Multiple actin-based motor genes in Dictyostelium.

Dictyostelium cells, devoid of conventional myosin, display a variety of motile activities, consistent with the presence of other molecular motors. The Dictyostelium genome was probed at low stringency with a gene fragment containing the conserved conventional myosin head domain sequences to identify other actin-based motors that may play a role in the observed motility of these mutant cells. One gene (abmA) has been characterized and encodes a polypeptide of approximately 135 kDa with a head region homologous to other myosin head sequences and a tail region that is not predicted to form either an alpha-helical structure of coiled-coil interactions. Comparisons of the amino acid sequences of the tail regions of abmA, Dictyostelium myosin I, and Acanthamoeba myosins IB and IL reveal an area of sequence similarity in the amino terminal half of the tail that may be a membrane-binding domain. The abmA gene, however, does not contain an unusual Gly, Pro, Ala stretch typical of many of the previously described myosin Is. Two additional genes (abmB and abmC) were identified using this approach and also found to contain sequences that encode proteins with typical conserved myosin head sequences. The abm genes may be part of a large family of actin-based motors that play various roles in diverse aspects of cellular motility.     

Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex

Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1- kbp portion of the yolk protein 2 locus, were sequenced in six individuals from each of four species: Drosophila melanogaster, D. simulans, D. mauritiana, and D. sechellia. The species and strains were the same as those of a previous study of a 1.9-kbp region of the period locus. No evidence was found for recent balancing or directional selection or for the accumulation of selected differences between species. Yolk protein 2 has a high level of amino acid replacement variation and a low level of synonymous variation, while zeste has the opposite pattern. This contrast is consistent with information on gene function and patterns of codon bias. Polymorphism levels are consistent with a ranking of effective population sizes, from low to high, in the following order: D. sechellia, D. melanogaster, D.mauritiana, and D. simulans. The apparent species relationships are very similar to those suggested by the period locus study. In particular, D. simulans appears to be a large population that is still segregating variation that arose before the separation of D. mauritiana and D. sechellia. It is estimated that the separation of ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The separations of D. sechellia and D. mauritiana from ancestral D. simulans appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged from ancestral D. simulans 0.1 Myr more recently than D. sechellia.      

Electron acceptor taxis and blue light effect on bacterial chemotaxis.

Salmonella typhimurium and Escherichia coli from anaerobic cultures displayed tactic responses to gradients of nitrate, fumarate, and oxygen when the appropriate electron transport pathway was present. Such responses were named "electron acceptor taxis" because they are elicited by terminal electron acceptors. Mutant strains of S. typhimurium and E. coli were used to establish that functioning electron transport pathways to nitrate and fumarate are required for taxis to these compounds. Aerotaxis in S. typhimurium was blocked by 1.0 mM KCN, which inhibited oxygen uptake. Similarly, a functioning electron transport pathway was shown to be essential for the tumbling response of S. typhimurium and E. coli to intense light (290 to 530 nm). Some inhibitors and uncouplers of respiration were repellents of S. typhimurium. We propose that behavioral responses to light or electron acceptors involve electron transport-mediated perturbations of the proton motive force.     

The sense of agency is action–effect causality perception based on cross-modal grouping

Sense of agency, the experience of controlling external events through one''s actions, stems from contiguity between action- and effect-related signals. Here we show that human observers link their action- and effect-related signals using a computational principle common to cross-modal sensory grouping. We first report that the detection of a delay between tactile and visual stimuli is enhanced when both stimuli are synchronized with separate auditory stimuli (experiment 1). This occurs because the synchronized auditory stimuli hinder the potential grouping between tactile and visual stimuli. We subsequently demonstrate an analogous effect on observers'' key press as an action and a sensory event. This change is associated with a modulation in sense of agency; namely, sense of agency, as evaluated by apparent compressions of action–effect intervals (intentional binding) or subjective causality ratings, is impaired when both participant''s action and its putative visual effect events are synchronized with auditory tones (experiments 2 and 3). Moreover, a similar role of action–effect grouping in determining sense of agency is demonstrated when the additional signal is presented in the modality identical to an effect event (experiment 4). These results are consistent with the view that sense of agency is the result of general processes of causal perception and that cross-modal grouping plays a central role in these processes.     

Digital image analysis of AgNORs in cervical smears of women with premalignant and malignant lesions of the uterine cervix

We performed a hospital-based, unmatched case-control study to investigate the association between progressive stages of cervical neoplasia and digital analysis of cell proliferation by silver stained nucleolus organizer region associated proteins (AgNORs). We measured cell proliferation levels in the cervical epithelial cells of 10 women with low grade squamous intraepithelial lesions (LG-SIL), eight with high grade squamous intraepithelial lesions (HG-SIL), 11 with cervical cancer (CC) and eight with no cervical lesions (controls) using the AgNORs technique. Cell proliferation was measured by digital image analysis (DIA). DIA revealed increased total areas of AgNORs in HG-SIL and CC compared to LG-SIL and control patients. AgNORs with a kidney or cluster shape exhibited greater areas than those with a spherical or long shape. We propose a cut-off of 118 pixels to differentiate benign (control and LG-SIL) from malignant (HG-SIL and CC) lesions. DIA of AgNORs is a simple and inexpensive method for studying proliferation. The increased total area of AgNORs in malignant lesions provides information regarding cell behavior and may be related to cervical carcinogenesis; however, further validation studies are required to establish its usefulness in cytological analysis.     

Specialized conservation of surface loops of myosin: evidence that loops are involved in determining functional characteristics

The molecular motor myosin has been the focus of considerable structure-function analysis. Of key interest are the portions of the protein that control the rate of ATP hydrolysis, the affinity for actin, and the velocity at which myosin moves actin. Two regions that have been implicated in determining these parameters are the "loop" regions at the junctions of the 25 kDa and 50 kDa domains and the 50 kDa and 20 kDa domains of the protein. However, the sequences of these regions are poorly conserved between different myosin families, suggesting that they are not constrained evolutionarily, and thus are relatively unimportant for myosin function. In order to address this apparent incongruity, we have performed an analysis of relative rates of observed evolutionary change. We found that the sequences of these loop regions appear to be actually more constrained than the sequences of the rest of the myosin molecule, when myosins are compared that are known to be kinetically or developmentally similar. This suggests that these loop regions could play an important role in myosin function and supports the idea that they are involved in modulating the specific kinetic characteristics that functionally differentiate one myosin isoform from another. Apparently "unconserved" loops may generally play a role in determining kinetic properties of enzymes, and similar analyses of relative rates of evolution may prove useful for the study of structure-function relationships in other protein families.