Anomalous regulation of the Drosophila Na(+)-Ca2+ exchanger by Ca2+

The Na(+)-Ca2+ exchanger from Drosophila was expressed in Xenopus and characterized electrophysiologically using the giant excised patch technique. This protein, termed Calx, shares 49% amino acid identity to the canine cardiac Na(+)-Ca2+ exchanger, NCX1. Calx exhibits properties similar to previously characterized Na(+)-Ca2+ exchangers including intracellular Na+ affinities, current-voltage relationships, and sensitivity to the peptide inhibitor, XIP. However, the Drosophila Na(+)-Ca2+ exchanger shows a completely opposite response to cytoplasmic Ca2+. Previously cloned Na(+)-Ca2+ exchangers (NCX1 and NCX2) are stimulated by cytoplasmic Ca2+ in the micromolar range (0.1-10 microM). This stimulation of exchange current is mediated by occupancy of a regulatory Ca2+ binding site separate from the Ca2+ transport site. In contrast, Calx is inhibited by cytoplasmic Ca2+ over this same concentration range. The inhibition of exchange current is evident for both forward and reverse modes of transport. The characteristics of the inhibition are consistent with the binding of Ca2+ at a regulatory site distinct from the transport site. These data provide a rational basis for subsequent structure-function studies targeting the intracellular Ca2+ regulatory mechanism.

Independent determination of symmetry and polarity in the Drosophila eye

In each facet of the Drosophila compound eye, a cluster of photoreceptor cells assumes an asymmetric trapezoidal pattern. These clusters have opposite orientations above and below an equator, showing global dorsoventral mirror symmetry. However, in the mutant spiny legs, the polarization of each cluster appears to be random, so that no equator is evident. The apparent lack of an equator suggests that spiny legs+ may be involved in the establishment of global dorsoventral identity that might be essential for proper polarization of the photoreceptor clusters. Alternatively, a global dorsoventral pattern could be present, but spiny legs+ may be required for local polarization of individual clusters. Using an enhancer trap strain in which white+ gene expression is restricted to the dorsal field, we show that white+ expression in spiny legs correctly respects dorsoventral position even in facets with inappropriate polarizations; the dorsoventral boundary is indeed present, whereas the mechanism for polarization is perturbed. It is suggested that the boundary is established before the action of spiny legs+ by an independent mechanism.

Behavioral genetics of thermosensation and hygrosensation in Drosophila

Whereas temperature and humidity are critical variables affecting physiology, behavior, and evolution, the genetic and neuronal underpinnings of thermosensation and hygrosensation remain poorly understood. We have initiated a behavioral-genetic investigation of these sensory systems in Drosophila. Behavioral tests are described for the rapid screening of mutants defective in thermosensation and hygrosensation. We demonstrate the strong responses of normal flies to temperature and humidity. Two mutants were found with defects in thermosensation, only one of which is also defective in hygrosensation, indicating that they involve different sensory mechanisms. Ablation experiments further separate these sensory systems by showing that thermoreceptors are housed in the third antennal segment, whereas hygroreceptors are located more distally in the antennal arista.

Transvection at the eyes absent gene of Drosophila

The Drosophila eyes absent (eya) gene is required for survival and differentiation of eye progenitor cells. Loss of gene function in the eye results in reduction or absence of the adult compound eye. Certain combinations of eya alleles undergo partial complementation, with dramatic restoration of eye size. This interaction is sensitive to the relative positions of the two alleles in the genome; rearrangements predicted to disrupt pairing of chromosomal homologs in the eya region disrupt complementation. Ten X-ray-induced rearrangements that suppress the interaction obey the same general rules as those that disrupt transvection at the bithorax complex and the decapentaplegic gene. Moreover, like transvection in those cases, the interaction at eya depends on the presence of normal zeste function. The discovery of transvection at eya suggests that transvection interactions of this type may be more prevalent than generally thought.

Presynaptic dysfunction in Drosophila csp mutants

Cysteine string proteins are synapse-specific proteins. In Drosophila, csp deletion mutants exhibit temperature-sensitive paralysis and early death. Here, we report that neuromuscular transmission is impaired presynaptically in these csp mutant larvae. At 22 degrees C, evoked transmitter release is depressed relative to wild type and rescued controls, and high frequency stimulation of the nerve leads to sporadic failures. At 30 degrees C, stimulus-evoked responses decline gradually before failing completely. When the temperature is returned to 22 degrees C, evoked responses recover. Spontaneous release events persist at both 22 degrees C and 30 degrees C. Since nerve conduction and postsynaptic sensitivity are unaffected, these data indicate that csp mutations disrupt depolarization-secretion coupling. This disruption explains the cellular basis of the temperature-sensitive paralysis of these organisms.

Rotation of photoreceptor clusters in the developing Drosophila eye requires the nemo gene

The Drosophila eye consists of a reiterative hexagonal array of photoreceptor cell clusters, the ommatidia. During normal morphogenesis, the clusters in the dorsal or ventral halves of the disc rotate 90 degrees in opposite directions, forming mirror images across a dorsoventral equator. In the mutant nemo (nmo), there is an initial turning of approximately 45 degrees, but further rotation is blocked. Genetic mosaic analysis indicates that the nmo gene acts upon each cluster as a whole; normal nmo function in one or more photoreceptor cells appears to be sufficient to induce full rotation. The nmo gene sequence encodes a serine/threonine protein kinase homolog, suggesting that the kinase is required to initiate the second step of rotation. In another mutant, roulette, excessive rotation through varying angles occurs in many ommatidia. This defect is suppressed by nmo, indicating that nmo acts upstream in a rotation-regulating pathway.

Ingrowth by photoreceptor axons induces transcription of a retrotransposon in the developing Drosophila brain

The development of the lamina, the first optic ganglion of the fly visual system, depends on inductive cues from the innervating photoreceptor axons. lacZ expression from a P-element insertion, A72, occurs in the anlage of the lamina coincident with axon ingrowth from the eye imaginal disc. In eyeless mutants lacking photoreceptor axons, lacZ expression did not occur. The P-element was found to have inserted within the 3′ long terminal repeat (LTR) of a ‘17.6′ type retrotransposon. The expression pattern of 17.6 transcripts in the brain in wild-type and eyeless mutants paralleled the expression of the lacZ reporter. Analysis of 17.6 cis-regulatory sequences indicates that the lamina-specific expression is due to the combined action of an enhancer element in the LTR and a repressor element within the internal body of the retrotransposon. The regulation of the 17.6 retrotransposon provides a model for the study of innervation-dependent gene expression in postsynaptic cells during neurogenesis.

bendless, a Drosophila gene affecting neuronal connectivity, encodes a ubiquitin-conjugating enzyme homolog

The Drosophila bendless (ben) gene was originally isolated as a mutation affecting the escape jump response. This behavioral defect was ascribed to a single lesion affecting the connectivity between the giant fiber and the tergotrochanter motor neuron. A closer examination of the ben phenotype suggests that ben activity is broader and affects a variety of other neurons including photoreceptor cells and their axons. Mosaic analysis indicates that the focus of ben activity is presynaptic. We have cloned the ben gene through a chromosomal walk and show that it is homologous to a class of ubiquitin-conjugating enzymes. The major role of ubiquitination in the protein degradative pathway suggests that ben regulates neural developmental processes such as growth cone guidance by targeting specific proteins for degradation.

Paralysis and early death in cysteine string protein mutants of Drosophila

Multimeric complexes of synaptic vesicle and terminal membrane proteins are important components of the neurotransmitter release mechanism. The csp gene of Drosophila encodes proteins homologous to synaptic vesicle proteins in Torpedo. Monoclonal antibodies demonstrate different distributions of isoforms at distinct subsets of terminals. Deletion of the csp gene in Drosophila causes a temperature-sensitive block of synaptic transmission, followed by paralysis and premature death.

Migration of glia along photoreceptor axons in the developing Drosophila eye

We have identified a set of retinal basal glia, designated RBG cells, in the axon layer of the developing Drosophila eye disc. In vivo pulse labeling with bromodeoxyuridine shows that these cells originate in the optic stalk and migrate into the disc. In mutants lacking photoreceptor axons, RBG cells accumulate in the optic stalk, but do not invade the disc. The association of RBG cells with photoreceptor axons, their origin in the optic stalk, and their migration into the retina are in common with the behavior of astrocytes in the developing mammalian retina.

Defective glia in the Drosophila brain degeneration mutant drop-dead

To understand better the cellular basis of late-onset neuronal degeneration, we have examined the brain of the drop-dead mutant of Drosophila. This mutant carries an X-chromosomal recessive mutation that causes severe behavioral defects and brain degeneration, manifested a few days after emergence of the adult. Analysis of genetically mosaic flies has indicated that the focus of the drop-dead mutant phenotype is in the brain and that the gene product is non-cell autonomous. We examined the adult drop-dead mutant brain prior to onset of symptoms and found that many glial cells have stunted processes, whereas neuronal morphology is essentially normal. Adult mutant glial cells resemble immature glia found at an earlier stage of normal brain development. These observations suggest that defective glia in the drop-dead brain may disrupt adult nervous system function, contributing to progressive brain degeneration and death. The normal drop-dead gene product may prevent brain degeneration by providing a necessary glial function.

The sluggish-A gene of Drosophila melanogaster is expressed in the nervous system and encodes proline oxidase, a mitochondrial enzyme involved in glutamate biosynthesis

Certain gene mutations in Drosophila melanogaster cause sluggish motor activity. We have localized the transcription unit of the sluggish-A gene to a 14.7-kb region at the base of the X chromosome and have cloned corresponding cDNAs. The predicted protein product has significant sequence similarity to Saccharomyces cerevisiae proline oxidase (EC 1.5.99.8), a mitochondrial enzyme which catalyzes the first step in the conversion of proline to glutamate. In the mutant fly, mitochondrial proline oxidase activity is reduced and has kinetic properties different from those of the wild type, providing further evidence that the gene encodes proline oxidase. Indeed, the free proline level in mutant flies is elevated. When the mutant is rescued by transformation, the proline oxidase and free proline levels, as well as the motor and phototactic behavior, are restored to normal. During embryonic development the sluggish-A transcript is predominantly expressed in the nervous system. Significantly, it has previously been reported that a mouse mutant, PRO/Re, which has reduced proline oxidase activity and elevated free proline levels, also exhibits sluggish behavior.

Calphotin: a Drosophila photoreceptor cell calcium-binding protein

Monoclonal antibody 23E9 identifies a calcium-binding protein, calphotin, in photoreceptor cells of the Drosophila melanogaster compound eyes and ocelli. The antigen is restricted to a defined cytoplasmic region; it is not present in the rhabdomeres, nuclei, mitochondria, or rough endoplasmic reticulum. A corresponding cDNA recognizes a 3-kb mRNA with retinal specificity similar to the antigen and maps to band 86E/F-87A/B on chromosome 3. An open reading frame of 2595 bp encodes an estimated 85-kDa protein of unusual amino acid composition, with > 50% proline, alanine, and valine and very few basic residues. The C-terminal segment contains a leucine zipper motif uninterrupted by prolines. We found no significant similarities with the GenBank or National Biomedical Resource Foundation data bases. The location of the protein within a distinct cytoplasmic region suggests that it might function as a calcium-sequestering "sponge" to regulate the amount of free cytoplasmic calcium.

The eyes absent gene: genetic control of cell survival and differentiation in the developing Drosophila eye

The eyes absent (eya) gene is required at an early stage in development of the D. melanogaster compound eye. In eya mutants, progenitor cells in the eye disc undergo programmed cell death anterior to the morphogenetic furrow, rather than proceeding into the pathway of retinal differentiation. A low level of cell death normally occurs at this stage, suggesting that eya activity influences the distribution of cells between differentiation and death. Molecular analysis identifies a nuclear protein expressed in progenitor cells prior to differentiation. Transformation with the cDNA prevents progenitor cell death and allows the events that generate the eye to proceed. eya activity is required for the survival of eye progenitor cells at a critical stage in morphogenesis.

The period gene encodes a predominantly nuclear protein in adult Drosophila

The period gene of Drosophila melanogaster (per) is important for the generation and maintenance of biological rhythms. Previous light microscopic observations indicated that per is expressed in a variety of tissues and cell types and suggested that the per protein (PER) may be present in different subcellular compartments. To understand how PER influences circadian rhythms, it is important to define its subcellular location, especially in adult flies where inducible promoter experiments suggested that it is most relevant to circadian locomotor activity rhythms. To this end, we report the results of an immunoelectron microscopic analysis of wild-type flies and per-beta-galactosidase (beta-gal) fusion gene transgenics using a polyclonal anti-PER antibody or an anti-beta-gal antibody, respectively. Most of the PER antigen and the fusion gene product were located within nuclei, suggesting that PER acts in that subcellular compartment to affect circadian rhythms. The results are discussed in terms of per's possible biochemical functions.

Subcellular localization of transcripts in Drosophila photoreceptor neurons: chaoptic mutants have an aberrant distribution

Photoreceptor neurons in the Drosophila retina are long (100 mu) and narrow, providing a system for the study of the intracellular distribution of transcripts and proteins. The chaoptic gene is expressed exclusively in photoreceptor neurons, and mutations of the gene result in reduced developmental competence of cells to generate normal rhabdomeric membranes. The mutant protein exhibited altered distribution both in developing and adult photoreceptor neurons. Furthermore, the transcript distribution in mutants was altered, decreasing with distance from the nucleus, instead of the normal uniform distribution throughout the cell soma. The deficit of transcript concentration correlated with the severity of developmental defect in rhabdomere formation along the cell. In contrast, the distribution of the opsin transcript was not affected by the chaoptic mutation. To observe RNA localization at the ultrastructural level, a high-resolution, electron microscopic in situ hybridization protocol was developed. The results indicate that the normal chaoptic transcript is present on the rough endoplasmic reticulum, which may be a vehicle for specific transcript distribution.

Twenty Drosophila visual system cDNA clones: one is a homolog of human arrestin

From a group of 436 Drosophila melanogaster cDNA clones, we selected 39 that are expressed exclusively or predominantly in the adult visual system. By sequence analysis, 20 of the clones appear to represent previously unreported distinct cDNAs. The corresponding transcripts are detected in the retina and optic lobes. The genes are scattered throughout the genome, some near mutations known to affect eye function. One of these clones has been identified, by sequence analysis, as the structural gene (Arr) for a Drosophila homolog of human arrestin. Vertebrate arrestin interacts with rhodopsin in phototransduction and has been associated with an autoimmune form of uveitis in primates. The presence of an arrestin homolog in Drosophila suggests that both the vertebrate and invertebrate phototransduction cascades are regulated in a similar manner.

Monoclonal antibody probes discriminate early and late mutant defects in development of the Drosophila retina

Many mutations in Drosophila melanogaster affect the morphology of the adult compound eye. However, the times at which the phenotypes first become manifest in development are, in most cases, unknown; they can occur at any of a series of stages. Among mutants in which eyes appear externally similar, the developmental stage of onset of each defect may be quite different. Pattern formation in the compound eye begins during the late third larval instar in the eye imaginal disc, when a wave of morphogenesis crosses the disc from posterior to anterior. As this wave crosses the disc, there appears in its wake an array of photoreceptor neuron clusters and accessory cells that will comprise the adult ommatidia. Eye discs from 20 abnormal-eye mutants were analyzed using monoclonal antibodies that highlight various aspects of the developing array, to observe the stage at which each anomaly becomes evident. Some mutations apparently affect precursor cells, others the setting up of the pattern, others maintenance of the pattern, and still others later morphogenetic events.

Targeted gene mutations in Drosophila

A cloned gene can be of interest because of its expression in a particular tissue or at a certain developmental stage, or because of homology to an interesting gene from another organism. In Drosophila its location in the genome is readily determined by in situ hybridization to the banded larval salivary gland polytene chromosomes, but it is more difficult to isolate mutations that may reveal its function. This paper describes a general method for detecting transposable element insertions into the gene in question. This "reverse genetics" then offers the possibility of observing a consequent mutant phenotype, providing a key to the normal function of the gene. The sensitivity of the polymerase chain reaction makes it possible to detect the occurrence of a single appropriate P-element transposon insertion among a population of mutagenized flies. This is accomplished by the use of oligonucleotide primers--one a sequence from within the cloned gene and the other homologous to the terminal sequence of the P-element DNA--to prime synthesis into the DNA flanking an insertion site. A segment of DNA, bounded by the two primers, will be a target for amplification only in a fly in which a P-element has inserted within about 2 kilobases of the gene primer. This technique has been used to detect P-element insertions near a gene expressed in the Drosophila compound eye. Potential problems with the technique and possible refinements in the screen are discussed. In principle, it could be utilized to detect insertion of a foreign element into any gene for which at least a partial sequence is known and could be extended to other organisms.

Use of a new strategy to isolate and characterize 436 Drosophila cDNA clones corresponding to RNAs detected in adult heads but not in early embryos

We describe a new strategy for producing tissue-specific cDNA libraries and subsequently identifying tissue-specific clones. This method was used to screen for cDNA clones corresponding to RNAs expressed in the Drosophila head that cannot be detected in the early embryo. RNA blots were used to assess the spatial and temporal patterns of expression of these RNAs. The ensemble of 436 head-not-embryo clones identified roughly 700 distinct RNAs that are differentially expressed in the Drosophila head. The RNA expression patterns can be classified into five major categories. it is argued that this ensemble of clones represents a large fraction of all genes differentially expressed in the adult head, but not detected in the early embryo. Many of these genes are likely to encode eye- and nervous system-specific products.

Photophobe (Ppb), a Drosophila mutant with a reversed sign of phototaxis; the mutation shows an allele-specific interaction with sevenless

We have isolated a dominant behavioral mutation, Photophobe (Ppb), on the second chromosome of Drosophila melanogaster. Although wild-type flies are attracted towards green light, flies homozygous for the Ppb mutation avoid it over an intensity range of six logarithms. Ppb interacts in a dominant way with mutations in the sevenless (sev) gene, an X-chromosomal gene necessary for photoreceptor cell 7 differentiation in the Drosophila retina. Specific alleles of sev alter the Ppb behavioral phenotype; of eight sev alleles tested, two alleles enhanced the negative phototaxis of Ppb, whereas six alleles had the opposite effect. In no mutant combination of Ppb and sev was photoreceptor cell 7 restored. These data show that the sev gene, in addition to its role in the differentiation of photoreceptor cell 7, plays a role along with Ppb in a common visual information-processing pathway.

The sevenless+ protein is expressed apically in cell membranes of developing Drosophila retina; it is not restricted to cell R7

In the sevenless (sev) mutants of Drosophila, a single cell type, photoreceptor R7, does not develop. We made monoclonal antibody against a sev+-beta-galactosidase fusion protein, and used it to determine the ultrastructural localization of the sev+ protein in the larval eye disc. The protein is expressed on the apical surface of the developing retina. It is not restricted to cell R7; it is expressed in all the presumptive photoreceptor cells, cone cells, and possibly others. The protein localizes to the cell membranes of the apical tips and their microvilli, away from the bulk of the cell-cell contacts. Possible mechanisms for generating the specificity of the sev phenotype are discussed in light of these results.

Molecular characterization and expression of sevenless, a gene involved in neuronal pattern formation in the Drosophila eye

The Drosophila sevenless mutation results in lack of a single neuron (photoreceptor cell R7) in every ommatidium of the compound eye; the developmental defect occurs in the larval eye disc. We created P-element-induced alleles and used them to isolate the sev gene. An 8.2 kb transcript is expressed in the eye disc, behind the morphogenetic furrow, coincident with recruitment and differentiation of photoreceptor clusters. The transcript becomes localized at the apical surface, persists in the prepupa, and fades out at pupation. It is again detected in the adult head. In some alleles the 8.2 kb transcript is absent. In others, the transcript is expressed, in spite of the absence of cell R7. Localization of the gene product in the eye disc was obtained with antibody raised against sev protein.

From monoclonal antibody to gene for a neuron-specific glycoprotein in Drosophila

A monoclonal antibody (MAb24B10), derived from mice immunized with Drosophila retina, exclusively stains photoreceptor cells in the retina and their axonal projections to the optic ganglia. The antigen (Ag24B10) is a 160-kDa glycoprotein comprising about 0.8% of the retina protein. By microsequencing, 19 of the first 21 amino acids at the NH2-terminal end of the protein have been determined. Using synthetic oligonucleotide probes corresponding to a portion of this amino acid sequence, we isolated a homologous lambda genomic clone. A partial DNA sequence of this clone, along with blot experiments on genomic DNA and RNA, indicate that this clone is part of the structural gene for Ag24B10. By in situ hybridization, the gene was localized to the tip of chromosome 3R.

Neuronal development in the Drosophila retina: monoclonal antibodies as molecular probes

The compound eye of D. melanogaster is a reiterative pattern of facets, each containing eight photoreceptor cells in a precise arrangement. This pattern is established in the eye imaginal disc during the third larval instar. A wave of morphogenesis sweeps from posterior to anterior across the disc, leaving in its wake organized clusters of photoreceptor cells. We have used monoclonal antibodies to highlight pattern elements that are not readily observable by other techniques. Monoclonal antibodies can be used to identify the molecules associated with particular patterns, providing links between observable structures and the genes. As an example, we present the purification and N-terminal sequence of a glycoprotein antigen specific to photoreceptor cells and their axons.

Monoclonal antibody cross-reactions between Drosophila and human brain

A panel of 146 monoclonal antibodies (MAbs), obtained with Drosophila melanogaster tissue as primary immunogen, was tested for cross-reactivity with the human central nervous system. Sites examined included spinal cord, cerebellum, hippocampus, and optic nerve. Nonnervous tissues tested were liver and lymph node. Approximately half of the antibodies reacted with one or more sites in the human central nervous system, identifying regional, cell class, and subcellular antigens. Some recognized neuronal, glial, or axonal subsets. Immunoblot analysis revealed that some antibodies reacted with similar antigen patterns in both species.

Monoclonal antibodies against the Drosophila nervous system

A panel of 148 monoclonal antibodies directed against Drosophila neural antigens has been prepared by using mice immunized with homogenates of Drosophila tissue. Antibodies were screened immunohistochemically on cryostat sections of fly heads. A large diversity of staining patterns was observed. Some antigens were broadly distributed among tissues; others were highly specific to nerve fibers, neuropil, muscle, the tracheal system, cell nuclei, photoreceptors, or other structures. The antigens for many of the antibodies have been identified on immunoblots. Monoclonal antibodies that identify specific molecules within the nervous system should prove useful in the study of the molecular genetics of neural development.

A Drosophila mutant with a temperature-sensitive block in nerve conduction

A mutant, napts (no action potential, temperature-sensitive), is described in which axonal conduction fails at high temperature. Synaptic transmission at the larval neuromuscular junction is unimpaired. Larvae and adults are rapidly paralyzed at restrictive temperatures; they recover rapidly when the temperature is decreased. The mutant gene is recessive and is located on the second chromosome at map position 56.

Courtship in Drosophila mosaics: sex-specific foci for sequential action patterns

Mosaic fate mapping is used to locate the foci determining sex-specific steps in the mating behavior of Drosophila. Male performance of following females and displaying wing vibration toward them requires that a focus inside the head be constituted of male tissue, regardless of the sex of the head sense organs, the legs, the wings, or the thoracic ganglion. For attempted copulation to occur, a second focus in the thoracic region must also be male. Courtship by males is induced by a posteriorly located focus in the female, but an anterior female focus determines receptivity to attempted copulation. The interplay of male and female foci in the complex behavioral sequence is delineated.

Neurophysiological defects in temperature-sensitive paralytic mutants of Drosophila melanogaster

A new temperature-sensitive paralytic mutant of Drosophila, comatose, is compared behaviorally and physiologically with the previously known types, para and shi. All three have different properties with respect to kinetics of paralysis at high temperature and recovery from paralysis; com is hypersensitive to paralysis by cooling. Neurophysiological experimeents indicate different mechanisms for paralysis in each of the mutants.

dunce, a mutant of Drosophila deficient in learning

Normal Drosophilia learn to avoid an odorant associated with electric shock. An X-linked mutant, dunce, has been isolated that fails to display this learning in spite of being able to sense the odorant and electric shock and showing essentially normal behavior in other respects.

Conditioned behavior in Drosophila melanogaster

Populations of Drosophila were trained by alternately exposing them to two odorants, one coupled with electric shock. On testing, the flies avoided the shock-associated odor. Pseudoconditioning, excitatory states, odor preference, sensitization, habituation, and subjective bias have been eliminated as explanations. The selective avoidance can be extinguished by retraining. All flies in the population have equal probability of expressing this behavior. Memory persists for 24 hr. Another paradigm has been developed in which flies learn to discriminate between light sources of different color.

Clock mutants of Drosophila melanogaster

Three mutants have been isolated in which the normal 24-hour rhythm is drastically changed. One mutant is arrhythmic; another has a period of 19 hr; a third has a period of 28 hr. Both the eclosion rhythm of a population and the locomotor activity of individual flies are affected. All these mutations appear to involve the same functional gene on the X chromosome.

Genetic dissection of the Drosophila nervous system by means of mosaics

Given a mutant having abnormal behavior, the anatomical domain responsible for the deficit may be identified by the use of genetic mosaicism. Individuals may be produced in which a portion of the body is mutant male while the rest is normal female. In such sex mosaics, or gynandromorphs, the division line between normal and mutant parts can occur in various orientations. Mutants of five different genes (cistrons) on the X-chromosome of Drosophila melanogaster, having various abnormalities in visual function, have been tested by this method. All of these have been found to be autonomous, i.e., a mutant eye always functions abnormally, regardless of the amount of normal tissue present elsewhere, indicating that the primary causes of the behavioral deficits in these mutants are within the eye.