Lineage analysis of transplanted individual cells in embryos of Drosophila melanogaster

Abstract

We describe the results of cell transplantation experiments performed to investigate mesodermal lineages in Drosophila melanogaster, particularly the lineages of the somatic muscles, the visceral muscles and the fat body. Cells to be transplanted were labelled by injecting a mixture of horseradish peroxidase (HRP) and fluorescein-dextran (FITC) in wild-type embryos at the syncytial blastoderm stage. For transplantation cells were removed from the ventral furrow, 8-12 min after the start of gastrulation, and individually transplanted into homotopic or heterotopic locations of unlabelled wild-type hosts of the same age. HRP labelling in the resulting cell clones was demonstrated histochemically in the fully developed embryo; histotypes could be distinguished without ambiguity. Mesodermal cells were already found to be committed to mesodermal fates at the time of transplantation. They developed only into mesodermal derivatives and did not integrate in non-mesodermal organs upon heterotopical transplantation. No evidence was found for commitment to any particular mesodermal organ at the time of transplantation. The majority of somatic muscle clones contributed cells to only one segment. However, clones were not infrequently distributed through two or even three segments. Clones of fat body cells were generally restricted to a small region. However, cells of clones of visceral musculature were widely distributed. With respect to the proliferative abilities of transplanted cells the clones were difficult to interpret due to the syncytial character of the somatic musculature and the fact that the organization of the other organs is poorly understood. Evidence from histological observations of developing normal embryos indicates only three mitoses for mesodermal cells. Clones larger than seven cells were not found when embryos were fixed previous to germ-band shortening; larger clones were found in the fat body and visceral musculature after fixing the embryos at the end of organogenesis. Quantitative considerations suggest that a few mesodermal cells might perform more than three mitoses.

A new Drosophila homeo box gene is expressed in mesodermal precursor cells of distinct muscles during embryogenesis.

“…This suggests that, at least within each parasegment, there are no apparent compartmental restrictions. Similar results have also been obtained by lineage analyses of the mesoderm (Lawrence and Johnston 1982;Beer et al 1987). In addition, the behavior of these cells shows that founder cells of two different types of muscles (in this case, 25 and 5) can be clonally related.…”

“…We do not know at what stage of embryonic development mesodermal cells become committed to particular muscular fates. In transplantation experiments, Beer et al (1987) found that shortly after their invagination, mesodermal cells are not yet committed to form particular muscles or even particular mesodermal tissues. The expression of S59 in several defined mesodermal cells ~2 hr later suggests that at least some mesodermal cells are singled out and assume a specific fate in the late phase of their proliferation or shortly thereafter.…”

A core transcriptional network for early mesoderm development in Drosophila melanogaster

“…The early Drosophila mesoderm is composed of a field of pluripotent cells (Beer et al 1987;Farrell and Keshishian 1999), expressing the TF Twist (Leptin 1991;Baylies and Bate 1996). After gastrulation, these cells dissociate from each other, proliferate, and migrate dorsally, while remaining unspecified.…”

Inducible ternary control of transgene expression and cell ablation in Drosophila

“…Mesoderm cells undergo up to three post-blastoderm mitoses within 4 h of cellular blastoderm, before mid stage 11 of embryogenesis, in which most of the the embryos examined here were found ( Fig. 3; Hartenstein and Campos-Ortega 1985;Beer et al 1987;Bate 1993). At late cellular blastoderm stage, when the heat shocks were performed, all cells are temporarily arrested in G2.…”