Rate of synthesis of nucleic acids and their precursors in developing ovaries of Galleria mellonella

Three groups of ovarioles were selected for study: previtellogenetic (I), those in the course of vitellogenesis (II), and postvitellogenetic (III). Previtellogenetic ovarioles showed the highest content of DNA and acid-soluble nucleotide fraction. The mean rate of incorporation of [³H]-thymine into the mononucleotide fraction within 2·5 min mainly depends on the rate of transport of the pyrimidine base into the ovarioles, and was found to be highest (35 × 10⁴ dis/min per μmole of nucleotide per min) in vitellogenetic ovarioles. The rate for [³H]-uracil is highest in previtellogenetic ovarioles.Incorporation of pyrimidine bases into the polynucleotide fraction was corrected for the mononucleotide pool available for synthesis. [³H]-Thymine is incorporated into the polynucleotide fraction most actively in group III of the ovarioles, being probably restricted to numerous follicular cells, whereas [³H]-uracil is mainly incorporated during vitellogenesis.     

Asexual reproduction and regeneration ofCatenula (Turbellaria,Archoophora)

Summary Studies were made onCatenula, a turbellarian of the order Catenulida, which had been cultured for 6 years in our laboratory. Fission begins inCatenula when the animal exceeds a specifically defined length. Neoblasts accumulate where the body wall narrows, near the subepithelial nerve cell. These cells have a large nucleus of condensed chromatin and a large active nucleolus. They have little cytoplasm, which in addition to free ribosomes, contains a small number of rough endoplastic reticular cisternae and a few mitochondria. Stem cells of epithelium were also found. These cells are similar to neoblasts, having additionally a bundle of centrioles in the cytoplasm.Differentiation of tissues and cells during regeneration proceeds in a manner identical to that during paratomy. After injury the neoblasts collect in two primordia of the brain, but do not form blastemae, as occurs in Tricladida. It is likely that dedifferentiation plays some role in each of the processes examined. A theoretical model of the mechanisms controlling paratomy and regeration is presented. The factors controlling these processes include the inductor formed by the subepithelial nerve cells and the inhibitor blocking it, formed by the brain. The inductor is probably a neurosecretion that combines with a competent receptor on the surface of cells capable of dedifferentiation.     

Homing in the Digger Wasp Bembix rostrata (Hymenoptera,Sphecidae) in Relation to Sex and Stage1

In the digger wasp Bembix rostrata in males and females of different stages the homing rates and times after release from different distances were investigated.

• 1 The homing rate decreased with increase of distance (up to 3000 m).
• 2 In females the homing rate increased with progressing stage, from emerging over digging to provisioning.
• 3 Numbers for homing times followed the same order: highest in emerging, medium in digging and lowest in provisioning females.
• 4 Males showed similar homing rates as digging females. No significant differences between age groups could be found.
• 5 The results indicate an effect of sex and stage on the homing capacity. Differences may be traced back to motivation (provisioning females) and lack of experience (emerging females). Landmark orientation, which may include particular search strategies, is a probable orientation mechanism.

     

Dexamethasone stimulates leptin release from human adipocytes: Unexpected inhibition by insulin

In the present study we have examined the effect of dexamethasone on ob gene mRNA expression and leptin release from isolated human subcutaneous adipocytes. Dexamethasone stimulated leptin release from cultured adipocytes in a time- and dose-dependent manner. A two-fold increase in leptin release was detectable by 36 h of treatment with 10⁻⁷ M dexamethasone. Leptin release was preceded by a significant 83±30% increase in ob mRNA after 24 h exposure to the compound. Co-incubation of cells with dexamethasone (10⁷ M) and insulin (10⁻⁷ or 10⁻⁹ M) completely blocked the dexamethasone-stimulated increase in ob mRNA and leptin release. These data demonstrate that insulin and glucocorticoids regulate leptin synthesis and release from human adipocytes in vitro. J. Cell. Biochem. 65:254–258. © 1997 Wiley-Liss, Inc.     

Response regulator PorX coordinates oligonucleotide signalling and gene expression to control the secretion of virulence factors

The PglZ family of proteins belongs to the alkaline phosphatase superfamily, which consists of metallohydrolases with limited sequence identity but similar metal-coordination architectures in otherwise divergent active sites. Proteins with a well-defined PglZ domain are ubiquitous among prokaryotes as essential components of BREX phage defence systems and two-component systems (TCSs). Whereas other members of the alkaline phosphatase superfamily are well characterized, the activity, structure and biological function of PglZ family proteins remain unclear. We therefore investigated the structure and function of PorX, an orphan response regulator of the Porphyromonas gingivalis TCS containing a putative PglZ effector domain. The crystal structure of PorX revealed a canonical receiver domain, a helical bundle, and an unprecedented PglZ domain, similar to the general organization of the phylogenetically related BREX-PglZ proteins. The PglZ domain of PorX features an active site cleft suitable for large substrates. An extensive search for substrates revealed that PorX is a phosphodiesterase that acts on cyclic and linear oligonucleotides, including signalling molecules such as cyclic oligoadenylates. These results, combined with mutagenesis, biophysical and enzymatic analysis, suggest that PorX coordinates oligonucleotide signalling pathways and indirectly regulates gene expression to control the secretion of virulence factors.     

Cytotoxic activity toward mouse melanoma following immunization of mice with transfected cells expressing a human melanoma-associated antigen

Summary B78H1 is a mouse melanoma cell line that is weakly antigenic in syngeneic mice. In an attempt to augment their immunogenicity, B78H1 cells were transfected with genomic DNA from a line of human melanoma cells expressing a 96-kDa melanoma-associated antigen (ICAM-1). A selective co-amplification procedure was employed that generated a population of transfected cells (Ui11) that expressed fivefold higher quantities of the melanoma-associated antigen than the cells from which the DNA was obtained. To test the transfected cells' relative capacity to generate a cellular immune response against B78H1 cells, Ui11 cells and B78H1 cells were administered (in parallel) to syngeneic C57BL/6 mice, susceptible to the growth of the melanoma. Each cell line (lethally iradiated beforehand) was injected intraperitoneally at weekly intervals into the mice. After two or three injections, a standard chromium-release assay was employed to detect the presence of cellular immunity toward B78H1 cells. The population of spleen cells from mice immunized with the transfected melanoma cells exhibited higher levels of cytotoxicity toward B78H1 cells than spleen cells from mice immunized with equivalent numbers of nontransfected cells. This observation is consistent with the notion that the transfected human melanoma-associated antigen acted as a second antigen capable of potentiating cellular immune responses against the weakly immunogenic determinants of the mouse melanoma cells. The introduction of genes for foreign antigens into weakly antigenic tumor cells may generate immunogens that can lead to augmented anti-tumor cellular immune responses.