Wingless mutation inDrosophila melanogaster

A temperature sensitive lethal allele of thewingless locus ofDrosophila melanogaster together with previously studied lethal and viable alleles in this locus, has been used to study some properties of this locus. These studies show the existence of two lethal phases for thewingless lesion; one during embryogenesis and another during pupation. By growing embryos with temperature sensitivewingless lesion at the permissive temperature and letting the larvae develop at non-permissive temperature, a large-scale cell death and subsequent regeneration were seen to occur in the mutant wing discs. This cell death followed by regeneration alters the normal developmental potential of the wing disc. Disc transplantation experiments show that these discs are incapable of differentiating into wing blade structures.     

Analysis of the compartments of the wing of Drosophila melanogaster mosaic for a temperature-sensitive mutation that reduces mitotic rate

Gynandromorphs of Drosophila melanogaster were analysed in which the female tissue was normal but the male tissue was hemizygous for a temperature-sensitive mutation, l(1)ts1126, which reduces mitotic rate. In gynandromorphs grown at restrictive temperature, the slow-growing l(1)ts1126 tissue survives preferentially when it is segregated from the wild-type tissue, i.e., when it occupies an entire imaginal disc or an entire anterior or posterior compartment within a disc. Mosaic compartments composed of both male, l(1)ts1126, and female wild-type tissue are found less frequently at restrictive temperature than at permissive temperature and when present, are composed mainly of wild-type tissue with very small patches of l(1)ts1126. These very small patches are found almost exclusively along the borders defining compartments. The implications of these results to theories concerning the way in which the compartment boundaries may be maintained is considered. In gynandromorphs grown at restrictive temperature, the size of compartments composed entirely of l(1)ts1126 tissue is drastically reduced, relative to those composed of wild-type tissue. The observations support the hypothesis that the sizes of the anterior and posterior compartments are autonomously controlled.     

Temperature sensitive periods ofcubitus interruptus mutants inDrosophila melanogaster

The temperature sensitive period for mutant expression was determined incubitus interruptus ofDrosophila melanogaster. Two stocks carrying the dominant alleleci ^D were compared, in which under the influence of temperature, mutant expression of the most conspicuous character (gap in fourth vein) changes in opposite directions.The effective period (T.E.P.) ofci ^D was found to be very similar in both stocks. It is relatively short and begins after puparium formation. The T.E.P. is also the same for mutant expression on the fourth and the fifth vein. But in contrast to the 4^th vein character, the 5^th vein reacted in the same direction in both stocks.The T.E.P. was again determined in the same two stocks after the recessive alleleci had been introduced instead ofci ^D . The T.E.P. ofci in both stocks occupies a large part of the larval period including the first instar. The genetic background difference that causes opposite temperature reactions ofci ^D , does not show up in the temperature reactions ofci.The significance of these facts and of T.E.P.'s in general are discussed.     

Isolation of temperature sensitive mutations blocking clone development inDrosophila melanogaster,and the effects of a temperature sensitive cell lethal mutation on pattern formation in imaginal discs

Summary A method of isolating temperature-sensitive (ts) mutations blocking clone development, based on the analysis of twin spots produced by X-ray induced somatic recombination is reported. From this screen 10 ts mutations were recovered which caused an absence of the lethal-bearing clone at the restrictive temperature. Eight of these mutations were analyzed. Seven proved to be autonomous ts cell lethals and one was an autonomous ts mutation which reversibly affected cell division and growth of imaginal disc cells and growth of larval cells. The effects on development of one of the cell lethal mutations,l(1)ts-504, are described. Heat pulses (29°C) 24–72 hrs long caused a high frequency (up to 90%) of morphologically abnormal animals. The abnormalities observed were of two major kinds: deficiencies and duplications of imaginal disc derivatives. In addition, alterations of tarsal segmentations occurred. Heat pulses to larvae also delayed pupariation and eclosion by as much as four days. In general, longer pulses led to a greater delay in pupariation and eclosion and a higher frequency of deficiencies and duplications than shorter pulses. Exposure to restrictive temperature early in larval development delayed pupariation and resulted in mostly normal animals; exposure during the second and early third larval instar also delayed pupariation and led to a high frequency of duplications; exposure later in larval life, i.e. mid and late third larval instar, caused no delay in pupariation but led to a high frequency of deficiencies. These results can be explained by the occurrence of areas of cell death, which can be seen in the imaginal discs of larvae exposed to restrictive temperature by staining with trypan blue. This conclusion is further supported by the observation in gynandromorphs of duplications of female nonmutant tissue. These results are discussed in relation to current theories of pattern formation.     

Analysis of a newly-isolated temperature sensitive maternal effect mutation of Drosophila melanogaster.

A mutation located near the tip of the X chromosome in Drosophila melanogaster has been isolated, and its developmental effects described. This mutation (1(1)ts-1 is temperature sensitive, and at permissive temperature (18 degrees C) develops normally. However, zygotes from females raised or aged at restrictive temperature (28 degrees C) never hatch, regardless of the embryonic genotype. Midgut formation is abnormal in lethal zygotes and dorsal closure is probably incomplete. Temperature shift experiments have shown that the zygotic lethality is governed by a temperature sensitive period in oocytes of stage seven or older. If viable 1(1)ts-1 embryos are shifted to restrictive temperatures, they develop as far as the pupal stage, but never eclose. The temperature sensitive period for pupal lethality includes the last 2.5 days of pupal development and does not involve a maternal effect.     

Selection and temperature effects on extra dorsocentral bristles inDrosophila melanogaster

Starting from base populations which showed a tendency to form supernumerary dorsocentral bristles, selection for high numbers of dorsocentrals was carried out. In all, 9 lines were selected 6 to 14 generations. Selection proved to be effective in all but two lines. Selection for reduced numbers in one of the lines also proved effective.Mean values of over 10 were reached in the females of certain high lines. Average counts in males were always lower than those of females. This sex difference is not a consequence of the difference in size between the sexes.The base populations were of mutant stock origin, and some of them segregated for mutant genes which proved to be correlated with extrabristle phenotype. Supernumerary bristles were not distributed in the same manner in all of the selection lines, nor was the reaction of phenotypic expression to temperature the same in various lines.     

A study of germinal mosaicism inDrosophila melanogaster

Summary Three-hundred and twenty fertile,pal-induced Y-chromosome mosaic males and females were obtained. Fractional analysis of the sons of 55 somatically mosaic flies that were also germinally mosaic tentatively suggests that the number of functional primordial germ cells inDrosophila melanogaster is variable and that it is seldom greater than 24. From the observed 0.17 frequency of germinal mosaicism it was estimated that the average number of pole cells at the end of blastoderm formation is 45. At present, the germ cells afford the only opportunity to compare genetic estimates of the number of blastoderm or primordial cells with available histological counts. The good agreement between them suggests that both the fractional and the mosaic frequency methods for estimating primordial or blastoderm cell numbers of various larval and imaginal anatomical structures provide reasonably close approximations of the actual values.     

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.     

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.     

A temperature sensitive mitochondrial mutation of Saccharomyces cerevisiae.

A mitochondrially inherited temperature sensitive respiratory deficient mutant of yeast has been isolated. Detection of nuclear suppressor mutations indicates an interaction between the nuclear and mitochondrial genomes. A preliminary biochemical characterization is presented.     

A male-specific lethal mutation in Drosophila melanogaster that transforms sex.

Sex-lethal, male-specific allele #1 (Sxl^M#1, 1–19.2) is a dominant, X-linked mutation that is lethal to males. It has no effect in females other than to rescue them from the otherwise lethal maternal effect of the autosomal mutation, daughterless. From a study of the effects of Sxl^M#1 on the development of sexually mosaic flies (gynandromorphs), it was observed that this lethal mutation can cause genetically male (haplo-X) tissue to differentiate as if it were female. With respect to its effect on sexual differentiation, the mutation transformer (tra, 3–45) is epistatic to Sxl^M#1, though the lethal effects of Sxl^M#1 are not modified by tra. In addition to its effect on sexual differentiation, Sxl^M#1 reduces the size of haplo-X imaginal disc and histoblast derivatives in general in a cell autonomous fashion. The viability of gynandromorphs with Sxl^M#1 tissue is very low, and the surviving mosaics have relatively little haplo-X tissue, suggesting that there is no single localized “lethal focus” for this mutation. The relationship between Sxl and daughterless is discussed, as well as the possible involvement of the Sxl locus in X-chromosome dosage compensation.