Pattern Formation in Asymmetrical and Symmetrical Imaginal Discs of Drosophila melanogaster

The polar coordinate model for pattern regulation in epimorphicfields (French et al., 1976) predicts that bilaterally symmetricalfields will show different kinds of regulative behavior dependingon the direction of the cut. These predictions have been testedusing the male genital disc of Drosophila melanogaster. First,a detailed fate map was established by examining the fate ofdisc fragments subjected to immediate metamorphosis in hostlarvae. Then the regulative abilities of various fragments wereexamined by culturing them for seven days in adult abdomens,before transfer to larvae for metamorphosis. When the disc wasbisected by a vertical cut (parallel to the line of symmetry)then fragments smaller than half of the disc underwent duplicationwith some simultaneous regeneration, while fragments largerthan half of the disc underwent regeneration. If the disc wasbisected by a bilaterally symmetrical cut across the line ofsymmetry, wound healing resulted in the confrontation of cellsfrom similar positions on the right and left sides of the fragment,and no regulation occurred. With the exception of regenerationoccurring during duplication of small lateral fragments, theseresults are as predicted by the polar coordinate model.     

The Mechanism of Evagination of Imaginal Discs of Drosophila melanogaster

The evagination of imaginal leg discs to produce legs is a usefulmodel for studying morphogenesis. Evagination of imaginal legdiscs occurs in vitro in defined culture media in the presenceof the molting hormone ß-ecdysone. Evagination involveslimited, organized movement of imaginal disc cells. The movementappears to be a result of contractile activity, coordinatedwith the presence of appropriate structural and surface propertiesof disc cells. However, ecdysone does not produce its effectsdirectly, but acts through the genome to cause evagination.Evagination is a result then of increased synthesis of differentproteins, one of which is myosin. If the results on discs aregeneralizable they indicate that similar morphogenetic processesare the direct result of the readout of the specific geneticprograms.     

In Vitro Development of Drosophila Imaginal Discs: Hormonal Control and Mechanism of Evagination

A new approach in the understanding of the role of the two moltinghormones, -ecdysone and ß-ecdysone, in disc developmentis described. A new culture medium has been developed whichallows discs, with either hormone, to undergo all steps of metamorphosis. Time-lapse cinematographic and scanning electron microscopicanalysis of the mechanism of evagination led to the conclusionthat cells probably do not move extensively with respect toone another. In contrast, changes in cell shape appear to playa major role in this process.     

Wood Grain Pattern Formation: A Brief Review

In trees, new wood develops from a layer of stem cells called the vascular cambium. A subpopulation of cambial cells—the fusiform initials—are elongated and capable of coordinated reorientation in response to internal and external stimuli. Changes in the orientation of fusiform initials in turn leads to changes in the grain pattern of developing wood. This article reviews the phenomenon of cambial orientation, with an emphasis on a recent computer model that takes the plant hormone auxin as the orienting signal. New model results are presented that demonstrate the surprisingly complex grain patterns that can emerge from simple initial conditions, in qualitative agreement with similar patterns found in wood. Lastly, an alternative theory of wood grain pattern that takes mechanical stress as the orienting signal is critically evaluated.     

The Regulation of Aldehyde Oxidase in Imaginal Wing Discs of Drosophila Hybrids: Evidence for cis- and trans-Acting Control Elements

The aldehyde oxidase (Aldox) distribution pattern was determined for wing discs of partial hybrids between D. melanogaster and D. simulans. In these animals the regulation of Aldox activity is not uniform over the disc epithelium as both cis-dominant and trans -acting control were evident in different regions of the disc. The Aldox expression was shown to be regulated by loci on the X chromosome, 2L and 3R of D. melanogaster and 2R and 3R of D. simulans.     

Pattern Formation and Tip Inhibition in the Cellular Slime Mold Polysphondylium pallidum

Abstract. We have shown that the apical tip of the developing sorogen prevents secondary tip formation during normal patterning in Polysphondylium pallidum . In one class of experiments the apical tip was excised and secondary tips soon formed over the surface of the remaining sorogen. In another, very large sorogens formed secondary basal tips spontaneously before regulating to a fixed radius to length ratio of 0.14, the ratio characteristic of control sorogens. These results are discussed in the light of a simple model.     

Book Review: Basic Neurochemistry: Molecular,Cellular, and Medical Aspects Sixth Edition

Neurochemical Research -     

Development Capacities of Mixed Normal and Neoplastic 1(3)gl Imaginal Discs and Neuroblast Tissue in Drosophila hydei

The pleiotropic mutant lethal(3)giant larvae [l(3)gl] of Drosophila hydei exhibits among other anatomical defects, hypertrophy of the larval brain and imaginal discs. Both hypertrophic tissues when transplanted into wild-type female flies behave as fast growing and lethal neoplasms. Implanted into mature wild-type larvae they fail to metamorphose. When l(3)gl neoplastic brain tissue or imaginal discs were mixed with normal imaginal discs, cultured in vivo in the abdomen of adult females and transplanted into mature wild-type larvae, the following results were obtained. The invasive l(3)gl brain neoplasm, while fatal for adult hosts, had no effect on the metamorphosis of normal imaginal disc tissue. On the other hand, the noninvasive l(3)gl imaginal disc neoplasms when mixed with normal imaginal disc tissue inhibited its development and metamorphosis in the wild-type host. This inhibitory effect was not observed when the tissues were injected as separate implants into the same host.     

Pattern Formation: The link between ovary and embryo

The Drosophila gene nudel may encode a spatially restricted serine protease involved in producing the ligand for the receptor Toll and linking dorsal–ventral polarity in the egg chamber to the developing embryonic axis.     

Purification and Heterogeneous Localization of Sarcophaga Lectin Receptor on the Surface of Imaginal Discs of Sarcophaga peregrina (Flesh Fly)

Previously, we reported autocrine involvement of Sarcophaga lectin in the development of Sarcophaga imaginal discs (Kawaguchi et al. , Dev. Biol. 144 , 86–93 (1991)). In this study, we purified Sarcophaga lectin binding protein from the membrane fraction of cultured embryonic cells of Sarcophaga to near homogeneity and raised a monoclonal antibody against it. Histochemical analysis using the monoclonal antibody revealed that this binding protein is distributed heterogeneously on the surface of leg imaginal discs. This binding protein was especially clearly localized in the central region of the basal side of leg discs which forms the junction between the leg and body, suggesting the participation of Sarcophaga lectin in morphogenesis of the basal region of the developing leg.