands form loops or appear as short, free-ending elements; their polymorphism suggests considerable lability, probably in connection with their assembly and disassembly. The existence of free-ending strands indicates that such structures can be used as attachment devices without being concomitantly involved in the formation of occluding zonules. In both types of junctions, the strands can be resolved into bars, approximately 80- 100nm long, frequently provided with terminal enlargements and intercalated particles which occur singly or in small clusters. These particles are morphologically similar to those present in communicating (gap) junctions. The mesothelium is also provided with isolate composite macular junctions. Throughout the mesothelium, the cleavage plane follows the outer contour of junctional strands and particles, suggesting that strand-to-strand interactions in the apposed membranes are weaker than interactions between each strand and underlying cytoplasmic structures. In their general geometry and cleavage characteristics, the mesothelial junctions resemble the junctions found in the venular endothelium.     

Morphofunctional characteristics of the skin of newborn rat pups with prenatal exposure to desoxycorticosterone acetate

Desoxycorticosterone acetate (DOCA) was injected intramuscularly to pregnant rats at the III, or II-III trimester of pregnancy. By the end of pregnancy with increasing body mass of the female rats, the hormonal dosage dropped. The newborn rat skin was studied. The prenatal effect of DOCA resulted in thinning the epidermis, the decreasing dosage in certain activation of the epithelial proliferative activity and in appearance of foci of its hyperplasia. The hormone in the dose 0.8-1.0 mcg/100 g of the body mass activates the proliferative ability of fibroblasts, elevates the quantity of tissue basophils, increases secretory activity of both of them; this produces thickening of the derm. In the microvessels morphofunctional activity of endothelium increases, in the basal membrane contents of PAS-positive substances drop, the wall is often infiltrated with lymphocytes. Correlations between the cells and other structural components of the skin intensify. When the dose of DOCA increases and the time of the injection is short, the proliferative and secretory activity of fibroblasts is inhibited, but morphofunctional properties of the tissue basophils are stimulated. Congestive phenomena develop in the microvessels, mitotic activity of endotheliocytes is inhibited, in the basal membrane amount of the PAS-positive substances sharply decreases, perivascular edema develops in the connective tissue. Weakening or imbalance of the correlations is observed.     

Comparative permeability of canine visceral and parietal pleura

To determine the permeability of canine pleural mesothelium, visceral and intercostal parietal pleura from mongrel dogs was carefully stripped from the underlying tissue and mounted as a planar sheet in a Ussing-type chamber. The hydraulic conductivity (Lp) was determined from the rate of volume flux in response to hydrostatic pressure gradients applied to either the mucosal or serosal surface of the pleural membrane. The diffusional permeability (Pd) of radiolabeled water, sucrose, inulin, and albumin was determined under equilibrium conditions from the unidirectional tracer flux. The Lp of the visceral pleura was 0.39 +/- 0.032 (SE) X 10(-4) ml.s-1.cmH2O-1.cm-2 and that Lp of parietal pleura was 1.93 +/- 0.93 X 10(-4) ml.s-1.cmH2O-1.cm-2 (P less than 0.001). The Pd of the visceral pleura ranged from 12.21 +/- 0.45 X 10(-4) cm/s for 3H2O to 0.34 +/- 0.03 X 10(-4) cm/s for [3H]albumin. The Pd of the parietal pleura for water and sucrose was similar to that of the visceral membrane, whereas its Pd for the larger inulin and albumin molecules was greater than that of visceral pleura (P less than 0.01). A spontaneous potential difference could not be detected across either membrane. The relatively higher parietal pleural Lp and Pd for larger solutes is probably due to the presence of stomata in this membrane. These results indicate that both the parietal and the visceral pleura are extremely permeable tissues which offer little resistance to water and solute flux.     

Effect of the time of the day when the lesion was produced on the course of mesothelial proliferation

The course of mitotic activity in the rabbit mesothelium of parietal peritoneum was studied depending upon the daytime when the lesion was produced. In the first series of experiments (I) the operation was performed from 8 to 10 a. m., and in the second series (II) - from 8 to 10 P. M. After the operation the animals were sacrifieced: one animal every 3 h during 5 days. Mitotic activity was investigated along 13 mm from the edge of the wound in flat film preparations. The data obtained were statistically treated applying approximation of the process course by the method of weighed sliding averages. The first mesothelial mitoses appeared: in the first series (I) of experiments - in 24 h, in the second series (II) of experiments - 21 h. Further, proliferation of the mesothelium appeared in different parts of the tissue with various intencity and was of wavy character. Regardless of the time when the lesion was produced, mitotic activity was the greatest in the first zone, 4.8 mm wide its maximum 33 h after the operation. The character of the regenerative process in the mesothelium depends on the circadian phase of the organism at the time of the operation, that influences the time when mitotic activity begins, its quantitative indices, the area of the tissue involving into the reaction, expressiveness of the rhythmicity of the process. During 5 days, in the II series of experiments three waves were noted, and in the I series - five waves were noted and their periods were near the diurnal.     

Postnatal development of the ovarian bursa of the golden hamster (Mesocricetus auratus): its complete closure and morphogenesis of lymphatic stomata

The golden hamster ovarian bursa was studied by light and electron microscopy to clarify the process of its complete closure and the development of lymphatics that leads to morphogenesis of stomata. The results were as follows. 1) The bursa completely closed at 9 days of age primarily due to development of the mesotubarium superius. 2) With the closure, the ovary and bursa became closely apposed, and most of the original bursal cavity disappeared. 3) Between 9 and 12 days of age U-shaped folds of the bursal mesothelium began to invade the connective tissue of the bursa. 4) Widening of the internal angle of the U-shaped folds contributed to reappearance of the bursal cavity, and thus separation of the bursa from the ovary. It also contributed to future geometrical proximity of lymphatics to the cavity of the bursa. 5) The separation of the bursa from the ovary began as early as 12 days of age in the cephalic half of the bursa. It occurred remarkably late in the caudal half. Juxtaposition of the window portion of the bursa to the ovary remained in some adult animals. 6) Development of lymphatics in the cephalic half of the bursa was divided into two stages, before and after days 21-24 of life. In the first stage, lymphatics grew in the submesothelial connective tissue, and the framework of lymphatics was formed. In the second stage, lymphatics extended small branches to form the submesothelial plexus or lymphatic lacuna. 7) Intercellular junctions between contiguous lymphatic endothelial cells were mostly tight and desmosomelike. Open junctions were, if they occurred at all, rare. (8) A smooth-surfaced area lined with the lymphatic endothelium was found in the bursa on day 27 of life, before the initiation of ovulation. Valvelike stomal orifices were absent before the initiation of ovulation and extremely rare even after the first ovulation. They were commonly present in the bursae after the fourth ovulation, however. The process of complete closure of the ovarian bursa is very complex and may be related to the later development of the bursal mesothelium and lymphatics. Some liplike stomal orifices are of purely developmental origin. However, all valvelike stomal orifices are assumed to be formed as a result of damage to the bursal mesothelium, as well as to the submesothelial connective tissue and lymphatics, by repetition of ovulation. It is possible that liplike stomal orifices may be formed in the process of repairing the damage.     

Behaviour of a New Composite Mesh for the Repair of Full-Thickness Abdominal Wall Defects in a Rabbit Model

Introduction

Composite biomaterials designed for the repair of abdominal wall defects are composed of a mesh component and a laminar barrier in contact with the visceral peritoneum. This study assesses the behaviour of a new composite mesh by comparing it with two latest-generation composites currently used in clinical practice.

Methods

Defects (7x5cm) created in the anterior abdominal wall of New Zealand White rabbits were repaired using a polypropylene mesh and the composites: Physiomesh^TM; Ventralight^TM and a new composite mesh with a three-dimensional macroporous polyester structure and an oxidized collagen/chitosan barrier. Animals were sacrificed on days 14 and 90 postimplant. Specimens were processed to determine host tissue incorporation, gene/protein expression of neo-collagens (RT-PCR/immunofluorescence), macrophage response (RAM-11-immunolabelling) and biomechanical resistance. On postoperative days 7/14, each animal was examined laparoscopically to quantify adhesions between the visceral peritoneum and implant.

Results

The new composite mesh showed the lowest incidence of seroma in the short term. At each time point, the mesh surface covered with adhesions was greater in controls than composites. By day 14, the implants were fully infiltrated by a loose connective tissue that became denser over time. At 90 days, the peritoneal mesh surface was lined with a stable mesothelium. The new composite mesh induced more rapid tissue maturation than Physiomesh^TM, giving rise to a neoformed tissue containing more type I collagen. In Ventralight^TM the macrophage reaction was intense and significantly greater than the other composites at both follow-up times. Tensile strengths were similar for each biomaterial.

Conclusions

All composites showed optimal peritoneal behaviour, inducing good peritoneal regeneration and scarce postoperative adhesion formation. A greater foreign body reaction was observed for Ventralight^TM. All composites induced good collagen deposition accompanied by optimal tensile strength. The three-dimensional macroporous structure of the new composite mesh may promote rapid tissue regeneration within the mesh.     

The ultrastructure of the peritoneal membrane in chronically dialysed rats with spontaneous peritonitis: preliminary observations

In this paper we describe ultrastructure of the peritoneal membrane from single peritoneal biopsies collected from chronically dialysed rats with spontaneous peritonitis. The results were compared with those obtained in chronically dialysed animals without peritonitis. In rats with peritonitis, peritoneum was much thicker than in peritonitis-free animals. The increased thickness of the peritoneum during peritonitis was due to infiltration of the submesothelial tissue with oedematous fluid and to the presence of huge amount of cells in the stroma. The connective tissue cells were accumulated just underneath the peritoneal surface. In deeper parts of the interstitium, infiltrating acute inflammatory cells were present (lymphocytes, polymorphonuclear cells: neutrophils and eosinophils). Inversely, the increased thickness of the peritoneum in peritonitis-free animals was mainly due to enhanced amounts of collagen. Additionally, in rats with peritonitis, the surface was often denuded of mesothelial cells. The damaged mesothelial cells that detached from the peritoneal surface were also found. In conclusion, the morphological changes observed in rats with peritonitis are similar to those reported in humans, thus the model of peritonitis in dialysed rats can be used for the study of peritoneal remodeling during peritoneal dialysis complicated by peritonitis.     

Evidence for matrotrophy in the viviparous sea cucumber Leptosynapta clarki: A role for the genital haemal sinus?

Summary

Viviparity, where the embryos develop in the female reproductive system, is a rare form of reproduction in marine invertebrates, being described in only 14 species of echinoderm. In the intraovarian brooding sea cucumber, Leptosynapta clarki Heding 1928 (cf., Sewell et al. 1995), we used direct evidence (changes in energetic content) to show that significant additional nutrients are provided to the embryos during viviparous development (matrotrophy). In the transition from a structure used to produce gametes to a long-term brooding structure there are visual, histological and transmission electron microscopy (TEM) changes in the structure of the ovarian wall. Changes occur primarily in the cells of the visceral peritoneum and involve an increase in size of the connective tissue/genital haemal sinus (CT/GHS). In the latter part of the brooding period the visceral peritoneum returns to a flattened form, and new oocytes develop along the tubule wall. Similar changes in the intraovarian brooding sea cucumber Oneirophanta mutabilis affinis lead us to suggest that there is a role for the genital haemal sinus in providing nutrition during the brooding period in viviparous echinoderms. Future research is suggested to focus on changes in the ovarian wall structure during the different phases of reproduction (gamete production/brooding) in these species.     

Fine structure of the dorsal papillae in the holothurioid Holothuria forskali (Echinodermata)

The dorsal surface of the holothurioid Holothuria forskali bears several longitudinal rows of modified podia called papillae. Each papilla consists of a conical stem topped by an hemispherical bud. Their gross tissue stratification is the same all along the papilla being made up of four tissue layers, viz. an inner mesothelium, a connective tissue layer, a nerve plexus and an outer epidermis. The latter is differently organized according to whether it belongs to the stem or to the bud. The epidermis of the bud is built up by ciliated cells that intimately contact the nerve plexus and have the classical structure of echinoderm sensory cells. The papillae are thus sensory organs involved in mechanoreception and possibly chemoreception.     

Differences between basophils and mast cells: failure to detect Charcot-Leyden crystal protein (lysophospholipase) and eosinophil granule major basic protein in human mast cells

Human eosinophils contain several distinctive proteins including eosinophil granule MBP and the membrane-associated CLC protein (lysophospholipase). Human basophils also contain these proteins, indicating biochemical similarities between eosinophils and basophils. To determine whether MBP or CLC protein is present in connective tissue mast cells, we studied human lung and cutaneous mast cells by immunofluorescence by utilizing specific antibodies to CLC and MBP. Cytocentrifuge slides of enriched lung mast cells and mast cells in sections of formalin-fixed, paraffin-embedded cutaneous tissue from urticaria pigmentosa lesions were stained for CLC and MBP. Neither pulmonary nor cutaneous mast cells stained for CLC protein or MBP. In contrast, lung and cutaneous eosinophils in the same preparations showed bright staining for both proteins. The failure to find CLC protein and MBP in mast cells provides additional evidence of dissimilarity between mast cells and basophils, and an immunochemical means to distinguish between them.