Evolutionary diversity of reverse (R) fluorescent chromosome bands in vertebrates

Mitotic chromosomes, interphase cell nuclei, and male meiosis of 41 species representing all vertebrate classes were analyzed with distamycin A/mithramycin counterstaining. The purpose of the study was to recognize differences and common characteristics in the reverse (R) fluorescent banding patterns in the chromosomes of vertebrate species at various stages of evolution. In contrast to the warm-blooded mammals and birds, the euchromatic segments in the chromosomes of most reptiles, amphibians, and fishes contain no multiple fluorescent R-bands. This is thought to be due to the absence of the long homogeneous regions (isochores) in the DNA of the cold-blooded vertebrates. Distamycin A/mithramycin banding specifically reveals the GC-rich constitutive heterochromatin in all vertebrates. In most of the vertebrate chromosomes examined, the heterochromatic regions have opposite staining properties with mithramycin and quinacrine. Mithramycin labels the nucleolus organizer regions very brightly in the karyotypes of fishes, amphibians, reptiles and birds, but not of mammals. The lack of mithramycin fluorescence at the nucleolus organizer regions of mammals is attributed to the relatively low level of redundancy of the GC-rich ribosomal DNA in their genomes. Studies on the various meiotic stages of the cold-blooded vertebrates show that the mithramycin labeling of the nucleolus organizers is independent of their state of activity. This can be confirmed by mithramycin fluorescence at the nucleoli of actinomycintreated cells.Dedicated to the memory of Professor Dr. Hans Bauer     

Heterogeneity of Benzodiazepine Receptors: Experimental Differences Between [3H]Flunitrazepam and [3H]Ethyl-β-carboline-3-carboxylate Binding Sites in Rat Brain Membranes

Abstract: This study was designed to analyze possible differences in the binding of [³H]flunitrazepam ([³H]FNZP) and [³H]ethyl - β - carboline - 3 - carboxylate ([³H]β-CCE), to rat brain membranes, in various experimental conditions. In cerebral cortex, hippocampus, cerebellum, and orain stem the number of binding sites for [³H]β-CCE was higher than for [³H]FNZP; both were displaced by clonazepam. Until the 7th day of postnatal brain development the numbers of [³H]FNZP and [³H]β-CCE sites were equivalent; but later on, the β-carboline sites increased to a higher level. Noradrenergic denervation by 6-hydroxydopamine was followed in the hippocampal formation. Already after 2 days, there was a decrease in [³H]FNZP sites, which reached 70% of control after 14 days. Similar results were obtained with DSP-4 denervation. This change was only in B_max and not in K_D, In contrast, the [³H]β-CCE sites did not change with denervation. Neonatal injection of l - 2,4,5 - trihydroxyphenylalamine or DSP-4 produced in the adult a decrease in [³H]FNZP sites in the cerebral cortex, in parallel with the noradrenergic denervation. On the other hand, there was an increase in the cerebellum and brain stem, in correspondence with the hyperinnervation by sprouting. In these rats, the number of sites for [³H]β-CCE did not change in the different brain regions. With 0.1% Triton X-100, applied to synaptosomal membranes, [³H]FNZP binding was reduced by 35%, while that of [³H]β-CCE was not significantly changed. These results suggest that there is heterogeneity of binding sites for benzodiazepine receptors in rat brain. A tentative interpretation of the experiments involving noradrenergic denervation and hyperinnervation, as well as those with Triton X-100, is that [³H]FNZP binds to pre- and postsynaptic receptors, while [³H]β-CCE binds mainly to postsynaptic benzodiazepine receptors.     

Stage specificity of selenium-mediated inhibition of mouse mammary tumorigenesis

The experiments reported herein examined the inhibitory role of selenium in chemical carcinogen-induced mouse mammary tumorigenesis. The results from four different experiments are presented herein and are summarized briefly. First, the results demonstrated that relatively low doses of dietary selenium (0.5–2.0 ppm) inhibited 7,12-dimethylbenzanthracene (DBMA)-induced mouse mammary tumorigenesis. At 2 ppm Se, the mammary tumor incidence was reduced from 56 to 15%. Second, the results suggested that the later stages of mammary tumorigenesis (preneoplastic to neoplastic transformation and tumor growth) are not as sensitive to selenium-mediated inhibition as the early stages, i.e., the induction and/or expression of mammary preneoplastic lesions. Finally, the results demonstrated that selenium markedly inhibited mammary tumorigenesis (from 42 to 8%) even when the mice were exposed to selenium only after the carcinogen treatments had been concluded. The results from these experiments are discussed from the viewpoint that selenium-mediated inhibition is a result of a direct block of DNA synthesis.     

Regulation of lipogenesis in vivo by glucose availability and insulin secretion in maternal and foetal tissues during late gestation in the rat. Effect of glucose intubation, streptozotocin-induced diabetes and starvation.

Administration of an oral load of glucose did not change the rate of lipogenesis in maternal liver during late gestation. However, streptozotocin-induced diabetes or starvation decreased maternal liver lipogenesis at 20-22 days of gestation. Glucose intubation, on the other hand, increased foetal lipogenesis at 21-22 days. In addition, maternal starvation decreased foetal lipogenesis and plasma insulin concentration. However, chronic hyperglycaemia induced by streptozotocin administration to the mother did not change foetal liver lipogenesis.     

Phytochrome in etiolated annual rye

Summary During a seven-fold increase in length the content of the coleoptile in photoreversible phytochrome increased four-fold and that of the primary leaf nine-fold. The phytochrome content, during growth, expressed on a fresh- or dry-weight basis did not vary greatly for either organ. Phytochrome per mg dry weight (OD⁷³⁰/mg=0.5) was nearly the same in the leaf as in the coleoptile. Coleoptiles studied had a constant DNA content of 4.1 g per organ. DNA content of the leaf increased with age. Phytochrome per DNA was much higher in the coleoptile than in the primary leaf and increased with growth in each of these organs. Thus, there was not a constant amount of phytochrome per cell in either tissue with increasing age and there was not the same amount of phytochrome per cell in the coleoptile as in the primary leaf at any age.This work was supported in part by U.S. Atomic Energy Commission Contract No. AT (30-I)2373.     

SDSE: A software package to simulate the evolution of a pair of DNA sequences

An algorithm to simulate DNA sequence evolution under a generalstochastic model, including as particular cases all the previouslyused schemes of nucleotide substitution, is described. The simulationis carried out on finite, variable length, DNA sequences througha strict stochastic process, according to the particular substitutionrates imposed by each scheme. Five FORTRAN programs, runningon an IBM PC and compatibles, carry out all the tasks neededfor the simulation. They are menu driven and interfaced to thesystem through a principal menu. All sequence data files usedand generated by the SDSE package conform to the standard GenBankdatabase format, thus allowing the use of any sequence retrievedfrom this databank, as well as the application of other packagesto analyse, manipulate or retrieve simulated sequences. Received on August 23, 1988; accepted on November 15, 1988