Centrifugation of developing oocytes leading to embryonic defects

Effects of the space environment on Drosophila melanogaster development. Implications of the IML-2 experiment

One hundred and sixty Drosophila females laid several thousands of embryos during the 14.5 days of the IML-2 spaceflight. The progeny were either recovered frozen (embryos at final stages of development and larvae), or maintained alive developing further until adulthood. All embryos, larvae, pupae and imagoes recovered were normal in morphology and function. Results from earlier experiments were reproduced in IML-2 with a better experimental design. We confirm that in Space there is a stimulation of oogenesis and that development is slightly delayed when compared to that of synchronous parallel ground controls. Nevertheless, it is clear from the accompanying 1 x g flight control centrifuge and from the 1.4 x g ground centrifuge samples, that centrifugation itself can produce similar effects, emphasizing the importance of reevaluating the role of the 1 x g on-flight controls. The results emphasize the apparent paradox that simple cellular model systems in microgravity show alterations in many fundamental processes such as those involved in cell signalling, while development, relying heavily on these key cellular mechanisms can proceed quite normally in the absence of gravity. The effects on development are small and more the consequence of a reaction to the abnormal Space environment in general than a specific effect of microgravity.

Genetic analysis of pattern-formation in the embryo ofDrosophila melanogaster : Characterization of the maternal-effect mutantBicaudal

The mutationbicaudal (Bull, 1966) causes embryos to develop a longitudinal mirror image duplication of the posteriormost abdominal segments, while head and thorax are missing. These embryos occur with varying frequencies among eggs laid by mutant females, irrespective of the paternal genotype. Recombination and deletion mapping indicate thatbicaudal (bic) is a recessive, hypomorphic, maternal-effect mutation mapping at a single locus on the second chromosome ofDrosophila melanogaster close tovg (67.0±0.1). The frequency of bicaudal embryos depends on the age of the mother, her genetic constitution and the temperature at which she is raised. Best producers are very young females hemizygous forbic (bic/Df(2)vg ^B ) at 28° C. Under these conditions 80% to 90% of the eggs which differentiate can show the bicaudal embryo phenotype. Upon ageing of the mother the frequency of bicaudal embryos declines rapidly, and most of the eggs develop the normal body pattern. Temperature shift experiments suggest a temperature-sensitive period at the onset of vitellogenesis.The mutation causes several types of abnormalities in the segment pattern of theDrosophila embryo, which are interpreted as various degrees of expression of the mutant character. The most frequent abnormal phenotype is the symmetrical bicaudal embryo with one to five abdominal segments duplicated. Less frequent are asymmetrical types, in which the smaller number of segments is always in the anterior reversed part. Other phenotypes are embryos with missing or rudimentary heads, and embryos with irregular gaps in the segment pattern. In bicaudal embryos, the pole cells, formed at the posterior pole of the egg prior to blastoderm formation, are not duplicated at the anterior. The significance of thebicaudal phenotypes for embryonic pattern-formation inDrosophila is discussed.

Interaction of different egg parts in determination of various body regions in Drosophila melanogaster

When Drosophila melanogaster embryos were ligated at very early stages of nuclear multiplication (45-60 min after egg deposition) for the entire period of embryogenesis, egg fragments of variable sizes were able to continue development up to the hatching stage. These ligated embryos differentiated larval structures; anterior fragments formed larval head and posterior fragments formed larval abdominal structures. Ligation always prevented the differentiation of some of the intermediate larval bands whereas the terminal ones were always formed. Identical results were obtained when embryos (45-60 min after egg deposition) were temporarily ligated for only 5 min. However, puncturing with a fine glass needle immediately after temporary ligation through the ligated area could give rise to complete differentiation of all the bands. Since puncturing disrupted the barrier produced by ligation, we propose that interaction between anterior and posterior egg regions is necessary to allow complete development.