Ultrastructural aspects of preglioma]

Investigation of submicroscopic changes in the astrocytes after the intracerebral injection of the carcinogen 9,10-dimethyl-1-2-benzanthracene suggested that the so-called substantial period of preglioma began from the 45th day of the experiment, when structurally atypical astrocytes appeared against the background of distrophic changes. The changes in the submicroscopic organization of the astrocytes during chemical carcinogenesis can be divided into three stages: 1) intracellular hyperplasia due to traumatic injury of the brain; 2) dystrophic changes connected with the vascular tissue disturbances and immediate action of the carcinogen on the tissue; 3) atypical ultrastructure reconstruction of the astrocytes.     

Differential cell affinity and sorting of anterior and posterior cells during outgrowth of recombinant avian limb buds

To examine the role of position-specific differences in cell-cell affinity, recombinant limb buds composed of dissociated and reaggregated cells derived from anterior (A) and posterior (P) limb bud fragments were analyzed. Dissociated anterior and/or posterior cells were differentially labeled, and their behavior was analyzed during recombinant limb bud outgrowth. We find that anterior and posterior cells sort out from one another to form alternating anterior and posterior stripes of cells that extend distally along the proximal-distal axis. These alternating stripes are prominent across the A/P axis in whole-mount preparations of recombinant limb buds after 48 h of outgrowth when the presumptive autopod is dorsal-ventrally flattened and digit rudiments are not evident. After 96 h, when digital and interdigital regions are clearly defined, we find evidence that A/P stripes do not follow obvious anatomical boundaries. The formation of A/P stripes is not inhibited by grafts of ZPA tissue, suggesting that polarizing activity does not influence cell-cell affinity early in limb outgrowth. In vitro studies provide evidence that cell sorting is not dependent on the limb bud ectoderm or the AER; however, cells sort out without organizing into stripes. Gene expression studies using anterior-specific (Alx-4) and posterior-specific (Shh, Bmp-2, and Hoxd-13) marker genes failed to reveal expression domains that corresponded to stripe formation. Control recombinant limb buds composed of anterior, central, or posterior mesenchyme formed digits in a position-specific manner. A/P recombinant limb buds that develop to later stages form digits that are characteristic of central recombinant limbs. These data provide the first definitive evidence of A/P cell sorting during limb outgrowth in vivo and suggest that differential cell affinities play a role in modulating cell behavior during distal outgrowth.     

F-Spondin, expressed in somite regions avoided by neural crest cells, mediates inhibition of distinct somite domains to neural crest migration

Neural crest (NC) cells migrate exclusively into the rostral half of each sclerotome, where they avoid the dermomyotome and the paranotochordal sclerotome. F-spondin is expressed in these inhibitory regions and throughout the caudal halves. In vitro bioassays of NC spreading on substrates of rostral or caudal epithelial-half somites (RS or CS, respectively) revealed that NC cells adopt on RS a fibroblastic morphology, whereas on CS they fail to flatten. F-spondin inhibited flattening of NC cells on RS. Conversely, F-spondin antibodies prevented rounding up of NC cells on CS. Addition of F-spondin to trunk explants inhibited NC migration into the sclerotome, and treatment of embryos with anti-F-spondin antibodies yielded migration into otherwise inhibitory sites. Thus, somite-derived F-spondin is an inhibitory signal involved in patterning the segmental migration of NC cells and their topographical segregation within the RS.     

Feather buds exert a polarizing activity when transplanted to chick limb buds

Homeoproteins have been shown to be expressed in a position-specific manner along the anterior-posterior axis in the developing chick feather bud, as seen also in the developing limb bud. These facts raise the possibility that there may be common mechanistic features in the establishment of the anterior-posterior polarity between both organs. In order to investigate this possibility, feather bud tissues were transplanted into the anterior region of limb buds to determine whether feather bud tissues possess properties such as the zone of polarizing activity of the limb bud. The manipulated limb bud formed a mirror image duplication of the skeletal elements, mainly (2)2234 digit pattern or sometimes 3(2)234. Both the anterior and posterior halves of feather bud tissue exhibited almost equal activity in inducing ectopic skeletal elements. Hox d-12 and Hox a-13 were expressed coordinately around the transplanted site of the operated limb bud. This secondary axis-inducing activity of the feather bud was enhanced when grafts were pretreated with trypsin. In contrast, the presumptive feather bud tissue and inter-feather bud tissue did not induce a secondary axis of the limb bud. These results suggest that the feather bud contains a region that exerts polarizing activity and that this region may play key roles in the formation of the anterior-posterior and, if it exists, proximal-distal axis of the feather bud, possibly via the regulation of region specific expression of Hox genes.     

Ultrastructural aspects of the goiter in cog/cog mice

Thyroids of congenitally goitrous (cog/cog) mice were studied with light and electron microscopy. The principal alteration in follicular cells was their largely overdistended rough endoplasmic reticulum (RER). Our findings resemble the ultrastructural features of human hypothyroid goiter caused by a thyroglobulin (TG) defect and thus support the previously suggested abnormalities of TG synthesis and/or processing in cog/cog mice.     

Ultrastructural aspects of Sertoli cells in infancy

In the present study some aspects of Sertoli cells of testicular-biopsy specimens of children from 0 to 8 years old are examined. We can distinguish two main morphological situations. In the first one, Sertoli cells with monomorphic aspect can be seen; in the second can be shown Sertoli cells with various aspects. In this polimorphic situation we can distinguish three Sertoli cell types differing in cellular shape, cytoplasme electron-density and amount of RER and Golgi complex.     

Anatomical aspects of the arteria inferior posterior cerebelli for posterior fossa surgery]

As the arteria inferior posterior cerebelli sometimes causes surprises of grave consequence at surgical approaches, its origin and course had to be described in detail. For this aim, we especially considered the local relationships of this artery with the medulla oblongata and the cranial nerves of the posterior fossa. Branches of the a. inferior posterior cerebelli supplying the medulla oblongata have been noticed in relation to the arterial supply of the medulla oblongata by corresponding vessels and the aa. spinales lateralis and posterior with special reference to all the possible collateralizations.     

Ultrastructural aspects of immune damage to Hymenolepis nana oncospheres in mice

When Hymenoiepis nana eggs were inoculated orally into unimmunized mice, the oncosphere larvae penetrated the intestinal villi and underwent postembryonic development. The ultra-structural changes during the 48 h after infection were characterized by the development of microvillar protrusions on the surface of the epithelium, development of many membranous vesicles in the epithelium, and proliferation of undifferentiated cells in the parenchyma with a rapid disappearance of penetration gland cells and muscle cells. The epithelium of larvae from a challenge infection of mice that had been immunized by oral infection with eggs was severely damaged as shown by the increased electron density, shrinking of the cytoplasm and formation of large empty vacuoles. Development of microvillar protrusions and intraepithelial vesicles were not seen. Changes of internal structure were similar to those changes seen in the larvae of unimmunized mice. It was evident that host immunity, resulting in the ultimate death of challenge larvae during 24 h after challenge, was primarily directed against the epithelium of the larva. Host cells which firmly adhered to the larva in unimmunized mice were monocytes and macrophages with occasional infiltration of eosinophils and plasma cells, whereas the host cells in immunized mice were almost exclusively eosinophils and macrophages. It was suggested that the degeneration of larvae in immunized mice was caused by the action of specific antibody directed against larval epithelium. The cooperative action of antibody and eosinophils or macrophages in killing challenge larvae was also suggested.     

Ultrastructural aspects of the adherence to target cells of in vitro differentiated lymphocytes.

The specific adherence to target fibroblasts of lymphocytes differentiated in vitro from blast cells after stimulation with pokeweed mitogen was studied under the electron microscope. Lymphocyte pseudopods were seen to penetrate into the target cells forming a close contact between the membranes of the two interacting cells. Microfilaments were the only cytoplasmic components that could be detected within or in the vicinity of the penetrating pseudopods. No morphological signs of secretion could be observed in the contact region. Morphological aspects of the contact region are discussed as related to the lytic mechanism.     

Growth and differentiation of fetal rat limb buds transplanted in athymic (nude) mice

Limb buds of day 14 rat fetuses were cut into pieces and transplanted into the subcutaneous tissue of athymic (nude) mice. In day 14 fetal limbs, mesenchymal cells have begun to condense to form cartilaginous anlage, but no cartilage has been formed. Within 7 days after grafting, masses of hyaline cartilage developed. Numerous osteoblasts appeared, and new bone formation began by 14 days. By 20 days, osteoclasts appeared, and the formation of bone trabeculae and marrow cavities progressed. The cytological characteristics of chondrocytes, osteoblasts and osteoclasts were essentially the same as those seen in vivo. Many grafts developed into long bones, having the diaphysis and epiphysis. The mode of chondrogenesis and osteogenesis in the grafts was histologically similar to the corresponding process in vivo, although the differentiation was slower in the grafted limbs. Since the grafted limb buds showed remarkable growth and tissue differentiation for at least several weeks, this heterotransplantation system would be of potential use for the study of bone formation and resorption as well as for developmental toxicological studies.     

Study of the germ cell migration to the gonad buds of quail embryo after the action of 2,4,5-trichlorophenoxyacetic acid]

At stages 16 and 18, the germ cells counts, in the quail embryos' gonads from control and 2,4,5-T treated eggs, show no significative difference. On the contrary, at stage 20, the gonocyte numbers of the treated embryos are strongly decreased. Actually, this mechanism cannot be stage precisely.     

Congenic method in the chick limb buds by electroporation

Electroporation is a powerful tool with which to study limb development. Limb development, however, remains an intricate series of events, requiring the precise dissection of developmental processes using relevant transgenes. In this review, we describe the anatomy of the limb field as the basis of targeted electroporation, and specific expression vectors are discussed. We share a useful protocol for electroporation of chick limb buds, and the expression pattern of enhanced green fluorescent protein in the limb buds is used to demonstrate relevant embryonic patterning. Finally, useful trouble-shooting techniques are described.