Using Bcr-Abl to examine mechanisms by which abl kinase regulates morphogenesis in Drosophila

Signaling by the nonreceptor tyrosine kinase Abelson (Abl) plays key roles in normal development, whereas its inappropriate activation helps trigger the development of several forms of leukemia. Abl is best known for its roles in axon guidance, but Abl and its relatives also help regulate embryonic morphogenesis in epithelial tissues. Here, we explore the role of regulation of Abl kinase activity during development. We first compare the subcellular localization of Abl protein and of active Abl, by using a phosphospecific antibody, providing a catalog of places where Abl is activated. Next, we explore the consequences for morphogenesis of overexpressing wild-type Abl or expressing the activated form found in leukemia, Bcr-Abl. We find dose-dependent effects of elevating Abl activity on morphogenetic movements such as head involution and dorsal closure, on cell shape changes, on cell protrusive behavior, and on the organization of the actin cytoskeleton. Most of the effects of Abl activation parallel those caused by reduction in function of its target Enabled. Abl activation leads to changes in Enabled phosphorylation and localization, suggesting a mechanism of action. These data provide new insight into how regulated Abl activity helps direct normal development and into possible biological functions of Bcr-Abl.     

Shifts in Social Structure of Black Howler (Alouatta pigra) Groups Associated with Natural and Experimental Variation in Population Density

We examined variation in the group structure of black howlers (Alouatta pigra) using the adult composition of 48 social groups. We compared the structure of groups at 5 sites with different population densities and variation in group structure over time with rising population density. In addition, we examined changes in the group structure of monkeys that were translocated from an area of high population density to an area with a much lower population density. We found at low population densities, groups comprised either heterosexual pairs or a single male with two females. At high population densities groups tended to be multimale and often contained >2 adult females. We suggest the relative costs and benefits of dispersal by maturing adults varies with population density, and in Alouatta pigra results in a shift from single to multimale groups of larger size with increasing population density.     

Low-frequency Raman scattering study of six nucleosides

Raman spectroscopy was used to study the low-frequency (?200?cm^?1) vibrations in crystalline samples of six naturally occurring nucleosides: deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), uridine (rU), cytidine (rC), and adenosine (rA). Such low-frequency vibrations are important for biological processes in which the conformation of a nucleic acid molecule changes. These experiments also provide a test for the low-frequency vibrational modes of dT, dC, and dA predicted by Shishkin et al.     

Bidirectional cytoplasmic and nuclear introgression in the New World cottons Gossypium barbadense and G. Hirsutum (Malvaceae)

Patterns of interspecific cytoplasmic (plastid and mitochondrial) and nuclear introgression are typically asymmetrical: cytoplasmic gene flow or “capture” is frequently observed without evidence of nuclear introgression. In contrast, nuclear introgression without concomitant cytoplasmic introgression has rarely been demonstrated. Gossypium barbadense L. and G. hirsutum L. have large indigenous ranges in the New World semiarid tropics, with an extensive area of sympatry in the Caribbean and Central America. Numerous accessions of both species were surveyed for diagnostic cpDNA restriction sites. These data, in conjunction with previous information on nuclear markers, lead to several conclusions: 1) introgression between G. hirsutum and G. barbadense is bidirectional for both nuclear and cytoplasmic genes; 2) patterns of introgression between the two species are not symmetrical—in G. barbadense, introgression of G. hirsutum alleles is largely restricted to modem cultivars and is uncommon in areas of sympatry; in contrast, introgression of G. barbadense alleles into G. hirsutum is relatively common in areas of sympatry and is rare in modem cultivars; 3) nuclear introgression is geographically more widespread and more frequently detected than cytoplasmic introgression. Several mechanisms may underlie the differential patterns of cytoplasmic and nuclear gene flow observed, including differential fitness of infraspecific and interspecific cytonuclear combinations and selection against female function in interspecific backcrosses. Possible explanations for the observed asymmetrical patterns of introgression include differences in population sizes combined with phenological differences that bias interspecific pollen transfer.     

Central projections of first-order ocellar interneurons in two orthopteroid insects Acheta domesticus and Periplaneta americana

Summary The central projections of ocellar first-order interneurons in the cricket, Acheta domesticus, and the cockroach, Periplaneta americana, were examined in silver-intensified cobalt preparations. Ten morphologically different types of ocellar interneurons among a total of 44 are recognized in the cricket, and five different types among a total of 26 in the cockroach, indicating that these species have simpler ocellar systems than those described previously in locusts. Ocellar interneurons arborize in the following regions of neuropil in both the cricket and cockroach: the ocellar foci of the posterior protocerebrum, the posterior deutocerebrum, the protocerebral bridge, the ocellar synaptic plexus, ocellar nerves and tracts, and the lobula and medulla of the optic lobes. Ocellar first-order interneurons thus project predominantly to sites where they are likely to synapse with other ocellar and optic-lobe interneurons.     

Role of the reticulum in the stability and shape of the isolated human erythrocyte membrane

In order to examine the widely held hypothesis that the reticulum of proteins which covers the cytoplamsic surface of the human erythrocyte membrane controls cell stability and shape, we have assessed some of its properties. The reticulum, freed of the bilayer by extraction with Triton X-100, was found to be mechanically stable at physiological ionic strength but physically unstable at low ionic strength. The reticulum broke down after a characteristic lag period which decreased 500-fold between 0 degrees and 37 degrees C. The release of polypeptide band 4.1 from the reticulum preceded that of spectrin and actin, suggesting that band 4.1 might stabilize the ensemble but is not essential to its integrity. The time-course of breakdown was similar for ghosts, the reticulum inside of ghosts, and the isolated reticulum. However, at very low ionic strength, the reticulum was less stable within the ghost than when free; at higher ionic strength, the reverse was true. Over a wide range of conditions the membrane broke down to vesicles just as the reticulum disintegrated, presumably because the bilayer was mechanically stabilized by this network. The volume of both ghosts and naked reticula varied inversely and reversibly with ionic strength. The volume of the naked reticulum varied far more widely than the ghost, suggesting that its deformation was normally limited by the less extensible bilayer. The contour of the isolated reticulum was discoid and often dimpled or indented, as visualized in the fluorescence microscope after labeling of the ghosts with fluoroscein isothiocyanate. Reticula derived from ghosts which had lost the ability to crenate in isotonic saline were shriveled, even though the bilayer was smooth and expanded. Conversly, ghosts crenated by dinitrophenol yielded smooth, expanded reticula. We conclude that the reticulum is a durable, flexible, and elastic network which assumes and stabilizes the contour of the membrane but is not responsible for its crenation.     

A study of the induction of cell division in amphibian oocytes by insulin

Ripe Xenopus oocytes, 1.4 mm in diameter, arrested in prophase of meiosis I undergo meiotic cell division in vitro upon exposure to insulin. The role of insulin binding in mediating the response of the oocyte has been investigated. Scatchard analysis of specific insulin binding to oocytes revealed curvilinear kinetics with a K_D of 1.4 nM and 4 × 10⁷ receptors per oocyte for the high-affinity component. However, the EC₅₀ for induction of cell division by insulin was 12 nM in the presence of 10 mg/ml bovine serum albumin. Oocytes treated with Pronase to remove all residual follicle cells still responded to sodium insulin, indicating induction occurred at the level of the oocyte. Using high levels of human anti-insulin receptor antibody, which was demonstrated to bind specifically to the oocyte, 50% of specific insulin binding was prevented. Under these conditions, neither the dose-response curve for induction of cell division by insulin nor the time course was changed by the presence of antireceptor antibody. Other studies demonstrate that pure insulin-like growth factor can induce cell division in oocytes. These results indicate that the induction of cell division in amphibian oocytes by insulin is not mediated by the high-affinity component of insulin binding and may involve interaction of insulin with insulin-like growth factor receptors.     

Molecular evolution of a multigene family in group A streptococci

The emm genes are members of a gene family in group A streptococci (GAS) that encode for antiphagocytic cell-surface proteins and/or immunoglobulin-binding proteins. Previously sequenced genes in this family have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein they will be referred to as the "emm gene family." The genes in the emm family are located in a cluster occupying 3-6 kb between the genes mry and scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain one to three tandemly arranged copies of emm-family genes in the cluster, but the alleles within the cluster vary among different strains. Phylogenetic analysis of the conserved sequences at the 3' end of these genes differentiates all known members of this family into four evolutionarily distinct emm subfamilies. As a starting point to analyze how the different subfamilies are related evolutionarily, the structure of the emm chromosomal region was mapped in a number of diverse GAS strains by using subfamily-specific primers in the polymerase chain reaction. Nine distinct chromosomal patterns of the genes in the emm gene cluster were found. These nine chromosomal patterns support a model for the evolution of the emm gene family in which gene duplication followed by sequence divergence resulted in the generation of four major-gene subfamilies in this locus.      

Resource availability and habitat use by mantled howling monkeys in a Nicaraguan coffee plantation: can agroforests serve as core habitat for a forest mammal?

Although shade coffee plantations are potentially valuable habitats for wildlife conservation, little information exists on the extent to which they provide resident wildlife populations with resources necessary for survival and reproduction. A 14-month study of the ecology of mantled howling monkeys Alouatta palliata living in a Nicaraguan shade coffee plantation was therefore conducted. Trees were surveyed at randomly located enumeration points in the coffee plantation and monitored for phenophase production to characterize resource availability. Day-long focal animal follows were used to characterize the ranging and habitat preferences of the howlers. The study site had a diverse canopy, with over 60 tree species providing shade for coffee cultivation; high tree diversity ensured year-round availability of the howlers' preferred foods. Howlers did not avoid feeding or ranging in areas of shade coffee cultivation. However, when foraging in coffee they favored large shade trees for feeding and were less likely to use areas of shade coffee with small trees and fewer arboreal pathways. Results suggest, in conjunction with controls on hunting and protection of nearby forests, that shade coffee can serve as alternate wildlife habitat and corridors between forest fragments for howling monkeys and possibly other forest mammals. Specific management recommendations to improve the conservation value of shade coffee for primates are made and the potential role of coffee plantations in primate conservation at a regional scale are discussed.