White Sectors Research Articles

Misregulation versus mutation in the alteration of gene expression by carcinogens through interactions with transposable elements in Drosophila melanogaster.

Carcinogens from different chemical series were tested on the wild-type allele of the complex white (w+) locus, which comprised some 5 recombinational subunits, the proximal part (w+4.5) exhibiting regulatory interactions with the neighbouring gene zeste (z). Three w+ loci were used, with different proximal regulatory sequences, including an unstable locus with a TE. Altered expression with each z w+ complex was assayed on the basis of the induction of aberrantly pigmented eye sectors known to be diagnostic of the interaction between z and the dosage of the functionally active w+4.5 subunits. All the tested carcinogens (DMN, DMBA and AFB1) were poorly active in the induction of the putative somatic deletions causing white (w-) eye sectors. In contrast, they were highly effective on the regulatory w+4.5 sequences in all test loci, as indicated by the significantly higher yield of red eye sectors (w-4.5) above the controls. However, this effect varied as a function of the chemical structure of the test compound and the genetic organisation of the regulatory targets. Germinal mutagenicity of the test compounds was assayed on X chromosomes carrying stable and unstable w+ loci, after the injection of adults and topical application on newly hatched larvae. Both techniques revealed that there was no association between the induction of somatic alterations in gene expression and the germinally induced mutations, including the TE w+4.5 deletions. Furthermore, the somatic events, unlike mutations, showed an association with the time of genetic determination during eye-disc cell differentiation. The present results were compatible with the concept of somatic gene misregulation by carcinogens.

Recombinogenic and mutagenic effects of the antitumour antibiotic bleomycin in Aspergillus nidulans

Bleomycin, an antibiotic and antineoplastic drug that inhibits DNA synthesis and causes several types of chromosomal aberration, was found to increase mitotic recombination in Aspergillus nidulans. Heterozygous prototrophic diploid strains grown on media containing bleomycin produced significant increases of yellow and white sectors compared with controls. Further, the increased colour segregants were due to mitotic crossing-over, whereas the non-disjunctional segregants remained at the control level. Bleomycin also induced point mutations in the methionine-suppressor system of the methG1 biA1 strain of Aspergillus nidulans. Conidia treated in suspension with various concentrations of Neomycin increased the methionine-independent mutants 30-fold and more.

Genetic activities of 4-chloromethylbiphenyl, the 4-hydroxy derivative and benzyl chloride in the soma and germ line of Drosophila melanogaster

The genetic activities of 4CMB, 4HMB and BC were assayed as regards the induction of somatic alterations in gene expression on an unstable w + locus with an intragenic TE and all the simultaneously induced germinal mutations on the X-chromosome carrying this locus. The compounds were applied topically in solution at equimolar doses on late embryos and newly hatched larvae. The somatic events were scored as aberrantly pigmented eye sectors in the emerging adult males and the germinal mutations in their F 2 progeny, according to the Muller-5 technique. The somatic events were expressed as red or white mosaic eye sectors; the former could be an outcome of the repression or deletion of the zeste-regulatory proximal subunits of w + locus, and the latter generally attributable to deletions ( w −) within its structural part. All 3 compounds were effective in the induction of red sectors at the higher tested doses (0.5–2.0 mM) and the level of this activity was virtually the same for 4CMB and 4HMB, but was 2-fold higher for BC. In contrast, the frequencies of the simultaneously scored white sectors were not raised significantly above the controls with 4CMB, but showed decisive increases above this level with both 4HMB and BC. The germinal X-chromosome mutations (recessive lethals and visibles) were only induced at the highest tested dose (2.0 mM), and their frequencies were virtually the same for all 3 compounds reaching a common level of about 0.6%, which is some 3-fold the normal control level for the test system. Specific-locus mutability at the TE w + was suggestively positive only with BC.

Biochemical Studies on the Iojap Mutant of Maize

The white leaf tissue of seedlings of Zea mays L. affected by the recessive nuclear gene iojap shows no photosynthetic activity; it contains about 1.4% of carotenoid and less than 0.1% of chlorophyll a content of normal green tissue. Neither fraction I protein nor chloroplast adenosine triphosphatase (EC 3.6.1.4) (CF(1)) is detectable. This confirms earlier observations that plastids of white sectors of iojap maize do not contain ribosomes. About 40% of the activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) in green leaves could be found in white leaves indicating that the phosphoenolpyruvate carboxylase EC 4.1.1.31 is made on cytoplasmic ribosomes. The oxygen consumption of iojap-affected leaves is decreased.

Modification of Pigmentation Patterns in Allophenic Mice by the W Gene

Mouse embryos heterozygous at the W locus were combined with embryos which were wild type at this locus but homozygous for albino. The resulting allophenics displayed an unusual pigmentation phenotype consisting of entirely white fur and ruby-coloured eyes. Microscopic examination showed the eye pigment to be located exclusively in the retinal epithelium, which was a mosaic of black and white sectors. This ruby-eyed white pattern corresponds to what would have been expected for WWCC in equilibrium wwcc mosaics but not for WwCC in equlibrium wwcc mice. WW mice are black-eyed whites, but Ww mice have black eyes and black fur, except for a small ventral white spot. These results suggest that melanocytes of the Ww genotype, although capable of producting normally pigmented fur in Ww animals, fail to populate hair follicles when the competition with wwcc (albino) melanocytes that are wild type at the W locus. The genotype of these WwCC in equilibrium wwcc alophenes was proved by progeny testing. This is apparently the first report of a single gene change affecting the competitive ability of cells in allophenic mice, and suggests that such changes may play a significant role in the clonal selection of embryonic cells during development.

THE ONTOGENY AND SPECTRAL SENSITIVITY OF POLAROTAXIS IN LARVAE OF THE CRAB RHITHROPANOPEUS HARRISI (GOULD)

1. To determine the ontogeny plus the intensity and spectral characteristics of polarotaxis in larvae of the crab, Rhithropanopeus harrisi, swimming paths in relation to the e-vector direction of linearly polarized light were monitored and recorded with a closed circuit video system. 2. All four zoeal stages were examined. Only stages II and III responded with significant directional swimming (stage II, perpendicular to the e-vector, stage III, parallel to the e-vector; Figs. 3 and 4). Stages I and IV appeared indifferent to the polarization plane (Figs. 2 and 5). Swimming under unpolarized light was consistently random (Table I). 3. Polarotaxis disappeared following dark adaptation of stage II larvae (Fig. 6). 4. The lower intensity threshold at 499-nm light for polarotaxis was found to be between 10-4 and 10-3 W/m2, while the upper threshold is in the range 10-1 to 2 x 10-1 W/m2 (Figs. 3 and 4). 5. Examination of selected wavelengths from 420-620 nm yielded greatest responsiveness at 499 nm (Fig. 7). A rise evident at 420 nm suggests a secondary maximum in the violet. 6. Stage II larvae showed significant positive phototaxis under depolarized light when a collar of alternating black and white quadrants surrounded the experimental vessel. With the e-vector of polarized light aligned parallel to the white sectors, phototaxis was reduced by polarotactic swimming into the black sectors (approximately perpendicular to the e-vector). 7. A comparison with phototaxis (Forward and Costlow, 1974) provides two items of evidence that polarotaxis and phototaxis are indeed separate responses. First, phototaxis is essentially unchanged during larval development, while polarotaxis appears only at stages II and III. Secondly, the responses have different optimum intensities.

Orientation-specific aftereffects and illusions in the perception of brightness

Orientation-specific brightness aftereffects were found when vertical and horizontal gratings of the same space-average luminance were viewed following alternate exposure to vertical and horizontal gratings that differed in space-average luminance. The vertical test grating appeared bright following exposure to a dim vertical grating, and dim after a bright vertical grating had been viewed. This aftereffect did not occur when the adaptation gratings had been seen by one eye and the test gratings by the other eye. An orientation-specific illusion in the perception of brightness was also found, with the white sectors of a vertical grating appearing brighter against a background of horizontal lines than they did against a background of vertical lines. Both distortions imply that there are detectors in the human visual system that are conjointly tuned to luminance and contour orientation.

A yeast strain for visual screening for the two reciprocal products of mitotic crossing over

A strain of Saccharomyces cerevisiae, D5, is described which allows for rapid, visual screening for mitotic crossing cover in colonies on solid media. D5 carries two phenotypically distinguishable and recessive alleles of the gene ade2. One allele, ade2–119, causes a leaky requirement for adenine, and a pink coloration of colonies. The other allele, ade2–40, causes a complete requirement for adenine and the formation of deeply red colonies. The two alleles complement each other to the effect that D5 forms white colonies and does not require adenine for growth. Mitotic crossing over generates two reciprocal products which show up together in colonies as pink and red sectors, twin-spotted colonies. Such twin-spotted colonies have been obtained after treatment with ultraviolet light, γ-rays and ethyl methanesulfonate (EMS). Tetrad analysis was performed with cells isolated from the red and the pink half of twin-spotted colonies. The results showed that the pink sectors had become homozygous for allele ade2–119, the red sectors were homozygous for the other allele, ade2–40. With one exception, other markers present in D5 in a heterozygous condition were still heterozygous. In addition to twin-spotted colonies, colonies with white and red or white and pink and even with red, white and pink sectors as well as completely pink or completely red colonies were found. These can be interpreted to result from a variety of mechanisms other than mitotic crossing over which are mentioned in the discussion.

Studies on the 70S Ribosomal Content of a Plastid Mutant in Gossypium hirsutum

Analysis of a mutation in cotton (Gossypium hirsutum), which is maternally inherited, revealed that the completely white sectors of leaves were deficient in the 70S class ribosomes, whereas the yellow sectors exhibited the same level of the latter as in the green leaves.

Untersuchungen zur Sproßvariation der Cupressaceae: 3. Quantitative Auswertung des Scheckungsmusters immerspaltender Periklinalchimären1)

The frequency of chimera-dissociation is examined in relation to the quantity of the leafpairs originating from a shoot tip in any ever-sporting periclinal chimeras of the family of Cupressaceae (Juniperus sabina variegata, Juniperus chinensis plumosa argenteo-variegata, Juniperus chinensis plumosa aureo-variegatn, Chamaecyparis thyoidcs variegata, Chamaecyparis nootkatensis argenteo-variegata) . White sports appear extremely rare in the new shoot tips of the axillary buds. Reduplications in L 1 followed by partial or total individualization of the chlorophylldefect tissue hardly take place in this shoot tips. The frequency of the white sports however strongly increases with proceeding distance of the axillary shoot tips from the originating-places measured in the number of the produced leaf-pairs. The morphological findings (origin of the first white sector in hitherto green branches) were confirmed by research of shoot tips in Juniperus sabina variegata : the frequency of periclinal divisions in L 1 increases with the distance of shoot tips from the originating-place. Chamaecyparis pisifera plumosa argentea shows with regard to the origin of white sports distinct differences between top side and bottom side of the dorsiventral raised branches. White sectors originate in the bottom sid more frequently (62%) than in the top side. Periclinal divisions are obviously more frequent in the bottom flank side of L 1 . Well defined differences cannot be established between top side and bottom side of branches in Chamaecyparis lawsoniana argenteo-variegata and Chamaecyparis nootkatensis argenteo-variegata .

The apparent lengths of arcs on white and black sectors of rotating discs

Abstract In Experiment I Ss made magnitude estimates of the apparent length of white arcs located on the black sector of a half-white, half-black disc which was rotating. Estimates were also made of the apparent length of black arcs located on the white secotr. Both white and black arcs lengthened as a function of increasing speed. The lengthening of the white arc is termed a negative Ansbacher Effect) was confirmed in Experiment II. The experiments demonstrated the importance of the relation between arc and surround for the appearance of shrinkage.

Influences of Temperature and Adenine Concentration upon the Cultural Instability of a Red Adenine Auxotroph of Candida albicans

Upon primary isolation from animal hosts, Candida albicans (Robin) Berkhout typically produces large, smooth colonies. When the organism is cultivated in vitro, variants which produce rough colonies or minute colonies often arise either spontaneously or under the influence of particular inducing agents (3, 16). Rough-colony variants tend to form true hyphae or pseudohyphae under conditions which usually favor blastospore production by their smooth-colony progenitors. The minutecolony variants exhibit sub-normal rates of growth and are known to be of at least two different sorts, physiologically. Alvarez and MacKinnon (1) showed that the minute variants produced either by aging cultures or by propagating cells in the presence of methyl green bear heritable impairments in their aerobic respiratory apparatus comparable to those characteristic of the petite mutants of Saccharonomyces. Bianchi (3, 4) described another kind of minute variant which arises spontaneously only in certain strains of C. albicans and possesses some, as yet undefined, derangement in its endogenous purine metabolism. The present communication describes a previously unreported type of colonial variant arising in populations of a red, adenine auxotroph of C. albicans. The variant was first detected in the form of overgrowing white sectors which appear in colonies of the parental strain developing at 37 C, but not at 25 C, on growth-limiting concentrations of adenine. Observations are presented on the genetic and physiological factors underlying the origin of the variant and its establishment in parental cell populations.

A developmental study of diploid oats by means of radiation-induced somatic mutations

The developmental behaviour of radiation-induced mutant cells in X 1 plants was studied using a strain of diploid oats heterozygous for the albino gene, al. Dry and 24-hr pre-soaked seeds were irradiated with X-rays, γ-rays and thermal neutrons. Distinct white stripes were observed in leaf 3 and upper leaves when dry seeds were irradiated, but from leaf 2 when pre-soaked seeds were treated. The different response in the pre-soaked seeds might be caused by the radiation-induced loss of reproductive integrity of most of the sensitized leaf 2 primordial cells followed by reorganization of the primordia in the embryos. The number of white stripes per leaf decreased with the progression of leaf order. From the relative widths of the stripes, the number of primordial or initial cells for each leaf in the mature embryos was estimated to be about 30 or less for leaf 3 and at least three to five for leaf 4 to 6. Since the stripes in leaf 3 from the treated dry seeds were induced independently from those in the upper leaves, leaf 3 seems to have been derived from an already differentiated primordial cell group, although such a group could not be detected histologically. The white stripes were more frequently observed near the centre of the leaf blade rather than in the marginal part with wider stripes tending to appear in the marginal region, indicating a differential development in the lateral direction. The tillers on the same orthostichy tended to behave similarly with regard to the appearance of the white stripes or sectors. The present study demonstrates that mutations having an appropriate phenotype induced in somatic tissues provide a useful means for detailed study of organogenesis in higher plants.

Action of mycophenolic acid on unstable diploids of Penicillium chrysogenum.

DIPLOIDS of Penicillium chrysogenum heterozygous for the genes y/Y (yellow versus green conidia) and w/W (white versus green conidia) have green conidia. On plating, these give rise to a majority of green colonies, together with a small percentage (less than 1 per cent) of yellow or white colonies, or green colonies with white and/or yellow sectors. The proportion of these ‘segregant’ colonies and sectors is strongly increased (by more than 20–30 per cent) if the conidia are treated with the nitrogen mustard, methyl-bis(β-chloroethyl)amine (HN–2) or with X-rays1. When certain of the colonies with sectors are sub-cultured by the plating of green conidia, they give rise to a population of colonies with sectors ; these colonies maintain the unstable character indefinitely in successive transfers. A dozen unstable clones were isolated, each of which showed sectors with a single phenotype (rarely two) characterized by the presence of nutritional markers as well as by the colour of the conidia. Manganous chloride, added to the agar medium at 40 mM concentration, inhibited the production of sectors with nearly all the unstable clones; the inhibition, however, was not of a permanent nature, and disappeared when the clones were subcultured on medium free from manganous chloride2.

Genetic response ofAntirrhinum majus to acute and chronic plant irradiation

Clonal lines ofAntirrhinum majus heterozygous for flower color have been used to study somatic mutations induced by irradiating plants with chronic gamma rays from cobalt-60 and acute X rays. Pink or white flecks and sectors of various sizes on the purple flowers are interpreted as resulting from mutational events at different times in flower development. Acute X-ray treatment of pre-flowering stages caused no visible change in flowers opening prior to the 15th day thereafter. On the 16th to 19th days there was dense mottling, and by the 20th or 21st day numerous eight-cell mutant spots could be counted. The number of spots induced by 1,000 r of X rays was used to obtain a preliminary estimate of an average mutation rate for the three genes studied of 6.33×10−6 per cell per roentgen. Chronic irradiation in a gamma radiation field and greenhouse showed a linear response of mutation rate to daily dose rate, the actual rate being subject to seasonal variation. There were occasional indications of non-linearity but further tests have failed to show any significantly higher mutagenic efficiency of dose rates below 6 r/day. In plants removed from chronic gamma irradiation the frequency of mutation spots returns to the spontaneous level after about six weeks. The appearance, however, of mutant sectors on plants several months after exposure to both acute and chronic radiation indicates the induction of persistent genetic changes. Progeny tests of seeds and cuttings are planned to test the nature of these genetic events.

A Visual Phenomenon

MR. DARTNALL1 has recently described an interesting visual phenomenon which, as has been pointed out by Mr. Wright2, is connected with the after-images of different colours possessing different rates of development. A visual phenomenon possibly connected with this differential rate of development came to my notice some time ago, and no doubt must have been observed by others as well. A stroboscopic disk painted in black and white sectors is run under illumination from an (ordinary) Osram neon lamp connected to A.C. supply (60 cycles). At speeds such that the pattern is not stationary but somewhat shifting, the white sectors appear to be distinctly coloured (rainbow type)—one edge pink and the other green. The same effect is seen, though not so clearly, when the neon lamp is replaced by an ordinary incandescent lamp, provided the illumination is not high.

Note on Mr. Mallock's observations on intermittent vision

In the paper communicated by Mr. Mallock on December 11, 1913, in order to account for the intermittences seen when watching a resolving disc or black and white sectors, at the moment when a slight mechanical shock is given to the head or body, he advances the hypothesis that a slight mechanical shock of any kind produces a periodic but rapidly extinguished paralysis of the perception of light, and that the nerves on which seeing depends cannot bear more than a certain amount of mechanical acceleration without loss of sensibility. This hypothesis of a momentary paralysis of the sense of vision seems unnecessary. The sector disc revolving at from two to six revolutions per second presents a uniform grey tint. At the moment when the intermittence occurs, by stamping the foot or tapping the head, the most prominent effect observed by the writer was not the momentary appearance of stationary grey or block sectors, but the enhanced brightness of stationary white sectors. A momentary paralysis, if it occurred, should produce momentary blackness of the entire disc, which is not what happens.

XVII. Colour photometry.—Part II. The measurement of reflected colours

In our first paper on this subject we have shown how the luminosity of the spectra of various sources of light can be measured; and the present paper is an extension of the subject, dealing with the measurement of the light reflected from bodies in terms of the colours of the spectrum of the light illuminating them. By the method which we adopted in the first part of "Colour Photometry” this can be effected, and, indeed, we carried that out in several instances. The method then employed was very simple. If we wished to measure the illuminating value of the spectrum of light reflected from a metal, we placed it at an angle in front of the slit of the spectroscope, so as to reflect the light from the crater of the positive pole of the electric light through the photometer, and measured the luminosity of each part of the spectrum thus formed by the method we indicated in our paper. Again, in experimenting with Gorham’s discs, such as Maxwell employed, where it became necessary to determine the light reflected from the different coloured papers or cards used in the discs, the plan first adopted was to replace the receiving shadow screen of zinc oxide (see § VI) by the coloured papers, and again to make a luminosity measurement. This plan answered its purpose, but it was rather laborious. When two or three colours are combined by rotation to form a grey, and black and white sectors are combined to match that grey, in order to ascertain the total luminosity of each colour, the angular value of the sectors being known, it is necessary to refer the luminosity to that of some standard reflecting surface, which is naturally a white one. As the comparison light is coloured by falling on coloured paper, the value of the spectrum reflected from such paper could not by this first method be directly compared with that reflected from the white screen. In the case of a coloured screen, the curve of spectrum luminosity would therefore have to be reduced to that in which the comparison light was white. This difficulty was surmounted by making half the receiving screen white and half of the colour whose luminosity was to be measured, illuminating the shadow of the rod thrown on the coloured paper by the spectrum colour, and that thrown on the white card by the white light reflected from the surface of the first prism (§ XXVI). This did away with any reduction or calculation; but still an objection remained, as, for definite comparison, it was almost necessary that the same observer should always make the measurement.

The “Chromatic Octave”

RENEWED attention to the “chromatic octave” tempts me to suggest an experiment. There used to be a gentleman, Smith, I believe, by name, who refuted the undulatory theory by means of a disc, divided into black and white sections, which he whirled with very high velocities, producing colours (so the Times positively stated) varying according to the velocities. It is plain that such a result might on the contrary confirm the theory, if, for instance, the disc were divided into 400 black and 400 white sectors, and whirled at the rate of one or two million million times a second. It is also plain that Mr. Smith, in the words of an authority who has been quoted in your columns for weightier judgments, would have blown his disc into smoke first. But once a second is only 40 octaves below a million million times; and it is just possible that something practicable between the two might throw light on the “chromatic octave,” among other things. There are some obvious objections: the question is, whether they make it not worth while to repeat Mr. Smith's experiments.