Physiological genetics of melanotic tumours in Drosophila melanogaster. VII. The relationship of dietary sterols to tumour penetrance

A strain ofDrosophila, homozygous for the variably penetrant genetu bw, which causes the formation of abnormal masses of melanizing haemocytes (melanotic tumours), has been reared on defined axenic diets containing various sterols, both singly and in pairs. Both optimal and deficient nutritional levels of sterol have been employed, as well as certain sterols inadequate by themselves to support development. The effect of these diets upon probability of tumour formation has been studied in relation to their nutritional adequacy, as defined by the growth-rate, survival, and in one case, adult body-weight.

The results demonstrate a rather complex pattern of interaction between dietary sterols in determining the variables of the phenotype produced, under circumstances suggesting that all the sterols investigated have entered the developing larvae. There is only a partial overall correlation, and occasionally an inverse relationship, between tumour suppressant and growth-promoting properties of particular sterols. Within single molecules, structural sterol features tend to exert their characteristic effects additively upon the phenotype, except for an inadequacy in utilization of molecules containing the Δ7double bond, which dominates at low concentrations. With pairs of dietary sterols, however, non-additive or ‘saving’ effects are sometimes seen.

It is suggested that thetu bwallele allows the resolution of several discrete developmental functions for sterols and/or their immediate metabolic products inDrosophila, which cannot synthesize its own sterol. However, the molecular nature of these functions is little understood.

Protein synthesis in the liver of rats injected with cholesteryl 14-methylhexadecanoate

1. Rats were injected intraperitoneally with cholesteryl 14-methylhexadecanoate and killed after various intervals of time up to 3 days; ribosomes and cell sap were isolated from their liver tissue. These fractions were tested for their ability to participate in protein synthesis. 2. Protein synthesis in complete systems containing ribosomes, cell sap and all necessary cofactors was significantly enhanced at 12 and 72h after the injection and significantly inhibited at 24h. At early times after injection isolated ribosomes had a slightly enhanced ability to bind nRNA. Peptide-elongation processes (i.e. binding of aminoacyl-tRNA to ribosomes, peptidyl transfer and polyphenylalanine synthesis) showed significant stimulation or inhibition depending on the time after injection of the ester. 3. A correlation was found between the ability of cell sap to stimulate polyphenylalanine synthesis and the relative cholesteryl 14-methylhexadecanoate content in the postmicrosomal supernatant at different time-intervals after administration of the ester. No significant changes were found in its content in the whole liver tissue. 4. Since the injected ester has previously been shown to accumulate in some enzymic fractions, the changes in its relative content may represent a regulatory mechanism modulating the rate of protein synthesis.

The effect of testosterone and testosterone metabolites on the fine structure of the rat prostate gland in organ culture

The action of testosterone and its metabolites, dihydrotestosterone and 3β-androstanediol on the fine structure of the rat ventral prostate gland in organ culture was investigated. In intact glands before explantation the epithelial cytoplasm showed a system of membrane-bound ergastoplasmic channels studded with ribosomes, a discrete Golgi body, associated with secretory vacuoles and microvilli projecting into the lumen.

In explants grown in non-supplemented medium the epithelium underwent a severe regression. The ergastoplasm collapsed and was fragmented and there was no discrete Golgi body. Microvilli were absent and a number of electron-dense bodies interpreted as lysosomes were scattered throughout the cytoplasm.

In explants grown in the presence of testosterone, dihydrotestosterone and 3β-androstanediol the fine structure was similar to that in the intact gland. Ergastoplasm and Golgi apparatus were well maintained, secretory vacuoles could be observed and the microvilli resembled in size and number those of the normal organ.

In hyperplastic areas of explants treated with dihydrotestosterone, the maintenance of the ergastoplasm was less complete but the Golgi zone and microvilli were well preserved.

In explants treated with testosterone or dihydrotestosterone, nucleolar bodies were observed in many nuclei of epithelium and stroma.

The effects of the steroids on the fine structure of the gland confirm those seen at the light microscopic level and support the suggestion that the action of testosterone is mediated through its metabolites.

Induction of sporangia in Phytophthora cinnamomi by a substance from bacteria and soil

Production of sporangia of Phytophthora cinnamomi on agar–mycelial disks in a mineral salts solution was induced by extracts of a soil pseudomonad. Acetone extracts of soil and of mixed populations of microorganisms from soil solution also stimulated the formation of these asexual reproductive structures. Active extracts stimulated sporangium production in aqueous dilutions as high as 10−9. Some extracts of the bacterium were less active at dilutions above or below a certain optimum concentration range. The unidentified, active substance was characterized as a nonvolatile, polar, heat-stable compound that is soluble in water and several organic solvents. Salts of Ca, Mg, K, and Fe in the suspending medium favored a limited production of sporangia in the absence of active substance, and abundant sporangia in its presence. Ca2+was essential for maximum response. The substance was detected by bioassay on paper and thin-layer chromatograms, and it was obtained partially purified.

Effect of exogenous steroids on sterol synthesis in L-cell mouse fibroblasts

A number of steroids have been tested in an L-cell tissue culture system to determine their effects on cellular sterol biosynthesis and cellular growth. Cholesterol, desmosterol, lathosterol, 7-dehydrocholesterol, and cholestanone reduce de novo synthesis and produce only limited toxicity at high concentrations of exogenous sterol. Considerable cellular toxicity is observed when cells are grown in the presence of coprostanol and Delta(4)-cholestenone. No marked effect on either cell growth or sterol biosynthesis is produced by cholestanol, beta-sitosterol, stigmasterol, campesterol, ergosterol, cholesteryl oleate, or cholestane.