Genetic Fine Structure of the Y Chromosome of DROSOPHILA HYDEI

A genetic map of the Y chromosome of Drosophila hydei has been constructed from deletion/complementation experiments, with the aid of male sterile mutants of the Y chromosome. A central conclusion of our experiments is that not more than a single complementation group can be detected in each of the lampbrush loop forming sites. Additional complementation groups, functionally independent of lampbrush loops, reside between these loci. Six complementation groups have been defined by several methods of mapping. An additional ten complementation groups are indicated, but their exact definition requires further investigation. The "synthetic sterility" of mutations in these ten loci contributes to the difficulty in unequivocally establishing their individual boundaries. Mapping problems also arise from the instability of certain mutants.     

The Parthenogenetic Capacities and Genetic Structures of Sympatric Populations of DROSOPHILA MERCATORUM and DROSOPHILA HYDEI

Drosophila mercatorum is a sexual species that can reproduce parthenogenetically in the laboratory. A previous study showed that a natural population of D. mercatorum inhabiting the Kamuela garbage dump on the Island of Hawaii could produce both viable parthenogenetic adults and self-sustaining parthenogenetic lines. The present study deals with a second screen for parthenogenesis and an isozyme survey performed on natural populations of D. mercatorum and D. hydei caught in patches of Opuntia tuna about 10 kilometers from Kamuela. Both cactus-patch species produced viable parthenogenetic adults, but only D. mercatorum produced parthenogenetic females themselves capable of parthenogenesis. Moreover, D. mercatorum produced several "hot" lines characterized by high parthenogenetic rates, while all lines of D. hydei had a homogenous low rate. The parthenogenetic capacity of the cactus-patch D. mercatorum was lower than that of the garbage-dump D. mercatorum. Moreover, both the cactus-patch D. mercatorum and D. hydei had lower levels of polymorphism (26% and 22%, respectively) then the garbagedump D. mercatorum (44%), and both cactus-patch populations had heterozygote deficiencies with respect to Hardy-Weinberg equilibrium, unlike the garbage-dump population. Consequently, these data do not support the idea that decreased levels of heterozygosity in a sexual population increase the chance that sexual females will produce totally homozygous, parthenogenetic progeny.     

A Review of the Eyeless Mutant in the Mexican Axolotl

SYNOPSIS. As a homozygous recessive, gene e in the Mexican axolotlprevents optic vesicles from forming, thus producing an eyelessanimal. Previous experimental evidence has indicated that thegene acts by affecting the ability of anterior medullary plateectoderm in the eye field to respond to inductive mesodermalsignals. Other possible mechanisms of gene action are described.The hypothalamus is also affected and "eyeless" animals aresterile. The absence of eyes results in increased levels ofcirculating MSH and thus the animal is also highly pigmented.Eyes may be grafted into the heads of "eyeless" axolotls. Theseeyes become functional and lead to normal pigmentation. Whenpresent as a homozygous recessive, gene r acts to allow thepenetration of heterozygous e (E/e r/r). This results in abnormaleye development.     

Variations in the Number of the Y Chromosomal Rrna Genes in DROSOPHILA HYDEI

The number of rRNA cistrons is measured by filter saturation hybridization in different stocks of D. hydei, where the wild-type X chromosome has one nucleolus organizer (NO) and the wild-type Y has two separated NO's. (see PDF) females having no X chromosomal NO show an rDNA content exceeding that of a Y chromosome. An even greater increase in the rRNA cistron number is measured in two translocation stocks where the (see PDF) is combined with one half of a Y and, therefore, each stock contains only one of the two Y chromosomal NO's. But when the same Y fragments are brought together with a wild-type X chromosome they lose about one-half of their rRNA cistrons within one generation. Males with two complementary Y fragments but having no X chromosomal NO show a considerably higher rDNA content than the (see PDF) females, although both are equal in respect of their NO number. Consideration is given to related phenomena in Drosophila melanogaster.     

CHROMOSOMAL DIFFERENTIATIONS OF THE LAMPBRUSH TYPE FORMED BY THE Y CHROMOSOME IN DROSOPHILA HYDEI AND DROSOPHILA NEOHYDEI

The nuclei of growing spermatocytes in Drosophila hydei and D. neohydei are characterized by the appearance of phase-specific, paired, loop-shaped structures thought to be similar to the loops in lampbrush chromosomes of amphibian oocytes. In X/O-males of D. hydei spermatogenesis is completely blocked before the first maturation division. No spermatozoa are formed in such testes. In the nuclei of X/O-spermatocytes, paired loop formations are absent. This shows the dependence of these chromosomal functional structures upon the Y chromosome. The basis of this dependence could be shown through an investigation of males with two Y chromosomes. All loop pairs are present in duplicate in XYY males. This proves that the intranuclear formations are structural modifications of the Y chromosome itself. These functional structures are species-specific and characteristically different in Drosophila hydei and D. neohydei. Reciprocal species crosses and a backcross showed that the spermatocyte nuclei of all hybrid males possess the functional structures corresponding to the species which donated the Y chromosome. This shows that the morphological character of the functional structures is also determined by the Y chromosome.     

Cell Clustering and Pleiotropy in White-Variegated Eyes and Malpighian Tubes of DROSOPHILA HYDEI

The type of variegation of eyes of white-mottled mutants of D. hydei, either small-spotted or large-spotted, depends on the specific chromosome rearrangement involved. This distinction between mutants, though handsome, is not absolute because very seldomly small-spotted types do show a larger pigment aggregate and some "large-spotted" flies have no large spots at all, but only minor spots. Because of a pleiotropic action of the white gene, we could study the variegation of Malpighian tubules. The quasi-linear array of Malpighian cells enables a thorough statistical analysis. The problem was in how far the variegation of the tubes that is correlated with the variegation of eyes (in as far as numbers of pigmented and unpigmented cells are concerned) is also connected with a cell-lineage type of determination. Statistics now show that in spite of temperature-induced great variation in the percentage of pigmented cells, all types studied show a nearly random distribution of pigmented and unpigmented cells in the Malpighian tubules. This implies that the cell-lineage type of determination is not only largely mutant-specific but also organ-specific, i.e., limited to eyes. A basic gradient, however, as characteristic for eyes, was also found in Malpighian tubes.     

MASS PREPARATION OF NUCLEI FROM THE LARVAL SALIVARY GLANDS OF DROSOPHILA HYDEI

A method has been developed for isolating gram quantities of salivary glands from late third instar larvae of Drosophila hydei. The isolated glands have a normal appearance and incorporate RNA and DNA precursors normally. Nuclei can be isolated from these glands in 90% yield with the use of detergents. These nuclei contain morphologically normal giant polytene chromosomes.     

The NOTCH Locus of DROSOPHILA HYDEI: Alleles, Phenotypes and Functional Organization

The Notch (N) locus of Drosophila hydei and a series of its alleles and phenotypes are described. Some models are discussed to explain the opposite effects of some alleles on the structure of the wing, the neomorphic action of N^Ax over typical N alleles and the interaction with the mutation Costal-nick (Cnk).     

STRUCTURAL AND FUNCTIONAL PROPERTIES OF POLYTENE NUCLEI ISOLATED FROM SALIVARY GLANDS OF DROSOPHILA HYDEI

Salivary gland nuclei of Drosophila hydei, isolated by a modification of the procedure described by Boyd et al. (9), retain their normal morphology during the isolation and subsequent incubation procedure. RNA synthesis was studied in isolated nuclei by biochemical and cytological techniques. In radioautographs 70% of the nuclei displayed a distribution of labeled RNA over the nuclear constituents similar to the distribution obtained after in vivo incorporation of radioactive precursor. Chromosome puffs and the nucleoli were specifically labeled. The remaining 30% of the nuclei showed a weak to very weak incorporation of radioactive precursor. In these nuclei most of the radioautographic grains were concentrated over the nucleolus, and a few grains were randomly distributed over the chromosomes. Actinomycin D and the absence of ATP, GTP, and CTP in the medium inhibited incorporation of radioactive precursor. The radioactive product was sensitive to combined pronase and RNase digestion. Addition of E. coli RNA polymerase to the incubation medium enhanced the specific labeling over the puffed regions. The sedimentation behavior of the RNA synthesized in isolated nuclei was different from that of RNA synthesized during a 20 min pulse of radioactive precursor administered to whole glands in vivo and in vitro. Neither the steroid ecdysterone nor a temperature treatment was effective in inducing new puffs in isolated nuclei.     

PRODUCTION AND RELEASE OF A LOCUS-SPECIFIC RIBONUCLEOPROTEIN PRODUCT IN POLYTENE NUCLEI OF DROSOPHILA HYDEI

A specific, 0.1–0.3-µm large ribonucleoprotein complex consisting of a central core with stalklike extensions on top of which 280–320-Å ribonucleoprotein particles are situated is found in an experimentally activated chromosome region, 2–48C, of the polytene chromosomes of Drosophila hydei. Alkaline hydrolysis, RNAse digestion, and uranyl-EDTA-lead staining indicated the ribonucleoprotein character of the 280–320-Å particles, whereas the central core seems to be devoid of RNA. The characteristic complexes are present in the nucleoplasm and at the nuclear membrane, but absent from the cytoplasm. It is suggested that the large RNP complexes are the specific products of the puff at 2–48C. Complexes similar to the ones described have not been observed in any other region of the polytene salivary gland chromosomes of this species.     

Paralog, a Control Mutant in DROSOPHILA MELANOGASTER

The genetic properties of a pleiotropic mutant mapping at 1.4 ± 0.1 in band 3B3 or its adjacent interbands on the X chromosome are described. The mutation is expressed autonomously in germ line cells, where it is recessive and has antimorphic properties. At 29°, the mutation blocks oocyte differentiation, causing female sterility. At lower temperatures, it disturbs the maternal information in the egg; as a result, the progeny lack germ line cells (grandchildless phenotype) and exhibit defects of the cuticular pattern. The mutation is also expressed in somatic cells through zygotic interactions with neighboring regions, including 3A2, 3A3 (zeste), 3C1–2, 3C4 and 3C6–8 (Notch). We interpret the data by postulating that the expression of sets of dispersed genes might be controlled by the local topology of the chromosome, itself constrained by pairing of dispersed repeated elements. We call the mutation paralog.     

A Meiotic Mutant Affecting Recombination in Female DROSOPHILA MELANOGASTER

mei-S282 is a female meiotic mutant isolated from a natural population of Drosophila melanogaster. It is a recessive mutation located at approximately map position 5 on the third chromosome which has two major effects. It causes a nonuniform decrease in recombination which is most drastic in distal chromosome regions and nondisjunction of all chromosome pairs is elevated at the first meiotic division. Nondisjunctional events are positively correlated; furthermore, nondisjoining chromosomes, themselves nonrecombinant, are preferentially recovered from cells in which nonhomologs are preferentially recovered from cells in which nonhomologs are also non-recombinant.-It is concluded that mei-S282 is a defect which occurs early in meiosis I prior to the time of exchange. In the mutant, the frequency of no-exchange tetrads for each of the major chromosomes is increased-and in cells which contain two or more no-exchange tetrads, an interaction between these chromosomes leads to correlated nondisjunction. mei-S282(+) then, is an exchange precondition necessary for the normal frequency and distribution of exchanges.     

A Meiotic Mutant Defective in Distributive Disjunction in DROSOPHILA MELANOGASTER

The female meiotic mutant no distributive disjunction (symbol: nod) reduces the probability that a nonexchange chromosome will disjoin from either a nonexchange homolog or a nonhomolog; the mutant does not affect exchange or the disjunction of bivalents that have undergone exchange. Disjunction of nonexchange homologs was examined for all chromosome pairs; nonhomologous disjunction of the X chromosomes from the Y chromosome in XXY females, of compound chromosomes in females bearing attached-third chromosomes with and without a Y chromosome, and of the second chromosomes from the third chromosomes were also examined. The results suggest that the defect in nod is in the distributive pairing process. The frequencies and patterns of disjunction from a trivalent in nod females suggest that the distributive pairing process involves three separate events-pairing, orientation, and disjunction. The mutant nod appears to affect disjunction only.