Sp1 modifies leg-to-wing transdetermination in Drosophila.

During Drosophila development, the transcription factor Sp1 is necessary for proper leg growth and also to repress wing development. Here we test the role of Sp1 during imaginal disc regeneration. Ubiquitous expression of wg induces a regeneration blastema in the dorsal aspect of the leg disc.

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.

Drosophila twin spot clones reveal cell division dynamics in regenerating imaginal discs.

Cell proliferation is required for tissue regeneration, yet the dynamics of proliferation during regeneration are not well understood. Here we investigated the proliferation of eye and leg regeneration in fragments of Drosophila imaginal discs. Using twin spot clones, we followed the proliferation and fates of sister cells arising from the same mother cell in the regeneration blastema.

Regeneration and transdetermination: the role of wingless and its regulation.

Imaginal discs of Drosophila have the remarkable ability to regenerate. After fragmentation wound healing occurs, ectopic wg is induced and a blastema is formed. In some, but not all fragments, the blastema will replace missing structures and a few cells can become more plastic and transdetermine to structures of other discs.

The twin spot generator for differential Drosophila lineage analysis.

In Drosophila melanogaster, widely used mitotic recombination-based strategies generate mosaic flies with positive readout for only one daughter cell after division. To differentially label both daughter cells, we developed the twin spot generator (TSG) technique, which through mitotic recombination generates green and red twin spots that are detectable after the first cell division as single cells. We propose wide applications of TSG to lineage and genetic mosaic studies.

Three genes control the timing, the site and the size of blastema formation in Drosophila.

Regeneration is a vital process to maintain and repair tissues. Despite the importance of regeneration, the genes responsible for regenerative growth remain largely unknown. In Drosophila, imaginal disc regeneration can be induced either by fragmentation and in vivo culture or in situ by ubiquitous expression of wingless (wg/wnt1).

A screen for genes that function in leg disc regeneration in Drosophila melanogaster.

Many diverse animal species regenerate parts of an organ or tissue after injury. However, the molecules responsible for the regenerative growth remain largely unknown. The screen reported here aimed to identify genes that function in regeneration and the transdetermination events closely associated with imaginal disc regeneration using Drosophila melanogaster.

Transdetermination: Drosophila imaginal disc cells exhibit stem cell-like potency.

Drosophila imaginal discs, the primordia of the adult fly appendages, are an excellent system for studying developmental plasticity. Cells in the imaginal discs are determined for their disc-specific fate (wingness, legness) during embryogenesis. Disc cells maintain their determination during larval development, a time of extensive growth and proliferation.

Onset of the DNA replication checkpoint in the early Drosophila embryo.

The Drosophila embryo is a promising model for isolating gene products that coordinate S phase and mitosis. We have reported before that increasing maternal Cyclin B dosage to up to six copies (six cycB) increases Cdk1-Cyclin B (CycB) levels and activity in the embryo, delays nuclear migration at cycle 10, and produces abnormal nuclei at cycle 14. Here we show that the level of CycB in the embryo inversely correlates with the ability to lengthen interphase as the embryo transits from preblastoderm to blastoderm stages and defines the onset of a checkpoint that regulates mitosis when DNA replication is blocked with aphidicolin.

Developmental analysis and squamous morphogenesis of the peripodial epithelium in Drosophila imaginal discs.

Imaginal discs of Drosophila provide an excellent system with which to study morphogenesis, pattern formation and cell proliferation in an epithelium. Discs are sac-like in structure and are composed of two epithelial layers: an upper peripodial epithelium and lower disc proper. Although development of the disc proper has been studied extensively in terms of cell proliferation, cell signaling mechanisms and pattern formation, little is known about these same processes in the peripodial epithelium.

Regulation of cellular plasticity in Drosophila imaginal disc cells by the Polycomb group, trithorax group and lama genes.

Drosophila imaginal disc cells can switch fates by transdetermining from one determined state to another. We analyzed the expression profiles of cells induced by ectopic Wingless expression to transdetermine from leg to wing by dissecting transdetermined cells and hybridizing probes generated by linear RNA amplification to DNA microarrays. Changes in expression levels implicated a number of genes: lamina ancestor, CG12534 (a gene orthologous to mouse augmenter of liver regeneration), Notch pathway members, and the Polycomb and trithorax groups of chromatin regulators.

Genetic interactions between Cdk1-CyclinB and the Separase complex in Drosophila.

Cdk1-CycB plays a key role in regulating many aspects of cell-cycle events, such as cytoskeletal dynamics and chromosome behavior during mitosis. To investigate how Cdk1-CycB controls the coordination of these events, we performed a dosage-sensitive genetic screen, which is based on the observations that increased maternal CycB (four extra gene copies) leads to higher Cdk1-CycB activity in early Drosophila embryos, delays anaphase onset, and generates a sensitized non-lethal phenotype at the blastoderm stage (defined as six cycB phenotype). Here, we report that mutations in the gene three rows (thr) enhance, while mutations in pimples (pim, encoding Drosophila Securin) or separase (Sse) suppress, the sensitized phenotype.

A transient cell cycle shift in Drosophila imaginal disc cells precedes multipotency.

When Drosophila imaginal discs regenerate, specific groups of cells can switch disc identity so that, for example, cells determined for leg identity switch to wing. Such switches in cell determination are known as transdetermination. We have developed a system by which individual cells are marked and monitored in vivo as they transdetermine so that their proliferation, cell sizes, and differentiation are accurately traced.

Both cyclin B levels and DNA-replication checkpoint control the early embryonic mitoses in Drosophila.

The earliest embryonic mitoses in Drosophila, as in other animals except mammals, are viewed as synchronous and of equal duration. However, we observed that total cell-cycle length steadily increases after cycle 7, solely owing to the extension of interphase. Between cycle 7 and cycle 10, this extension is DNA-replication checkpoint independent, but correlates with the onset of Cyclin B oscillation.

Transdetermination in Drosophila imaginal discs: a model for understanding pluripotency and selector gene maintenance.

Drosophila imaginal disc cells have the ability to undergo transdetermination, a process whereby determined disc cells change fate to that of another disc identity. For example, leg disc cells can transdetermine to develop as wing cells. Such events can occur after mechanical disc fragmentation and subsequent regeneration.

A genetic screen for suppressors and enhancers of the Drosophila cdk1-cyclin B identifies maternal factors that regulate microtubule and microfilament stability.

Coordination between cell-cycle progression and cytoskeletal dynamics is important for faithful transmission of genetic information. In early Drosophila embryos, increasing maternal cyclin B leads to higher Cdk1-CycB activity, shorter microtubules, and slower nuclear movement during cycles 5-7 and delays in nuclear migration to the cortex at cycle 10. Later during cycle 14 interphase of six cycB embryos, we observed patches of mitotic nuclei, chromosome bridges, abnormal nuclear distribution, and small and large nuclei.

Lumenal transmission of decapentaplegic in Drosophila imaginal discs.

Drosophila imaginal discs are sac-like appendage primordia comprising apposed peripodial and columnar cell layers. Cell survival in disc columnar epithelia requires the secreted signal Decapentaplegic (DPP), which also acts as a gradient morphogen during pattern formation. The distribution mechanism by which secreted DPP mediates global cell survival and graded patterning is poorly understood.

Segmentation of the central nervous system in ligated embryos ofDrosophila melanogaster.

We have visualized segmentation in theDrosophila embryoniccentral nervous system (CNS) by staining for acetylcholinesterase activity. This technique was used to evaluate the effect of ligation on segments in the ventral CNS. When embryos were ligated prior to cellularization (60 min) fewer segmental ganglia developed in posterior fragments than when embryos were ligated at the blatoderm stage (3 h).

Acquisition of differentiative competence in the imaginai leg discs ofDrosophila.

When first leg imaginai discs from early third instar larvae are forced to differentiate immediately by transplantation into larval hosts ready to pupate, they fail to differentiate all the adult leg structures. Even though the variability among these incomplete differentiations is wide, we were able to draw the following conclusions. Even if only little differentiations, limited to a few hairs and bristles, were observed, the structures were always identifiable as the most proximal and the most distal structures of the leg.

["Anlageplan", determination and capacity for transdetermination of the male foreleg disc of Drosophila melanogaster].

1. Various fragments of the disc of the foreleg of the late third instar were implanted individually into host larvae of the same age. The imaginal discs ofDrosophila melanogaster have a mosaic determination.