Erythropoiesis in the yolk sac of the bat Tadarida brasiliensis cynocephala

The process of erythropoiesis and vasculogenesis in the yolk sac of the bat (Tadarida brasiliensis cynocephala) has been studied through the use of both light and electron microscopy. Stem cells arise from the leading edge of the migrating splanchnic mesoderm and transform into primitive erythroblasts. Differentiation involves either contact or association with the endodermal cells, since all erythropoietic activity occurs on the endodermal side of the expanding vascular bed, and many of the cells are in close apposition to the lateral or basal plasma membranes of the endodermal cells. Endodermal cells also phagocytize developing primitive erythroblasts during the later stage of the process when erythropoiesis is subsiding in the yolk sac. Cells destined to become the endothelium of the expanding vascular bed also arise from the leading edge of the migrating splanchnic mesoderm. Their process of differentiation involves the development of cytoplasmic extensions that may surround a group of differentiating erythroblasts, enclosing them in the newly formed lumen of the blood vessel. The cytoplasmic extensions make contact and develop junctional complexes with similar processes from other cells to complete the lumen of the lengthening vascular bed. Cells of the granulocyte series or megakaryocytes are not observed in the yolk sac of the bat as has been described in certain other species.     

Erythropoiesis in the yolk sac of the bat Tadarida brasiliensis cynocephala.

The process of erythropoiesis and vasculogenesis in the yolk sac of the bat (Tadarida brasiliensis cynocephala) has been studied through the use of both light and electron microscopy. Stem cells arise from the leading edge of the migrating splanchnic mesoderm and transform into primitive erythroblasts. Differentiation involves either contact or association with the endodermal cells, since all erythropoietic activity occurs on the endodermal side of the expanding vascular bed, and many of the cells are in close apposition to the lateral or basal plasma membranes of the endodermal cells. Endodermal cells also phagocytize developing primitive erythroblasts during the later stage of the process when erythropoiesis is subsiding in the yolk sac. Cells destined to become the endothelium of the expanding vascular bed also arise from the leading edge of the migrating splanchnic mesoderm. Their process of differentiation involves the development of cytoplasmic extensions that may surround a group of differentiating erythroblasts, enclosing them in the newly formed lumen of the blood vessel. The cytoplasmic extensions make contact and develop junctional complexes with similar processes from other cells to complete the lumen of the lengthening vascular bed. Cells of the granulocyte series or megakaryocytes are not observed in the yolk sac of the bat as has been described in certain other species.     

Diurnal variations of the glycogen and fat stores in the liver and breast muscle of the insect bat, Tadarida nigeriae

A study of the glycogen and fat stores in the liver and breast muscle of the insect bat, Tadarida nigeriae was carried out in relation to their roosting and feeding behaviour. Glycogen concentration in the liver increased at mid-day but dropped precipitously in the evening. Muscle glycogen increased two-fold in the evening. Liver and muscle fat increased markedly at mid-day, but while liver fat dropped considerably in the evening, muscle rat remained unchanged. These results are discussed in comparison with those previously reported for the fruit bat, Eidolon helvum.     

Acarine infracommunities associated with the Mexican free-tailed bat, Tadarida brasiliensis mexicana (Chiroptera: Molossidae) in arid regions of Mexico

The Mexican free-tailed bat, Tadarida brasiliensis mexicana, is one of the most widely distributed bats, and its range includes the whole Mexican territory. Ectoparasites of this bat have been the subject of isolated reports, but no studies of its community ecology have been conducted. The acarine infracommunities associated with this bat were analyzed, comparing bat populations from three arid regions of Mexico: an abandoned factory in Nombre de Dios, Durango; a cave in Santiago, Nuevo León; and a church in Concepción del Oro, Zacatecas. The acarine infracommunity in Nuevo Le6n's bats exhibited the highest levels of diversity as reflected by a higher richness, a lower dominance, and a moderate and relatively homogeneous abundance in this locality in relation to the other two. This pattern is influenced by stable cave conditions relative to artificial habitats. Notwithstanding, further studies are required to determine whether or not different habitat conditions are a primary factor in the process of structuring the acari infracommunities.     

Uptake and storage of thorotrast by the rodent yolk sac placenta: An electron microscopic study

Electron microscopy was used to investigate the uptake and storage of electrondense particulate matter by the rodent yolk sac placenta. Pregnant hamsters were given single intra-uterine injections of Thorotrast on day 13, 14 or 15 of gestation and killed at intervals between 15 minutes and 48 hours thereafter. Electron microscopic examination of yolk sacs removed from the injected animals revealed the rapid and progressive uptake of the tracer particles by the visceral epithelial cells of these fetal membranes. Pinocytic vacuoles (phagosomes) containing Thorotrast were visible in the apical cytoplasm of epithelial cells as early as 15 minutes after injection and became increasingly abundant in these cells at later post-injection intervals up to 18 hours. Epithelial cells which became fully engorged with Thorotrast vacuoles exhibited various pathologic changes, possibly caused by the interference of the metabolically inert metal particles with intracellular digestive mechanisms (the lysosome system). There was no evidence, however, of transport of Thorotrast particles through or between the yolk sac epithelial cells. The connective tissue spaces and blood vessels of the yolk sac, as well as underlying fetal compartments, were free of the tracer particles at all observed intervals after injection.     

Differentiation of the embryonic disc,amnion, and yolk sac in the rhesus monkey

The inner cell mass of the blastocyst has differentiated into epiblast and hypoblast (primitive endoderm) prior to implantation. Since endoderm cells extend beyond the epiblast, it can be considered that both parietal and visceral endoderm are present. At implantation, epiblast cells begin to show marked evidence of polarity. They form a spherical aggregate with their basal ends toward the basal lamina and apical ends toward the interior. The potential for an internal space is formed by this change in polarity of the cells. No cytological evidence of separation of those cells that will form amniotic epithelium from the rest of the epiblast is seen until a cavity begins to form. The amniotic epithelium is originally contiguous with overlying cytotrophoblast, and a diverticulum remains in this position during early development. Epiblast forms a pseudostratified columnar epithelium, but dividing cells are situated toward the amniotic cavity rather than basally. The first evidence of a trilaminar disc occurs when a strand of cells contiguous with epiblast is found extending toward visceral endoderm. These presumptive mesoderm cells are undifferentiated, whereas extraembryonic mesoderm cells are already a distinct population forming extracellular materials. After implantation, visceral endoderm cells proliferate forming an irregular layer one to three cells thick. Visceral endoderm cells have smooth apical surfaces, but very irregular basal surfaces, and no basal lamina. At the margins of the disc, visceral endoderm is continuous with parietal endoderm and reflects back over the apices of the marginal visceral endoderm cells. This sacculation by visceral endoderm cells precedes pinching off of the secondary yolk sac from the remaining primary yolk sac.     

Morphology and histogenesis of yolk sac tumors in the testis

The differentiation of yolk sac tumor cells was similar to the processes of development of embryonic and extraembryonic endoderm during the first 7 wk after cleavage. Two ways of yolk sac tumor histogenesis are discussed: differentiation of embryonal carcinoma cells, and redifferentiation of the polypotent undifferentiated anaplastic seminoma cells. Histogenesis features described may be responsible for aggressive nature and high malignancy of yolk sac tumors.     

Evidence for the transformation of seminoma to yolk sac tumor, with histogenetic considerations.

Recent ultrastructural, cytogenetic, and ploidy analyses indicate that seminoma acts as a precursor from which other forms of testicular germ cell tumor may originate. Ten cases of primary or metastatic testicular germ cell tumors were investigated that showed possible transformation of seminoma to yolk sac tumor. Such transformation was identified in six cases in which foci of abrupt change from seminoma to various patterns of yolk sac tumor occurred, often at the periphery of otherwise pure lobules of seminoma. Immunostains for cytokeratins, placental-like alkaline phosphatase, and alpha-fetoprotein demonstrated the expected changes in reactivity at the foci of such transformation. Four additional cases were regarded as either seminomas with artifactual microcystic change or the close association of seminoma and yolk sac tumor but lacking evidence for transformation. These data support the theory that seminoma is not an "endpoint" neoplasm but may serve a precursor role in the progression to nonseminomatous germ cell tumors.     

Development, differentiation, and maturation of fetal mouse yolk sac macrophages in cultures

The development and differentiation of macrophages in the fetal mouse yolk sac were studied morphologically in four different culture experiments. In the culture of mouse embryos with yolk sac, the development of fetal macrophages was demonstrated to precede that of promonocytes and monocytes in the yolk sac. In vitro differentiation of the fetal macrophages was consistent with the results of our previous in vivo observation indicating that fetal macrophages were differentiated from primitive macrophages, but not from the monocytic cell series. Differentiation of primitive macrophages into fetal macrophages, before the development of promonocytes and monocytes, was reproduced in the culture of cell suspensions from the fetal mouse yolk sacs, with a mouse bone marrow stromal cell clone (ST2) particularly with those at 8 days of gestation. In the soft agar or liquid culture of yolk sac cells with LP3-conditioned medium, monocyte-macrophage colonies were effectively induced, but not fetal macrophage colonies. The results provide evidence for the existence, in yolk sac hematopoiesis, of two distinct macrophage populations: a fetal macrophage population and a monocyte-derived macrophage population. The data indicate an obvious difference in development and differentiation between the two populations and the temporal precedence of fetal macrophages appearing before monocyte-macrophages.     

A new lipid storage myopathy observed in individuals with the Ruvalcaba-Myhre-Smith syndrome

Four patients with the Ruvalcaba-Myhre-Smith syndrome (primary macrocephaly with associated anomalies including pigmented macules on the penis in affected males, hamartomatous intestinal polyps, and lipomas) had evidence of delayed psychomotor development and/or hypotonia in childhood. Electromyography in 3 patients showed evidence of a myopathic process. Muscle biopsy in all four demonstrated a lipid storage myopathy with increased numbers of neutral lipid droplets--predominatly in type 1 fibers. The type 2 fibers were consistently smaller than expected. Electron microscopy was unremarkable except for evidence of lipid accumulation. Muscle carnitine and carnitine palmityl transferase levels were normal in one patient. This appears to be a previously unreported type of lipid storage myopathy characteristic of the Ruvalcaba-Myhre-Smith syndrome, a probable autosomal dominant trait.     

The permeability of the guinea pig parietal yolk sac placenta to peroxidase and ferritin

The permeability of the guinea pig parietal yolk sac placenta late in gestation was investigated by means of electron microscopy using the tracer proteins ferritin and peroxidase. The parietal yolk sac consists of a layer of trophoblast, a thick extracellular lamina (Reichert's membrane) and a layer of endoderm. After injection into the maternal vascular system, the proteins crossed the trophoblast by means of small pinocytotic vesicles. Both proteins readily permeated Reichert's membrane and then moved by an intercellular pathway between endoderm cells to reach the uterine lumen. After injection of ferritin into the uterine lumen, the protein was observed between endoderm cells and throughout Reichert's membrane. Presumably the marked permeability of the endodermal epithelium to the tracer molecules is due to the absence of zonulae occludentes around the endoderm cells. Parietal endoderm cells exhibited limited pinocytotic activity regardless of the site of injection. The results indicate that the parietal yolk sac placenta of the guinea pig is permeable to relatively large molecules and therefore it may be an important pathway in overall maternal-fetal exchange in this species.     

Freeze-fracture observations on the visceral yolk sac placenta of rats, mice and hamsters

Summary Freeze-fracture replicas of visceral yolk sac from rats, mice and hamsters in late stages of gestation were studied by electron microscopy. Special attention was directed toward determining the types of junctional specializations that exist between the columnar endoderm cells of this placental membrane. In all three species, well-developed, zonular tight (occluding) junctions were found on the contiguous lateral surfaces of the endoderm cells. The tight junctional network, located in an immediate subluminal position, was from 0.2–0.5 m in depth and consisted at any point of 2–5, interconnecting, 9 m wide, strands (P-face) or shallow furrows (E-face). Patch-like aggregations of irregular intramembrane particles, characteristic of desmosomes (maculae adherentes), also were observed at scattered sites below the tight junctions. However, no evidence of gap (communicating) junctions was encountered. The endoderm cells of the rodent visceral yolk sac have been shown to play a central role in the selective transport of macromolecular substances from the maternal to the fetal system. Tight junctions may be vital to this endodermal cell function by preventing random paracellular fluxes of macromolecules.This investigation was supported by U.S. National Institutes of Health Grant HD-09585     

Morphological and functional features of endodermal cells in rat yolk sac, with special reference to the fetal macrophage differentiation

Morphological and functional features of the yolk sac endodermal cells with special reference to the fetal macrophage differentiation were investigated morphologically under the light and electron microscopes and immunologically with the antigen phenotypic analysis and the phagocytic activity-test, using the syngeneic DA rat-embryos from 8 to 16 days of gestation. Based on the staining property with toluidin blue and the ultrastructural features, the endodermal layer from day 8 to 16-yolk sacs has been known to consist of two kinds of cell type; 10% "clear" cells with clear cytoplasm and 90% "dark" cells with dark cytoplasm. Numerous primary lysosomes, phagolysosomes, lipid droplets and coated vesicles distributed preferentially in the supranuclear portion of endodermal cells. A broad intercellular space was found between "clear" cells and "dark" cells, indicating the loose intercellular binding. It was often found that "clear" cells tend to migrate from the endodermal layer into the mesenchymal layer, where the poor development of basement membrane was seen between them. Cells phagocytosing red blood cells, that resemble morphologically "clear" cells, were also observed in the fetal liver. At ten hours after latex-injection into the yolk sac cavity of 14 days embryos, some cells which phagocytosed latex beads in their cytoplasm were found in the endodermal layer, and also in the liver tissue and loose connective tissue of fetus. These cells were stained positively with monoclonal antibody Mar3 which recognizes preferentially rat-mononuclear phagocyte system. In vitro-latex uptake of separated endodermal cells was also demonstrated by the culture-study of endodermal cell suspension. The present findings indicate that the yolk sac-endodermal layer derived from the proximal endoderm consists of at least two kinds of cell-population with a great similarity to tissue macrophages in morphological and functional senses, and support the concept that some cell-populations of endodermal layer may migrate into fetal tissue and are closely related to the differentiation of fetal macrophages and their precursors.