Genetic analyses of signalling in flower development using Arabidopsis

Flower development can be divided into four major steps: phase transition from vegetative to reproductive growth, formation of inflorescence meristem, formation and identity determination of floral organs, and growth and maturation of floral organs. Intercellular and intracellular signalling mechanisms must have important roles in each step of flower development, because it requires cell division, cell growth, and cell differentiation in a concerted fashion. Molecular genetic analysis of the process has started by isolation of a series of mutants with unusual flowering time, with aberrant structure in inflorescence and in flowers, and with no self-fertilization. At present more than 60 genes are identified from Arabidopsis thaliana and some of them have cloned. Although the information is still limited, several types of signalling systems are revealed. In this review, we summarize the present genetic aspects of the signalling network underlying the processes of flower development.     

A Novel Assay System for Anti-Human Immunodeficiency Virus Type 1 (HIV-1) Activity Using a Subclone of a Monocytic Cell Line,U937

A subclonal cl.1–14 cell was established from a monocytic cell line U937 by a limiting dilution method. The anti-HIV-1 activity of some antiviral compounds was evaluated in HIV-1-infected cl.1–14 cells. The results demonstrated that although AZT was a potent inhibitor of HIV-1 replication in cl.1–14 cells, its 50% effective concentration (EC₅₀) values was 80 times higher than that in HIV-1 infected MT-4 cells; the EC₅₀ of AZT was 0.16 μM and 0.002 μM in cl.1–14 and MT-4 cells, respectively. In contrast, the anti-HIV-1 activity of ddA, ddI and ddC in cl.1–14 cells was comparable to that in MT-4 cells. The antiviral activity of nevirapine, dextran sulfate, curdlan sulfate and T22 did not differ significantly between the cl. 1–14 and MT-4 cells. The antiviral activity of several compounds in the HIV-1-infected cl.1–14 cells was similar to that in the HIV-1jr -fl -infected human peripheral macrophages. Our results suggest that cl.1–14 cell cultures are very useful for estimating antiviral activity and more advantageous than the use of peripheral blood macrophages.     

Are daughters more costly to produce for Japanese macaque mothers?: Sex of the offspring and subsequent interbirth intervals

Based on a sample of 237 live births recorded over a period of 30 years, a tendency for longer interbirth intervals following the birth of daughters than sons was recognized, in the provisioned Arashiyama troop of Japanese macaques. This may indicate that female infants were more costly to produce than male infants. This tendency seemed to be independent of a mother’s rank.     

Molecular cloning of two tandemly arranged peroxidase genes from Populus kitakamiensis and their differential regulation in the stem

A genomic library was prepared from Populus kitakamiensis and screened with the cDNA for an anionic peroxidase from P. kitakamiensis. One genomic clone was isolated that contained two tandemly oriented genes for anionic peroxidases, prxA3a and prxA4a. Both genes consisted of four exons and three introns; the introns had consensus nucleotides, namely, GT and AG, at their 5 and 3 ends, respectively. The prxA3a and prxA4a genes encoded 347 and 343 amino acid residues, respectively, including putative signal sequences at the amino-termini. Putative promoters and polyadenylation signals were found in the flanking regions of both genes. The sequence of the coding region of prxA3a was completely identical to that of the cDNA clone pA3, whereas the sequence of the coding region of prxA4a was only 73% identical to that of the cDNA clone pA3. Northern blot analysis showed that the patterns of expression of the mRNAs that corresponded to prxA3a and prxA4a differed in stems of P. kitakamiensis.     

Maintaining genetic code through adaptations of tRNA synthetases to taxonomic domains

The universal genetic code is determined by the aminoacylation of tRNAs. In spite of the universality of the code, there are barriers to aminoacylation across taxonomic domains. These barriers are thought to correlate with the co-segregation of sequences of synthetases and tRNAs into distinct taxonomic domains. By contrast, we show here examples of eukaryote-like synthetases that are found in certain prokaryotes. The associated tRNAs have retained their prokaryote-like character in each instance. Thus, co-segregation of domain-specific synthetases and tRNAs does not always occur. Instead, synthetases make adaptations of tRNA-protein contacts to cross taxonomic domains.     

Absence of generalized immunosuppression in C57BL/6J mice implanted with Lewis T241 fibrosarcoma or Lewis lung carcinoma

Summary The immune status of C57BL/6J mice implanted with Lewis T241 fibrosarcoma or Lewis lung (LL) carcinoma was investigated on days 14 and 28 after implantation. Splenic lymphocyte responses were assessed in mitogen (Con A, LPS) mixed lymphocyte culture (MLC), natural killer (NK), graft-vs-host (GVH), and interleukin production assays. Except for NK-cell cytotoxicity, all other immunologic parameters were either comparable to those in medium-implanted controls or augmented. NK cytotoxicity was reduced in both tumor-bearing groups on day 28. The provision of NK potentiation therapy (-interferon, polyinosinic: polycytidylic acid) to T241 mice under various treatment conditions did not have any significant effect on lung metastasis or survival.The results of this study do not support the thesis that T241-or LL-bearing C57BL/6J mice are generally immunosuppressed. Indeed, when immune functions were assessed on the basis of total splenic activity, each of the measured immunologic parameters was substantially greater in animals with tumors than without. Further it seems improbable, considering the magnitude of the NK-cell defect in T241 mice on days 14 and 28 after implantation and the absence of a therapeutic response to NK-cell stimulants, that NK-cell cytotoxicity is intrinsically associated with resistance to tumor progression in this model.     

Formation of regular packets of Staphylococcus aureus cells.

Staphylococcus aureus, which usually forms grape-like clusters, has the ability to form regularly arranged cell packets. These regular cell packets are formed when the activity of its separation enzyme(s) is lost either by treatment with detergents, such as sodium dodecyl sulfate or Trition X-100, or by mutation of the cells. These cell packets consisted of 8 to 64 spherical cells that have a three-dimensional arrangement. Some irregularity in the arragement of cells in packets, however, can be observed by scanning electron microscopy. It is concluded that S. aureus fundametally divides along three definitely oriented planes that are located at right angles to each other. After cell division, the cells usually become translocated due to the action of a separation enzyme(s) to form grape-like clusters.