Transmission distortion of t-haplotypes is due to interactions between meiotic partners

The T/t-complex of the mouse includes a series of recessive lethal and semi-lethal mutations but, despite such lethalities, mutant t-haplotypes are found in high frequency in wild mouse populations. This polymorphism is apparently maintained because heterozygous males preferentially transmit the t-bearing chromosome to their offspring. Despite many attempts to define the basis of the transmission ratio distortion, it has been unclear whether this is because t-bearing sperm have better than average fertilizing ability or whether +-bearing sperm in heterozygous males are rendered defective. To examine this point, we constructed male (XY in equilibrium XY) chimaeras containing +/+ and +/tw73 genotypes, marked respectively by albino and pigmented coat colours, and two isozyme variants. Such males produce a mixture of three different sperm types: +-bearing sperm from the +/+ genotype, +-bearing sperm from the +/t genotype, and t-bearing sperm from the +/t genotype. Appropriate matings can distinguish between these three types, and our data, reported here, show that t-bearing sperm in chimaeric mice maintain their advantage over their 'meiotic partners' but do not have any advantage over sperm from the +/+ genotype.     

Synthesis of brome mosaic virus subgenomic RNA in vitro by internal initiation on (-)-sense genomic RNA

The genomes of many (+)-stranded RNA viruses, including plant viruses and alphaviruses, consist of polycistronic RNAs whose internal genes are expressed via subgenomic messenger RNAs. The mechanism(s) by which these subgenomic mRNAs arise are poorly understood. Based on indirect evidence, three models have been proposed: (1) internal initiation by the replicase on the (-)-strand of genomic RNA, (2) premature termination during (-)-strand synthesis, followed by independent replication of the subgenomic RNA and (3) processing by nuclease cleavage of genome-length RNA. Using an RNA-dependent RNA polymerase (replicase) preparation from barley leaves infected with brome mosaic virus (BMV) to synthesize the viral subgenomic RNA in vitro, we now provide evidence that subgenomic RNA arises by internal initiation on the (-)-strand of genomic RNA. We believe that this also represents the first in vitro demonstration of a replicase from a eukaryotic (+)-stranded RNA virus capable of initiating synthesis of (+)-sense RNA.     

Pharmacologic therapeutic window of pramiracetam demonstrated in behavior, EEG, and single neuron firing rates

Following oral or intravenous administration, a representative cognition activator drug, pramiracetam sulfate, is shown to have a pharmacologic therapeutic window at three different levels of study: learned behavior, gross EEG activity of the frontal cortex and hippocampus, and firing rate of single hippocampal neurons.     

H2 receptor antagonists and human granulopoiesis

Summary The effect of 2 H₂ receptor antagonists (ranitidine and cimetidine) on the in vitro growth of human granulomonopoietic precursors (CFU-GM) was studied. Ranitidine, although having an anti H₂ receptor activity much greater than that of cimetidine, displays the same toxicity for CFU-GM.Acknowledgments. This work was supported by CNR, Rome, PFCCN and AIRC, Milan.     

A molecular solution to the riddle of the giant panda's phylogeny

Although it is generally agreed that the giant panda (Ailuropoda melanoleuca) is a member of the order Carnivora, there has long been disagreement over whether it should be classified with bears, raccoons or as a single member of its own family. Four independent molecular and genetic measures lead to a consensus phylogeny for the giant and lesser pandas. The lesser panda diverged from New World procyonids at approximately the same time as their departure from ursids, while ancestors of the giant panda split from the ursid lineage much later, just before the radiation which led to modern bears. The giant panda's divergence was accompanied by a chromosomal reorganization which can be partially reconstructed from the ursid karyotype, but not from that of procyonids or the lesser panda. The apparently dramatic, but actually limited, distinctions between the giant panda and the bears in chromosomal and anatomical morphology provide a graphic mammalian example of the discordance of molecular and morphological (and chromosomal) evolutionary change.     

The effects of vitamin A nutritional status on glutathione levels and microsomal lipid peroxidation in rat lung

Summary In vitamin A-deficient rats, the glutathione level in lung was diminished and microsomal lipid peroxidation much increased. In vitamin A-loaded animals, however, both were depressed below control. Thus vitamin A protection against lipid peroxidation is independent of glutathione.Acknowledgments. We thank Dr L. Y. Y. Fong and Mr David Y. H. Woo for preparing the animals used in this research, for retinol determinations and for valuable discussions, and also the China Medical Board of New York and the University of Hong Kong for the award of a Fellowship to V.P.     

Spontaneous excision of a large composite transposable element of Drosophila melanogaster

The TE1 family of transposable elements (TEs) of Drosophila consists of unusually large transposons, cytologically visible in larval polytene chromosomes as one or more bands. They are composite elements, as their termini consist of foldback (FB) sequences which are themselves transposable. The location of FB elements at the termini of transposable elements suggests that these sequences have a direct role in the genetic instability of TEs. To investigate the structural and phenotypic consequence of TE excision, we have cloned genomic DNA required for the expression of the no-ocelli (noc) gene of Drosophila; this gene has been mutated by the insertion of TE146, a member of the TE1 family carrying six polytene chromosome bands including functional copies of the white (w+) and roughest (rst+) genes. As reported here, our experiments indicate that the spontaneous excision of TE146, which results in the loss of the w+ and rst+ markers, can occur either as a single-step event or following a partial internal deletion. In either case, the end product is an imprecise excision in which a residual portion of the element, varying in size from 3 to 10 kilobases (kb), is left at the insertion site. These residual sequences share homology with the FB family. Furthermore, despite their imprecise nature, all these spontaneous excisions restore a wild-type noc+ phenotype.