Mitochondrial gene order is not conserved in arthropods: prostriate and metastriate tick mitochondrial genomes

The entire mitochondrial genome was sequenced in a prostriate tick, Ixodes hexagonus, and a metastriate tick, Rhipicephalus sanguineus. Both genomes encode 22 tRNAs, 13 proteins, and two ribosomal RNAs. Prostriate ticks are basal members of Ixodidae and have the same gene order as Limulus polyphemus. In contrast, in R. sanguineus, a block of genes encoding NADH dehydrogenase subunit 1 (ND1), tRNA(Leu)(UUR), tRNA(Leu)(CUN), 16S rDNA, tRNA(Val), 12S rDNA, the control region, and the tRNA(Ile) and tRNA(Gln) have translocated to a position between the tRNA(Glu) and tRNA(Phe) genes. The tRNA(Cys) gene has translocated between the control region and the tRNA(Met) gene, and the tRNA(Leu)(CUN) gene has translocated between the tRNA(Ser)(UCN) gene and the control region. Furthermore, the control region is duplicated, and both copies undergo concerted evolution. Primers that flank these rearrangements confirm that this gene order is conserved in all metastriate ticks examined. Correspondence analysis of amino acid and codon use in the two ticks and in nine other arthropod mitochondrial genomes indicate a strong bias in R. sanguineus towards amino acids encoded by AT-rich codons.      

From nest to nest--influence of ecology and reproduction on the active period of adult Gombe chimpanzees

The time spent between sleeping periods, which is called the active period, has to accommodate all essential activities, including feeding, resting, social behavior, and reproduction. To minimize costs in terms of, e.g., predation risk, suboptimal foraging, or sleep deficiency, the active period of diurnal animals should be less than or equal to the daylight period. Thus, the active period of an animal should be shaped by local environmental conditions as well as by metabolic and reproductive demands. Chimpanzees, which exhibit reduced predator pressure and a flexible fission-fusion society, were chosen as a model to explore these links. We investigated the influence of sex, female reproductive status, dominance rank, and season on the duration of the active period of adult chimpanzees at Gombe National Park, Tanzania (1975-1992). Sexually nonreceptive females had shorter active periods compared to males, while receptive females had even longer active periods than males. Dominance rank did not influence the duration of the active period of nonreceptive females, but high- and middle-ranking males had shorter active periods compared to low-ranking males. Nonreceptive females exhibited longer active periods during the dry season than in the wet season. No seasonal effect was discovered for males, perhaps because they already had long active periods in the wet season. Nonreceptive females seem to be able to accommodate all essential activities in the daylight period available, probably because they live less socially than males. Thus, the active period does not reflect differences in female competitive abilities, but does reflect such differences in males. The duration of the active period appears to be a simple, reliable tool for exploring basic responses and constraints in animal societies.     

The maternal Xenopus beta-catenin signaling pathway, activated by frizzled homologs, induces goosecoid in a cell non-autonomous manner

In spite of abundant evidence that Wnts play essential roles in embryonic induction and patterning, little is known about the expression or activities of Wnt receptors during embryogenesis. The isolation and expression of two maternal Xenopus frizzled genes, Xfrizzled-1 and Xfrizzled-7, is described. It is also demonstrated that both can activate the Wnt/beta-catenin signaling pathway as monitored by the induction of specific target genes. Activation of the beta-Catenin pathway has previously been shown to be necessary and sufficient for specifying the dorsal axis of Xenopus. beta-Catenin is thought to work through the cell-autonomous induction of the homeobox genes siamois and twin, that in turn bind to and activate the promoter of another homeobox gene, goosecoid. However, it was found that the beta-catenin pathway regulated the expression of both endogenous goosecoid, and a goosecoid promoter construct, in a cell non-autonomous manner. These data demonstrate that maternal Frizzleds can activate the Wnt/beta-catenin pathway in Xenopus embryos, and that induction of a known downstream gene can occur in a cell non-autonomous manner.     

Identification of residues important for DNA binding in the full-length human Rad52 protein

Human Rad52 (HsRad52) is a DNA-binding protein (418 residues) that promotes the catalysis of DNA double strand break repair by the Rad51 recombinase. HsRad52 self-associates to form ring-shaped oligomers as well as higher order complexes of these rings. Analysis of the structural and functional organization of protein domains suggests that many of the determinants of DNA binding lie within the N-terminal 85 residues. Crystal structures of two truncation mutants, HsRad52(1-212) and HsRad52(1-209) support the idea that this region makes up an important part of the DNA binding domain. Here, we report the results of saturating alanine scanning mutagenesis of the N-terminal domain of full-length HsRad52 in which we identify residues that are likely involved in direct contact with single-stranded DNA (ssDNA). Our results largely agree with the position of side-chains seen in the crystal structures but also suggest that certain DNA binding and cross-subunit interactions differ between the 11 subunit ring in the crystal structures of the truncation mutant proteins versus the seven subunit ring formed by full-length HsRad52.     

Target size of the ryanodine receptor from junctional terminal cisternae of sarcoplasmic reticulum

Target inactivation analysis was carried out on the ryanodine receptor. This receptor recently has been implicated as the channel involved in the calcium release process in excitation-contraction coupling and was localized to the junctional terminal cisternae of sarcoplasmic reticulum from skeletal muscle [Fleischer, S., Ogunbunmi, E. M., Dixon, M. C., & Fleer, E.A.M. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7256-7259]. Irradiation of the junctional terminal cisternae resulted in an exponential decrease in ryanodine binding with radiation dose, thereby consistent with target theory. The target molecular weight was found to be 138,000 +/- 21,000, i.e., smaller than the polypeptide that binds ryanodine. The calcium pump protein in the same membrane preparation served as an internal control to validate the methodology.     

"An ape's view of the Oldowan" revisited

In 1989, Wynn and McGrew published an explicit comparison between Oldowan technology and what was then known of chimpanzee technology. They compared the range and variety of tools, adaptive role of tools, carrying distances, spatial cognition, manufacturing procedures, and modes of learning. They concluded that everything archeologists had reconstructed about the behavior of Oldowan hominins could be accommodated within the ape adaptive grade; that is, a paraphyletic group united by overall similarities in anatomy and, in this case, behavior. The only Oldowan activities that were almost unknown for modern apes were the long-distance transport of objects and direct competition with carnivores, which was implied by meat acquisition activities. "In its general features Oldowan culture was ape, not human. Nowhere in this picture need we posit elements such as language, extensive sharing, division of labor, or pair-bonded families, all of which are part of the baggage carried by the term human."