Annual protidic cycle and electrophoregrams of the savanna varan]

The circannual chronobiology of Varanus exanthematicus exanthematicus Bose, lacertilian reptile of Senegal, is characterized by a period of rest from January to June during the dry season and a period of activity from July to December during the wet season. The study of proteidemia and of the ratio of weight and height shows that the hydratation of corporal compartments is average from November to April and undergoes through changes from May to October. The electrophoresis of proteins shows the total disappearance of one of the fraction during the complete metabolic rest of the Varanus (from January to April). Finally the study of the electrophoresis of lipoproteins leads to the hypothesis that the Varanus can only make an insufficient biosynthesis of lipoproteins during the animal over feeding; besides this biosynthesis seems to be pratically stopped from January to May.     

Effect of bacterial pyrogen on three lizard species

1. Three lizard species (Callopistes maculatus, Gerrhosaurus major, and Varanus exanthematicus) were tested for their response to intraperitoneal injection of alcohol-killed Aeromonas sobria. 2. A paired experimental design, in which each animal received an injection of sterile saline and 1 x 10(10) A. sobria, was utilized. 3. C. maculatus demonstrated a statistically significant increase in mean selected body temperature (MSBT) after bacteria injection. 4. G. major and V. exanthematicus did not demonstrate a statistically significant increase in MSBT. 5. C. maculatus is the first lizard species outside of the family Iguanidae to exhibit a febrile response to bacterial pyrogen.     

Annual lipid cycle of the grassland Varanian lizard]

The circannual chronobiology of Varanus exanthematicus exanthematicus Bosc, lacertilian reptile of Senegal, is characterized by a period of rest from January to June (dry season) and a period of activity from July to December (wet season). The study of the lipids metabolism shows a two month deplacement period: as a matter of fact from November to April the lipogenesis prevails, while from May to October it is the lipolysis. These two phases correspond to the periodicity of the development of the gonads, which are at rest from November to April and in activity from May to October. The synchronism of the phases of lipolysis and of gonads muturation argues in favour of the lipids utilization for the growth of the gonads.     

Primary structure of hemoglobin from monitor lizard (Varanus exanthematicus albigularis--Squamata)

The primary structure of the major hemoglobin component from the Monitor Lizard Varanus exanthematicus albigularis is presented. The polypeptide subunits were separated by reversed-phase high-performance liquid chromatography on Nucleosil C-4 column. The amino-acid sequence was established by automatic Edman degradation of the native polypeptide and its tryptic and hydrolytic cleavage products in a spinning cup sequencer. The structural data are discussed with reference to other reptiles.     

Successful hyperimmune bovine colostrum treatment of Savanna monitors (Varanus exanthematicus) infected with Cryptosporidium sp

Therapy based on the protective passive immunity of hyperimmune bovine colostrum (HBC) (raised against Cryptosporidium parvum in cows) was applied to 4 Savanna monitors (Varanus exanthematicus) with gastric Cryptosporidium sp. infections. All lizards were moderately emaciated, and their fecal and gastric lavage samples contained moderate numbers of Cryptosporidium sp. oocysts. The first 3 of 7 gastric HBC treatments at 1-wk interval each decreased the numbers of oocysts in the fecal and gastric samples to undetectable levels. Neither feces nor lavages of the HBC-treated lizards contained Cryptosporidium sp. oocysts after the HBC therapy, whereas such samples of a single control lizard remained positive for oocysts. Two of the HBC-treated lizards died spontaneously due to metastasized carcinoma and septicemia of unknown etiology, respectively, and 2 lizards treated and killed during the experiment were histologically negative for developmental stages of Cryptosporidium sp. The control lizard died spontaneously of septicemia of unknown etiology and contained developmental stages of Cryptosporidium sp. in the gastric region. The HBC therapy was efficacious in V. exanthematicus and is recommended for lizards with gastric cryptosporidiosis.     

Alterations of endocrine pancreas B cells in a sahelian reptile (Varanus exanthematicus) during starvation

During the long starvation period (November to June) of the lizard (Varanus exanthematicus), pancreatic B cells undergo profound modification. The degeneration of beta granules observed in electron microscopy appears correlated with the diminution of the immunoreactive insulin-like content of the pancreas. The analogy between the phenomena observed here and those reported in animals treated with alloxan is discussed.     

Cis-retinoids and the chemistry of vision

We discuss here principal biochemical transformations of retinoid molecules in the visual cycle. We focus our analysis on the accumulating evidence of alternate pathways and functional redundancies in the cycle. The efficiency of the visual cycle depends, on one hand, on fast regeneration of the photo-bleached chromophores. On the other hand, it is crucial that the cyclic process should be highly selective to avoid accumulation of byproducts. The state-of-the-art knowledge indicates that single enzymatically active components of the cycle are not strictly selective and may require chaperones to enhance their rates. It appears that protein–protein interactions significantly improve the biological stability of the visual cycle. In particular, synthesis of thermodynamically less stable 11-cis-retinoid conformers is favored by physical interactions of the isomerases present in the retina with cellular retinaldehyde binding protein.     

Cell cycle parameters and proliferative activity in chorioallantois tissues at various stages in chick embryo development

Two peculiarities of cell population kinetics are characteristic of the provisional tissues of the chick embryo chorioallantois. The one is that the proliferative pool is relatively small at relatively early stages of embryogenesis (8 day incubation). The other is that at the final stages of embryogenesis, when proliferative activity in the embryo cell populations is still high, the cell reproduction is practically stopped. The process of tissue differentiation in chorioallantois, on the one hand, is accompanied with a withdrawal of a considerable part of cells from the cycle of reproduction, but on the other hand this differentiation affects the cells that have remained in the proliferative compartment which is reflected in modifications of either the cell cycle structure or the cell population composition.     

Dysfunctional Telomeres at Senescence Signal Cell Cycle Arrest via Chk2

Loss of telomere integrity can have two outcomes with opposite predicted effects on tumorigenesis. On the one hand, shortened telomeres in normal cells may trigger cell cycle arrest, leading to tumour suppression. On the other hand, in a tumour cell in which neither the p53 nor pRb pathway is intact, shortened telomeres could initiate chromosome instability and promote tumorigenesis A major issue in telomere research is to understand how shortened dysfunctional telomeres can regulate the onset of cellular senescence. Recent studies have revealed that critically shortened or acutely uncapped telomeres share molecular features with damaged DNA. We have recently linked the phosphorylation and activation of one major DNA damage effector checkpoint kinase, Chk2, to telomere erosion in signalling cell cycle arrest in normal fibroblasts. Here, we discuss several hypotheses to explain the molecular events occurring at shortened telomeres that ultimately lead to cell cycle arrest or increased genomic instability.     

Clustering of sequential enzymes in the glycolytic pathway and the citric acid cycle

In recent years, evidence has been accumulating that metabolic pathways are organized in vivo as multienzyme clusters. Affinity electrophoresis proves to be an attractive in vitro method to further evidence specific associations between purified consecutive enzymes from the glycolytic pathway on the one hand, and from the citric acid cycle on the other hand. Our results support the hypothesis of cluster formation between the glycolytic enzymes aldolase, glyceraldehydephosphate dehydrogenase, and triosephosphate isomerase, and between the cycle enzymes fumarase, malate dehydrogenase, and citrate synthase. A model is presented to explain the possibility of regulation of the citric acid cycle by varying enzyme-enzyme associations between the latter three enzymes, in response to changing local intramitochondrial ATP/ADP ratios.     

Synthesis and characterization of nuclear matrix proteins during the cell cycle of Physarum polycephalum

Pulse-labelling with [³⁵S]-methionine/cysteine of macroplasmodia of the myxomycete Physarum polycephalum at different time points of the cell cycle reveals that the majority of nuclear matrix proteins is synthesized and assembled into nuclear structures without a pronounced cell cycle periodicity. Bulk nuclear histones on one hand and nuclear matrix associated histones on the other hand assemble with a different cell cycle periodicity suggesting specific functions of nuclear matrix bound chromatin. Characterization of the nuclear matrix by immunoblotting and immunofluorescence techniques with several antisera against vertebrate lamins shows the existence of lamin-homologous proteins in Physarum.     

Control of Cell Cycle and Cell Growth by Molecular Chaperones

Cells adapt their size to both intrinsic and extrinsic demands and, among them, those that stem from growth and proliferation rates are crucial for cell size homeostasis. Here we revisit mechanisms that regulate cell cycle and cell growth in budding yeast. Cyclin Cln3, the most upstream activator of Start, is retained at the endoplasmic reticulum in early G1 and released by specific chaperones in late G1 to initiate the cell cycle. On one hand, these chaperones are rate-limiting for release of Cln3 and cell cycle entry and, on the other hand, they are required for key biosynthetic processes. We propose a model whereby the competition for specialized chaperones between growth and cycle machineries could gauge biosynthetic rates and set a critical size threshold at Start.     

Further serial transmission electron microscopy studies of auditory hair cell innervation in lizards and in a snake

Auditory hair cells of three lizard and one snake species were studied by serial transmission electron microscopy (TEM) sections of two unidirectional hair cells (UHC) and two bidirectional hair cells (BHC) and by nonserial section montages of each entire papilla cut at 2-microns intervals across the papillar width. The unidirectional hair cell region of the agamid lizard, Acanthosaura crucigera, lacked efferent innervation. Another agamid lizard, Agama agama, studied by nonserial section only, also lacked efferent innervation to the UHC. Afferent innervation to both the UHC and BHC of Acanthosaura was primarily exclusive (each nerve fiber innervates only one hair cell), although an occasional nerve fiber innervated two hair cells. Both the UHC and the BHC of the anguid, Celestus costatus, were exclusively innervated. Both hair cell types of the varanid, Varanus exanthematicus, were nonexclusively innervated (all afferent nerve fibers innervate two or more hair cells). The auditory papilla of the colubrid snake, Elaphe obsoleta, has only one type of hair cell and each is nonexclusively innervated. The numbers of afferent and efferent nerve fibers and of afferent synapses are presented in tabular form.     

DNA damage-dependent cell cycle checkpoints and genomic stability

In response to genotoxic stress, which can be caused by environmental or endogenous genotoxic insults such as ionizing or ultraviolet radiation, various chemicals and reactive cellular metabolites, cell cycle checkpoints which slow down or arrest cell cycle progression can be activated, allowing the cell to repair or prevent the transmission of damaged or incompletely replicated chromosomes. Checkpoint machineries can also initiate pathways leading to apoptosis and the removal of a damaged cell from a tissue. The balance between cell cycle arrest and damage repair on one hand and the initiation of cell death, on the other hand, could determine if cellular or DNA damage is compatible with cell survival or requires cell elimination by apoptosis. Defects in these processes may lead to hypersensitivity to cellular stress, and susceptibility to DNA damage, genomic defects, and resistance to apoptosis, which characterize cancer cells. In this article, we have noted recent studies of DNA damage-dependent cell cycle checkpoints, which may be significant in preventing genomic instability.     

Novel functions of plant cyclin-dependent kinase inhibitors, ICK1/KRP1, can act non-cell-autonomously and inhibit entry into mitosis

In animals, cyclin-dependent kinase inhibitors (CKIs) are important regulators of cell cycle progression. Recently, putative CKIs were also identified in plants, and in previous studies, Arabidopsis thaliana plants misexpressing CKIs were found to have reduced endoreplication levels and decreased numbers of cells consistent with a function of CKIs in blocking the G1-S cell cycle transition. Here, we demonstrate that at least one inhibitor from Arabidopsis, ICK1/KRP1, can also block entry into mitosis but allows S-phase progression causing endoreplication. Our data suggest that plant CKIs act in a concentration-dependent manner and have an important function in cell proliferation as well as in cell cycle exit and in turning from a mitotic to an endoreplicating cell cycle mode. Endoreplication is usually associated with terminal differentiation; we observed, however, that cell fate specification proceeded independently from ICK1/KRP1-induced endoreplication. Strikingly, we found that endoreplicated cells were able to reenter mitosis, emphasizing the high degree of flexibility of plant cells during development. Moreover, we show that in contrast with animal CDK inhibitors, ICK1/KRP1 can move between cells. On the one hand, this challenges plant cell cycle control with keeping CKIs locally controlled, and on the other hand this provides a possibility of linking cell cycle control in single cells with the supracellular organization of a tissue or an organ.     

Somatostatin-like immunoreactivity in pancreatic extracts of a sahelian lizard (Varanus exanthematicus) during starvation

In the Varanus exanthematicus, the pancreatic complex comprises the true pancreas as well as an intrasplenic islet comparable to a Brockmann's body. Somatostatin content and concentration were estimated by radioimmunoassay in acetic acid extracts of both organs. Relatively large amounts of somatostatin (SLI) are present in the pancreas (2.17 +/- 0.07 micrograms) without any difference in distribution between the cranial (CP) and mediocaudal (MCP) regions. The intrasplenic islet contains as much SLI material as the whole pancreas (3.38 +/- 0.85 microgram); thus, this primitive organ presents a very high hormonal concentration (109.34 +/- 40.30 ng/mg wt). Serial dilutions of the extracts gave parallel immunoassay displacement curves and gel-filtration revealed two immunoreactive peaks: the most important one was found in the synthetic tetradecapeptide fraction, the other one near the void volume fraction. These results show an immunological similarity between the SLI substance of the pancreatic complex and the synthetic somatostatin; however, a molecular heterogeneity must not be excluded. The results are discussed from a phylogenetic point of view.     

Regional LCA in a global perspective. A basis for spatially differentiated environmental life cycle assessment

Background, aim and scope  

In the context of environmental life cycle assessment (LCA), life cycle impact assessment (LCIA) is one of the central issues with respect to modelling and methodological data collection. The thesis described in this paper focusses on the assessment of toxicity-related impacts, and on the collection of normalisation data. A view on the complementary roles of LCA toxicity assessment on the one hand and human and environmental risk assessment (HERA) on the other is presented, and the global, spatially differentiated LCA toxicity assessment model GLOBOX for the assessment of organics and metals is described. Normalisation factors for the year 2000 are calculated on a global as well as on a European level.     

Glycogen Synthase Kinase - 3 Phosphorylates and Regulates the Stability of p27kip1 Protein

p27 Kip1 is a critical regulator of the eukaryotic cell cycle. It acts as a check point proteinand regulates cell cycle progression at the G1 and G1/S phase as well as predominantlyblocks cell cycle progression in the absence of growth factors. Intracellular turnover of p27is tightly regulated at the level of translation as well as by posttranslational modification.The mechanism by which p27 protein is rapidly degraded during the G1 and G1/S phasetransition is well characterized. However, the process by which p27 remains extremelystable in the absence of growth factors remains unknown. Here, we report that GSK-3dependent phosphorylation of p27 protein is essential for its enhanced stability. p27 proteinharbours 2 functional GSK-3 phosphorylation sites at the C- terminus, which was found tobe effectively phosphorylated by the cognate enzyme both in vitro and in vivo. Combinedwith earlier observation which shows that it phosphorylates and triggers cyclin Ddegradation; GSK-3 now appears to be a central mediator of the cell-cycle regulatorynetwork, where it acts as a two-way switch, phosphorylating and targeting pro-proliferativefactors for degradation on one hand and simultaneously phosphorylating and stabilizing ananti-proliferative factor on the other hand. This dual mode of activity may doubly ensurethat cell cycle progression is aptly prohibited under conditions of limited growth factoravailability.     

Separation of live cells in different phases of the cell cycle for gene expression analysis

BACKGROUND: Homogeneity of cell populations is a basic requirement for gene expression analyses of the cell cycle, such as those based on microarrays. The most common approach to obtain specific populations is the use of synchronization methods that increase the number of cells representing a certain cell cycle stage. On the one hand, conventional synchronization usually causes undesirable effects. On the other hand, cell separation methods may imply loss of RNA quality, another limiting factor for expression profiling. We describe a new strategy to specifically separate live cells in different phases of the cell cycle (G(1) and G(2)/M) to obtain good quality RNA for gene expression analyses. METHODS: The experimental design included sorting G(1) and G(2)/M cells with the vital fluorochrome Hoechst 33342, followed by RNA isolation from the sorted cells. RESULTS: Sorted living G(1) and G(2)/M cells, analyzed by immunocytochemistry and laser scanning cytometry, showed strong enrichment. The quality and specificity of the isolated RNA were demonstrated by northern blot. CONCLUSIONS: This new approach has many potential applications, such as expression profiling of specific cell populations after eliminating the irrelevant data produced by cells in other stages of the cycle.