Cheryl L. Weill

The HIV protein, GP120, activates nuclear protein kinase C in nuclei from lymphocytes and brain

Nuclear pool(s) of protein kinase C (PKC) may be a common target for hormones and growth factors which affect the trophic state of cells. The data presented demonstrate a time and dose-dependent activation of nuclear PKC by the HIV coat protein, gp120, in isolated nuclei from rat spleen and hippocampus. This gp120-stimulated PKC response was blocked by specific PKC inhibitors, a monoclonal antibody to PKC, and a monoclonal antibody directed against the murine T4 analog, L3T4. It is suggested that the gp120 interaction with the nuclear trophic factor-PKC system may impair normal gene expression, and thus result in the clinical symptoms associated in AIDS infection.

Somatostatin (SRIF) Prevents Natural Motoneuron Cell Death in Embryonic Chick Spinal Cord

Natural motoneuron cell death is a developmental process that effects the loss of about 50% of the cells in the lateral motor column of the spinal cord. The present study demonstrates that the systemic treatment of developing chick embryos with somatostatin (somatotropin release-inhibiting factor, SRIF) during the period of natural motoneuron cell death resulted in a 13-22% increase in the number of surviving motoneurons, suggesting that SRIF may be an endogenous contributor to motoneuron survival during normal development. It is hypothesized that SRIF may act, through its ability to reduce intraneuronal calcium, as an endogenous antagonist of neuronal death both during development and in the course of adult neurodegenerative diseases.

Characterization of androgen receptors in embryonic chick spinal cord.

While androgen binding sites have been localized to motoneurons of the lateral motor column (LMC) of 10-18-day chick embryo spinal cord, they have yet to be characterized biochemically. Studies were undertaken to characterize the binding of the androgen [3H]5a-dihydrotestosterone ([3H]DHT) to spinal cord cytosols. Saturable, high-affinity binding of [3H]DHT to cytosols prepared from both 6 and 10-day spinal cords was observed. The binding component was a macromolecular species as it displayed a sedimentation coefficient of 8S upon centrifugation in sucrose gradients; proteinaceous, as binding was eliminated by heating cytosols; and displayed steroid-specific binding, as other non-androgen steroid agonists did not significantly inhibit [3H]DHT binding. The number of binding sites increased 10-fold from embryonic day 6 to day 10. The availability of testosterone and presence of androgen receptors in spinal cord motoneurons as spontaneous limb motility begins suggests a possible role for androgen-receptor-dependent gene expression in the process of target-dependent differentiation of LMC motoneurons.

cGMP accumulation by spinal cord neurons during the period of neuromuscular junction formation

A 4--5-fold increase in cGMP levels in spinal cord neurons has been demonstrated in vitro and in vivo upon association with skeletal muscle. The increase on cGMP was temporally coincident with the onset of neuromuscular junction formation and independent of any concomitant change in cAMP. The response was specific for spinal cord neurons cocultured with skeletal muscle; glial cells could not be substituted for spinal cord neurons nor could fibroblasts be substituted for muscle cells. The response was not dependent upon action potential activity, synaptic transmission or muscle contractile activity. Muscle conditioned medium was found to produce the largest increase of cGMP in spinal cord neurons of 23-fold.

Changes in glucose-6-phosphate dehydrogenase activity in developing embryonic chick skeletal muscle and spinal cord

Glucose 6-phosphate dehydrogenase (G6PDH) activity was examined in the developing embryonic chick in brachial and lumbar spinal cord and pectoral and leg muscle. Enzyme activity was generally highest at the earliest stage examined, embryonic day 5. The developmental profiles for G6PDH activity in the two muscles were similar: a sharp initial decrease occurred between days 5 and 9, with relatively low levels present by day 18; peaks of G6PDH activity at days 12 and 16 were more prominent in leg muscle. Similar levels of G6PDH were also detected in spinal cord with the developmental profile in the brachial spinal cord resembling that seen in muscle. In lumbar spinal cord, initial G6PDH activity was lower than in brachial spinal cord; the developmental profile, however, resembled that seen in the brachial spinal cord, with an initial drop in enzyme activity seen between days 5 and 7. Neural regulation of G6PDH activity in mature muscle is believed to repress enzyme synthesis. The drop in G6PDH activity observed in embryonic spinal cord and muscle between days 5 and 9 coincides with the initiation of functional neuromuscular contacts. Hence, the normal regulation of G6PDH during embryonic development may involve the repression of G6PDH in spinal cord neurons and muscle, possibly effected by their interaction.

Characterization of glucocorticoid receptors in whole and cellular subfractions of embryonic chick spinal cord

Steroid-specific binding sites for tritiated corticosterone have been localized, via autoradiography, to motoneurons in the lateral motor columns of the adult rat spinal cord. Binding sites in adult rat spinal cord have been characterized biochemically and shown to possess the properties of a putative glucocorticoid receptor. The presence of receptors for glucocorticoids in embryonic chick spinal cord was determined and their characterization undertaken as a prelude to the study of the functions under regulation by glucocorticoids during development. Assay conditions were defined and binding of [3H]dexamethasone [( 3H]Dex) to cytosols of 6- and 10-day embryonic spinal cord and cellular subfractions of 6-day spinal cord determined. Saturable, high-affinity binding of [3H]Dex to cytosols prepared from both whole 6- and 10-day spinal cords and cells of all 3 cellular subfractions of 6-day spinal cords was observed. The binding component in 10-day cytosols was (1) proteinaceous, as binding was eliminated by heating cytosols, and (2) a macromolecular species, as it displayed a sedimentation coefficient of 8S upon centrifugation in sucrose gradients. The putative receptor displayed binding specific for glucocorticoids in a competition assay, with the exception that some inhibition of binding by the androgen ligand, methyltrienolone (R1881) was observed. The binding affinity decreased as the values for KD increased from 3.4 +/- 0.9 nM on day 6 to 15.7 +/- 1.8 nM on day 10, while the values for Bmax increased from 270 to 855 fmol/mg protein over the same period.(ABSTRACT TRUNCATED AT 250 WORDS)

The prevention of natural motoneuron cell death by dibutyryl-cyclic GMP in the spinal cord of White Leghorn chick embryos

The effect of dibutyryl-cyclic guanosine monophosphate (db-cGMP) treatment of White Leghorn chick embryos on the extent of natural motoneuron cell death in the lumbar spinal cord was examined. A dose of 1.59 mumol of db-cGMP effected an increase in motoneuron survival of 26.7%. No effect on motoneuron survival was observed with equimolar doses of 8-bromo-cGMP, db-cAMP, GMP, guanosine, or butyric acid.

Cyclic nucleotide content of ciliary and dorsal root ganglia during embryonic development in the chick

The concentration of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) was measured in developing chick ciliary (CG) and dorsal root ganglia (DRG) as a function of embryonic age from day 8 through day 18 using radioimmunoassays. The concentration of cAMP and cGMP increased in both ganglia from day 8 through day 14. cAMP levels were nearly two-fold higher in DRG than in CG. Normalization of the data for ciliary ganglia to the number of cells per ganglion and calculation of their molar concentrations indicates a 48% increase in cGMP and a 3.2-fold increase in cAMP during the developmental process of natural neuronal cell death.