Dosage compensation and ontogenic expression of suppressed and transformed Vermilion flies in Drosophila

Mechanism of suppression inDrosophila melanogasterVIII. Comparison ofsu(s) alleles for ability to suppress the mutants purple, vermilion, and speck

The suppressor of sable [su(s)2] restores the function of vermilion (v), purple (pr) and speck (sp) as well as sable (s) inDrosophila melanogaster. In this report various alleles ofsu(s) are compared for their relative effectiveness on three target mutations,v,prandsp. Three criteria for suppression ofprandvwere employed: visible phenotype, eye pigment levels (drosopterins and xanthommatin) and enzyme levels (sepiapterin synthase and tryptophan oxygenase). Forsponly the visible phenotype was examined. By all three criteriaprwas found to be more easily suppressed thanv;vandspwere comparable. By use ofprwith various alleles ofsu(s) either homozygously or in heterozygous combination withsu(s)+, the extent of suppression ofprcan be best demonstrated by observing the levels of sepiapterin synthase; normal levels of drosopterins were found in females when sepiapterin synthase was only 20% of normal. On the other hand, the extent of suppression ofvis best demonstrated by the amount of xanthommatin eye pigment, because even the suppressed vermilion fly has < 10% of wild-type activity of tryptophan oxygenase when 1-day-old flies are examined; in older flies this enzyme can be as high as 50% of wild type. From these results we also demonstrated thatsu(s)2, and other alleles, are not recessive but, in heterozygous combination withsu(s)+, cause marked suppression ofprand slight, but reproducible, suppression ofv. The purple mutation, therefore, is particularly useful for studying the mechanism of suppression as well as for obtaining new mutant alleles ofsu(s).

The tryptophan oxidation pathway in mosquitoes with emphasis on xanthurenic acid biosynthesis

Oxidation of tryptophan to kynurenine and 3-hydroxykynurenine (3-HK) is the major catabolic pathway in mosquitoes. However, 3-HK is oxidized easily under physiological conditions, resulting in the production of reactive radical species. To overcome this problem, mosquitoes have developed an efficient mechanism to prevent 3-HK from accumulating by converting this chemically reactive compound to the chemically stable xanthurenic acid. Interestingly, 3-HK is a precursor for the production of compound eye pigments during the pupal and early adult stages; consequently, mosquitoes need to preserve and transport 3-HK for compound eye pigmentation in pupae and adults. This review summarizes the tryptophan oxidation pathway, compares and contrasts the mosquito tryptophan oxidation pathway with other model species, and discusses possible driving forces leading to the functional adaptation and evolution of enzymes involved in the mosquito tryptophan oxidation pathway.

Recombination of recessive upsilon+ transformants in Drosophila melanogaster

Recessive transformants (col) obtained fromv(vermilion) embryos treated withv+DNA are shown to map at 1−0·02, a position not distinguishable from that ofsu(s) (suppressor-of-sable) and in agreement with observations indicating phenotypic allelism ofcolwithsu(s) mutants. Recombination in they–col–gtsegment of theXchromosome, over a total map length of O·3 units, was studied among the progeny ofcolv1/y1gtE6cvv1fandy1colgtE6cvv1f/v1females. The data from both crosses exhibit the following features: (1) recovery of reciprocal recombinants betweeny1andcol; (2) recovery of reciprocal recombinants betweencolandgtE6and (3) striking negative interference in they–col–gtsegment. These results allow three alternative interpretations: (1) that recombination in they–col–gtsegment results from conventional crossing-over, with high coincidence of crossovers in the two subsegments; (2) that it results from symmetrical gene conversion at thecolsite (coltocol+, andcol+tocol), which may be accompanied by single cross-overs in either of the adjacent regions; (3) thatcolbehaves like a transposable element, formally symbolizedsu(s)+·col, and that recombination insu(s)+·col/su(s)+(i.e.col/col+) heterozygotes results from transposition of thecolelement from homolog to homolog, accompanied sometimes by crossing-over, either in they–colsubsegment or in thecol-gtsubsegment.

Gene transfer in Drosophila melanogaster: genetic transformations induced by the DNA of transformed stocks

DNA prepared from transformed stocks ofDrosophila melanogasterinduces second-step transformations resembling the original. The gross yield of transformants induced by transformed DNA is several times higher than that induced by the original allo-DNA, but much of this high frequency is attributable to a few exceptionally large clusters of transformants among flies treated with transformed DNA. When these large clusters are omitted from the data, the frequency of transformants induced by DNA from transformed stocks is the same as that induced by allo-DNA. The data therefore support the conclusion that the original DNA-induced alterations resulted from the transfer of genetic material capable of indefinite replication.