Centromere ultrastructure in germ-line chromosomes of Parascaris

Ultrastructural analysis of the centromere in germ-line mitotic chromosomes of Parascaris univalens and Parascaris equorum revealed that these chromosomes are holocentric. In thin longitudinal sections of both species the kinetochore appeared as a continuous plate (up to 3.8 μm long) and displayed a layered structure. This structure consisted of electron-dense inner and outer layers (average width 10 nm) separated by a less dense middle layer (25 nm wide), which had transverse electron-dense bars (10 nm wide) regularly spaced every 25–30 nm. Thus the ladderlike kinetochore profile observed in Parascaris gonial mitotic chromosomes represents a different type of organization from that of the classical trilaminar kinetochore found in both holocentric and monocentric chromosomes.This work was supported in part by Euroatom grant BI0-E-45

Neuronal ultrastructure and somatostatin immunolocalization in the ciliary ganglion of chicken and quail

Ciliary and choroid neurons of the avian ciliary ganglion innervate different targets in the eye bulb. By light microscopic immunocytochemistry, somatostatin (SOM) has been localized to a subset of ganglionic neurons believed to be, for the most part, choroid neurons. Although several studies have been published on the physiology, afferent and efferent innervation, and response to experimental injury of this population of cells, their morphological features are still unclear. This has led us to perform a fine structural and immunocytochemical study on the ciliary ganglia of adult chickens and quails to provide the first thorough characterization of the choroid neurons and to analyze whether or not they can be unequivocally identified by expression of SOM. Here, we show that standard and immuno-electron microscopy provide firm criteria for the distinction of ciliary and choroid neurons, whose populations overlap in cell size and territory of distribution. The satellite cell sheaths form compact myelin lamellae around ciliary neurons and flattened processes around choroid neurons. Moreover, ciliary neurons are innervated by a larger number of boutons than choroid neurons. Chicken ciliary neurons are invested by boutons only over one pole of the cell body, while their quail counterparts have an almost complete shell of presynaptic boutons over the entire cell body. Ciliary neurons form mixed synaptic junctions (chemical and electrical), while choroid neurons form only chemical synapses. Crest synapses are present in ciliary neurons of both species. Nematosomes occur in both ciliary and choroid neurons. Choroid neurons contain a larger complement of large dense core vesicles than ciliary neurons and their Golgi apparatuses are more prominent. In the light microscope, somatostatin-immunostaining appears noticeably different in the two species: mostly granular in the chicken and skein-shaped in the quail. Immuno-electron microscopy reveals that somatostatin-like immunoreactivity is localized to Golgi apparatus and large dense core vesicles. Somatostatin is expressed by all the choroid neurons, but not by the ciliary neurons. This neuropeptide is, therefore, a true cell population marker. **Corresponding author: MED

ULTRASTRUCTURAL ALTERATIONS INDUCED IN QUAIL CILIARY NEURONS BY POSTGANGLIONIC NERVE CRUSH AND BY RICINUS TOXIN ADMINISTRATION, SEPARATELY AND IN COMBINATION

The response to postganglionic nerve crush and Ricinus toxin administration by the ciliary neurons of the quail ciliary ganglion was investigated at the ultrastructural level. The toxin was either applied at the crush site on the postganglionic nerves or injected into the anterior eye chamber without any other operative intervention. Crush of postganglionic nerves without toxin administration and saline injection into the anterior eye chamber served as controls for the two toxin administration procedures. Postganglionic nerve crush caused a distinct chromatolytic reaction, accompanied by massive detachment of the preganglionic axon terminals from the ciliary neurons and loss of most of the synapses, both chemical and electrical. This process does not induce cell death and is reversible. Saline injection in the anterior eye chamber caused a moderate retrograde reaction in some of the ciliary neurons, presumably as a consequence of paracentesis. The changes consisted mainly of an increase of perikaryal neurofilaments with, at most, a minor detachment of the preganglionic boutons from a small portion of the cell body at the nuclear pole. Ricinus toxin administration induced neuronal degeneration following a pattern common to both delivery modes. The degenerative process consisted of disruption and detachment of polyribosomes from the tough endoplasmic reticulum, an increase of smooth cisterns and tubules, a dramatic increase of neurofilament bundles, compartmentalization of the cytoplasmic organelles and, finally, karyorrhexis and cell lysis. The final stages of Ricinus toxin degeneration involve a progressive accumulation of extracellular flocculo-filamentous material and cell lysis. After administration of Ricinus toxin to the crush site, ricin-affected neurons showed withdrawal of the preganglionic boutons from a portion of the ciliary neuron, especially at the nuclear pole. After Ricinus toxin injection into the anterior eye chamber, however, the bouton shell surrounding the affected ciliary neurons remained intact in the early stages of degeneration. Detachment of the preganglionic terminals and disruption of the cell junctions, therefore, is the consequence of nerve crush and not of the toxin itself. This study demonstrates that quail ciliary neurons are a suitable model for experimental neuropathology and neurotoxicology

QUANTITATIVE STUDY OF NEURONAL DEGENERATION INDUCED BY RICINUS TOXIN AND CRUSH OF POSTGANGLIONIC NERVES IN THE CILIARY GANGLION OF QUAIL

The effects of Ricinus toxin on the neurons of the ciliary ganglia were investigated in the quail. The neuronal death and the morphological alterations of the ganglionic cells were assessed following injection of the toxin in the anterior chamber of the eye or after application of the toxin on the postganglionic nerves at a crush site. A 45% loss of choroid neurons without loss of ciliary neurons was observed after postganglionic nerve crush alone. Injection of the toxin in the anterior chamber of the eye led to a selective loss of ciliary neurons (38%). Application of the toxin to the crushed postganglionic nerves led to a loss from both neuronal populations (40% of total neurons). This work indicates that different procedures result in selective lesion of the different neuronal populations in the ciliary ganglion

Early alterations in gene expression and cell morphology in a mouse model of Huntington’s disease

Several mouse models for Huntington’s disease (HD) have been produced to date. Based on differences in strain, promoter, construct, and number of glutamines, these models have provided a broad spectrum of neurological symptoms, ranging from simple increases in aggressiveness with no signs of neuropathology, to tremors and seizures in absence of degeneration, to neurological symptoms in the presence of gliosis and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling) positivity, and finally to selective striatal damage associated with electrophysiological and behavioral abnormalities. We decided to analyze the morphology of striatum and hippocampus from a mouse transgenic line obtained by microinjection of exon 1 from the HD gene after introduction of a very high number of CAG repeat units. We found a massive darkening and compacting of striatal and hippocampal neurons in affected mice, associated with a lower degree of more classical apoptotic cell condensation. We then explored whether this morphology could be explained with alterations in gene expression by hybridizing normal and affected total brain RNA to a panel of 588 known mouse cDNAs. We show that some genes are significantly and consistently up-regulated and that others are down-regulated in the affected brains. Here we discuss the possible significance of these alterations in neuronal morphology and gene expression. Key Words: Huntington’s disease— Gene expression—Apoptosis—Neuronal inclusions— Neurodegeneration

Silver positivity of the NOs during embryonic development of "Xenopus laevis".

Transcriptional activity of ribosomal RNA (rRNA) genes is detectable around blastula-gastrula transition during the embryonic development of amphibians and other non-mammalian systems. The silver staining reaction, known to selectively stain transcriptionally active nucleolus organizer regions (NORs) both in interphase and metaphase chromosomes allowed us to follow the activation of the NORs during the embryonic development of Xenopus laevis

Nuclear lamina assembly in the first cell cycle of rat liver regeneration.

The nuclear lamina is a fibrous structure at the nucleoplasmic surface of the inner nuclear membrane. Its assembly state is regulated by phosphorylation of its protein components, the lamins A, B, and C. The isoprenylation of the lamins is essential for their proper membrane anchoring and functionality. The content and the membrane association of nuclear lamins and the subcellular localization at light and electron microscopical levels were studied at different times of rat liver regeneration. This model for the good synchrony of the first cell cycle is particularly suited for the study of cell-cycle-dependent modifications and is particularly interesting for the increased protein prenylation found in S phase. The biochemical results show an increased lamin content in nuclear proteins in G1 phase and a decreased content in M phase, along with an enhanced cytosolic localization of A and C lamins at later stages. The morphological results show in M phase, also in nondividing cells, a decreased lamin-like immunoreactivity around the nucleus with an apparent nuclear lamina disassembly. These data emphasize the dynamic organization of nuclear lamina not only in mitosis but also in interphase. The reduction and partial solubilization of nuclear lamina in M phase suggest a reorganization of the nuclear envelope also in those cells that do not appear in mitosis but have replicated their DNA content that will result in a higher degree of polyploidy

Chromosome length and DNA loop size during early embryonic development of Xenopus.

The looped organization of the eukaryotic genome mediated by a skeletal framework of non-histone proteins is conserved throughout the cell cycle. The radial loop/scaffold model envisages that the higher order architecture of metaphase chromosomes relies on an axial structure around which looped DNA domains are radially arranged through stable attachment sites. In this light we investigated the relationship between the looped organization and overall morphology of chromosomes. In developing Xenopus laevis embryos at gastrulation, the bulk of the loops associated with histone-depleted nuclei exhibit a significant size increase, as visualized by fluorescence microscopy of the fully extended DNA halo surrounding high salt treated, ethidium bromide stained nuclei. This implies a reduction in the number of looped domains anchored to the supporting nucleoskeletal structure. The cytological analysis of metaphase plates from acetic acid fixed whole embryos, carried out in the absence of drugs inducing chromosome condensation, reveals a progressive thickening and shortening of metaphase chromosomes during development. We interpret these findings as a strong indication that the size and number of DNA loops influence the thickness and length of the chromosomes, respectively. The quantitative analysis of chromosome length distributions at different developmental stages suggests that the shortening is timed differently in different embryonic cells

Insulin binding and internalization in rat hepatocytes during prenatal and postnatal life

Insulin binding to isolated rat hepatocytes was studied during prenatal and postnatal life. Results show that in hepatocytes isolated from prenatal, postnatal and adult rat there is a constant increase in the number of insulin binding sites per cell, whereas the affinity of plasma membrane receptors for the hormonal ligand remains unaltered from prenatal to adult hepatocytes. Autoradiographic studies indicate a greater internalization of hormone during prenatal life and, taking into account the increase of cell size, suggest an unchanged surface density of receptor sites before and after birth. © 1981