Control of hepatic mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase during the foetal/neonatal transition, suckling and weaning in the rat.

(1) We assayed active and total (i.e. active plus succinylated) 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase in mitochondria isolated from foetal, neonatal, suckling or weaned rats. (2) HMG-CoA synthase was substantially succinylated and inactivated in mitochondria isolated from term-foetal, (1-h-old, 6-h-old, 1-day-old) neonatal, suckling and high carbohydrate/low-fat (hc)-weaned rats. Succinylation of HMG-CoA synthase was very low in mitochondria isolated from the livers of foetal, 30-min-old neonatal and high-fat/carbohydrate-free (hf)-weaned rats. (3) There was a negative correlation between active HMG-CoA synthase and succinyl-CoA content in mitochondria isolated from term-foetal, suckling and hc-weaned rats. (4) Differences in active enzyme could not be entirely accounted for by differences in succinylation and inactivation of the synthase. Immunoassay confirmed that the absolute amounts of mitochondrial HMG-CoA synthase increased during the foetal/neonatal transition and decreased with hc weaning. The levels remained elevated with hf weaning. (5) From these data we propose that mitochondrial HMG-CoA synthase is controlled by two different mechanisms in young rats. Regulation by succinylation provides a mechanism for rapid modification of existing enzyme in response to changing metabolic states. Changes in the absolute amounts of HMG-CoA synthase provide a more long-term control in response to nutritional changes.     

Staining of hyaluronan in rat cerebellum with a hyaluronectin-antihyaluronectin immune complex

Summary The presence of hyaluronan was studied histochemically in the adult rat cerebellum. We used the hyaluronectin-antihyaluronectin immune complex technique based on the high affinity of hyaluronectin for hyaluronan. The immune complex was prepared with hyaluronectin from a human brain extract and an anti-hyaluronectin monoclonal antibody, which does not react with rat hyaluronectin. This is a specific probe for detecting hyaluronan in rat tissues without any reaction for tissue hyaluronectin.Hyaluronan was found at the nodes of Ranvier, in the perineuronal microenvironment of the deep nuclei and at the Purkinje cells surrounding the initial segment of the axon. It was located at the same places as hyaluronectin, in areas specialized in ion exchanges and neurotransmission. This suggests that the hyaluronectin-hyaluronan complex could be involved in these processes. The immune complex technique with anti-hyaluronectin monoclonal antibody thus seems to be a specific and valuable tool for investigations of the distribution of hyaluronan in the rat cerebellum.     

Estimation of phenological stages and physiological states of grasslands from remote sensing data

Two radiometers measuring reflectance factors have been used at a height of 1.50 m above some grasslands in C. France. The results show that both spectral data are sensitive to the photosynthetic activity of the grassland. Measurements made in April, May, June and July show that grasslands have quite different spectral behaviour according to soil conditions or to grazing level. Grasslands on dry or wet soils may be separated from those of normal soils for which overgrazing and trampling affecting the growth of species, are shown by the different spectral values. Such on the ground remote sensing measurements may then be proposed for evaluating the range of growth and development of different grasslands.Convention C.N.E.S./I.N.A.P-G. ref.: 80/CNES/24 I thank CNES and IGN for the facilities given to assume this experiment. Many thanks to Lynn Erselius, who revised the text. Mr. Lecordix, a student from the Ecole Nationale des Sciences Géographiques and Mr. Besnard, a student from the Orsay University (Plant Biology) helped in the collection and handling of spectral resp, floristical data.     

Biochemical and strain properties of CJD prions: complexity versus simplicity

Prions, the agents responsible for transmissible spongiform encephalopathies, are infectious proteins consisting primarily of scrapie prion protein (PrP(Sc)), a misfolded, β-sheet enriched and aggregated form of the host-encoded cellular prion protein (PrP(C)). Their propagation is based on an autocatalytic PrP conversion process. Despite the lack of a nucleic acid genome, different prion strains have been isolated from animal diseases. Increasing evidence supports the view that strain-specific properties may be enciphered within conformational variations of PrP(Sc). In humans, sporadic Creutzfeldt-Jakob disease (sCJD) is the most frequent form of prion diseases and has demonstrated a wide phenotypic and molecular spectrum. In contrast, variant Creutzfeldt-Jakob disease (vCJD), which results from oral exposure to the agent of bovine spongiform encephalopathy, is a highly stereotyped disease, that, until now, has only occurred in patients who are methionine homozygous at codon 129 of the PrP gene. Recent research has provided consistent evidence of strain diversity in sCJD and also, unexpectedly enough, in vCJD. Here, we discuss the puzzling biochemical/pathological diversity of human prion disorders and the relationship of that diversity to the biological properties of the agent as demonstrated by strain typing in experimental models.     

Glucose transporter expression in rat mammary gland.

The expression of different glucose transporter isoforms was measured during the development and differentiation of the rat mammary gland. Before conception, when the mammary gland is mainly composed of adipocytes, Glut 4 and Glut 1 mRNAs and proteins were present. During pregnancy, the expression of Glut 4 decreased progressively, whereas that of Glut 1 increased. In the lactating mammary gland only Glut 1 was present, and was expressed at a high level. The absence of Glut 4 suggests that glucose transport is not regulated by insulin in the lactating rat mammary gland.     

Alpha6beta1 integrin expressed by sperm is determinant in mouse fertilization

Background  

Based on inhibition tests, the alpha6beta1 integrin was suggested to be a sperm receptor, but further experiments using gene deletion techniques have shown that neither oocyte alpha6, nor beta1 integrin subunits were essential for mouse fertilization.     

Reduced fertility of female mice lacking CD81

In somatic cells, the tetraspanins CD81 and CD9 associate with each other, with additional tetraspanins and with non-tetraspanin molecules to form proteolipidic complexes. Here we show that CD81 is expressed on the surface of oocytes where it associates with tetraspanin-enriched membrane structures. A major CD9 and CD81 partner, CD9P-1, is also expressed by oocytes. Deletion of CD81 gene in mice results in a 40% reduction of female fertility. In vitro insemination indicated that this infertility is due to a deficiency of oocytes to fuse with sperm. While the fertility of CD9-/- mice is severely but not completely impaired, double knock-out CD9-/- CD81-/- mice were completely infertile indicating that CD9 and CD81 play complementary roles in sperm-egg fusion. Finally, a fraction of CD9 was transferred from CD81-/- oocytes to sperm present in the perivitelline space indicating that the defect of fusion of CD81-/- oocytes does not result from an impaired initial gamete interaction.     

His499 Regulates Dimerization and Prevents Oncogenic Activation by Asparagine Mutations of the Human Thrombopoietin Receptor

Ligand binding to the extracellular domain of the thrombopoietin receptor (TpoR) imparts a specific orientation on the transmembrane (TM) and intracellular domains of the receptors that is required for physiologic activation via receptor dimerization. To map the inactive and active dimeric orientations of the TM helices, we performed asparagine (Asn)-scanning mutagenesis of the TM domains of the murine and human TpoR. Substitution of Asn at only one position (S505N) activated the human receptor, whereas Asn substitutions at several positions activated the murine receptor. Second site mutational studies indicate that His⁴⁹⁹ near the N terminus of the TM domain is responsible for protecting the human receptor from activation by Asn mutations. Structural studies reveal that the sequence preceding His⁴⁹⁹ is helical in the murine receptor but non-helical in peptides corresponding to the TM domain of the inactive human receptor. The activating S505N mutation and the small molecule agonist eltrombopag both induce helix in this region of the TM domain and are associated with dimerization and activation of the human receptor. Thus, His⁴⁹⁹ regulates the activation of human TpoR and provides additional protection against activating mutations, such as oncogenic Asn mutations in the TM domain.