Earliest renin containing cell differentiation during ontogenesis in the rat

Summary The differentiation of renin containing cells was studied by immunocytochemistry in normal rat fetuses by the use of highly specific renin, angiotensin I and II antisera.Renin synthesizing cells were detectable as early as the 15th day of gestation outside the nephrogen territories within the walls of mesonephrotic-gonadic and renal arteries. Intrarenal differentiation began at the 17th day and progressed along the intrarenal arterial tree. AII immunostaining appeared concomitantly in the renin containing cells and developed considerably during ontogenesis, suggesting intracellular biosynthesis.It can be suggested that in the fetus newly synthesized AH may contribute to the early systemic and renal blood pressure regulation.     

Change in protein synthesis and enzyme activity in avian endocrine glands during ontogenesis

The synthesis of cytoplasmic proteins and the activity of cAMP-dependent protein kinase were studied in the thyroid gland and thymus of intact and irradiated (0.05 Gr) embryos and chicks. The increase in labeled amino acid incorporation into proteins of irradiated chicken endocrine organs during postnatal development was more apparent in thyrocytes. Stimulation of protein kinase activity in the thyroid gland and thymus was observed at the same periods of time. It was supposed that minor doses of ionizing radiation stimulate synthetic processes as well as phosphorylation of proteins responsible for differentiation of avian endocrine organs.     

A novel role for retinoids in patterning the avian forebrain during presomite stages

Retinoids, and in particular retinoic acid (RA), are known to induce posterior fates in neural tissue. However, alterations in retinoid signalling dramatically affect anterior development. Previous reports have demonstrated a late role for retinoids in patterning craniofacial and forebrain structures, but an earlier role in anterior patterning is not well understood. We show that enzymes involved in synthesizing retinoids are expressed in the avian hypoblast and in tissues directly involved in head patterning, such as anterior definitive endoderm and prechordal mesendoderm. We found that in the vitamin A-deficient (VAD) quail model, which lacks biologically active RA from the first stages of development, anterior endodermal markers such as Bmp2, Bmp7, Hex and the Wnt antagonist crescent are affected during early gastrulation. Furthermore, prechordal mesendodermal and prospective ventral telencephalic markers are expanded posteriorly, Shh expression in the axial mesoderm is reduced, and Bmp2 and Bmp7 are abnormally expressed in the ventral midline of the neural tube. At early somite stages, VAD embryos have increased cell death in ventral neuroectoderm and foregut endoderm, but normal cranial neural crest production, whereas at later stages extensive apoptosis occurs in head mesenchyme and ventral neuroectoderm. As a result, VAD embryos end up with a single and reduced telencephalic vesicle and an abnormally patterned diencephalon. Therefore, we propose that retinoids have a dual role in patterning the anterior forebrain during development. During early gastrulation, RA acts in anterior endodermal cells to modulate the anteroposterior (AP) positional identity of prechordal mesendodermal inductive signals to the overlying neuroectoderm. Later on, at neural pore closure, RA is required for patterning of the mesenchyme of the frontonasal process and the forebrain by modulating signalling molecules involved in craniofacial morphogenesis.     

Taxonomic notes on some species of the Cercospora complex (VI)

The new species Cercosporella pergulariae sp. nov., Pseudocercospora catalpicola sp. nov., Sirosporium rhamnigenum sp. nov., and Spiropes desmodiicola sp. nov. are described and Cercospora commelinicola Chupp is validated. Cercostigmina curta (Syd.) comb, nov., Eriocercosporella vitis-heterophyllae (Henn.) comb, nov., Mycovellosiella lactucae (Henn.) comb, nov., M. trichostemmatis (Henn.) comb, nov., M. tylophorae (Hansf.) comb, nov., Passalora caespitosa (Ellis & Everh.) comb, nov., P. chionanthi (Ellis & Everh.) comb, nov., Prathigada condensata (Ellis & Kellerm.) comb, nov., Pseudocercospora carrii (Barthol.) comb, nov., P. glaucescens (G. Winter) comb, nov., P. pamelae-ellisiae (G.P. Agarwal & N.D. Sharma) comb, nov., Pseudophaeoramularia angolensis (T. Cavalho &O. Mendes) comb, nov., Sporidesmium seminale (Ellis & Everh.) comb, nov., and Stenella praelonga (Syd.) comb. nov. are introduced. Cercospora litseae Henn. is reduced to synonym with Mycovellosiella litseae Meenu et al., and a second collection of Cercosporella indica from Vietnam is recorded.     

Cytological studies on the nuclear differentiation in microspore division of some angiosperms

In all of the 32 species studied the chromatin in one of the daughter nuclei produced by microspore division was found to diffuse earlier than the chromatin of the other. The former developed into a vegetative nucleus and the latter into a generative nucleus. The stage at which this difference between daughter nuclei was first found appeared to vary widely among species. The earliest was found to be at mid-anaphase observed inHemerocallis thunbergii andMagnolia denudata, and the latest at early interphase observed inLilium japonicum, Pogonia japonica andEpipactis thunbergii. InNarcissus jonquilla and 4 other species the nuclear differentiation started at late anaphase, inHaplopappus gracilis and 13 other species at early telophase, and inTradescantia paludosa and 7 other species at mid-telophase.     

Some introductory notes on the organization of the forebrain in tetrapods.

As an introduction to the main theme of this conference an overview of the organization of the tetrapod forebrain is presented with emphasis on the telencephalic representation of sensory and motor functions. In all classes of tetrapods, olfactory, visual, octavolateral, somatosensory and gustatory information reaches the telencephalon. Major differences exist in the telencephalic targets of sensory information between amphibians and amniotes. In amphibians, three targets are found: the lateral pallium for olfactory input, the medial pallium for visual and multisensory input, and the lateral subpallium for visual, octavolateral and somatosensory information. The forebrains of reptiles and mammals are similar in that the dorsal surface of their cerebral hemisphere is formed by a pallium with three major segments: (a) an olfactory, lateral cortex; (b) a 'limbic' cortex that forms the dorsomedial wall of the hemisphere, and (c) an intermediate cortex that is composed entirely of isocortex in mammals, but in reptiles (and birds) consists of at least part of the dorsal cortex (in birds the Wulst) and a large intraventricular protrusion, i.e. the dorsal ventricular ridge. In birds, the entire lateral wall of the hemisphere is involved in this expansion. The intermediate pallial segment receives sensory projections from the thalamus and contains modality-specific sensory areas in reptiles, birds and mammals. The most important differences between the intermediate pallial segment of amniotes concern motor systems.     

Gene dynamics and nuclear architecture during differentiation

Abstract Recent advances have demonstrated that placing genes in a specific nuclear context plays an important role in the regulation of coordinated gene expression, thus adding an additional level of complexity to the mechanisms of gene regulation. Differentiation processes are characterized by dynamic changes in gene activation and silencing. These alterations are often accompanied by gene relocations in relation to other genomic regions or to nuclear compartments. Unraveling of mechanisms and dynamics of chromatin positioning will thus expand our knowledge about cellular differentiation.     

Earliest renin containing cell differentiation during ontogenesis in the rat. An immunocytochemical study

The differentiation of renin containing cells was studied by immunocytochemistry in normal rat fetuses by the use of highly specific renin, angiotensin I and II antisera. Renin synthesizing cells were detectable as early as the 15th day of gestation outside the nephrogen territories within the walls of mesonephrotic-gonadic and renal arteries. Intrarenal differentiation began at the 17th day and progressed along the intrarenal arterial tree. AII immunostaining appeared concomitantly in the renin containing cells and developed considerably during ontogenesis, suggesting intracellular biosynthesis. It can be suggested that in the fetus newly synthesized AII may contribute to the early systemic and renal blood pressure regulation.     

Plasticity of endothelial cells during arterial-venous differentiation in the avian embryo

Remodeling of the primary vascular system of the embryo into arteries and veins has long been thought to depend largely on the influence of hemodynamic forces. This view was recently challenged by the discovery of several molecules specifically expressed by arterial or venous endothelial cells. We here analysed the expression of neuropilin-1 and TIE2, two transmembrane receptors known to play a role in vascular development. In birds, neuropilin-1 was expressed by arterial endothelium and wall cells, but absent from veins. TIE2 was strongly expressed in embryonic veins, but only weakly transcribed in most arteries. To examine whether endothelial cells are committed to an arterial or venous fate once they express these specific receptors, we constructed quail-chick chimeras. The dorsal aorta, carotid artery and the cardinal and jugular veins were isolated together with the vessel wall from quail embryos between embryonic day 2 to 15 and grafted into the coelom of chick hosts. Until embryonic day 7, all grafts yielded endothelial cells that colonized both host arteries and veins. After embryonic day 7, endothelial plasticity was progressively lost and from embryonic day 11 grafts of arteries yielded endothelial cells that colonized only chick arteries and rarely reached the host veins, while grafts of jugular veins colonized mainly host veins. When isolated from the vessel wall, quail aortic endothelial cells from embryonic day 11 embryos were able to colonize both host arteries and veins. Our results show that despite the expression of arterial or venous markers the endothelium remains plastic with regard to arterial-venous differentiation until late in embryonic development and point to a role for the vessel wall in endothelial plasticity and vessel identity.     

A population of neurons expressing tyrosine hydroxylase and migrating from olfactory placode into forebrain during ontogenesis in rats

Olfactory placodes, that give rise to the olfactory and respiratory epithelia during ontogenesis, are a source of many neurons migrating into forebrain in the direction of growth of the olfactory nerves. The neurons expressing gonadotropin releasing hormone (GnRH) are among the best studied in the population in question. This hormone is responsible for the central regulation of reproduction in adult animals. It was already shown that, in addition to the GnRH-immunoreactive neurons, a small amount of neurons expressing tyrosine hydroxylase (TH), the first enzyme of catecholamine synthesis, migrates into the forebrain. Such a transient population of TH-immunoreactive neurons was shown by means of single and double immmunohistochemical labeling. The TH neurons were first found on branches of the olfactory, terminal, and vomeronasal nerves, along the trajectory of migration of GnRH-immunoreactive neurons on day 15 of embryogenesis, which preceded the appearance of GnRH-immunoreactive neurons. On days 17-21 of embryogenesis, both populations of neurons were found in almost the same areas and on day 21 single neurons contained both GnRH and TH. There were no neurons expressing decarboxylase of aromatic acids (DAA), the second enzyme of catecholamine synthesis, among TH-immunoreactive neurons, thus suggesting noncatecholaminergic nature of these neurons. However, single nonenzymatic DAA-immunoreactive neurons were found in the area of anterior olfactory nuclei in the forebrain, which suggests their involvement in local cooperative synthesis of catecholamines in the area where GnRH-immunoreactive neurons penetrate in the forebrain. Thus, the neurons expressing TH, TH and GnRH, and DAA were found in rats during prenatal period in the nasal part of the head along the nerves projecting into the forebrain and in the rostral part of forebrain. The origin and functional significance of these neurons are discussed.     

Correlative morphological and cytochemical observations on the nucleoli and nuclear bodies during avian oogenesis.

A correlative morphological and cytochemical study has been made of the nucleoli and nuclear bodies in the growing oocytes of the crow (Corvus splendens) and common myna (Acridotheres tristis). The nucleoli show morphological and cytochemical changes during oocyte growth, which are described in detail. In young oocytes at diplotene stage, two to six nucleoli, which are attached to condensed diplotene chromosomes, show RNA, lysine-rich histones and some non-histones, the proteins contain S-S and SH groups. In subsequent stages of oocyte growth, the cortex of nucleolus also develops arginine-rich histones whereas the medulla shows lysine-rich histones. The significance of both morphological and cytochemical changes of nucleoli has been discussed in relation to oocyte growth. Seven types of nuclear bodies are described. They are composed of proteins and carbohydrates. Their shape, size and structure vary during different stages of oocyte growth. Finally, their material is transported into the ooplasm.     

A change in nuclear pore complex composition regulates cell differentiation

Nuclear pore complexes (NPCs) are built from ～30 different proteins called nucleoporins or Nups. Previous studies have shown that several Nups exhibit cell-type-specific expression and that mutations in NPC components result in tissue-specific diseases. Here we show that a specific change in NPC composition is required for both myogenic and neuronal differentiation. The transmembrane nucleoporin Nup210 is absent in proliferating myoblasts and embryonic stem cells (ESCs) but becomes expressed and incorporated into NPCs during cell differentiation. Preventing Nup210 production by RNAi blocks myogenesis and the differentiation of ESCs into neuroprogenitors. We found that the addition of Nup210 to NPCs does not affect nuclear transport but is required for the induction of genes that are essential for cell differentiation. Our results identify a single change in NPC composition as an essential step in cell differentiation and establish a role for Nup210 in gene expression regulation and cell fate determination.     

Influence of histone H5 on mononucleosome structure during differentiation in the avian erythroid series

Changes in nucleosome repeat length during avian erythroid development have been previously correlated with changes in H5 content. In order to determine the effects of H5 on the length of DNA in mononucleosomal particles as a function of differentiation, a two-dimensional electrophoretic system was used to analyse DNA and histones of particles generated by micrococcal nuclease digestion of nuclei from several stages of erythroid development. Although the relative proportions of H5- to H1-containing mononucleosomes increased during development, only in mature erythrocytes did H5 protect a greater length of linker DNA from micrococcal nuclease digestion than did H1. These results suggest that changes in average nucleosome repeat length during erythroid development can be attributed only partially to an increase in the proportion of H5-containing nucleosomes which contribute to this average.     

On the attachment of the nuclear pore complex

Electron microscope examination of isolated rat liver nuclei after treatment with the detergent Triton X-100 revealed the complete removal of both the inner and outer membranes of the nuclear envelope. The envelope-denuded nuclei did not show any change in either shape or internal ultrastructure. Most strikingly, the nuclear pore complexes, which in untreated nuclei appear to be integral components of the nuclear envelope, were retained in their characteristic location at the distal ends of the channels leading through the peripheral heterochromatin. Determination of the chemical composition of detergent-treated nuclei showed that over 95% of the nuclear phospholipid was solubilized, thus corroborating the morphological absence of nuclear membranes. Furthermore, detergent treatment also solubilized approximately 10% of the nuclear protein. Analysis of the solubilized protein by polyacrylamide gel electrophoresis in the presence of SDS indicated that these proteins belong to a few specific classes which presumably represent the major polypeptides of the nuclear membranes. The total absence of the nuclear envelope on both morphological and biochemical grounds supports the idea that the nuclear pore complex does not require the membranes either for attachment to the nucleus or for maintenance of its own structural integrity.     

Gene expression and nuclear architecture during development and differentiation

Development requires a precise program of gene expression to be carried out. Much work has focussed on the regulatory networks that control gene expression, for example in response to external cues. However, it is important to recognize that these regulatory events take place within the physical context of the nucleus, and that the physical position of a gene within the nuclear volume can have strong influences on its regulation and interactions. The first part of this review will summarize what is currently known about nuclear architecture, that is, the large-scale three-dimensional arrangement of chromosome loci within the nucleus. The remainder of the review will examine developmental processes from the point of view of the nucleus.