Bristle patterns and clones along a compartment border in the anterior wing margin ofDrosophila hydei

Summary The bristle pattern along the first longitudinal vein of the wing ofD. hydei differs from that ofD. melanogaster. Instead of a triple row,D. hydei and some allied species show a pattern of five parallel bristle rows of which the medial row (MR) is comparable to the medial triple row (MTR) ofD. melanogaster. Cells of the MR can be made homozygousyellow (y) by induction of mitotic recombination in heterozygousy/y ⁺ females. Until 70 h after egg laying (AEL), the MR clones inD. hydei overlap with one or more of the accompanying dorsal and ventral bristle rows. Between 70 and 120 h AEL the MR clones only overlap with dorsal bristle rows. Some time later they also become separated from both dorsal rows. The resulting MR clone pattern fits with the overall longitudinal clone pattern in the wing blade ofD. melanogaster described by Bryant (1970) and others. The MR clones inD. hydei, however, often show a fragmented appearance with many indentations of the surroundingy ⁺ tissue even when induced after fixation of the DV compartment boundary. This result contrasts with the commonly held notion, derived from work withD. melanogaster, that compartment boundaries are smooth lines.     

Evolution of single-copy DNA and the ADH gene in seven drosophilids

Summary Single-copy DNA was isolated fromDrosophila melanogaster and hybridized with total genomic DNA ofD. melanogaster, D. mauritiana, D. simulans, D. pseudoobscura, D. willistoni, D. hydei andD. virilis. The duplexes were thermally eluted from hydroxyapatite and the data used to assess the relatedness of each species toD. melanogaster. The general pattern of relatedness was similar to that predicted by morphological methods but with some notable exceptions. The rate of nucleotide substitution was estimated to be greater than 0.66% of bases per million years. An unexpected, rapidly evolving component ofD. melanogaster single-copy DNA was identified. The relatedness of these species was also studied with respect to the gene coding for alcohol dehydrogenase (ADH). The ADH gene, previously cloned fromD. melanogaster (Goldberg 1980), was hybridized with Southern blots of genomic digests of the seven species. The intensity and position of the hybridizing bands suggest the amount of divergence of the gene. Divergence was quantitated by reassociation of a fragment of the cloned ADH gene with total DNA of the seven drosophilids and thermal elution of the resultant duplexes from hydroxyapatite. The ADH gene was isolated from genomic clone libraries ofD. melanogaster, D. simulans andD. mauritiana and further studied by comparison of position of restriction sites. Species relationships deduced from comparison of total single-copy DNA and the ADH gene were consistent, demonstrating that a single gene can reflect divergence of the entire genome.     

Expression of the H-Y Antigen on thymus cells and skin: Differential genetic control linked toK end ofH-2

The strength of the H-Y antigen on thymus cells and on skin was compared in differentH-2-congenic mouse strains using a host-versus-graft reaction popliteal lymph node assay, and skin grafts from males of parental strains grafted to F₁ hybrid females. The results revealed considerable differences in the strength of the H-Y antigen among different congenic strains; these differences demonstrate the effect of theH-2-linked gene on the expression of the H-Y antigen. The linkage withH-2 was also confirmed in tests with segregating F₂ generations. In the strains bearing recombinantH-2 haplotypes, the strength of the H-Y antigen is similar to that of parental strain from which the recombinant received itsK end, and the responsible gene (or genes) map to the left ofI-C. The effect of theH-2-linked gene(s) on thymus cells and skin is different. The gene linked to theK end ofH- 2^b determines a strong H-Y antigen on thymus cells, but a relatively weak H-Y antigen on skin. The gene linked to theK end ofH- 2^k determines a weak H-Y antigen on thymus cells, but a strong H-Y antigen on skin. The gene linked to theK end ofH- 2^d determines a weak H-Y antigen on both thymus cells and skin. Our observations raise the possibility that the structural gene for the H-Y antigen is linked toH-2. Alternative (but not exclusive) explanations invoke regulatory effects ofH-2 on the expression of the H-Y antigen, possibly by means of the control of the cellular andogen receptors.     

An approach to study the evolution of theDrosophila 5S ribosomal genes using P-element transformation

Summary The P-element-mediated gene transfer system was used to introduceDrosophila teissieri 5S genes into theDrosophila melanogaster genome. Eight transformedD. melanogaster strains that carryD. teissieri 5S mini-clusters consisting of 9–21 adjacent 5S units were characterized. No genetic exchanges betweenD. melanogaster andD. teissieri 5S clusters were detected over a 2-year survey of the eight strains. The occurrence of small rearrangements within theD. melanogaster 5S cluster was demonstrated in one of the transformed strains.     

Effects ofPax3Modifier Genes on Craniofacial Morphology, Pigmentation, and Viability: A Murine Model of Waardenburg Syndrome Variation

Waardenburg syndrome type 1 is caused by mutations inPAX3.Over 50 humanPAX3mutations that lead to hearing, craniofacial, limb, and pigmentation anomalies have been identified. APAX3mutant allele, segregating in a family, can show reduced penetrance and variable expressivity that cannot be explained by the nature of the mutation alone. TheMus musculus Pax3mutationSp^d(Splotch-delayed, Pax3[formula]), coisogenic on the C57BL/6J (B₆) genetic background, produces in heterozygotes a white belly spot with 100% penetrance and very few other anomalies. By contrast, manySp^d/+ BC₁progeny [F₁♀Sp^d/+ (♀Sp^d/+ B₆× ♂ +/+Mus spretus) × ♂ +/+ B₆] exhibit highly variable craniofacial and pigmentary anomalies. Of the BC₁Sp^d/+ progeny, 23.9% are estimated to be nonviable, and 32.1% are nonpenetrant for the white belly spot. The penetrance and expressivity of theSp^d/+ genotype are controlled in part by the genetic background and the sex of the individual. A minimum of two genes interact withSp^dto influence the craniofacial features of these mice. One of these genes may be either X-linked or sex-influenced, while the other is autosomal. TheA-locus (Agouti) or a gene closely linked toAalso plays a role in determining craniofacial features. At least one additional gene, possibly theA-locus or a gene linked toA,interacts withSp^dand determines the presence and size of the white belly spot. The viability of BC₁mice is influenced by at least three factors:Sp^d,A-locus alleles or a gene closely linked to theA-locus, and the sex of the mouse. These BC₁mice provide an opportunity to identify genes that interact with and modify the expression ofPax3and serve as a model to identify the genes that modify the expression of humanPAX3mutations.     

The distribution of the transposable elementBari-1 in theDrosophila melanogaster andDrosophila simulans genomes

The distribution of the transposable elementBari-1 inD. melanogaster andD. simulans was examined by Southern blot analysis and byin situ hybridization in a large number of strains of different geographical origins and established at different times.Bari-1 copies mostly homogeneous in size and physical map are detected in all strains tested. Both inD. melanogaster and inD. simulans a relatively high level of intraspecific insertion site polymorphism is detectable, suggesting that in both speciesBari-1 is or has been actively transposing. The main difference between the two sibling species is the presence of a large tadem array of the element in a well-defined heterochromatic location of theD. melanogaster genome, whereas such a cluster is absent inD. simulans. The presence ofBari-1 elements with apparently identical physical maps in allD. melanogaster andD. simulans strains examined suggests thatBari-1 is not a recent introduction in the genome of themelanogaster complex. Structural analysis reveals unusual features that distinguish it from other inverted repeat transposons, whereas many aspects are similar to the widely distributedTc1 element ofC. elegans.     

Evolution of thedec-1 eggshell locus inDrosophila. I. Restriction site mapping and limited sequence comparison in themelanogaster species subgroup

Summary We have analyzed 18 kb of DNA in and upstream of thedefective chorion-1 (dec-1) locus of the eight known species of themelanogaster species subgroup ofDrosophila. The restriction maps ofD. simulans, D. mauritiana, D. sechellia, D. erecta, andD. orena are shown to have basically the restriction map ofD. melanogaster, whereas the maps ofD. teissieri andD. yakuba were more difficult to align. However, the basic amount of DNA and sequence arrangement appear to have been conserved in these species. A small deletion of varying length (65–200 bp) is found in a repeated sequence of the central transcribed region ofD. melanogaster, D. simulans, andD. erecta. Restriction site mapping indicated that thedec-1 gene is highly conserved in themelanogaster species subgroup. However, sequence comparison revealed that the amount of nucleotide and amino acid substitution in the repeated region is much larger than in the 5 translated region. The 5 flanking region showed noticeable restriction site polymorphisms between species. Based on calculations from the restriction maps a dendrogram was derived that supports earlier published phylogenetic relationships within themelanogaster species subgroup except that theerecta-orena pair is placed closer to themelanogaster complex than toD. teissieri andD. yakuba.     

The evolutionary genetics of thehobo transposable element in theDrosophila melanogaster complex

Hobo elements are a family of transposable elements found inDrosophila melanogaster and its three sibling species:D. simulans, D. mauritiana andD. sechellia. Studies inD. melanogaster have shown thathobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level somehobo-hybridizing sequences have also been found in the other members of themelanogaster subgroup and in many members of the relatedmontium subgroup. Surveys of older collected strains ofD. melanogaster suggest that completehobo elements were absent prior to 50 years ago and that they have recently been introduced into this species by horizontal transfer. In this paper we review our findings and those of others, in order to precisely describe the geographical distribution and the evolutionary history ofhobo in theD. melanogaster complex. Studies of the DNA sequences reveal a different level of divergence between the groupD. melanogaster, D. simulans andD. mauritiana and the fourth speciesD. sechellia. The hypothesis of multiple transfers in the recent past into theD. melanogaster complex from a common outside source is discussed.     

Rapid sequence divergence in a heat shock locus of Drosophila

In situ hybridization of cRNA transcribed from cloned D. melanogaster heat shock sequences to D. hydei chromosomes has shown that the D. hydei locus 2–32 A corresponds to the D. melanogaster locus 87 A/C and the D. hydei locus 2–36 A to the D. melanogaster locus 95 D, while the D. hydei locus 4–81 B corresponds to the D. melanogaster locus 63 BC. No hybridization to D. hydei chromosomes was found with cRNA transcribed from a clone containing the sequences encoded by the D. melanogaster locus 87 C. Neither D. melanogaster heat shock RNA nor D. virilis heat shock RNA hybridized significantly to the D. hydei heat shock locus 2–48 B. Furthermore, D. hydei heat shock RNA did not hybridize to the cytological homologs of locus 2–48 B found in D. repleta or in D. virilis. D, hydei heat shock. RNA did hybridize to the cytological homologs of locus 2–48 B in D. neohydei and D. eohydei, both of which belong to the hydei subgroup.     

The effects of ascorbic acid and sodium propionate on the relative viability of a mutant ofDrosophila melanogaster

Food shortage resulting from crowding is a direct cause of reduced relative viability of theebony ¹¹ mutant ofD. melanogaster and this in turn is a major factor in reduction of the frequency of thee ¹¹ gene in cage populations. Since some insects require ascorbic acid and someebony mutants have been reported deficient in it, and since some doubt exists as to the presence of ascorbic acid in the food supply, a test was made to determine whether mutant inviability could be oftset by ascorbic acid. Substitution of ascorbic acid for live baker's yeast showed that dietary ascorbic acid has no effect on the relative viability ofe ¹¹/e ¹¹ or on the total yield of F₂ progeny, either with or without sodium propionate.Sodium propionate acts in addition to food shortage in decreasing the frequency ofe ¹¹/e ¹¹.Work aided by funds from the State of Washington Initiative Measure No. 171 for the Support of Biological and Medical Research.     

Variation in alcohol dehydrogenase activity in vitro in flies from natural populations ofDrosophila melanogaster

Alcohol dehydrogenase (ADH) activity variation in male flies taken directly from seven natural populations ofDrosophila melanogaster is largely accounted for by segregation of alleles at theAdh structural gene locus. There was little overlap in the ADH activities ofAdh ^F andAdh ^s homozygotes. Body weights varied only slightly betweenAdh genotypes and contributed little to ADH variation. Between and within population variation in ADH activity and ADH protein in flies in the wild is mainly due to the relative frequencies ofAdh ^F andAdh ^s.     

Drosophila virilis histone gene clusters lacking H1 coding segments

Summary Approximately 30–40% ofDrosophila virilis DNA complementary to clonedDrosophila histone genes is reduced to 3.4-kilobase-pair (kbp) segments by Bgl I or Bgl II digestion. The core histone genes of a 3.4-kbp Bgl II segment cloned in the plasmid pDv3/3.4 have the same order as theD. melanogaster core histone genes in the plasmid cDm500: . Nonetheless, pDv3/3.4 and cDm500 have different histone gene configurations: In pDv3/3.4, the region between the H2B and H3 genes contains 0.35 kbp and cannot encode histone H1; in cDm500, the region contains 2.0 kbp and encodes histone H1. The lack of an H1 gene between the H2B and H3 genes in 30–40% ofD. virilis histone gene clusters suggests that changes in histone gene arrays have occurred during the evolution ofDrosophila. The ancestors of modernDrosophila may have possessed multiple varieties of histone gene clusters, which were subsequently lost differentially in thevirilis andmelanogaster lineages. Alternatively, they may have possessed a single variety, which was rearranged during evolution. The H1 genes ofD. virilis andD. melanogaster did not cross-hybridize in vitro under conditions that maintain stable duplexes between DNAs that are 75% homologous. Consequently,D. virilis H1 genes could not be visualized by hybridization to an H1-specific probe and thus remain unidentified. Our observations suggest that the coding segments in the H1 genes ofD. virilis andD. melanogaster are >25% divergent. Our estimate of sequence divergence in the H1 genes ofD. virilis andD. melanogaster seems high until one considers that the coding sequences of cloned H1 genes from the closely related speciesD. melanogaster andD. simulans are 5% divergent.     

P-related sequences inDrosophila bifasciata: A molecular clue to the understanding of P-element evolution in the genusDrosophila

Summary Two P-elements (bif1 and bif2) were isolated from a genomic library ofDrosophila bifasciata. Both elements are internally deleted and have lost the coding capacity for a functional transposase. One of the elements (bif2) contains an insert consisting of a repetitive sequence. The terminal inverted repeats and the segments necessary for passive mobility are well conserved. Element bif2 has retained rudiments of the coding sequence of exon 0 and exon 3, but the reading frame is destroyed by insertions and deletions. The comparison of theD. bifasciata P-elements with P-elements ofDrosophila melanogaster andDrosophila nebulosa reveals that the two latter sequences are more similar to each other than either of them is to theD. bifasciata elements. This finding contradicts the phylogenetic relationship of the species and can be taken as an indirect but unequivocal evidence for recent horizontal gene transfer from a relative ofD. nebulosa to the gene pool ofD. melanogaster. The P-elements ofD. bifasciata are phylogenetically ancient and have evolved independently for about 50 million years. A higher substitution rate at the third codon position as well as a predominance of conservative replacements at the amino acid level indicates that the P-elements ofD. bifasciata have been under selective constraint over a long period and that immobilization has occurred only recently.     

ISOLATION AND CHARACTERIZATION OF A CELL WALL‐DEFECTIVE MUTANT OF CHLAMYDOMONAS MONOICA (CHLOROPHYTA)1

Cell wall–defective strains of Chlamydomonas have played an important role in the development of transformation protocols for introducing exogenous DNA (foreign genes or cloned Chlamydomonas genes) into C. reinhardtii. To promote the development of similar protocols for transformation of the distantly related homothallic species, C. monoica, we used UV mutagenesis to obtain a mutant strain with a defective cell wall. The mutant, cw‐1, was first identified on the basis of irregular colony shape and was subsequently shown to have reduced plating efficiency and increased sensitivity to lysis by a non‐ionic detergent as compared with wild‐type cells. Tetrad analysis of crosses involving the cw‐1 mutant confirmed 2:2 segregation of the cw:cw⁺ phenotypes, indicating that the wall defect resulted from mutation of a single nuclear gene. The phenotype showed incomplete penetrance and variable expressivity. Although some cells had apparently normal cell walls as viewed by TEM, many cells of the cw‐1 strain had broken cell walls and others were protoplasts completely devoid of a cell wall. Several cw‐1 isolates obtained from crosses involving the original mutant strain showed a marked enhancement of the mutant phenotype and may prove especially useful for future work involving somatic cell fusions or development of transformation protocols.     

Evidence for interspecific transfer of the transposable element mariner betweenDrosophila andZaprionus

Summary The transposable element mariner occurs widely in themelanogaster species group ofDrosophila. However, in drosophilids outside of themelanogaster species group, sequences showing strong DNA hybridization with mariner are found only in the genusZaprionus. the mariner sequence obtained fromZaprionus tuberculatus is 97% identical with that fromDrosophila mauritiana, a member of themelanogaster species subgroup, whereas a mariner sequence isolated fromDrosophila tsacasi is only 92% identical with that fromD. mauritiana. BecauseD. tsacasi is much more closely related toD. mauritiana than isZaprionus, the presence of mariner inZaprionus may result from horizontal transfer. In order to confirm lack of a close phylogenetic relationship between the genusZaprionus and themelanogaster species group, we compared the alcohol dehydrogenase (Adh) sequences among these species. The results show that the coding region of Adh is only 82% identical betweenZ. tuberculatus andD. mauritiana, as compared with 90% identical betweenD. tsacasi andD. mauritiana. Furthermore, the mariner gene phylogeny obtained by maximum likelihood and maximum parsimony analyses is discordant with the species phylogeny estimated by using the Adh genes. The only inconsistency in the mariner gene phylogeny is in the placement of theZaprionus mariner sequence, which clusters with mariner fromDrosophila teissieri andDrosophila yakuba in themelanogaster species subgroup. These results strongly suggest horizontal transfer.     

The mitochondrial genome of Chlamydomonas. II. Genetic analysis of non-mendelian obligate photautotrophic mutants

Summary Among a collection of obligate photoautotrophic (dark-dier,dk) mutants isolated inChlamydomonas reinhardtii, two have been found which are inherited in crosses to wild type in a non-Mendelian, biparental and apparently random fashion. F₁ progeny include not only cells which show thedk and wildtype parental phenotypes but also many which possess intermediate phenotypes between wild type anddk. When F₁ progeny withdk, intermediate or wild-type phenotype were backcrossed to wild type, thedk phenotype continued to be inherited in a biparental and random fashion. Upon selection, neither mutant formed stable clones producing onlydk progeny, suggesting that the two mutants segregatedk and wild-type progeny somatically and that the homozygousdk condition may be lethal. The biparental transmission of these two non-Mendeliandk mutations resembles the transmission of acriflavin-inducedminute mutations ofChlamydomonas and is distinct from the uniparentally inherited chloroplast mutations of this alga. Both thedk andminute mutations may alter mitochondrial DNA and thereby alter mitochondrial functions.     

Resistance to rust (<Emphasis Type="Italic">Puccinia psidii</Emphasis> Winter) in<Emphasis Type="Italic"> Eucalyptus</Emphasis>: mode of inheritance and mapping of a major gene with RAPD markers

Rust is one of the most-damaging eucalypt diseases in Brazil and is considered a potential threat to eucalypt plantations worldwide. To determine the mode of inheritance of resistance in the Eucalyptus grandis—Puccinia psidii pathosystem, ten full-sib families, generated from crosses between susceptible and resistant trees, were inoculated with a single-pustule isolate of the pathogen and rust severity was scored. The observed segregation ratios in segregating families suggested major gene control of rust resistance, although clearly incomplete penetrance, variable expressivity and minor genes are also involved in the global rust-resistance response. To identify markers linked to the resistance locus, screening of RAPD polymorphisms was conducted using bulked segregant analysis in a large full-sib family. A linkage group was built around the Ppr1 gene (P. psidii resistance gene 1) encompassing six RAPD markers, with a genetic window spanning 5 cM with the two most-closely linked flanking markers. Besides these two flanking markers, RAPD marker AT9/917 co-segregated with Ppr1 without a single recombinant in 994 meioses. This tightly linked marker should prove useful for marker-assisted introgression and will provide an initial lead for a positional cloning effort of this resistance allele. This is the first report of a disease resistance gene identified in Eucalyptus, and one of the few examples of the involvement of a major gene in a non-coevolved pathosystem.Communicated by D.B. Neale     

Complexity in evolved regulatory variation for alcohol dehydrogenase genes in HawaiianDrosophila

Summary The alcohol dehydrogenase gene (Adh gene) ofDrosophila affinidisjuncta is expressed at a higher level in the larval midgut and Malpighian tubules than the homologous gene fromDrosophila hawaiiensis. This study analyzed thecis-acting sequences responsible for these regulatory differences in larval tissues ofDrosophila melanogaster transformants. A series of 10 chimeric and deletedAdh genes was introduced into the germ line ofD. melanogaster, and tissue-specific expression levels were quantified by gel electrophoresis of tissue extracts. Sequences in the upstream region of the two genes had the strongest influence on enzyme production in the midgut and Malpighian tubules. Other sequence elements also showed effects, some of which were tissue specific. Most gene fragments displayed context-dependent effects, thus supporting the proposed model of polygenic regulation ofAdh gene expression.     

Molecular systematics of theDrosophila hydei subgroup as inferred from mitochondrial DNA sequences

The phylogeny of theDrosophila hydei subgroup, which is a member of theD. repleta species group, was inferred from 1,515 base pairs of mitochondrial DNA sequence of the cytochrome oxidase subunits I, II, and III. Four of the seven species in the subgroup were examined, which are placed into two taxonomic complexes: theD. bifurca complex (D. bifurca) andD. nigrohydei) and theD. hydei complex (D. hydei and (D. eohydei). Both complexes appear to be monophyletic, although theD. bifurca complex is only weakly supported. The evolution of chromosomal change, interspecific crossability, sperm gigantism, and divergence times of the subgroup is discussed in a phylogenetic context. Correspondence to: G. Spicer