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The structural and histological characteristics of the limiting layer between the cortex and medulla of the bursa of Fabricius in the duck are described in relation to different functional moments of the organ. On E.M. study the limiting layer, in duck having 30 days of age, is constituted of reticular-epithelial cells palisades in shape with many cytoplasmics extension. Lymphatic migration occur in interstitial spaces.
The embryonic zebrafish provides a relatively simple and accessible experimental system for understanding the underlying Bauplan of a vertebrate central nervous system (CNS) and for uncovering interactions critical for patterning. We show that features of CNS organization in normal, mutant, and developmentally ventralized zebrafish embryos can be explained by a three-axis hypothesis: Specifications occur according to position relative to coordinates along the anterior-posterior, dorsal-ventral, and luminal-pial axes of the neural tube. Midline tissues may be responsible for directly establishing the dorsal-ventral coordinates, but may only be indirectly involved in patterning along the anterior-posterior axis.
Brain structure of the shark Scyliorhinus canicula has been studied on the basis of a series of embryonic stages. The incubation time was 157 days in average (under constant conditions of 15 centigrades and density of 1.026). 1. The first predominant characters of the external brain shape are the optic tectum, cerebellum, telencephali hemispheres and oculomotor root. In addition, the brain axis is characterized by new flexures in the cerebellar and prosencephalic level. A nuchal flexure in absent. 2. The ontogenetic pattern of the matrix layer differs in different brain parts. Generally, ventral columns develop earlier than dorsal ones. Matrix development and cell proliferation occur especially late in the cerebellum. For the most part the results agree with findings by KAHLE (1951) concerning the human brain. The telencephalon is an exception and shows a developmental retardation, while a regular development is observed in Scyliorhinus. 3. The hypothalamus overlaps the other regions of the diencephalon. The ventral thalamus is small, a dorsal thalamus is not observed. The pretectal region is remarkably differentiated and contains a rich set of nuclei. 4. The epithalamus is asymmetrical; a phenomenon that occurs after hatch. The left habenula is distinctly larger than the right-one.
Morphological study of allotransplants of rat embryonic neocortex 14-18 months after transplantation into the neocortex, lateral cerebral ventricle, and sciatic nerve of adult animals revealed death of nerve and glial cells in the delayed postoperation period independently on the site of transplantation. After heterotopic transplantation the count of degenerated neurons was 2 times higher that after homotopic transplantation. In heterotopic transplants a considerable number of grafted neurons underwent reversible and irreversible degenerative changes accompanied by their premature aging. Neuronal death is probably determined by insufficiency of trophic influence from afferent structures and target tissues. We hypothesized that antiapoptotic preparations can be used for prevention of transplanted cell death. It was also found that degeneration of neurons was associated with impaired vascularization of transplants and pronounced immune reaction of the recipient in late posttransplantation period. Transplantation of embryonic brain structures can serve as a model system in studies concerning involutive and pathological processes in the central nervous system and in the search for factors improving survival of neurons.
Sympathetic ganglia contain 2 adrenergic derivatives of the neural crest: principal neurons and small, intensely fluorescent (SIF) cells. The developmental mechanisms responsible for the generation of these 2 cell classes in vivo are not well understood. To examine the possible developmental and lineage relationships between differentiating principal neurons and SIF cells, a fluorescence microscopic study utilizing antibodies against tyrosine hydroxylase (TH) and catecholamine histofluorescence has been combined with the ultrastructural examination of embryonic and postnatal rat superior cervical ganglia (SCG). On embryonic day 12.5, before neuroblasts had become postmitotic, the cells in the SCG possessed intense TH immunoreactivity and had weak to bright catecholamine histofluorescence, but no cells displayed the fine structure of mature SIF cells or neurons. At embryonic days 16.5 and 18.5, postmitotic principal neurons expressed more moderate levels of TH and catecholamines characteristic of the late embryonic and postnatal SCG. By contrast, a small number of cells containing intense TH or catecholamine fluorescence were present in embryonic day 16.5 and older ganglia. Almost all of the intensely fluorescent cells observed were found apposed to capillaries within the ganglion. These embryonic intensely fluorescent cells were larger than SIF cells seen postnatally. Ultrastructural examination of developing ganglia confirmed that cells containing numerous large, dense-cored vesicles (LDCVs) were a prominent feature of ganglia that also contained intensely fluorescent cells. In addition, some embryonic cells containing LDCVs were mitotic. From these and other studies, it seems likely that during development, neuron precursors, in response to differentiation factors such as fibroblast growth factor (FGF) and/or NGF, acquire overt neuronal traits and become postmitotic. Subsequently, cells resembling mature SIF cells appear next to blood vessels, where they may have received other instructional signals such as glucocorticoids. This developmental scheme suggests that the differentiation of principal neurons and SIF cells is independently regulated, and that the ability of SIF cells to convert into principal neurons observed in vitro cannot account for the generation of neurons in vivo.
OL-protocadherin (OL-pc) is a homophilic cell adhesion molecule that belongs to the cadherin gene superfamily. We cloned and characterized the chicken homologue of OL-pc and examined its expression pattern in chick embryos mainly from embryonic day (E) 3.5 to E6.5. The structure of chick OL-pc was found to be essentially the same as that of mammalian OL-pc's except for some small deletions and insertions in the amino acid sequence. OL-pc protein was detected prominently along developing axonal fibers in the brain and also in the peripheral nervous system. In addition, it was detected in some mesenchymal cells and in the embryonic ectoderm of the mandible and limb bud. In the spinal cord, OL-pc was specifically expressed in motor neurons, and the protein was distributed along motor nerves. Motor nerves merged gradually with sensory nerves showing negative/faint OL-pc expression, but their fibers remained separated as small bundles in the nerves. Interestingly, OL-pc-positive motor nerves such as those to the sternocoracoideus became segregated from OL-pc-faint/weak motor nerves at the plexus region. Moreover, OL-pc was distributed along the path of the branchial nerves. These results suggest that OL-pc might play some roles in axon navigation such as in axon elongation, selective fasciculation, and pathfinding in the early stage of neural development.
Premature eruption of teeth occurs in 1 of every 2,000 births. The reported association between natal teeth and serious, rare, inherited syndromes suggests that particular caution should be exercised in examination of newborns having prematurely erupted teeth. The ectomesenchyma, from which the orofacial structures develop, undergoes a complex, coordinated series of steps of proliferation and differentiation during the first two months in utero. At approximately seven weeks the presumptive mandibular and maxillary arches show a bandlike ectodermal thickening called the dental lamina. Odontogenesis (tooth development) begins with budding of the dental lamina and continues into the second week of life. Remnants of odontogenic epithelium or of epithelium covering the embryonic facial processes may develop into cystic structures, causing intraoral swellings on the alveolar ridges or palate (i.e., Bohn's nodules and Epstein's pearls). Prematurely erupted natal and neonatal teeth are generally normal deciduous incisors. Hypermobility of these teeth, resulting from poorly formed roots, may stabilize within a short period of time. Extraction of natal and neonatal teeth should not be done precipitously.
Tissue remodeling during embryonic development and in the adult organism relies on a subtle balance between cell growth and apoptosis. As angiogenesis involves restructuring of preexisting endothelium, we examined the role of apoptosis in new vessel formation. We show that apoptosis occurs before capillary formation but not after vessels have assembled. Using the human umbilical vein endothelial cell (HUVEC) in vitro Matrigel angiogenesis model, we show that vascular-like structure formation requires apoptotic cell death through activation of a caspase-dependent mechanism and mitochondrial cytochrome c release. Vascular-like structure formation was further blocked by caspase inhibitors such as z-VAD or Ac-DEVD-CHO, using HUVEC and human lung microvascular endothelial cells. Overexpression of anti-apoptotic human Bcl-2 or baculovirus p35 genes in HUVEC altered endothelial cell rearrangement during in vitro angiogenesis, causing impaired vessel-like structure formation. Caspase inhibitors blocked VEGF- or bFGF-induced HUVEC angiogenesis on 2- or 3-D collagen gels, respectively, confirming that apoptosis was not the result of nonspecific cell death after seeding on the matrix. In an in vivo angiogenesis assay, caspase inhibitors blocked VEGF-dependent vascular formation at the alignment step, as demonstrated histologically. This evidence indicates that endothelial cell apoptosis may be relevant for precise vascular tissue rearrangement in in vitro and in vivo angiogenesis.
tau-Crystallin is a taxon-specific structural protein found in eye lenses. We present here the cloning and sequencing of complete tau-crystallin cDNA from the embryonic lens of Crocodylus palustris and establish it to be identical to the a-enolase gene from non-lenticular tissues. Quantitatively, the tau-crystallin was found to be the least abundant crystallin of the crocodilian embryonic lenses. Crocodile tau-crystallin cDNA was isolated by RT-PCR using primers designed from the only other reported sequence from duck and completed by 5'- and 3'-rapid amplification of cDNA ends (RACE) using crocodile gene specific primers designed in the study. The complete tau-crystallin cDNA of crocodile comprises 1305 bp long ORF and 92 and 409 bp long untranslated 5'- and 3'-ends respectively. Further, it was found to be identical to its putative counterpart enzyme a-enolase, from brain, heart and gonad, suggesting both to be the product of the same gene. The study thus provides the first report on cDNA sequence of tau-crystallin from a reptilian species and also re-confirms it to be an example of the phenomenon of gene sharing as was demonstrated earlier in the case of peking duck. Moreover, the gene lineage reconstruction analysis helps our understanding of the evolution of crocodilians and avian species.
Formation of developmental congenital defects of organ of vision finds its direct basis in the course of eye embryogenesis. Author of this work presents on the base of the literature, the crucial stages of embryonal development of eyeball and its individual structures. At every stage of development, the critical moments are shown, when the disturbance of the developmental process may lead to the origination of different groups of congenital eye defects. The knowledge of the potential period of particular congenital eye defects formation, facilitates the identification of eventual teratogenic factors, that have acted during pregnancy. It enables, to state the activity of gradually discovered genes, that regulate the course of embryonal development of the eye.
The current model to explain the organization of the mammalian nervous system is based on studies of anatomy, embryology, and evolution. To further investigate the molecular organization of the adult mammalian brain, we have built a gene expression-based brain map. We measured gene expression patterns for 24 neural tissues covering the mouse central nervous system and found, surprisingly, that the adult brain bears a transcriptional "imprint" consistent with both embryological origins and classic evolutionary relationships. Embryonic cellular position along the anterior-posterior axis of the neural tube was shown to be closely associated with, and possibly a determinant of, the gene expression patterns in adult structures. We also observed a significant number of embryonic patterning and homeobox genes with region-specific expression in the adult nervous system. The relationships between global expression patterns for different anatomical regions and the nature of the observed region-specific genes suggest that the adult brain retains a degree of overall gene expression established during embryogenesis that is important for regional specificity and the functional relationships between regions in the adult. The complete collection of extensively annotated gene expression data along with data mining and visualization tools have been made available on a publicly accessible web site (www.barlow-lockhart-brainmapnimhgrant.org).
Organs form during morphogenesis, the process that gives rise to specialized biological structures of specific shape and function in early embryonic development. Morphogenesis is under strict genetic control, but shape evolution itself is a physical process. Here we report the results of experimental and modeling biophysical studies on in vitro biological structure formation. Experimentally, by controlling the interaction between cells and their embedding matrices, we were able to build living structures of definite geometry. The experimentally observed shape evolution was reproduced by Monte Carlo simulations, which also shed light on the biophysical basis of the process. Our work suggests a novel way to engineer biological structures of controlled shape.
The pattern of cell division is very regular in Arabidopsis embryogenesis, enabling seedling structures to be traced back to groups of cells in the early embryo. Recessive mutations in the FASS gene alter the pattern of cell division from the zygote, without interfering with embryonic pattern formation: although no primordia of seedling structures can be recognised by morphological criteria at the early-heart stage, all elements of the body pattern are differentiated in the seedling. fass seedlings are strongly compressed in the apical-basal axis and enlarged circumferentially, notably in the hypocotyl. Depending on the width of the hypocotyl, fass seedlings may have up to three supernumerary cotyledons. fass mutants can develop into tiny adult plants with all parts, including floral organs, strongly compressed in their longitudinal axis. At the cellular level, fass mutations affect cell elongation and orientation of cell walls but do not interfere with cell polarity as evidenced by the unequal division of the zygote. The results suggest that the FASS gene is required for morphogenesis, i.e., oriented cell divisions and position-dependent cell shape changes generating body shape, but not for cell polarity which seems essential for pattern formation.
Whilst antihypertensive, structural and functional roles have been proposed for the cells of the renomedullary interstitium in the adult kidney, little is known about its role in renal development. Rat kidneys were studied throughout development, prenatally at gestational ages E14-E21 and postnatally at 0-28 days, by light microscopy, transmission and scanning electron microscopy and following immunocytochemistry. Renomedullary interstitial cells were observed as early as embryonic day E14, forming a loose, orderly network around branches of the ureteric bud. Paralleling the development of the first nephron structures, renomedullary interstitial cells were arranged in a concentric circular manner around collecting ducts. Following tubular and vascular growth from the cortex into the medulla, this arrangement resulted in the characteristic 'rungs of a ladder' appearance of interstitial cells between tubules, blood vessels and the collecting ducts. Renomedullary interstitial cells were closely adherent to basement membranes of tubules, blood vessels and collecting ducts from early in development. Contacts were absent between renomedullary interstitial cells and tubular structures in the process of remodelling, such as the hair-pin bends of the loops of Henle. At these foci laminin, a basement membrane glycoprotein was specificially localised to intracellular epithelial sites, whereas in more developed areas, laminin was restricted to epithelial basement membranes. Associated with the more mature structures, laminin was also localised to intracellular granules of renomedullary interstitial cells. Thus, renomedullary interstitial cells are present prior to and appear to be actively associated with tubule repositioning in the medulla, establishing themselves as integral to the process of renal development.
Anti-Ro/SSA antibodies are the antinuclear antibodies most commonly found in everyday clinical practice and are closely associated with Sjögren's syndrome, systemic lupus erythematosus and neonatal lupus. They play a pathogenic role in a variety of clinical manifestations, including skin lesions and neonatal lupus heart block. Autoantibodies to Ro(SS-A) recognize a ribonucleoprotein complex composed of small single-stranded RNAs (hYRNAs) and of one or more peptides. Four molecular forms of this complex have been differentiated based on the nature of the peptide: a lymphocyte and an erythrocyte Ro with a 60 kDa peptide, a lymphocyte Ro with a 52 kDa peptide and an erythrocyte Ro with a 54 kDa peptide. The Ro complex is found in most tissues and cells (erythrocytes, platelets), with differences in structure and quantity across tissues, species and embryonic development stages. Although its function remains unknown, its ability to bind nucleic acids and the fact that it shares homologies with gene regulation proteins suggest that it may participate in RNA transcription processes. A number of environmental factors (exposure to ultraviolet radiation, viral infections) may cause translocation of the Ro complex to nucleocytoplasmic and membrane sites where it is not normally found, thereby leading to the development of autoimmunity. The structure of the Ro(SS-A)-hYRNA complex and the development of autoimmunity are currently the focus of active research efforts that can be expected to improve our understanding of the clinical manifestations directly related to anti-Ro(SS-A) antibodies.
The Ser/Thr kinase MARK2 phosphorylates tau protein at sites that cause detachment from microtubules in Alzheimer neurofibrillary degeneration. Homologs of MARK2 include Par-1 in C. elegans and Drosophila, which generates embryonic polarity. We report the X-ray structure of the catalytic and ubiquitin-associated domains (UBA) of human MARK2. The activity was altered by mutations in the ATP binding site and/or activation loop. The catalytic domain shows the small and large lobes typical of kinases. The substrate cleft is in an inactive, open conformation in the inactivated and the wild-type structure. The UBA domain is attached via a taut linker to the large lobe of the kinase domain and leans against a hydrophobic patch on the small lobe. The UBA structure is unusual because the orientation of its third helix is inverted, relative to previous structures. Possible implications of the structure for the regulation of kinase activity are discussed.
DNA sequences have been obtained for embryonic chick feather and scale keratin genes. Strong homologies exist between the protein coding regions of the two gene types and between the deduced amino acid sequences of the keratin proteins. Scale keratins are larger than feather keratins and the size difference is mainly attributable to four 13-amino acid repeats between residues 77 and 128 which compose a peptide sequence rich in glycine and tyrosine. The strong similarities between the two peptide structures for feather and scale in the homologous regions suggests a similar conformation within the protein filaments. A likely consequence is that the additional repeat region of the scale protein is located externally to the core filament. Tissue-specific features of filament aggregation may be attributable to this one striking sequence difference between the constituent proteins. It is believed that the genes share a common ancestry and that feather-like keratin genes may have evolved from a scale keratin gene by a single deletion event.
Kidney development has often served as a model for epithelial-mesenchymal cell interaction where the branching epithelium of the ureteric bud induces the metanephrogenic mesenchyme to form epithelial nephrons. In a screen for genes differentially expressed during kidney development, we have identified a novel gene that is dynamically expressed in the branching ureter and the developing nephrons. It was designated Emu1 since it shares an N-terminal cysteine-rich domain with Emilin1/2 and Multimerin. This highly conserved EMI domain is also found in another novel protein (Emu2) of similar protein structure: an N-terminal signal peptide followed by the EMI domain, an interrupted collagen stretch, and a conserved C-terminal domain of unknown function. We identified two further secreted EMI domain proteins, prompting us to compare their gene and protein structures, the EMI domain phylogeny, as well as the embryonic expression pattern of known (Emilin1/2, Multimerin) and novel (Emu1/2, Emilin3, Multimerin2) Emu gene family members. Emu1 and Emu2 not only show a similar structural organization, but furthermore a striking complementary expression in organs developing through epithelial-mesenchymal interactions. In these tissues, Emu1 is restricted to epithelial and Emu2 to mesenchymal cells. Preliminary biochemical analysis of Emu1/2 confirmed that they are secreted glycoproteins which are attached to the extracellular matrix and capable of forming homo- and heteromers via disulfide bonding. The widespread, but individually distinct expression patterns of all Emu gene family members suggest multiple functions during mouse embryogenesis. Their multidomain protein structure may indicate that Emu proteins interact with several different extracellular matrix components and serve to connect and integrate the function of multiple partner molecules.