Developmental expression of the white locus of Drosophila melanogaster

Monitoring of switches in heterochromatin-induced silencing shows incomplete establishment and developmental instabilities

Position effect variegation (PEV) in Drosophila results from new juxtapositions of euchromatic and heterochromatic chromosomal regions, and manifests as striking bimodal patterns of gene expression. The semirandom patterns of PEV, reflecting clonal relationships between cells, have been interpreted as gene-expression states that are set in development and thereafter maintained without change through subsequent cell divisions. The rate of instability of PEV is almost entirely unexplored beyond the final expression of the modified gene; thus the origin of the expressivity and patterns of PEV remain unexplained. Many properties of PEV are not predicted from currently accepted biochemical and theoretical models. In this work we investigate the time at which expressivity of silencing is set, and find that it is determined before heterochromatin exists. We employ a mathematical simulation and a corroborating experimental approach to monitor switching (i.e., gains and losses of silencing) through development. In contrast to current views, we find that gene silencing is incompletely set early in embryogenesis, but nevertheless is repeatedly lost and gained in individual cells throughout development. Our data support an alternative to locus-specific "epigenetic" silencing at variegating gene promoters that more fully accounts for the final patterns of PEV.

Drosophila melanogaster White Mutant w1118 Undergo Retinal Degeneration

Key scientific discoveries have resulted from genetic studies of Drosophila melanogaster, using a multitude of transgenic fly strains, the majority of which are constructed in a genetic background containing mutations in the white gene. Here we report that white mutant flies from w1118 strain undergo retinal degeneration. We observed also that w1118 mutants have progressive loss of climbing ability, shortened life span, as well as impaired resistance to various forms of stress. Retinal degeneration was abolished by transgenic expression of mini-white+ in the white null background w1118 . We conclude that beyond the classical eye-color phenotype, mutations in Drosophila white gene could impair several biological functions affecting parameters like mobility, life span and stress tolerance. Consequently, we suggest caution and attentiveness during the interpretation of old experiments employing white mutant flies and when planning new ones, especially within the research field of neurodegeneration and neuroprotection. We also encourage that the use of w1118 strain as a wild-type control should be avoided.

Dual functionality of cis-regulatory elements as developmental enhancers and Polycomb response elements

Here, Erceg et al. studied the occupancy of the Drosophila PhoRC during embryogenesis and revealed extensive co-occupancy at developmental enhancers. By using an established in vivo assay for Polycomb response element (PRE) activity, they show that a subset of characterized developmental enhancers can function as PREs and silence transcription in a Polycomb-dependent manner, thereby suggesting that reuse of the same elements by the PcG system may help fine-tune gene expression and ensure the timely maintenance of cell identities.

Developmental gene expression is tightly regulated through enhancer elements, which initiate dynamic spatio–temporal expression, and Polycomb response elements (PREs), which maintain stable gene silencing. These two cis-regulatory functions are thought to operate through distinct dedicated elements. By examining the occupancy of the Drosophila pleiohomeotic repressive complex (PhoRC) during embryogenesis, we revealed extensive co-occupancy at developmental enhancers. Using an established in vivo assay for PRE activity, we demonstrated that a subset of characterized developmental enhancers can function as PREs, silencing transcription in a Polycomb-dependent manner. Conversely, some classic Drosophila PREs can function as developmental enhancers in vivo, activating spatio–temporal expression. This study therefore uncovers elements with dual function: activating transcription in some cells (enhancers) while stably maintaining transcriptional silencing in others (PREs). Given that enhancers initiate spatio–temporal gene expression, reuse of the same elements by the Polycomb group (PcG) system may help fine-tune gene expression and ensure the timely maintenance of cell identities.

ATP-binding cassette (ABC) transporter expression and localization in sea urchin development

BACKGROUND

ATP-binding cassette (ABC) transporters are membrane proteins that regulate intracellular concentrations of myriad compounds and ions. There are >100 ABC transporter predictions in the Strongylocentrotus purpuratus genome, including 40 annotated ABCB, ABCC, and ABCG "multidrug efflux" transporters. Despite the importance of multidrug transporters for protection and signaling, their expression patterns have not been characterized in deuterostome embryos.

RESULTS

Sea urchin embryos expressed 20 ABCB, ABCC, and ABCG transporter genes in the first 58 hr of development, from unfertilized egg to early prism. We quantified transcripts of ABCB1a, ABCB4a, ABCC1, ABCC5a, ABCC9a, and ABCG2b, and found that ABCB1a mRNA was 10-100 times more abundant than other transporter mRNAs. In situ hybridization showed ABCB1a was expressed ubiquitously in embryos, while ABCC5a was restricted to secondary mesenchyme cells and their precursors. Fluorescent protein fusions showed localization of ABCB1a on apical cell surfaces, and ABCC5a on basolateral surfaces.

CONCLUSIONS

Embryos use many ABC transporters with predicted functions in cell signaling, lysosomal and mitochondrial homeostasis, potassium channel regulation, pigmentation, and xenobiotic efflux. Detailed characterization of ABCB1a and ABCC5a revealed that they have different temporal and spatial gene expression profiles and protein localization patterns that correlate to their predicted functions in protection and development, respectively.

The white gene of Drosophila melanogaster encodes a protein with a role in courtship behavior

The white gene of Drosophila melanogaster has been extensively studied, yet it is still not understood how its ectopic overexpression induces male-male courtship. To investigate the cellular basis of this behavior, we examined the sexual behavior of several classes of mutants. We find that male-male courtship is seen not only in flies overexpressing the white gene, but also in mutants expected to have mislocalized White protein. This finding confirms that mislocalizing White transporter in the cells in which it is normally expressed will produce male-male courtship behaviors; the courtship behavior is not an indirect consequence of aberrant physiological changes elsewhere in the body. Male-male courtship is also seen in some mutants with altered monoamine metabolism and deficits in learning and memory, but can be distinguished from that produced by White mislocalization by its reduced intensity and locomotor activity. Double mutants overexpressing white and with mutations in genes for serotonergic neurons suggest that male-male courtship produced by mislocalizing White may not be mediated exclusively by serotonergic neurons. We also find decreased olfactory learning in white mutants and in individuals with mutations in the genes for White's binding partners, brown and scarlet. Finally, in cultured Drosophila and mammalian cells, the White transporter is found in the endosomal compartment. The additional genes identified here as being involved in male-male courtship increase the repertoire of mutations available to study sexual behavior in Drosophila.

Drosophila ABC transporter mutants white, brown and scarlet have altered contents and distribution of biogenic amines in the brain

Monoamines such as dopamine, histamine and serotonin (5-HT) are widely distributed throughout the brain of the fruit fly Drosophila melanogaster, where many of their actions have been investigated. For example, histamine is released from photoreceptor synapses in the lamina neuropile of the visual system. Mutations of the genes white, an important eye pigmentation marker in fly genetics that encodes an ABC transporter, and its binding partner brown, cause neural phenotypes not readily reconciled solely with actions in eye pigmentation. We find that flies mutant for these genes, and another binding partner, scarlet, have about half the wild-type amount of histamine in the head, as well as reduced 5-HT and dopamine. These differences parallel reductions in immunoreactivity to the corresponding biogenic amines. They also correlate with the amine content of fractions after differential centrifugation of head homogenates. Thus, most of the amine is found in the vesicle-rich fraction of wild-type head homogenates, whereas it is found in the supernatant fractions from white, brown and scarlet flies. White co-expresses in lamina epithelial glia with Ebony, which conjugates histamine to β-alanine. Histamine is then released when the conjugate is hydrolyzed in photoreceptors, by Tan. Mutant white ameliorates the effects of tan on head histamine whereas it exacerbates the effects of ebony. Our results are consistent with the proposal that histamine uptake by the epithelial glia may be white dependent. Behavioral abnormalities in white, brown and scarlet mutants could arise because aminergic neurons in the Drosophila brain have reduced amine for release.

Transcriptional activity of the telomeric retrotransposon HeT-A in Drosophila melanogaster is stimulated as a consequence of subterminal deficiencies at homologous and nonhomologous telomeres

Drosophila melanogaster telomeres have two DNA domains: a terminal array of retrotransposons and a subterminal repetitive telomere-associated sequence (TAS), a source of telomere position effect (TPE). We reported previously that deletion of the 2L TAS array leads to dominant suppression of TPE by stimulating in trans expression of a telomeric transgene. Here, we compared the transcript activities of a w transgene inserted between the retrotransposon and TAS arrays at the 2L telomere in genotypes with different lengths of the 2L TAS. In contrast to individuals bearing a wild-type 2L homologue, flies with a TAS deficiency showed a significant increase in the level of telomeric w transcript during development, especially in pupae. Moreover, we identified a read-through w transcript initiated from a retrotransposon promoter in the terminal array. Read-through transcript levels also significantly increased with the presence of a 2L TAS deficiency in trans, indicating a stimulating force of the TAS deficiency on retrotransposon promoter activity. The read-through transcript contributes to total w transcript, although most w transcript originates at the w promoter. While silencing of transgenes in nonhomologous telomeres is suppressed by 2L TAS deficiencies, suggesting a global effect, the overall level of HeT-A transcripts is not increased under similar conditions.

Drosophila GAGA factor directs histone H3.3 replacement that prevents the heterochromatin spreading

Epigenetic maintenance of the expression state of the genome is critical for development. Drosophila GAGA factor interacts with FACT and modulates chromatin structure for the maintenance of gene expression. Here we show that the GAGA factor-FACT complex and its binding site just downstream from the white gene are crucial for position effect variegation. Interestingly there is a dip of histone H3 Lys 9 methylation and a peak of H3 Lys 4 methylation at this site. The GAGA factor and FACT direct replacement of histone H3 by H3.3 through association of HIRA at this site, and maintain white expression under the heterochromatin environment. Based on these findings we propose that the GAGA factor and FACT-dependent replacement of Lys 9-methylated histone H3 by H3.3 counteracts the spreading of silent chromatin.

Volatile general anesthetics reveal a neurobiological role for the white and brown genes of Drosophila melanogaster

Molecular and cellular evidence argues that a heterodimer between two ABC transporters, the White protein and the Brown protein, is responsible for pumping guanine into pigment-synthesizing cells of the fruit fly, Drosophila melanogaster. Previous studies have not detected White or Brown outside pigment-synthesizing cells nor have behavioral effects of null mutants been reported, other than those that are visually dependent. Nevertheless, we show here that exposure to the volatile general anesthetic (VGA) enflurane reveals a difference in neuromuscular performance between wild-type flies and those that carry a null allele in either the white or brown gene. Specifically, in a test of climbing ability, w1118 or bw1 flies are much less affected by enflurane than are congenic controls. Altered anesthetic sensitivity is still observed when visual cues are reduced or eliminated, arguing that white and brown contribute to neural function outside the eye. This hypothesis is supported by the detection of white message in heads of flies that are genetically altered so as to lack pigment-producing cells. The w1118 or bw1 mutations also alter the response to a second VGA, halothane, albeit somewhat differently. Under some conditions, the combination of w1118 with another mutation that affects anesthesia leads to a drastically altered phenotype. We consider several ways by which diminished transport of guanine could influence neural function and anesthetic sensitivity.

Developmental regulation of heterochromatin-mediated gene silencing in Drosophila

The roles of differentiation, mitotic activity and intrinsic promoter strength in the maintenance of heterochromatic silencing were investigated during development using an inducible lacZ gene as an in vivo probe. Heterochromatic silencing is initiated at the onset of gastrulation, approximately 1 hour after heterochromatin is first visible cytologically. A high degree of silencing is maintained in the mitotically active imaginal cells from mid-embryogenesis until early third instar larval stage, and extensive relaxation of silencing is tightly associated with the onset of differentiation. Relaxation of silencing can be triggered in vitro by ecdysone. In contrast, timing and extent of silencing at both the initiation and relaxation stages are insensitive to changes in cell cycle activity, and intrinsic promoter strength also does not influence the extent of silencing by heterochromatin. These data suggest that the silencing activity of heterochromatin is developmentally programmed.

Cosuppression in Drosophila: gene silencing of Alcohol dehydrogenase by white-Adh transgenes is Polycomb dependent

When two to six copies of a white promoter-Alcohol dehydrogenase (Adh) reporter fusion gene are introduced into the genome, the expression is progressively reduced both in larvae and adults rather than the expected gene dosage effect. In addition, multiple transgenes reduce endogenous Adh transcripts, a result that is strongly analogous to "cosuppression" phenomena described in many plant species but which has not been previously observed in animals. Silencing of the Adh gene is not influenced by zeste-dependent transvection but strongly affected by the Polycomb and Polycomblike mutations. Polycomb and polyhomeotic proteins are bound to the chromatin at the sites of the repressed w-Adh transgenes.

The repair of UV-induced cyclobutane pyrimidine dimers in the individual genes Gart, Notch and white from isolated brain tissue of Drosophila melanogaster

We have measured the induction and removal of UV-induced cyclobutane pyrimidine dimers from defined, DNA sequences in brains isolated from wild-type Drosophila melanogaster third instar larvae. Brains were exposed to a single dose of 500 J/m2 UVB and kept in the dark for up to 48 h. Within 48 h after irradiation, 50% of the dimers are removed from the actively transcribed genes Gart and Notch. Moreover, these kinetics are similar to the time course of dimer removal measured in the transcriptionally inactive white gene. It is further demonstrated that the genome overall is repaired at a similar rate. The results are discussed with respect to the in vivo irradiation of brains and to the data found for gene-specific repair in other eukaryotes.

The structure, sequence and developmental pattern of expression of the white gene in the blowfly Lucilia cuprina

We have sequenced the complete coding region of the white gene of Lucilia cuprina. Strong sequence identity exists between this gene and its homologue from Drosophila melanogaster at both nucleotide and derived amino acid levels (68% and 78% respectively). The exon/intron structure of the two genes is also largely conserved, although the Lucilia gene contains one extra intron. Expression of the gene peaks during mid-pupal stage, with secondary peaks in late larval and early adult stages. Comparisons between this and other white genes will contribute to a better understanding of ATP-binding transmembrane transport proteins. The white gene should also serve as a useful marker gene in the development of a gene transformation system for the sheep blowfly.

Developmental timing and tissue specificity of heterochromatin-mediated silencing

Heterochromatic position-effect variegation (PEV) describes the mosaic phenotype of a euchromatic gene placed next to heterochromatin. Heterochromatin-mediated silencing has been studied extensively in Drosophila, but the lack of a ubiquitous reporter gene detectable at any stage has prevented a direct developmental characterization of this phenomenon. Current models attribute variegation to the establishment of a heritable silent state in a subset of the cells and invoke differences in the timing of silencing to explain differences in the patch size of various mosaic patterns. In order to follow the course of heterochromatic silencing directly, we have generated Drosophila lines variegating for a lacZ reporter that can be induced in virtually all cells at any developmental stage. Our data indicate that silencing begins in embryogenesis and persists in both somatic and germline lineages. A heterogeneity in the extent of silencing is also revealed; silencing is suppressed in differentiated tissues but remains widespread in larval imaginal discs containing precursor cells for adult structures. Using eye development as an example, we propose that the mosaic phenotype is determined during differentiation by a variegated relaxation in heterochromatic silencing. Though unpredicted by prevailing models, this mechanism is evident in other analogous systems.

Regulatory interactions and role in cell type specification of the Malpighian tubules by the cut, Krüppel, and caudal genes of Drosophila

Krüppel and caudal genes are both required for normal segmentation of the embryo, and the developmental regulatory gene cut is necessary for the normal specification of external sensory organs. These three genes are also expressed in the Malpighian tubules before and during differentiation. Two of the genes, Krüppel and cut, are known to be required for development of the tubules. We report that the absence of maternal and zygotic caudal function reduces their normal growth and elongation. Normal Krüppel function, which is known to be required for caudal expression, is also required for cut expression, while cut and caudal are expressed independently of each other. Cell type transformations of Malpighian tubules were studied by examining the effects of mutations on the expression of markers specific to Malpighian tubules, hindgut, or midgut of normal embryos. Loss of Krüppel activity confers hindgut characteristics on those cells that normally form the Malpighian tubules with all markers tested. Loss of cut function alters the expression of some markers but not others. The pathway of tissue specific gene regulation, apparently, branches beyond Krüppel to form at least a cut and a caudal branch.

A trans-acting regulatory gene that inversely affects the expression of the white, brown and scarlet loci in Drosophila

A trans-acting regulatory gene, Inr-a, that alters the level of expression of the white eye color locus as an inverse function of the number of its functional copies is described. Several independent lines of evidence demonstrate that this regulatory gene interacts with white via the promoter sequences. Among these are the observations that the inverse regulatory effect is conferred to the Adh gene when fused to the white promoter and that cis-regulatory mutants of white fail to respond. The phenotypic response to Inr-a is found in all tissues in which white is expressed, and mutants of the regulator exhibit a recessive lethality during larval periods. Increased white messenger RNA levels in pupal stages are found in Inr-a/+ individuals versus +/+ and a coordinate response is observed for mRNA levels from the brown and scarlet loci. All are structurally related and participate in pigment deposition. These experiments demonstrate that a single regulatory gene can exert an inverse effect on a target structural locus, a situation postulated from segmental aneuploid studies of gene expression and dosage compensation.

Nucleolus organizer-suppressed position-effect variegation in Drosophila melanogaster

The white locus is inactivated in a cell-by-cell variegated pattern when juxtaposed with the proximal or distal parts of the nucleolus organizer region (NO) by X chromosome inversion. Recombinants for two such inversions, wm51b and wm4, were obtained and randomized for genetic background. White locus activity was much higher in the wm4 recombinant duplicated for most of the NO and much lower in the wm51b recombinant deficient for it. Although there may be other molecular differences between the heterochromatic regions of the recombinants, the most obvious is the dosage of NO. Suppression of a NO region-evoked variegated phenotype by additional NO doses is discussed in relation to four different classes of models for position-effect variegation (PEV): chromatin structure, nuclear geometry, incomplete transposition of mobile elements, and heterochromatin promoter-driven transcription. A corollary of the structural model is functional subdivision of heterochromatin, which would enable the use of PEV as a tool for its study.

Cloning and characterization of the white and topaz eye color genes from the sheep blowfly Lucilia cuprina

Clones carrying the white and topaz eye color genes have been isolated from genomic DNA libraries of the blowfly Lucilia cuprina using cloned DNA from the homologous white and scarlet genes, respectively, of Drosophila melanogaster as probes. On the basis of hybridization studies using adjacent restriction fragments, homologous fragments were found to be colinear between the genes from the two species. The nucleotide sequence of a short region of the white gene of L. cuprina has been determined, and the homology to the corresponding region of D. melanogaster is 72%; at the derived amino acid level the homology is greater (84%) due to a marked difference in codon usage between the species. A major difference in genome organization between the two species is that whereas the DNA encompassing the D. melanogaster genes is free of repeated sequences, that encompassing their L. cuprina counterparts contains substantial amounts of repeated sequences. This suggests that the genome of L. cuprina is organized on the short period interspersion pattern. Repeated sequence DNA elements, which appear generally to be short (less than 1 kb) and which vary in repetitive frequency in the genome from greater than 10(4) copies to less than 10(2) copies, are found in at least two different locations in the clones carrying these genes. One type of repeat structure, found by sequencing, consists of tandemly repeating short sequences. Restriction site and restriction fragment length polymorphisms involving both the white and topaz gene regions are found within and between populations of L. cuprina.

The FLP recombinase of yeast catalyzes site-specific recombination in the Drosophila genome

We have transferred the site-specific recombination system of the yeast 2 micron plasmid, the FLP recombinase and its recombination targets (FRTs), into the genome of Drosophila. Flies were transformed with an FLP gene under the control of hsp70 regulatory sequences and with a white gene flanked by FRTs. The heat-induced recombinase catalyzes recombination between FRTs, causing loss of white (seen somatically as white patches in the eye) and, less frequently, gain of white (seen as dark-red patches). Loss and gain frequencies vary with the severity of the heat shock, and patterns of mosaicism vary with the developmental stage at which the heat shock is applied. The recombinase is also active in the germline, producing white-eyed and dark-red-eyed progeny.

Spatial regulation of zerknüllt: a dorsal-ventral patterning gene in Drosophila

zerknüllt (zen) is one of approximately 10 zygotically active genes that control the differentiation of the dorsal-ventral (D/V) pattern during early embryogenesis in Drosophila. Past genetic analyses suggest that maternal factors repress the expression of zen in ventral regions, thereby restricting zen products to dorsal and dorsal-lateral regions of precellular embryos. Subsequent interactions with other zygotic D/V regulatory genes refine the zen pattern, restricting expression to the dorsal-most ectoderm. Here we describe the use of zen promoter fusions and P-element transformation to identify cis elements that are responsible for the complex spatial pattern of zen expression. The zen promoter shows a two-tier organization: Distal sequences mediate its initial response to maternal factors, whereas proximal sequences are responsible for the refinement of the pattern in older embryos. The distal regulatory element has the property of a silencer (or anti-enhancer) element and can act over a distance to repress ventral expression of a heterologous promoter. Also, we discuss evidence that proximal promoter sequences interact with factors that may be modulated by a cell-cell communication pathway.

Eye color pigment granules in Drosophila mauritiana: mosaics produced by excision of a transposable element

Compound eyes of the white-peach (wpch) mutant strain of Drosophila mauritiana have some pigment and receptor cells with wild-type eye color pigmentation. These eyes are mosaic, because excision of a transposable element reverts wpch to wild type during the development of somatic cells. Wild-type patches have three types of pigment granule residing in three respective cell types: primary pigment cells, secondary pigment cells, and retinula (visual receptor) cells. Most aspects of these granules, as well as all other aspects of compound eye ultrastructure, are exactly as in the better studied sibling species D. melanogaster. In the wpch parts of the eye, small and giant unpigmented "pigment granules" reside in secondary pigment cells. These white granules are just like the corresponding granules of w mutant D. melanogaster. Small vs. large patches of pigmented cells likely represent excision events occurring late vs. early respectively during development. Mosaics of eye color markers have been important in developmental analyses; the ease of constructing mosaics of D. mauritiana gives this preparation advantages for mosaic analyses.

The nature of radiation-induced mutations at the white locus of Drosophila melanogaster

X-Ray- and neutron-induced mutations at the white locus of Drosophila melanogaster were used to study the nature of radiation-induced genetic damage. Genetic analysis showed the presence of multi-locus deficiencies in 15 out of 31 X-ray mutants and in 26 out of 35 mutants induced by neutrons. The DNA from 11 X-ray and 4 neutron mutants, which were not multi-locus deficiencies, was analyzed by Southern blot-hybridization. Deletions were observed in 2 X-ray and 1 neutron mutant. In combination with cytogenetic techniques, chromosomal rearrangements affecting the white locus (translocations, inversions, etc.) were identified in 3 X-ray and in 2 neutron mutants. A hot-spot for translocation breakpoints was identified in the left arm of the third chromosome. 5 X-ray mutants, which apparently did not contain large deletions, were subjected to further analysis by the nuclease S1 protection method, after cloning of the white gene. In 4 mutants a small deletion could indeed be detected in this way. Thus it seems that by far the main part of X-ray- and neutron-induced white mutants have arisen through large changes in the white gene, especially deletions.

A detailed developmental and structural study of the transcriptional effects of insertion of the Copia transposon into the white locus of Drosophila melanogaster

The copia insertion responsible for the wa mutation is 3' to the white promotor and in the same transcriptional orientation as white. First, we have analyzed the effects of the wa copia insertion on levels of polyadenylated white transcripts and find large, developmentally programmed effects. Second, we have isolated and sequenced an LTR-excision event involving the copia insertion at wa. This represents the first documented case of an LTR-excision event in Drosophila. This single copia LTR has developmentally programmed effects on white transcript levels qualitatively similar to the intact copia element. Third, we have characterized the structures of white transcripts from wa. We find polyadenylated white transcripts apparently having 3' termini in or near the 3' LTR of the wa copia insertion, as has been reported in limited studies of wa transcription in adults by others. These earlier studies also revealed wa transcripts apparently corresponding to polyadenylated terminus formation in the 5' LTR of the copia transposon; however, our more detailed studies reveal that these transcripts probably have other origins and that little, if any, polyadenylated terminus formation for white transcripts occurs in the 5' LTR of the wa copia insertion. Moreover, we find no polyadenylated terminus formation for white transcripts occurring in the single LTR of the wa LTR-excision product. Fourth, we find that each of three mutant alleles at su(wa) produces elevated levels of several classes of RNAs apparently corresponding to transcriptional readthrough of the wa copia transposon. Elevated levels of one presumptive readthrough transcript were observed previously in one su(wa) mutant strain. Fifth, we have confirmed the existence of a transcript initiated in the 3' LTR of the wa copia insertion and find the levels of this transcript to be strongly influenced by developmental stage and genetic background. Lastly, we have analyzed white transcripts produced by the whd81b11 allele, which carries an insertion of copia in the opposite transcriptional orientation and in a different position than the wa copia insertion. In contrast to the wa copia insertion allele, the whd81b11 allele produces polyadenylated white transcript levels very similar to the w+ case at the stages examined. Moreover, the whd81b11 copia element apparently produced polyadenylated terminus formation in white transcripts and we observe no effect of the allelic state of su(wa) on apparent readthrough of this stop site.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence that two mutations, wDZL and z1, affecting synapsis-dependent genetic behavior of white are transcriptional regulatory mutations

Both the white mutant allele, wDZL, and the zeste mutant allele, z1, reduce white transcript levels in adult head tissues, but have no effect on these levels in other tested adult tissues. wDZL results from insertion of a complex transposon approximately 5.0 kb 5' to white. Juxtaposition of this transposon to white produces a novel transcription unit beginning in the transposon and producing a mature transcript containing both white and transposon sequences. Head-specific expression of this novel transcription unit correlates with the observed repression of wild-type white transcript levels. wDZL and z1 are known to cause synapsis-dependent repression of w+ expression in trans as assessed by eye pigment deposition. Collectively, these results suggest an unexpected and informative correspondence between cis and synapsis-dependent trans regulatory effects. We discuss the implied mechanistic relationship between regulation of transcription and transvection effects in Drosophila.