The two origins of hemocytes in Drosophila.

As in many other organisms, the blood of Drosophila consists of several types of hemocytes, which originate from the mesoderm. By lineage analyses of transplanted cells, we specified two separate anlagen that give rise to different populations of hemocytes: embryonic hemocytes and lymph gland hemocytes. The anlage of the embryonic hemocytes is restricted to a region within the head mesoderm between 70 and 80% egg length. In contrast to all other mesodermal cells, the cells of this anlage are already determined as hemocytes at the blastoderm stage. Unexpectedly, these hemocytes do not degenerate during late larval stages, but have the capacity to persist through metamorphosis and are still detectable in the adult fly. A second anlage, which gives rise to additional hemocytes at the onset of metamorphosis, is located within the thoracic mesoderm at 50 to 53% egg length. After transplantation within this region, clones were detected in the larval lymph glands. Labeled hemocytes are released by the lymph glands not before the late third larval instar. The anlage of these lymph gland-derived hemocytes is not determined at the blastoderm stage, as indicated by the overlap of clones with other tissues. Our analyses reveal that the hemocytes of pupae and adult flies consist of a mixture of embryonic hemocytes and lymph gland-derived hemocytes, originating from two distinct anlagen that are determined at different stages of development.

FlyMove--a new way to look at development of Drosophila.

Development of any organism requires a complex interplay of genes to orchestrate the many movements needed to build up an embryo. Previously, work on Drosophila melanogaster has provided important insights that are often applicable in other systems. But developmental processes, which take place in space and time, are difficult to convey in textbooks. Here, we introduce FlyMove (http://flymove.uni-muenster.de), a new database combining movies, animated schemata, interactive "modules" and pictures that will greatly facilitate the understanding of Drosophila development.

The formation of syncytia within the visceral musculature of the Drosophila midgut is dependent on duf, sns and mbc.

The visceral musculature of the Drosophila midgut consists of an inner layer of circular and an outer layer of longitudinal muscles. Here, we show that the circular muscles are organised as binucleate syncytia that persist through metamorphosis. At stage 11, prior to the onset of the fusion processes, we detected two classes of myoblasts within the visceral trunk mesoderm. One class expresses the founder-cell marker rP298-LacZ in a one- to two-cells-wide strip along the ventralmost part of the visceral mesoderm, whereas the adjacent two to three cell rows are characterised by the expression of Sticks-and-stones (SNS). During the process of cell fusion at stage 12 SNS expression decreases within the newly formed syncytia that spread out dorsally over the midgut. At both margins of the visceral band several cells remain unfused and continue to express SNS. Additional rP298-LacZ-expressing cells arise from the posterior tip of the mesoderm, migrate anteriorly and eventually fuse with the remaining SNS-expressing cells, generating the longitudinal muscles. Thus, although previous studies proposed a separate primordium for the longitudinal musculature located at the posteriormost part of the mesoderm anlage, our cell lineage analyses as well as our morphological observations reveal that a second population of cells originates from the trunk mesoderm. Mutations of genes that are involved in somatic myoblast fusion, such as sns, dumbfounded (duf) or myoblast city (mbc), also cause severe defects within the visceral musculature. The circular muscles are highly unorganised while the longitudinal muscles are almost absent. Thus the fusion process seems to be essential for a proper visceral myogenesis. Our results provide strong evidence that the founder-cell hypothesis also applies to visceral myogenesis, employing the same genetic components as are used in the somatic myoblast fusion processes.

Mapping and identification of essential gene functions on the X chromosome of Drosophila.

The Drosophila melanogaster genome consists of four chromosomes that contain 165 Mb of DNA, 120 Mb of which are euchromatic. The two Drosophila Genome Projects, in collaboration with Celera Genomics Systems, have sequenced the genome, complementing the previously established physical and genetic maps. In addition, the Berkeley Drosophila Genome Project has undertaken large-scale functional analysis based on mutagenesis by transposable P element insertions into autosomes. Here, we present a large-scale P element insertion screen for vital gene functions and a BAC tiling map for the X chromosome. A collection of 501 X-chromosomal P element insertion lines was used to map essential genes cytogenetically and to establish short sequence tags (STSs) linking the insertion sites to the genome. The distribution of the P element integration sites, the identified genes and transcription units as well as the expression patterns of the P-element-tagged enhancers is described and discussed.

Clonal analysis of the blastoderm anlage of the Malpighian tubules in Drosophila melanogaster.

Genetically marked maroon-like (mal) clones were induced by mitotic recombination with X-rays at the blastoderm stage in mal/mal + heterozygotes and were analysed in differentiated Malpighian tubules (MT). Marked cells were not confined to single anterior (MA) or posterior (MP) tubules, but were distributed among the four tubules. About 70% of the clones with two or more cells were fragmented, i.e. mal cells were separated by wild-type cells. Since the clones contain, on average, 6 cells and the differentiated MT consist of 484 cells (2 × 136 MA cells, 2 × 106 MP cells), we estimate that there are about 80 cells in the blastoderm anlage which on average pass through two to three mitoses. With increasing radiation doses (254 R, 635 R, 1270 R) a linear increase in clone frequency is observed. The mean sizes and size distributions of clones, however, remain unchanged. Since the increasing radiation dose also results in fewer differentiated Malpighi cells, we assume that regeneration does not occur. Therefore, size distributions of marked clones presumably represent real mitotic patterns in normogenesis. We suggest that essentially three successive mitoses take place, with a decreasing fraction of cells showing mitotic activity. Only a small fraction of cells goes through a fourth or even a fifth mitosis. Marked non-Minute clones induced in Minute heterozygotes are more frequent, but are not larger than non-Minute clones in wild-type background. Therefore, compartment boundaries cannot be recognized by this method. However, frequencies of marked cells found simultaneously in MA and MP pairs or in several single tubules of the same individuals are significantly higher than frequencies of multiple recombination events predicted by the Poisson distribution. From this, we conclude that neither the MA pair nor the MP pair nor single tubules represent compartments of the MT anlage.

Cell lineage restrictions in the genital disc ofDrosophila revealed byMinute gynandromorphs.

The genital imaginal disc ofDrosophila differentiates the terminalia, i.e. the genitalia and analia, of both sexes. It represents a composite anlage, containing a female genital primordium, a male genital primordium and an anal primordium. In normal males and females, only one of the two genital primordia differentiates; the other is developmentally repressed. Therefore, cell-lineage relationships between the male and female genital primordia can only be studied in sexual mosaics which differentiate female and male cells. We producedMinute (M)‖non-Minute(M+) gynandromorphs and selected those with sexually mosaic terminalia for a cell-lineage analysis. In these mosaics, either the male (XO) or female (XX) cells wereM + and thus had a growth advantage. The differential growth rates served as a tool to detect clonal restrictions. In control gynandromorphs (M +‖M +), the amount of female genitalia differentiated was largely independent of the amount of male genitalia present. In contrast, male and female anal structures, as a rule, added up to one full set. The same was true for the experimentalM‖M + gynandromorphs, but the contribution ofXX andXO cells to mosaic terminalia changed drastically due toM + cells competing successfully against the more slowly growingM cells. Specific subsamples ofM‖M + gynandromorphs showed thatM cells in a non-mosaic primordium are shielded from cell competition taking place in the neighbouring mosaic primordium. We conclude that the three primordia of the genital disc represent developmental compartments. In the genital primordia, even developmentally repressedM + cells compete successfully against developmentally activeM cells.

[Developmental studies on gynandromorphs ofDrosophila melanogaster : IV. Comparison of morphogenetic fate maps of larval and imaginal structures]. / Entwicklungsgenetische Untersuchungen an Gynandern vonDrosophila melanogaster : IV. Vergleich der morphogenetischen Anlagepläne larvaler und imaginaler Strukturen.

Gynandromorphs with female XX-and male XO-areas result from the loss of an unstable ring-X-chromosome in the early cleavage mitoses of ring/rod-X-chromosome heterozygotes. The phenotypes of the recessive alleles on the rod-X-chromosome are expressed in the XO-areas.377 larval gynandromorphs of the genotypeR(1)2, In(1)w vC /y w sn3Iz50e mal were examined and scored for the phenotypes of 13 paired and 10 unpaired structures (Table 2, Fig. 2). This was possible mainly by the cell-autonomous expression of aldehyde oxidase activity in soft tissues and by the comparison of the distribution of enzyme activity in wildtype and gynander larvae. The distances between pairs of structures were calculated in sturt-units (Tables 3 and 4). A morphogenetic fate map with the presumptive areas of larval structures was constructed (Fig. 3). The relative positions of the structures agree well with Poulson's fate map (Fig. 4). In addition, the distribution of phenotypes was scored in 380 adult gynandromorphs Table (5). The fate map (Fig. 5) which was constructed from these data is very similar to the fate map of larval structures. This similarity becomes even more pronounced if fate maps are constructed which contain only structures analogous in larva and imago (Table 6, Fig. 6). Therefore an attempt was made to set up an integrated morphogenetic fate map containing the presumptive areas of both larval and imaginal structures (Fig. 7). The possibilities of further blastoderm mapping are discussed.

[Developmental studies on gynandromorphs ofDrosophila melanogaster : I. The internal organs of the imago]. / Entwicklungsgenetische Untersuchungen an Gynandern vonDrosophila melanogaster : I. Die inneren Organe der Imago.

In ring/rod-X-chromosome heterozygotes the ring-X-chromosome is frequently lost in the early cleavage mitoses. The resulting gynandromorphs are mosaics with female XX- and male XO-areas. The phenotypes of the recessive alleles on the rod-X-chromosome are expressed in the XO-areas.The genemaroonlike (mal) on the X-chromosome influences the activity of the enzyme aldehyde oxidase. This fact was used to test the cell autonomy of aldehyde oxidase activity by histochemical methods in gynandromorphs of the genotypesR(1)2,In(1)w vC /y w mal andR(1)2,In(1)w vC /y w sn 3 lz 50e mal. The results show that in the cells of the imaginal Malpighian tubules the phenotypes ofwhite (w) andmaroonlike (mal) always occur together; XX-cells are pigmented and show aldehyde oxidase activity, whereas colorless XO-cells have no such enzyme activity (Figs. 1 and 2). This cell autonomy of aldehyde oxidase activity most likely applies also to the imaginal gut and the inner genitalia.The distribution of XX- and XO-areas in the Malpighian tubules, the gut and the inner genitalia was examined in 355 gynandromorphs. Approximately half of the gynanders have Malpighian tubules with an XX/XO-mosaic (Table 1, 2 and 3). A large fraction of the mosaic tubules (62%; Table 4) shows a pattern of alternating small cell clusters of different genotypes. It is supposed that this pattern develops during the formation of the tubes, especially during their elongation. The number of primitive Malpighian cells is estimated to be about 140.72% of the gynanders have mosaic guts (Table 1 and 5). The border between tissues of different genotypes is found very frequently in the posterior third of the anterior midgut (Fig. 3) and may correspond to the border between the tissues which develop from the anterior and posterior midgut rudiments. The estimates of the numbers of primitive cells for the gut structures are 2-3, as far as the crop, the cardia and the rectal valve are concerned, whereas a number of several hundred is estimated for the anterior as well as for the posterior midgut.Mosaics were also found in the inner genitalia consisting of combinations of male and female structures. In 16 gynandromorphs the paragonia or the ductus ejaculatorius were mosaic (Fig. 4); i.e. in male structures with XO-genotype areas with aldehyde oxidase activity were found. Nothing is known about the origin of these XX-cells, but the possibility must be considered that in gynandromorphs cells of female genotype can participate in the development of male genital structures.

[Developmental studies on gynandromorphs ofDrosophila melanogaster : II. The morphogenetic fate map]. / Entwicklungsgenetische Untersuchungen an Gynandern vonDrosophila melanogaster : II. Der morphogenetische Anlageplan.

The distribution of XX- and XO-areas within the cuticle and in the internal organs was examined in 355 adult gynandromorphs of the genotypeR(1)2,In(1)w vC /y w sn 3 lz 50e mal, whereby XO-areas could be recognized by the phenotypes of the recessive alleles on the rod-X-chromosome.The percentage of gynandromorphs in which selected pairs of structures show different genotypes is taken as a measurement (in sturt-units) for the distance between the presumptive areas of these structures in early developmental stages. The calculated distances between cuticular structures (Table 2) agree well with those reported by Hotta and Benzer (1972). The structures of internal organs were therefore localized in the fate map of Hotta and Benzer. The resulting morphogenetic map (Fig. 1) is discussed in comparison with Poulson's embryonic fate map.

[Autonomous determination for pigment formation inwhite position-effect ofDrosophila melanogaster]. / Autonome Determination für Pigmentbildung beimwhite-Positionseffekt vonDrosophila melanogaster.

Inwhite position-effect ofDrosophila melanogaster, determination for the potential of pigment formation of eye cells takes place at the end of the first larval instar. Eye discs, prior to or after this developmental stage, were transplanted together with some larval tissue into the abdomens of adult females. After a cultivation period of 5 to 7 days, the implants were transplanted back into larvae. Imaginal differentiation occurred in these metamorphosing hosts. It could be shown that eye disc cells become autonomously determined during the cultivation period. An influence of the larval tissues transplanted together with the eye discs on determination could not be demonstrated. Therefore, this determinative event most likely is independent on the specific larval milieu.