ISOPRENE SYNTHASE GENES FORM A MONOPHYLETIC CLADE OF ACYCLIC TERPENE SYNTHASES IN THE TPS‐B TERPENE SYNTHASE FAMILY

Many plants emit significant amounts of isoprene, which is hypothesized to help leaves tolerate short episodes of high temperature. Isoprene emission is found in all major groups of land plants including mosses, ferns, gymnosperms, and angiosperms; however, within these groups isoprene emission is variable. The patchy distribution of isoprene emission implies an evolutionary pattern characterized by many origins or many losses. To better understand the evolution of isoprene emission, we examine the phylogenetic relationships among isoprene synthase and monoterpene synthase genes in the angiosperms. In this study we identify nine new isoprene synthases within the rosid angiosperms. We also document the capacity of a myrcene synthase in Humulus lupulus to produce isoprene. Isoprene synthases and (E)‐β‐ocimene synthases form a monophyletic group within the Tps‐b clade of terpene synthases. No asterid genes fall within this clade. The chemistry of isoprene synthase and ocimene synthase is similar and likely affects the apparent relationships among Tps‐b enzymes. The chronology of rosid evolution suggests a Cretaceous origin followed by many losses of isoprene synthase over the course of evolutionary history. The phylogenetic pattern of Tps‐b genes indicates that isoprene emission from non‐rosid angiosperms likely arose independently.     

The Egr-1 promoter contains information for constitutive and inducible expression in transgenic mice.

Egr-1 is an immediate early gene that couples short-term changes in the extracellular milieu to long-term changes in gene expression. Under in vitro conditions, the Egr-1 gene is expressed in many cell types and is induced by a wide variety of extracellular signals. The mechanisms by which the Egr-1 gene is regulated in vivo remain poorly understood. In this study, we have generated transgenic mice with a construct containing 1200 bp of the mouse Egr-1 promoter coupled to nuclear localized LacZ. In multiple independent lines of mice, reporter gene expression was detected in subsets of endothelial cells, vascular smooth-muscle cells, cardiomyocytes, neurons, and hepatocytes. This pattern closely resembled that of the endogenous gene. After partial hepatectomy, reporter gene activity was upregulated between two- and fivefold in regenerating livers. Taken together, these findings suggest that the Egr-1 promoter contains information for appropriate spatial and temporal expression in vivo.     

Structural organization of the oxidizing side of photosystem II. Exogenous reductants reduce and destroy the Mn-complex in photosystems II membranes depleted of the 17 and 23 kDa polypeptides

Removal of 23 and 17 kDa water-soluble polypeptides from PS II membranes causes a marked decrease in oxygen-evolution activity, exposes the oxidizing side of PS II to exogenous reductants (Ghanotakis, D.F., Babcock, G.T. and Yocum, C.F. (1984) Biochim. Biophys. Acta 765, 388–398) and alters a high-affinity binding site for Ca²⁺ in the oxygen-evolving complex (Ghanotakis, D.F., Topper, J.N., Babcock, G.T. and Yocum, C.F. (1984) FEBS Lett. 170, 169–173). We have examined further the state of the functional Mn complex in PS II membranes from which the 17 and 23 kDa species have been removed by high-salt treatment. These membranes contain a structurally altered Mn complex which is sensitive to destruction by low concentrations of NH₂OH which cannot, in native PS II membranes, cause extraction of functional Mn. In addition to NH₂OH, a wide range of other small (H₂O₂, NH₂NH₂, Fe²⁺) and bulky (benzidine, hydroquinone) electron donors extract Mn (up to 80%) from the polypeptide-depleted PS II preparations. This extraction is due to reduction of the functional Mn complex since light, which would generate higher oxidation states within the Mn complex, prevents Mn release by reductants. Release of Mn by reductants does not extract the 33 kDa water-soluble protein implicated in Mn binding to the oxidizing side of PS II, although the protein can be partially or totally extracted from Mn-depleted preparations by exposure to high ionic strength or to high (0.8 M) concentrations of Tris. We view our results as evidence for a shield around the Mn complex of the oxygen-evolving complex comprised of the 33 kDa polypeptide along with the 23 and 17 kDa proteins and tightly bound Ca²⁺.     

Prolactin-induced alpha-lactalbumin activity in mammary explants from pregnant rabbits. A role for epidermal growth factor and glucocorticoids.

Exogenous prolactin alone can induce alpha-lactalbumin activity in rabbit mammary explants. Under these conditions, exogenous corticosol has no effect. However, low levels of epidermal growth factor (EGF) can markedly inhibit the induction by prolactin, and this inhibitory effect, in turn, can be prevented by cortisol. The steroid can, in fact, convert EGF from a potent inhibitor into an agent which enhances the induction. None of the other growth factors tested inhibits induction of alpha-lactalbumin activity by prolactin, and no other type of steroid tested overcomes the effect of EGF. The results suggest that, under physiological conditions, glucocorticoid may be essential for induction of alpha-lactalbumin activity in the rabbit in order to override the effect of serum EGF.     

Super-active forms of placental lactogen and prolactin

Both placental lactogen and prolactin can be converted into super-active forms. These super-active hormones, in combination with insulin and hydrocortisone, stimulate accumulation of α-lactalbumin and increase RNA synthesis in explants from mouse mammary glands to an extent greater than the maximal level obtained with the native hormones. Also, they are able to stimulate RNA synthesis by suspensions of mammary epithelial cells which have lost the ability to respond to native lactogen and prolactin.     

Prolactin-induced accumulation of casein mRNA in mouse mammary explants: A selective role of glucocorticoid

The role of glucocorticoid in the prolactin-induced accumulation of casein mRNA in mammary explants from midpregnant mice has been studied after an initial 4-day incubation to allow the level of messenger to decline to undetectable levels. Subsequent culture for 3 days: 1) with insulin and glucocorticoid did not result in detectable accumulation of messenger; 2) with insulin and prolactin resulted in a very small accumulation; 3) with insulin, glucocorticoid and prolactin elicited a 20-fold greater accumulation of casein mRNA than the system with only insulin and prolactin. Therefore, although glucocorticoids are not an absolute requirement for casein gene expression in mouse mammary tissue, they are necessary for massive accumulation of casein mRNA induced by prolactin. It appears that this dependence is not a result of either mRNA stabilization or alteration in prolactin receptors. By contrast, stimulation of total epithelial RNA synthesis by prolactin does not have this glucocorticoid dependency.     

Fatal congenital Neospora caninum infection in a lamb

Neospora caninum tissue cysts were found in the brain and spinal cord of a 1-wk-old lamb that was unable to stand after birth. The lamb was originally diagnosed as having toxoplasmosis, but ultrastructural and immunohistochemical techniques used in the present study permitted a definitive diagnosis of Neospora caninum tissue cysts in the brain and spinal cord of this lamb. This is the first report of N. caninum in sheep.