Gene amplification in dipteran chromosomes

Genome reorganization from polyteny to polyploidy in the nurse cells found in onion fly (Delia antiqua) and cabbage root fly (Delia radicum) ovaries (Diptera, Anthomyiidae)

The material required to ensure successful embryogenesis in the onion fly (Delia antiqua) and the cabbage root fly (Delia radicum) (Diptera, Anthomyiidae) is supplied by 15 nurse cells, while the oocyte chromosomes enter a quiescent stage during prophase I of meiosis. This level of transcription is achieved by the polyploidization of the nurse cell DNA. Elongate polytene chromosomes form in both species, but lack the banding and conspicuous puffing commonly seen in other dipteran tissues. The polytene chromosomes contract until they finally appear as small, densely staining spheres. These fragment into large numbers of endochromosomes that are much smaller than their mitotic counterparts, which then despiralize, resulting in the flocculate appearance of the nurse cell nucleus. Photodensitometry revealed a gradient of DNA values between nurse cells near the oocytes and those further away. Final DNA values 1000 times the haploid level were recorded in the nurse cell nearest to the oocyte compared with 336 times the C-value in the most distal cell. At lower temperatures (< 10 degrees C), the polytene chromosomes become banded and longer. None of the onion flies kept in these conditions produced viable eggs, though there was some reproductive success among the cabbage root flies.

Molecular characterization of an 18 kb segment of DNA puff C4 of Bradysia hygida (Diptera, sciaridae)

The data presented here are an extension of the molecular characterization of DNA puff C4 of Bradysia hygida. A cDNA related to a gene amplified in this puff and expressed when puff C4 expands was cloned and sequenced. Analysis of the amino acid sequence deduced from the open reading frame present in the cDNA indicate that the encoded protein is secreted and comprises mostly alpha-helical coiled-coil. An 18 kb genomic segment containing the transcription unit of this gene was also cloned and the structure and expression of the 1.4 kb mRNA was determined. Quantitative slot blot hybridization of DNA complementary to the transcription unit shows that this gene is amplified about 21 times in the salivary gland, confirming data previously obtained. Fragments upstream of the 5' end, and beyond the 3' end, of the gene transcription unit were also analysed and shown to be amplified at least eight and five times, respectively. Based on these data we discuss how amplification could occur at DNA puffs.

Acetylcholinesterase and butyrylcholinesterase genes coamplify in primary ovarian carcinomas

The genes for acetylcholinesterase (ACHE) and butyrylcholinesterase (CHE) are expressed in multiple tumor tissues, including ovarian carcinomas. Both CHE and ACHE genes coamplify in leukemias. To examine the relationship of gene amplification to the expression of these genes in tumors, ACHE and CHE genes and their expression were studied in primary ovarian carcinomas. DNA blot hybridization demonstrated a significant amplification and mutagenesis of both genes in 6 of 11 malignant tumors studied. This was greater or of the same order of magnitude as the amplification of the oncogenes c-rafi, v-sis, and c-fes in these tumors. No amplification was found in normal ovarian tissues or benign ovarian cysts. Xenopus oocyte microinjections, blot and in situ hybridizations, and immuno- and cytochemical staining revealed translatable CHEmRNA and its active protein product in discrete tumor foci. The frequent coamplification in ovarian carcinomas of ACHE and CHE genes implicates cholinesterases in neoplastic growth and/or proliferation.