Volume 22, Issue 3
June 1997, pages 273-405
pp 273-285 June 1997
Oestradiol acts both as a mitogen and as an inducer of differentiation of target cells. The cellular responses to oestradiol are generally mediated through the regulation of gene expression, although nongenomic modes of action are also documented. The present observations show that the regulation of keratin gene expression in rat vaginal epithelial cells is under the influence of oestradiol. It is observed that oestradiol regulates both the qualitative and quantitative expressions of keratin polypeptides in a time dependent and sequence specific manner. These regulatory effects are the result of modulations in transcriptional, post-transcriptional and translational processes of these genes, brought about by the hormone in vaginal epithelial cells.
pp 287-298 June 1997
The heme-regulated enkaryotic initiation factor-2α (eIF-2α) kinase, also called the heme-regulated inhibitor (HRI), is a key regulator of protein synthesis in mammalian reticulocyte. HRI is almost undetectable in blood samples of normal rabbits and it increases by 12–15-fold in the reticulocytes of anemic rabbits. In order to determine if such an increase in the quantity of HRI is gradual during anemia, and if it could be an indicator of anemia, we have carried out a detailed analysis on the expression of HRI and its eIF-2α kinase activity in rabbit reticulocyte lysates during various stages of acetylphenylhydrazine (APH)-induced anemia. In a 9-day schedule of induction of anemia, using an anti-HRI monoclonal antibody, HRI was detectable immediately after completion of fourth injection (day 5) and it increased gradually during the entire period reaching its maximum (24-fold) on day 9. Furthermore, when rabbits recovered from anemia due to individual response to the drug, quantity of HRI decreased significantly. Northern blot analysis results were similar to those of the Western blot. The other parameters that are generally used to monitor anemia in human patients, namely, reticulocyte count, haematocrit level and haemoglobin content although changed at the onset of anemia, did not change significantly during its progression. These results thus indicate that HRI could be a more appropriate and sensitive indicator of drug-induced anemia.
pp 299-314 June 1997
Endothelin-1, a potent vasoconstrictor peptide produces concentration dependent contractions in lamb tracheal smooth muscle. These contractions are not inhibited by low doses (up to 20 μM) of trifluoroperazine and W-7, the calmodulin/myosin light chain kinase (MLCK) inhibitors. At higher concentrations (200 μM), a delayed and poor reversal of isometric tensions results. These relaxations are coupled with a partial dephosphorylation of regulatory myosin light chain (MLC). Preincubation of fiber strips in MLCK inhibitors (200 μM) results in a delayed and attenuated contractile response but without a dephosphorylation of MLC. H-7, a putative protein kinase C antagonist (25–100 μM) abolishes endothelin-1 induced contractile effects rapidly (50% relaxation within 1–3 min). Moreover, such relaxations are accompanied by complete dephosphorylation of MLC. Phorbol 12, 13-dibutyrate, an exogenous activator of protein kinase C potentiates the endothelin induced contractions. Inactive phorbol ester, 4α-phorbol ester does not elicit any contractile response in the muscle. The down regulation of protein kinase C, on the other hand suppresses such potentiated contractile responses. These results suggest that endothelin-1 induced contractile tensions in tracheal smooth muscle are mediated by a mechanism that involves an activation of enzyme protein kinase C.
pp 315-324 June 1997
The tachykinins are a family of gastrointestinal peptides comprising eight members: substance P, neurokinin A, neurokinin B, eledoisin, physalemin, uperolein, kassinin and phyllomedusin. Consensus dynamics was carried out on anensembleof seven tachykinins to determine the binding conformation of the common C-terminal fragment: Phe-X-Gly-Leu-Met-NH2,the ’message sequence’ of tachykinins. Three binding modes for the C-terminal pentapeptide were determined. The first binding conformation is folded due to an intramolecular H-bond between the NH of the variable residue (X) and CO of Met. Other features include γ-bends at both the variable amino acid (X) and at Gly. The global minimum of the simulation has this conformation for the C-terminal pentapeptide. The other two binding modes have slightly higher energies. The second is chiefly characterized by a β-turn around the segment X-Gly-Leu-Met, with additional β-bends at the variable amino acid (X) and Met. The final binding conformation is composed of β-bends around the variable amino acid (X) and Leu, and a ’pseudo’ γ-bend at the terminal Met.
pp 325-338 June 1997
Oviposition preference for ureasupplemented food was assayed by simultaneous choice trials on five pairs of closely related laboratory populations ofDrosophila melanogaster.Each pair of populations had been derived from a separate ancestral population about 85 generations prior to this study. One population in each pair had been subjected to selection for larval tolerance to the toxic effects of urea; the other population served as a control. Considerable variation in oviposition preference was seen both within and among populations, with four of the ten populations showing a significant mean preference for ureasupplemented food. The degree of specificity shown by individual females was surprisingly high, leading to a bimodal distribution of oviposition preference in some populations. Overall, selection for larval tolerance to urea did not significantly affect oviposition preference. However, the data indicated that pairwise comparisons between randomly selected populations from the two larval selection regimes would lead to a range of possible outcomes, suggesting, in several cases, that selection for larval urea tolerance had led to significant differentiation of adult oviposition preference for urea in one or the other direction. The results, therefore, highlight the importance of population level replication and caution against the practice, common in ecological studies, of assaying oviposition preference in two populations that utilize different hosts in nature, and then drawing broad evolutionary inferences from the results.
pp 339-344 June 1997
Plant regeneration from mesophyll protoplasts of pepper,Capsicum annuumL. cv. California Wonder has been demonstrated via shoot organogenesis. Protoplasts isolated from fully expanded leaves of 3-week-old axenic shoots when cultured in TM medium supplemented with 1 mg l−1NAA, 1 mg l−12,4-D, 0 5 mg l−1BAP (CM 1) resulted in divisions with a frequency ranging from 20–25 %. Antioxidant ascorbic acid and polyvinylpyrrolidone (PVP) in the medium and incubation in the dark helped overcome browning of protoplasts. Microcalli and macrocalli were formed in TM medium containing 2 mg l−1NAA and 0.5 mg l−1BAP (CM II) and MS gelled medium containing 2 mg 1−1NAA and 0 5 mg 1−1BAP (CM III), respectively. Regeneration of plantlets was possible via caulogenesis. Microshoots, 2–5 percallus appeared on MS gelled medium enriched with 0.5 mg l−1IAA, 2mg l−1GA and l0mg l−1BAP (CM IVc). Rooting of microshoots was obtained on half strength gelled medium containing 1 mg l−1NAA and 0.5mg l−1BAP. Protoplasts isolated from cotyledons failed to divide and degenerated eventually.
pp 345-355 June 1997
The photoinhibition of photosynthesis was investigated on intact attached leaves and isolated thylakoid membranes ofPopulus deltoides.Our studies demonstrate that in intact leaves photoinhibition takes place under high irradiance which is more pronounced at higher temperatures. No net loss of Dl and other proteins associated with photosystem II (PSII) were observed even after 64 % photoinhibition suggesting that the degradation of polypeptides associated with PSII is not the only key step responsible for photoinhibition as observed by other workers. Electron transport studies in isolated thylakoid membranes suggested water oxidation complex as one of the damaged site during high light exposure. The possible mechanisms of photoinhibition without net loss of D1 protein are discussed.
pp 357-365 June 1997
Intraperitoneal administration of 500 mg/kg and 625 mg/kg doses of the germ cell mutagen, ethyl methanesulphonate (EMS) in 5 consecutive days to the house rat,Rattus rattuscaused a dose-dependent reduction in its body weight, cauda epididymides weight, concentration, motility and percentage of live spermatozoa with simultaneous increase in the percentage of their abnormal forms. Compared to 0·65% spermatozoa with abnormal heads in the cauda epididymidis of untreated control rats, 24·86% and 65·72% such spermatozoa were observed in rats on day 14 post treatment with 500 mg/kg and 625 mg/kg doses of EMS respectively. On day 28 post treatment corresponding values for abnormal spermatozoa were 16·21% and 14·32%. Similarly, spermatozoa with abnormal flagella increased from 0.78% in control rats to 9·25% and 5·75% on day 14 post treatment of 500 and 625 mg/kg doses of EMS respectively and declined to 2·91% and 2·40% on day 28 post treatment. Abnormality in the sperm head was mainly due to acrosomelessness and in the flagellum due to bending at proximal region. However, the main effect of EMS was the development of spermatozoa without or deformed acrosomes which may impair the fertility of rats. Analysis of various stages of differentiation of spermatozoa inthe testis revealed that population of preleptotene and pachytene spermatocytes and of round spermatids showed a gradual decline which became significantly less than controls on day 28 of EMS treatment. Occurrence of abnormal heads of testicular spermatids indicated that the sperm head abnormalities originated in the testis during late spermiogenesis.
pp 367-374 June 1997
Gastrimargus africanus orientalis,an acridid grasshopper has revealed the existence of karyotypic mosaicism in the male germ line cells of a few individuals with 2n= 23, 19, 21, 25 and 27 chromosomes. Details of this chromosomal instability are presented in this paper.
pp 375-397 June 1997
Extracellular signals are transduced across the cell by the cell surface receptors, with the aid of G-proteins, which act at a critical point of signal transduction and cellular regulation. Structurally, G-proteins are heterotrimeric consisting α, β and γ subunits but in functionally active state they dissociate into α subunit coupled to GTP and as βγ dimer. G-proteins can be broadly divided into two classes based on their sensitivity to pertussis toxin and cholera toxin. Existence of various forms of each of the subunit allows molecular diversity in the subunit species of G-proteins. These subunits interact with a wide range of receptors and effectors, facilitated by post translational modification of their subunits. Different types of G-proteins mediate several signalling events in different parts of the body. This review summarizes the features of (i) structural and functional heterogenity among different subunits of G-proteins, (ii) interaction of G-proteins and their subunits with effectors with specific cases of G-protein mediated signalling in olfaction, phototransduction in the retina,ras andrasrelated transduction and (iii) disease conditions associated with malfunctioning of G-proteins.
pp 399-405 June 1997
What determines whether or not an immune response takes place? The older view that it is only the presence or absence of T cells bearing appropriate receptors that matters has been replaced by one which lays at least equal emphasis on inflammation: whether or not antigenpresenting cells become activated and secrete proinflammatory cytokines. The evidence for this view comes partly from older work on animal models of autoimmunity and tolerance, partly signs of “immunological neglect” in transgenic mice akin to “immunological privilege”, and partly from some remarkably supportive genetics. The genetics includes genome scanning for quantitative trait loci determining disease susceptibility and case/control disease associations. Migration inhibitory factor is an interesting proinflammatory cytokine which does not yet fit into this scheme. We ask but do not answer the question whether protective T cell populations are subject to the same rules of activation.