Cytophotometric evidence for the transformation of oocytes into nurse cells in Drosophila melanogaster

A small proportion of ovarian chambers from females homozygous for the otu7 (for ovarian tumor) mutation contain an "oocyte" that in its nuclear morphology resembles a nurse cell. Such transformed oocytes also appear in colchicine-poisoned wild type ovaries. Cytophotometric estimates demonstrate that these oocytes have undergone 3-4 additional DNA replications, but that they lag behind the adjacent nurse cells by an average of 1.3 replication cycles. It follows that, under certain circumstances, the definitive oocyte can switch to the nurse cell developmental pathway and therefore that a mechanism normally exists for preventing the further replication of its DNA. In the case of otu7, oocytes sometimes restart their endocyclic DNA replications and produce paired, polytene, homologous chromosomes.     

A mutant affecting the crystal cells inDrosophila melanogaster

Summary Black cells (Bc, 2-80.6±) mutant larvae ofDrosophila melanogaster have pigmented cells in the hemolymph and lymph glands. In this report we present evidence that these melanized cells are a mutant form of the crystal cells, a type of larval hemocyte with characteristic paracrystalline inclusions.Bc larvae lack crystal cells. Furthermore, the distribution pattern of black cells inBc larvae parallels that of experimentally-blackened crystal cells in normal larvae (phenocopy).InBc/Bc zygotes black cells appear during mid embryonic development but inBc ⁺/Bc zygotes pigmented cells are not found until late in the first larval instar.Crystal cells are present in the heterozygous larvae until this time, and paracrystalline inclusions can be seen in some of the cells undergoing melanization in these larvae.The rate of phenol oxidase activity inBc ⁺/Bc larval cell-free extracts is less than half that ofBc ⁺/Bc ⁺extracts whereas enzyme activity is undetectable inBc/Bc larvae. We propose that theBc ⁺gene product is required for maintaining the integrity of the paracrystalline inclusions; inBc/Bc larvae either the product is absent or nonfunctional so an effective contact between substrate and enzyme results in melanization of the cells.Phenol oxidase itself is either destroyed or consumed in the melanization process accounting for the absence of enzyme activity inBc/Bc larvae. These studies confirm that the crystal cells store phenolic substrates and are the source of the hemolymph phenol oxidase activity in the larva ofD. melanogaster.     

Evidence for overdominance inDrosophila melanogaster

In artificial populations ofDrosophila melanogaster the mutantsvermilion (v) andcinnabar (cn), both interfering with eye pigment formation, appeared to be balanced against wild type, indicating that the heterozygotesv/+ andcn/+ have a selective advantage over the respective homozygotes. In a population homozygous forv, the mutantcn in competition with its wild type allele tended to be eliminated. Ifcn was homozygous,v showed a similar tendency. Thus in competion experiments it was found that the heterozygotes for one of the two recessive genes,v andcn, ceased to be heterotic when the other recessive is homozygous. These findings are considered to be evidence for the existence of overdominance.     

Evidence for myosin heterogeneity inDrosophila melanogaster

Summary Electrophoresis of myosin extracts from larvae and adult tissues ofDrosophila melanogaster under non-dissociating conditions indicate that two of the bands seen are myosins. They stain for Ca²⁺ ATPase activity and when cut and re-run under dissociating conditions are found to contain a myosin heavy chain that co-migrates with rabbit skeletal muscle myosin heavy chain. One of the forms of myosin seen is found primarily in extracts from the leg. The other is common to the adult fibrillar flight muscles and the larval body wall muscles.The electrophoretic evidence for two myosin types is strengthened by the histochemical demonstration of two myofibrillar ATPases on the basis of their lability to acid or alkali preincubation. The myofibrillar ATPase in the leg and the Tergal Depressor of the Trochanter (TDT) are shown to be relatively acid labile and alkali stable. The larval body wall muscles and the adult fibrillar flight muscles have an ATPase which is acid stable and alkali labile. This distribution of the two myofibrillar ATPase coincides with that predicted by electrophoresis of extracts from whole tissue and also locates the two myosins to specific muscle types.     

Direct evidence for transformation of differentiated iris epithelial cells into lens cells

Although it is generally assumed that the lens regenerated in the newt eye after complete lentectomy is formed by cells derived from the dorsal iris epithelium, experimental evidence so far obtained for this transformation does not rule out participation of cells from the dorsal iris stroma. When the normal dorsal iris epithelium of adult Notophthalmus (Triturus) viridescens was isolated and cultured in the presence of frog retinal complex, newt lens tissue was produced in 88% of cultures. These lens tissues were positive for immunofluorescence for lens-fiber-specific gamma crystallins as well as for total lens protein. On the basis of a study of stromal cells contaminating the samples of dorsal iris epithelium and a test for the lens-forming capacity in vitro of the dorsal iris stroma in the presence of frog retinal complex, it is concluded that lens formation observed in the above experiment is not dependent on the contaminating stromal cells. This implies that, in Wolffian lens regeneration, fully differentiated adult cells completely withdrawn from the cell cycle are transformed into another cell type. An additional culture experiment demonstrated that lens-forming capacity is not restricted to the dorsal half of the iris epithelium, but extends into its ventral half.     

Cytophotometric studies on cells from the ovaries of otu mutants of Drosophila melanogaster

Summary Amounts of chromosomal DNA were estimated for Feulgen-stained, ovarian cells from flies carrying certain mutant alleles of the otu (ovarian tumor) gene. Epithelial sheath cells and lumen cells were found to contain the diploid (2C) amount of DNA and therefore served as internal, cytophotometric standards. Mitotically active follicle cells over young tumors-from homozygous otu ¹ females contained either the 2C or 4C amounts of DNA; whereas, the tumor cell population contained 2C, 4C and 8C nuclei and many intermediate values. Egg chambers also occur in homozygous otu ⁷ females. Follicle cells above these oocytes undergo a maximum of four cycles of endomitotic DNA replication. The accompanying nurse cells (PNC) contain polytene chromosomes. These undergo a maximum of 12 endonuclear replication cycles. The PNCs show the expected levels of DNA for the first 6 cycles and the fraction failing to replicate during subsequent cycles may be as small as 10%. Lower than expected levels of DNA were detected in PNCs from an otu ¹/otu ³ ovary, reflecting roughly 20% underreplication. The latter PNCs may have been interrupted before DNA synthesis was concluded. No simple model of genomic underreplication accounts for the several different patterns of DNA behavior observed for various otu mutants.     

Cytophotometric studies on cells from the ovaries of otu mutants of Drosophila melanogaster

Amounts of chromosomal DNA were estimated for Feulgen-stained, ovarian cells from flies carrying certain mutant alleles of the otu (ovarian tumor) gene. Epithelial sheath cells and lumen cells were found to contain the diploid (2C) amount of DNA and therefore served as internal, cytophotometric standards. Mitotically active follicle cells over young tumors from homozygous otu1 females contained either the 2C or 4C amounts of DNA; whereas, the tumor cell population contained 2C, 4C and 8C nuclei and many intermediate values. Egg chambers also occur in homozygous otu7 females. Follicle cells above these oocytes undergo a maximum of four cycles of endomitotic DNA replication. The accompanying nurse cells (PNC) contain polytene chromosomes. These undergo a maximum of 12 endonuclear replication cycles. The PNCs show the expected levels of DNA for the first 6 cycles and the fraction failing to replicate during subsequent cycles may be as small as 10%. Lower than expected levels of DNA were detected in PNCs from an otu1/otu3 ovary, reflecting roughly 20% underreplication. The latter PNCs may have been interrupted before DNA synthesis was concluded. No simple model of genomic underreplication accounts for the several different patterns of DNA behavior observed for various otu mutants.     

Suppression of abdominal legs inDrosophila melanogaster

Summary Drosophila melanogaster normally have six thoracic legs and no abdominal legs. However, one or two legs often appear in the first abdominal segment ofbithoraxoid mutants. The extent to which these extra legs develop is determined both by thecis-regulatory action ofbithoraxoid lesions onUltrabithorax and by the number of copies of the adjacent homeotic geneabdominal-A. Thebithoraxoid region does notcis-regulateabdominal-A.     

Development of thoracic curvature inDrosophila melanogaster

Summary The influence of muscle development on thorax morphogenesis has been investigated inDrosophila melanogaster. The development of an indirect flight muscle, the dorsal longitudinal muscle (DLM), has been thought to be responsible for the formation of the distinct thoracic curvature. Using aDrosophila mutant (sr/Df(3)sr) in which the DLM is completely missing, we have shown that a normally curved thorax still is produced. Such results indicate that an external structure (epidermis) is capable of developing wholly independent of an absent internal structure (muscle).     

Genomic imprinting of chromatin inDrosophila melanogaster

During gametogenesis, chromosomes may become imprinted with information which facilitates proper expression of the DNA in offspring. We have used a position effect variegation mutant as a reporter system to investigate the possibility of imprinting inDrosophila melanogaster. Genetic crosses were performed in which the variegating gene and a strong modifier of variegation were present either within the same parental genome or in opposite parental genomes in all possible combinations. Our results indicate that the presence of the variegating chromosome and a modifier chromosome in the same parental genome can alter the amount of variegation formed in progeny. The genomic imprinting we observed is not determined by the parental origin of the variegating chromosome but is instead determined by the genetic background the variegating chromosome is subjected to during gametogenesis.     

A diallel cross for mating speeds inDrosophila melanogaster

A diallel cross inDrosophila melanogaster for the mating speeds of previously unmated pairs aged 6 days was carried out for 6 inbred lines and their hybrids. Pairs were observed for 40 minutes.There was extreme hybrid vigour especially in mating frequency for 10 minutes but the degree of hybrid vigour was relatively smaller for 40 minutes.Considerable variability occurred between the inbred lines indicating the genotypic control of mating speed.An analysis of variance on the hybrids revealed significant general and specific combining abilities, and reciprocal effects. The mating frequency for 10 minutes gave heritability in the narrow sense, h²=0.605, 20 minutes gave h²=0.510 and 40 minutes gave h²=0.342.The progressive reduction in h² is due to a decrease in additive genetic variance and an increase in dominance variance with time. Thus either the dominance relations of genes controlling mating speeds change with time. or different loci control this character at different times.     

The occurrence of the transposable elementpogo inDrosophila melanogaster

We examined the genomic occurrence of the transposable elementpogo in over 120 strains ofDrosophila melanogaster, from around the world and from different eras. All had multiple copies of a 2.1 kilobase (kb)pogo element, and multiple copies of several size classes between 1.0 and 1.8 kb. There were differences between strains in intensities or presences of deletion-derivative size classes, suggesting current or recent mobility in the species. We were unable to find anypogo-hybridization in eight other species in the genus, in three subgenera, or in the relatedScaptomyza pallida. Thepogo element may be a ‘middle-aged’ element in the genome ofD. melanogaster, having entered the species since its divergence from its sibling species, but long before theP andhobo elements.