Larval Discs Research Articles

Uncoupling of Related Structural Changes in Metamorphosing Torrent-Dwelling Tadpoles

the gape, and resorption of the tail during metamorphosis. In the torrent-dwelling tadpoles of Ansonia longidigita (Bufonidae) and of species of Amolops (Ranidae), this coupling is significantly modified and larval oral discs, beaks, and denticles are retained much longer into metamorphosis. These specialized tadpoles are thereby able to cling to rocks in the larval environment until the tail is largely resorbed. As a result, compared to generalized tadpoles, these tadpoles probably suffer less risk of predation due to the loss of locomotor efficiency characteristic of the period of metamorphic climax. The lower eyelid appears to develop earlier in the torrent-dwelling tadpoles than in generalized larvae of Bufo and Rana from the same region. This difference may reflect early development of aerial vision in tadpoles living in torrents where frequently their eyes are likely to be momentarily out of water.

The development of the sensory organs of the legs in the blowfly,Phormia regina

The development of the sensory neurons of the legs of the blowfly, Phormia regina has been described from the third instar larva to the late pupa using immunohistochemical staining. The leg discs of the third instar larva contain 8 neurons of which 5 come to lie in the fifth tarsomere of the developing leg. Whereas 2 neurons persist at least to the late pupa, the other cells degenerate. The first neurons of gustatory sensilla arise in the fifth tarsomere at about 1.5 h after formation of the puparium. Most of these sensilla, however, appear within a short time period beginning at about 18 h. The femoral chordotonal sensory neurons first appear at the time of formation of the puparium, as a mass of cells situated in the distal femur. During later pupal development 2 groups of these cells come to lie at the femur-trochanter border, where they become the proximal femoral chordotonal organ of the adult; the remaining cells become the distal femoral chordotonal organ. Other scolopidial neurons appear later in development. The nerve pathways of the late pupal leg are established either by the axons of the cells that are present in the larval leg disc or by new outgrowing processes of sensory neurons. In the tibia, the initial direction of new outgrowth differs in different regions of the segment: proximal tibial neurons grow distally, while distal tibial neurons grow initially proximally.

Cdc2 and the regulation of mitosis: six interacting mcs genes

A cdc2-3w weel-50 double mutant of fission yeast displays a temperature-sensitive lethal phenotype that is associated with gross abnormalities of chromosome segregation and has been termed mitotic catastrophe. In order to identify new genetic elements that might interact with the cdc2 protein kinase in the regulation of mitosis, we have isolated revertants of the lethal double mutant. The suppressor mutations define six mcs genes (mcs: mitotic catastrophe suppressor) that are not allelic to any of the following mitotic control genes: cdc2, wee 1, cdc13, cdc25, suc1 or nim1. Each mcs mutation is recessive with respect to wild-type in its ability to suppress mitotic catastrophe. None confer a lethal phenotype as a single mutant but few of the mutants are expected to be nulls. A diverse range of genetic interactions between the mcs mutants and other mitotic regulators were uncovered, including the following examples. First, mcs2 cdc2w or mcs6 cdc2w double mutants display a cell cycle defect dependent on the specific wee allele of cdc2. Second, both mcs1 cdc25-22 or mcs4 cdc25-22 double mutants are nonconditionally lethal, even at a temperature normally permissive for cdc25-22. Finally, the characteristic suppression of the cdc25 phenotype by a loss-of-function wee1 mutation is reversed in a mcs3 mutant background. The mcs genes define new mitotic elements that might be activators or substrates of the cdc2 protein kinase.

Changing spatial patterns of DNA replication in the developing wing of Drosophila

Using an antibody against bromodeoxyuridine we have analyzed the distribution of S-phase nuclei in the wing disc of Drosophila as the larval disc transforms into the adult wing during metamorphosis. On the basis of the timing of replication three cell populations can be distinguished: the cells of the presumptive wing margin, the precursor cells of the longitudinal veins, and those of the intervein regions. In each of these populations the cell cycle is first arrested and later resumes at a specific time, so that at each developmental time point a characteristic spatial pattern of S-phase nuclei is seen. An interpretation of these changing patterns in terms of vein formation, compartments, and neural development is offered.

Restoration of wing margins in Lyra mutants of Drosophila melanogaster

Lyra is a dominant, homozygous lethal mutation of Drosophila melanogaster; in heterozygotes the wings lack portions of the anterior and posterior margins including the characteristic bristles. We have found that, in addition to the loss of bristle forming cells, there is a decrease in the number of wing surface cells that varies between 10 and 20%. However, we observed no histological evidence of excessive cell death in either the larval discs or the pupal wing precursors in Lyra flies. Restoration of all or part of the normal wing margins occurs in some, but not all, cases of morphogenetic mosaics, in which there were patches of wild-type cells in Lyra wing margins due to irradiation-induced mitotic recombination. Analysis of these restorations, using margin bristles as indicators, shows that the Lyra wild-type gene is not involved in bristle formation per se and further that its expression is not cell autonomous. Instead the effect of the Lyra mutation appears to be associated with development of a margin forming subpopulation of cells and to influence the characteristic pattern of cells and bristles in the wing margin via an inductive interaction. The dorsal-ventral boundary can be demonstrated in the de facto wing margins of Lyra mutants suggesting that its origin is independent of any function Lyra might have in normal wing margin morphogenesis. In wing margin restorations the dorsal-ventral boundary is clearly delimited by trichomes and somewhat less rigorously shown by the margin bristles. Further, in these restorations ventral clones induce dorsal bristles, as well as ventral ones, and vice versa, indicating that the influence of Lyra is not restricted by the dorsal-ventral boundary.

In vitro differentiation ofPieris brassicae imaginal wing discs: Effects and metabolism of ecdysone and ecdysterone.

Imaginal wing discs ofPieris brassicae can be cultured in vitro for extended periods. Their ultrastructural development was investigated after culture in the presence of various concentrations of ecdysone and ecdysterone. When ecdysone or low concentrations of ecdysterone (2×10-7 M) were added to culture media, larval discs secreted a pupal cuticle and they subsequently differentiated scales; prepupal discs completed their imaginal development. With a higher concentration of ecdysterone (2×10-6 M), all discs produced abundant but fragmentary cuticular material.Prepupal discs were able to metabolize both hormones in vitro. Ecdysterone was mainly converted into a polar compound detectable after a short period of incubation. Ecdysone was transformed, at a slower rate, forming a polar compound and 26-hydroxyecdysone but no ecdysterone.

Development of the haptor of Urocleidus adspectus Mueller, 1936 (Monogenea: Ancyrocephalinae)

Urocleidus adspectus Mueller, 1936 (Ancyrocephalinae) was transmitted experimentally to Perca flavescens and development of its haptor studied at 20 °C.The oncomiracidial haptor unfolds into a ventrally directed disc with 14 marginal hooks. Hamulus rudiments appear in multinuclear oncoblasts lying immediately anterior to the larval disc. The four oncoblasts move into the disc in synchrony and rudiments develop into blades. Five days postinfection, when most larvae were found on the gills, the disc is differentiating into the haptor of adult worms. The tissue enclosing the partially developed blades of the hamuli initially projects from the posteroventral surface of the haptor; tips of the ventral blades point anteriorly or anteroventrally and tips of the dorsal blades point dorsally or anterodorsally. With further growth the tissue enclosing the blades comes to project posteriorly from the haptor; tips of the ventral blades point anteroventrally and tips of the dorsal blades point anterodorsally. During differentiation, the tips of the blades of marginal hooks II come to point ventrally. The posterolateral margins of the larval disc fold dorsally and carry marginal hooks III and IV onto the dorsal surface of the haptoral lobes. Marginal hooks V come to lie laterally on the lobes while I, VI, and VII are ventral. Seven days postinfection, the haptoral sclerites of many worms are fully developed and some worms produce eggs.

Chromosomal rearrangements which affect the chromosomal integration of the ribosomal genes in drosophila melanogaster

Sucrose gradient analysis of DNA from detergent-pronase lysates of whole adult flies has been used to examine a variety of genotypes for the presence of ribosomal genes not integrated into the DNA of the chromosome. Such genes were found in females in which one X chromosome carries an inversion, having one of its breakpoints between the nucleolus organizer and the centromere. These inversions move the nucleolus organizer to the distal end of the X chromosome. Other inversions which do not move the nucleolus organizer, as well as a series of bobbed deficiencies, did not induce unintegrated genes. The same inversions which induce unintegrated genes in adults also produce them in the diploid brain and imaginal discs of larvae. On the other hand, in the polytene salivary glands, unintegrated genes were found in every genotype examined.

Evagination of imaginal discs in the fleshflySarcophaga crassipalpis: Hormonal control in vivo

The hormonal control of evagination of the imaginal leg discs of the fleshflySarcophaga crassipalpis was studied by means of ectopic transplantation of discs from mature larvae or prepupae onto prepupal hosts. Evagination was influenced by the age of the donor and the developmental commitment of the host. Discs from non-diapuse as well as diapause-committed donors did not differ in their capacity to evaginate and differentiate. Mature larval discs from either type of donor could evaginate only when transplanted onto non-diapause hosts; they failed to evaginate on diapause-committed hosts even though host discs evaginated in situ about 40 h after transplantation. Discs from white prepupae evaginated whether transplanted onto non-diapause or onto diapause-committed hosts.

The ultrastructure of the differentiating pupal leg ofDrosophila melanogaster.

The ultrastructure of the developing pupal leg ofDrosophila melanogaster is investigated at various stages from white prepupa to pharate adult. All the different cell types found in the leg at each stage examined are traced developmentally. This includes general epithelium which secretes both a pupal and adult cuticle and specialized epithelial structures such as apodemes, bristles and other sense organs. Muscle, nerve and tracheal tissue develop within the leg cavity. Particular attention was paid to the development of muscle tissue which was shown to differentiate from the adepithelial cells of the larval disc. The development of theDrosophila leg is compared with that ofCalliphora (van Ruiten and Sprey, 1974) especially with respect to the different stages at which new structures appear in the two species.

Studies on reef corals. I. Skeleton formation by newly settled planula larva of Pocillopora damicornis

Initiation of coral-skeleton formation was studied in the reef-coral Pocillopora damicornis Lamarck. Observations were made on sequential skeletal growth stages of newly settled planula larvae during the first 22 days following settling onto glass microscope slides. Techniques used include phase light microscopy, scanning and transmission electron microscopy, and powder X-ray and selected area electron micro-diffraction. Formation of the skeleton is initiated immediately on settling of the larva. The primary calcareous elements are of two types — flattened spherulitic platelets, and smaller rod-like granules. Rudimentary primary septa are clearly defined within 6 h after settling. Fusion of the primary calcareous elements results in the formation of the larval basal disc within 48 to 72 h. With transmission electron microscopy, this basal disc is found to differ from subsequent adult calcification in (1) considerably lesser degree of mineralization, (2) smaller crystal size, (3) more random orientation of the crystals, and (4) the presence of trace amounts of calcite in addition to aragonite. The basal disc with its septal rudiments constitutes a true larval skeleton, differing in morphology, micro-architecture, and crystal type from the fibrous growth characterizing the adult skeleton.

Morphogenic effects of halogenated thymidine analogues on Drosophila. I. Quantitative analysis of lesions induced by 5-bromodeoxyuridine and 5-fluorouracil

When 5-fluorouracil (FU) is offered simultaneously with 5-bromodeoxyuridine (BUdR) to Drosophila larvae, a variety of bristle modifications and hyperplastic growths are found on the wings of the adult flies. Administration of FU alone will not stimulate growth in Drosophila, while high concentrations of BUdR offered alone will induce a lower frequency of growth modifications than induced by BUdR plus FU. Comparison of the morphological response induced by sequential treatment with the two analogues and that by simultaneous treatment with the analogues at the same concentrations indicates that maximum response is achieved by the presence of both analogues at the same time. These observations suggest that BUdR may be the primary agent in upsetting morphogenesis in Drosophila, while FU plays a subsidiary role leading to intensification of the morphogenic effects when it is present during the treatment period. The incorporation of BUdR-H3 and FU-H3 in Drosophila tissues was demonstrated by autoradiography. BUdR-H3 was incorporated in nuclei of both larval and imaginal disc cells, and the isotopic label was removable by deoxyribonuclease. Following dietary administration of FU-H3, tritium was found in RNA, primarily in cytoplasmic regions. Since BUdR is a known mutagen, consideration was given to the hypothesis that the altered growth patterns in Drosophila wings are the result of somatic cell mutational events induced by BUdR. Validity of the argument that recessive mutations on the X chromosomes can be readily expressed in the somatic cells of the male with one X chromosome as opposed to the female with two X chromosomes was tested by comparing the frequency of the induced somatic cell lesions in male and female zygotes. The males showed a higher frequency of induced supernumeraries, while the icidence of bristle effects and total wings affected was the same in both sexes.

Effects of hormones on RNA and protein synthesis in the imaginal wing disks of the Ricini silkworm

the present study examines the capacity of larval and pharate pupal wing disks of Samia cynthia ricini to synthesize RNA and proteins and the relation of these syntheses to endogenous and injected juvenile hormone and ecdysone during metamorphosis. The dry weight of the wing disks was found to increase in a linear fashion whereas RNA and protein synthesis showed cyclical patterns. Depending on the stage of development, injection of hormones and their analogues induced changes in the synthetic capacities of the wing disks. An injected hormone had its greatest effect when its endogenous level was lowest and vice versa. At no time were the endogenous titres of juvenile hormone and ecdysone simultaneously high. An antagonistic behaviour was observed when a mixture of two hormones was injected. Although the wing disks do not undergo apolysis and are relieved of the responsibility to synthesize cuticle, their metabolism is affected by injection of the ecdysone. This result suggests a possible rôle for ecdysone besides the induction of moulting.

Studies on protein synthesis in imaginal discs of Drosophila melanogaster

Comparisons have been made of protein synthesis in imaginal discs of different developmental stages using acrylamide gel electrophoresis of 3H-and 14C-labeled protein. No qualitative differences were found between middle third instar discs and late third instar discs and small differences between late third instar discs and early prepupal discs. Using actinomycin D the functional half-life of m-RNA of imaginai discs has been minimally estimated to be approximately 2 1 2 hr long. It has been proposed, on the basis of the life of m-RNA, that no large differences in the pattern of protein synthesis in late larval and prepupal discs would be expected because the existing m-RNA would buffer the system against changes.

Regulation capacities of the wing- and halterediscs of wild type and bithoraxDrosophila.

1. On removal of one dorsal mesothoracic disc from third-instar larvae ofDrosophila melanogaster (wild stock), regulation took place in one fourth of the cases, by the activity of the corresponding disc of the intact side. 2. In larvae of abithorax stock, regulation took place in the majority of cases, but it was due to the activity of thebx dorsal metathoracic disc of the operated side. 3. The sternopleura is present after extirpation of the wing disc but absent after extirpation of the ventral mesothoracic disc. 4. The findings under 1 and 2 are discussed in connection with previous work on regulation in larval discs.