Transplantationsversuche zur Blastemgliederung, Regenerations- und Differenzierungsleistung der Beinanlagen vonCulex pipiens (L.)

The three leg imaginal discs of Drosophila: "Vive la différence"

The imaginal discs of Drosophila are the larval primordia for the adult cuticular structures of the adult fly. Fate maps of different discs have been generated that show the localization of prospective adult structures. Even though the three legs differ in their morphology, only the fate map for the T1 (prothoracic) leg disc has been generated. Here we present fate maps for the T2 (meso-) and T3 (metathoracic) leg discs. We show that there are many similarities to the map of the T1 leg disc. However, there are also significant differences in the contributions of each disc to the thorax, in the morphology of joints connecting the legs to the thorax, in bristle patterns, and in the positioning of some sensory organs. We also tested the developmental potential of disc fragments and observed that T2 and T3 leg discs have more limited plasticity and are unable to transdetermine. The differences in the cuticle patterns between legs are robust and conserved in many species of dipterans. While most previous analyses of imaginal disc development have not distinguished between the different leg discs, we believe that the underlying differences of the three leg discs demonstrated here cannot be ignored when studying leg disc development.

The origin and evolution of stereotyped patterns of macrochaetes on the nota of cyclorraphous Diptera

A long-standing problem in evolutionary biology is how genetic variation arises within populations and evolves to make species anatomically different. Many of the morphological differences in body plans between animal groups are thought to result from changes in gene expression during development. The rules governing the structure and evolution of cis-regulatory gene sequences are unknown, however, and the evolution of traits between closely related species remains relatively unexplored at a molecular level. To study the evolution of gene regulation, it is necessary to find a tractable trait that varies between species and for which the genetic regulation is well known in at least one of the species. The stereotyped, two-dimensional pattern of bristles on the thorax of Drosophila has been intensively investigated and is due to a precise spatial expression of proneural genes. Other species of flies have different bristle patterns and so comparisons between them provide a good paradigm for the study of changes in gene regulation. Here, we review the current state of understanding of these changes.

Conservation of upstream regulators of scute on the notum of cyclorraphous Diptera

Bristles on the notum of many cyclorraphous flies are arranged into species-specific stereotyped patterns. Differences in the spatial expression of the proneural gene scute correlate with the positions of bristles in those species looked at so far. However, the examination of a number of genes encoding trans-regulatory factors, such as pannier, stripe, u-shaped, caupolican and wingless, indicates that they are expressed in conserved domains on the prospective notum. This suggests that the function of a trans-regulatory network of genes is relatively unchanged in derived Diptera, and that many differences are likely to be due to changes in cis-regulatory sequences of scute. In contrast, in Anopheles gambiae, a basal species with no stereotyped bristle pattern, the expression patterns of pannier and wingless are not conserved, and expression of AgASH, the Anopheles proneural gene, does not correlate in a similar manner with the bristle pattern. We discuss the possibility that independently acting cis-regulatory sequences at the scute locus may have arisen in the lineage giving rise to cyclorraphous flies.

Differentiation capacities of the dorsal metathoracic (haltere) disc ofDrosophila melanogaster : I. Normal organ map

The mature haltere disc, when implanted into a larva of the same age, undergoes metamorphosis along with the host, and produces a haltere, haltere sclerite, notum III, and pleural process. Implants ordinarily form an inverted vesicle, into which the haltere is frequently everted, usually only partly. Many "adventitious bristles" may be formed which are not foundin situ. It was found thatsc may reduce, andmwh may increase the number of sensilla.On the basis of results obtained from transplanted disc fragments an organ map of the haltere disc was constructed, which shows the presumptive haltere area to be located in the posterio-central part of the disc, while the anterio-medial part forms the thoracic structures dorsal to the haltere, and the posterio-lateral part the thoracic structures ventral to it. The anlage of the "adventitious bristles" is probably within the notum area. The haltere anlage proper is concentric; the prospective distal capitellum is located in the center, and is surrounded by the anlagen of the more proximal segments.The organ map of the haltere disc is compared with that of other discs. Organ maps seem to be basically concentric. There is a close homology between the maps of the wing and the haltere disc.