Duplications of the wing-hinge structures in the Pth mutants of drosophila melanogaster]

The Pth mutation of Drosophila melanogaster, a unique dominant mutation obtained by us, causes the notum duplications that are followed by the duplications of ventral and dorsal wing-hinge structures. The duplications of the wing hinge have a strictly coordinated structure, can be ranged in a continuous series, and are divided into four distinct types, none of which overlaps with the other. The order of the emergence of the ventral wing-hinge structures was determined in duplication forms, and the shape, size, and location of these structures were compared with normal parameters. The growth of the presumptive wing-hinge region was shown to have a vectorial mode; the directions of the main vectors and their center were determined. A geometrical model is proposed, which adequately explains the strict specificity in the structure of duplications as well as the agreement between the duplication forms to one another in each of the four types.     

Regeneration following duplication in imaginal wing disc fragments of Drosophila melanogaster

Fragments from the imaginal wing disc of Drosophila melanogaster were cultured in vivo for periods up to 28 days. One type of edge fragment first duplicated and then ceased to grow, but others often continued to grow following initial duplication and regenerated structures characteristic of other areas of the disc. After 28 days of culture, about 50% of fragments from the presumptive ventral hinge region of the disc grew extensively and produced regenerated as well as original structures. The regenerated structures in some implants were produced at the line of mirror-image symmetry. Regeneration was associated with fragment growth and in many cases was accompanied by loss of duplicate structures. Fragments which were only duplicated after the culture period could in some cases be stimulated to grow by additional culture in fresh hosts, but the results of coculturing two fragments in each host show that culture conditions alone do not control growth and regulation in the fragments. The large, normally regenerating fragment, complementary to the ventral fragment, did not appear to grow following regeneration and only occasionally produced supernumerary structures during prolonged culture. Intact wing discs cultured under similar conditions never produced supernumerary structures. Our results suggest that a duplicated pattern is less stable than a complete, regenerated pattern, which in turn is less stable than an intact disc. We propose that the growth of duplicated disc fragments is stimulated by polarity reversals present at lines of mirror-image symmetry.     

The wings ofBombyx mori develop from larval discs exhibiting an early differentiated state: a preliminary report

Lepidopteran insects present a complex organization of appendages which develop by various mechanisms. In the mulberry silkworm,Bombyx mori a pair of meso- and meta-thoracic discs located on either side in the larvae gives rise to the corresponding fore- and hind-wings of the adult. These discs do not experience massive cell rearrangements during metamorphosis and display the adult wing vein pattern. We have analysed wing development inB. mori by two approaches, viz., expression of patterning genes in larval wing discs, and regulatory capacities of larval discs following explantation or perturbation. Expression of Nubbin is seen all over the presumptive wing blade domains unlike inDrosophila, where it is confined to the hinge and the wing pouch. Excision of meso- and meta-thoracic discs during the larval stages resulted in emergence of adult moths lacking the corresponding wings without any loss of thoracic tissues suggesting independent origin of wing and thoracic primordia. The expression of wingless and distal-less along the dorsal/ventral margin in wing discs correlated well with their expression profile in adultDrosophila wings. Partially excised wing discs did not showin situ regeneration or duplication suggesting their early differentiation. The presence of adult wing vein patterns discernible in larval wing discs and the patterns of marker gene expression as well as the inability of these discs to regulate growth suggested that wing differentiation is achieved early inB. mori. The timings of morphogenetic events are different and the wing discs behave like presumptive wing buds opening out as wing blades inB. mori unlike evagination of only the pouch region as wing blades seen inDrosophila.     

Reciprocal roles for bowl and lines in specifying the peripodial epithelium and the disc proper of the Drosophila wing primordium

Central to embryonic development is the generation of molecular asymmetries across fields of undifferentiated cells. The Drosophila wing imaginal disc provides a powerful system with which to understand how such asymmetries are generated and how they contribute to formation of a complex structure. Early in development, the wing primordium is subdivided into a thin layer of peripodial epithelium (PE) and an apposing thickened layer of pseudostratified columnar epithelium (CE), known as the disc proper (DP). The DP gives rise to the wing blade, hinge and dorsal mesothorax, whereas the PE makes only a minor contribution to the ventral hinge and pleura. The mechanisms that generate this major asymmetry and its contribution to wing development are poorly understood. The Lines protein destabilizes the nuclear protein Bowl in ectodermal structures. Here, we show that Bowl accumulates in the PE from early stages of wing development and is absent from the DP. Broad inhibition of Bowl in the PE resulted in the replacement of the PE with a mirror image duplication of the DP. The failure to generate the PE severely compromised wing growth and the formation of the notum. Conversely, the activation of bowl in the DP (by removal or inhibition of lines function) resulted in the transformation of the DP into PE. Thus, we provide evidence that bowl and lines act as a binary switch to subdivide the wing primordium into PE and DP, and assign crucial roles for this asymmetry in wing growth and patterning.     

Spalt major controls the development of the notum and of wing hinge primordia of the Drosophila melanogaster wing imaginal disc

The Drosophila wing and the dorsal thorax develop from primordia within the wing imaginal disc. Here we show that spalt major (salm) is expressed within the presumptive dorsal body wall primordium early in wing disc development to specify notum and wing hinge tissue. Upon ectopic salm expression, dorsally located second leg disc cells develop notum and wing hinge tissue instead of sternopleural tissue. Similarly, by salm over-expression within the wing disc, wing blade formation is suppressed and a mirror-image duplication of the notum and wing hinge is formed. In large dorsal clones, which lack salm and its neighboring paralogue spalt related (salr), the cells of the notum primordium do not grow; these dorsal cells are not specified as notum, hence no notum outgrowth develops. These results suggest that the zinc finger factors encoded by the salm/salr complex play important roles in defining cells of the early wing disc as dorsal body wall cells, which develop into a large dorsal body wall territory and form mesonotum and some wing hinge tissue, and in delimiting the wing primordium. We also find that salm activity is down-regulated by its own product and by that of the Pax gene eyegone.     

Developmental compartments in the Drosophila melanogaster wing disc

Distribution of the enzyme aldehyde oxidase (AO) within the pouch of the mature wing disc is precise and differential. General locations of compartmental boundaries have been identified by fate mapping and studies of AO distribution. The suspected locations of the boundaries were verified by analyzing the distribution of AO-negative cells within an AO-stained background in gynandromorphs and in X-ray-induced clones of AO-negative cells. The anterior/posterior border appeared slightly anterior to the junction of the AO⁺ anterior presumptive wing surfaces and AO^? posterior wing surfaces. A narrow band of AO⁺ cells extending proximodistally on both presumptive wing surfaces belongs to the posterior compartment. Two dorsal/ventral (dor./vent.) restrictions were found. The dor./vent. restriction equivalent to the dor./vent. border found in the adult wing was located at the ventral most edge of the AO-stained presumptive wing margin. A second restriction which was less strictly obeyed was found on the dorsal edge of the wing margin. We conclude that the whole presumptive wing margin is part of the dorsal compartment. Within the anterior wing margin an intensively stained oval was also found to be clonally restrictive. Therefore, territories were found within the prospective wing margin for which no such features have been identified in the adult Drosophila melanogaster wing.     

JAK/STAT signaling is required for hinge growth and patterning in the Drosophila wing disc

JAK/STAT signaling is localized to the wing hinge, but its function there is not known. Here we show that the Drosophila STAT Stat92E is downstream of Homothorax and is required for hinge development by cell-autonomously regulating hinge-specific factors. Within the hinge, Stat92E activity becomes restricted to gap domain cells that lack Nubbin and Teashirt. While gap domain cells lacking Stat92E have significantly reduced proliferation, increased JAK/STAT signaling there does not expand this domain. Thus, this pathway is necessary but not sufficient for gap domain growth. We show that reduced Wingless (Wg) signaling dominantly inhibits Stat92E activity in the hinge. However, ectopic JAK/STAT signaling does not perturb Wg expression in the hinge. We report negative interactions between Stat92E and the notum factor Araucan, resulting in restriction of JAK/STAT signaling from the notum. In addition, we find that the distal factor Nub represses the ligand unpaired as well as Stat92E activity. These data suggest that distal expansion of JAK/STAT signaling is deleterious to wing blade development. Indeed, mis-expression of Unpaired within the presumptive wing blade causes small, stunted adult wings. We conclude that JAK/STAT signaling is critical for hinge fate specification and growth of the gap domain and that its restriction to the hinge is required for proper wing development.     

Development of the embryonic chick wing bud from stage 24 to stage 32

If a graft is placed in an early chick wing bud, the location of the graft after several days of further development cannot be predicted solely from the rate of proximal-distal outgrowth. The movement of the graft depends on the rate of outgrowth of the wing but also on morphogenetic tissue movements intrinsic to the wing and on accommodation to the growth and morphogenetic movements of the body of the embryo. Numerous experiments have been reported in which tissue grafted into ectopic sites in the wing causes abnormal wing development. These experiments have been discussed in terms of pattern formation or positional information. However, until the movement of wing tissue during normal development is understood, it cannot be known in what way the development of grafts placed in ectopic sites is abnormal. Previous experiments have demonstrated that carbon particles placed in the wing move in the same manner as grafts of wing mesenchyme, but the carbon particles do not affect normal wing development. Carbon particles were placed in the wing, dorsal to the base of the wing, and cranial and caudal to the wing, to plot the expected movement of a graft and to discover how this movement can be predicted from the tissue movements at the base of the wing. It is concluded that three tissue movements are responsible for the movement of a graft. These are outgrowth at a rate determined by the rate of cell division, formation of the shoulder through caudal movement of the tissues cranial to the wing, and ventral movement of prospective flank ventral to somite 19. These three tissue movements and their influence on normal wing development are discussed.     

Function and regulation of homothorax in the wing imaginal disc of Drosophila

The gene homothorax (hth) is originally expressed uniformly in the wing imaginal disc but, during development, its activity is restricted to the cells that form the thorax and the hinge, where the wing blade attaches to the thorax, and eliminated in the wing pouch, which forms the wing blade. We show that hth repression in the wing pouch is a prerequisite for wing development; forcing hth expression prevents growth of the wing blade. Both the Dpp and the Wg pathways are involved in hth repression. Cells unable to process the Dpp (lacking thick veins or Mothers against Dpp activity) or the Wg (lacking dishevelled function) signal express hth in the wing pouch. We have identified vestigial (vg) as a Wg and Dpp response factor that is involved in hth control. In contrast to its repressing role in the wing pouch, wg upregulates hth expression in the hinge. We have also identified the gene teashirt (tsh) as a positive regulator of hth in the hinge. tsh plays a role specifying hinge structures, possibly in co-operation with hth.     

Enhancement of short wing formation and ovarian growth in the genetically defined macropterous strain of the brown planthopper,Nilaparvata lugens

When JH II, III or methoprene was applied in the nymphal stages to two different strains of the brown planthopper which were selected to produce long (macropterous) or short (brachypterous) wing forms, no effect was observed on the molting profile or metamorphosis. Brachypterization of a majority of the presumptive macropters was, however, observed by application of these chemicals, although there was no effect on wing form in the presumptive brachypters. The results show that the sensitive periods for the brachypterization of the presumptive macropters falls between early antepenultimate instar and within 1 or 2days of the penultimate instar, and that the chemicals were effective, in the following order of potency: methoprene>JH III>JH II. Ovarian growth was greatly enhanced in the presumptive macropters when JH III or methoprene was applied twice, within 12h of the 3rd or 4th nymphal instar and 6h before adult emergence. JH II on the other hand had no effect on ovarian growth when applied to the presumptive macropters at any of the nymphal stages. None of the chemicals had any effect on ovarian growth in the presumptive brachypters.     

In-Vivo Imaging of the Drosophila Wing Imaginal Disc over Time: Novel Insights on Growth and Boundary Formation

In developmental biology, the sequence of gene induction and pattern formation is best studied over time as an organism develops. However, in the model system of Drosophila larvae this oftentimes proves difficult due to limitations in imaging capabilities. Using the larval wing imaginal disc, we show that both overall growth, as well as the creation of patterns such as the distinction between the anterior(A) and posterior(P) compartments and the dorsal(D) and ventral(V) compartments can be studied directly by imaging the wing disc as it develops inside a larva. Imaged larvae develop normally, as can be seen by the overall growth curve of the wing disc. Yet, the fact that we can follow the development of individual discs through time provides the opportunity to simultaneously assess individual variability. We for instance find that growth rates can vary greatly over time. In addition, we observe that mechanical forces act on the wing disc within the larva at times when there is an increase in growth rates. Moreover, we observe that A/P boundary formation follows the established sequence and a smooth boundary is present from the first larval instar on. The division of the wing disc into a dorsal and a ventral compartment, on the other hand, develops quite differently. Contrary to expectation, the specification of the dorsal compartment starts with only one or two cells in the second larval instar and a smooth boundary is not formed until the third larval instar.     

Functional peculiarities of stretch receptors of the flight apparatus in the cockroach Periplaneta americana]

Functional peculiarities of stretch receptors in wing articulations of the cockroach are considered and possible functional role of these receptors in maintenance of stable rhythm of flight is discussed. Stretch receptors of wing articulations are of phasictonic type they exhibit slow and incomplete adaptation, discharging when the wing goes upward. The pattern of impulse response of the receptor depends both on the angle and the velocity of displacement of wing platelet. The scheme of presumptive pacemaker of wing beats is discussed in detail.     

Regulative interaction of mature imaginal disc Fragments with embryonic and immature disc tissues inDrosophila

Summary These experiments examined whether inDrosophila immature imaginal disc tissue and tissues from embryonic stages can influence pattern regulation in a disc fragment in the same way as can mature imaginal discs. Immature imaginal discs, or the cells of whole embryos, were mixed with a test fragment (presumptive notum) from a mature wing disc. The immature tissues in each mixture were genetically marked and had been heavily irradiated (25 Kr gamma) prior to mixing to prevent growth and maturation during subsequent culture in vivo. Alteration of the regulative behavior of the test fragment (that is, regeneration of wing) thus provided an assay for the communication of positional information by the immature tissues. The results suggest that this capacity arises well before competence to metamorphose, as early as the 16th hour of embryonic development, whereas prior to 16 h, essentially no stimulation of regeneration occurred. It is suggested that the imaginal disc (or presumptive disc) cells of the embryo may have been responsible for this early stimulatory capacity.     

Quantitative description and discrimination of butterfly wing patterns using moment invariant analysis

Studies examining and using pattern variation in insects for identification and characterization of individuals and populations have been limited by the methods available for quantifying wing patterns objectively. In this paper, differences in wing pattern are demonstrated statistically using moment invariant data sets generated automatically from digitized images of the speckled wood butterfly, Pararge aegeria (Linnaeus). Studies with other biological subjects have already shown moment invariants to work well with outline shapes and silhouettes. A pilot study with replicated monochrome photographs of a single butterfly showed the method could detect pattern differences between wing surfaces, even in the presence of simulated wing fading and damage. In a further study of the wings of 228 specimens, multivariate analyses of variance using the moment data reliably detected differences between groups of butterflies according to sex, geographical origin and culture history. Potential applications and future improvements of the moment methodology are considered.     

Comparative morphology of the carpel in the Liliaceae: Uvularieae

Three genera of the Uvularieae (Kreysigia, Schelhammera, Uvularia) have tricarpellate, syncarpous pistils. Ventral bundles (presumably the united simple septal and placental bundles of a carpellary wing) may be present in Kreysigia and Schelhammera. In Kreysigia the two presumptive ventral bundles from adjoining carpels are fused basipetally in each septum. The septal bundles of the other two genera are either simple (Schelhammera) or in part compound (united) below and simple (separate) above (Uvularia) , hence fused acropetally. In Uvularia , the dorsal bundle of the carpel and the median bundle of the tepal are uniquely tripartite and probably homologous. No raphides were found in the carpels of these genera.     

Regulation and metamorphosis of the abdominal histoblasts ofDrosophila melanogaster

Summary The development of the adult abdomen ofDrosophila melanogaster was analyzed by histology, microcautery, and genetic strategies. Eight nests of diploid histoblasts were identified in the newly hatched larva among the polytene epidermal cells of each abdominal segment: pairs of anterior dorsal, posterior dorsal, and ventral histoblast nests and a pair of spiracular anlagen. The histoblasts do not divide during larval life but begin dividing rapidly 3 h after pupariation, doubling every 3.6 h. Initially they remain confined to their original area, but 15 h after pupariation the nests enlarge, and histoblasts replace adjacent epidermis cell by cell. The histoblasts cover half the abdomen by 28 h after pupariation and the rest by 36 h. Polytene epidermal cells of the intersegmental margin are replaced last. Cautery of the anterior dorsal nest caused deletion of the whole corresponding hemitergite, whereas cautery of the posterior dorsal nest caused the deletion of the macrochaetae of the posterior of the hemitergite. Cautery of the ventral nest deleted the hemisternite and the pleura, whereas cautery of the spiracular anlagen deleted the spiracle. Results of cautery also revealed that no macrochaetae formed on the tergite in the absence of adjacent microchaetae. Clonal analysis revealed that there were no clonal restrictions within a hemitergite at pupariation. Cautery of polytene epidermal cells other than those of the intersegmental margin failed to affect tergite development. However, cautery of polytene epidermal cells of the intersegmental margin adjacent to either dorsal histoblast nest caused mirror-image duplications of the anterior or posterior of the hemitergite in 10% of the hemitergites. Forty percent of the damaged presumptive hemitergites formed complete hemitergites, indicating extensive pattern regulation and regeneration. Pattern duplication and regeneration were accounted for in terms of intercalation and a model of epimorphic pattern regulation (French et al., 1976). Histoblasts in adjacent segments normally develop independently, but if they are enabled to interact by deleting the polytene epidermal cells of the intersegmental margin, they undergo intercalation which results in duplication or regeneration. The possible role of the intersegmental margin cells of insects in development was analyzed.     

A dual role for homothorax in inhibiting wing blade development and specifying proximal wing identities in Drosophila

The Drosophila wing imaginal disc gives rise to three body parts along the proximo-distal (P-D) axis: the wing blade, the wing hinge and the mesonotum. Development of the wing blade initiates along part of the dorsal/ventral (D/V) compartment boundary and requires input from both the Notch and wingless (wg) signal transduction pathways. In the wing blade, wg activates the gene vestigial (vg), which is required for the wing blade to grow. wg is also required for hinge development, but wg does not activate vg in the hinge, raising the question of what target genes are activated by wg to generate hinge structures. Here we show that wg activates the gene homothorax (hth) in the hinge and that hth is necessary for hinge development. Further, we demonstrate that hth also limits where along the D/V compartment boundary wing blade development can initiate, thus helping to define the size and position of the wing blade within the disc epithelium. We also show that the gene teashirt (tsh), which is coexpressed with hth throughout most of wing disc development, collaborates with hth to repress vg and block wing blade development. Our results suggest that tsh and hth block wing blade development by repressing some of the activities of the Notch pathway at the D/V compartment boundary.