Studies in experimental behavior genetics. V. Negative geotaxis and further chromosome analyses in Drosophila melanogaster

Thinking about visual behavior; learning about photoreceptor function

Visual behavioral assays in Drosophila melanogaster were initially developed to explore the genetic control of behavior, but have a rich history of providing conceptual openings into diverse questions in cell and developmental biology. Here, we briefly summarize the early efforts to employ three of these behaviors: phototaxis, the UV-visible light choice, and the optomotor response. We then discuss how each of these assays has expanded our understanding of neuronal connection specificity and synaptic function. All of these studies have contributed to the development of sophisticated tools for manipulating gene expression, assessing cell fate specification, and visualizing neuronal development. With these tools in hand, the field is now poised to return to the original goal of understanding visual behavior using genetic approaches.

Ceramide transfer protein function is essential for normal oxidative stress response and lifespan

Ceramide transfer protein (CERT) transfers ceramide from the endoplasmic reticulum to the Golgi complex, a process critical in synthesis and maintenance of normal levels of sphingolipids in mammalian cells. However, how its function is integrated into development and physiology of the animal is less clear. Here, we report the in vivo consequences of loss of functional CERT protein. We generated Drosophila melanogaster mutant flies lacking a functional CERT (Dcert) protein using chemical mutagenesis and a Western blot-based genetic screen. The mutant flies die early between days 10 and 30, whereas controls lived between 75 and 90 days. They display >70% decrease in ceramide phosphoethanolamine (the sphingomyelin analog in Drosophila) and ceramide. These changes resulted in increased plasma membrane fluidity that renders them susceptible to reactive oxygen species and results in enhanced oxidative damage to cellular proteins. Consequently, the flies showed reduced thermal tolerance that was exacerbated with aging and metabolic compromise such as decreasing ATP and increasing glucose levels, reminiscent of premature aging. Our studies demonstrate that maintenance of physiological levels of ceramide phosphoethanolamine by CERT in vivo is required to prevent oxidative damages to cellular components that are critical for viability and normal lifespan of the animal.

Gravitaxis in Drosophila melanogaster: a forward genetic screen

Perception of the earth's gravitational force is essential for most forms of animal life. However, little is known of the molecular mechanisms and neuronal circuitry underlying gravitational responses. A forward genetic screen using Drosophila melanogaster that provides insight into these characteristics is described here. Vertical choice mazes combined with additional behavioral assays were used to identify mutants specifically affected in gravitaxic responses. Twenty-three mutants were selected for molecular analysis. As a result, 18 candidate genes are now implicated in the gravitaxic behavior of flies. Many of these genes have orthologs across the animal kingdom, while some are more specific to Drosophila and invertebrates. One gene (yuri) located close to a known locus for gravitaxis has been the subject of more extensive analysis including confirmation by transgenic rescue.

Genetics of graviperception in animals

Gravity is a constant stimulus for life on Earth and most organisms have evolved structures to sense gravitational force and incorporate its influence into their behavioral repertoire. Here we focus attention on animals and their diverse structures for perceiving and responding to the gravitational vector-one of the few static reference stimuli for any mobile organism. We discuss vertebrate, arthropod, and nematode models from the perspective of the role that genetics is playing in our understanding of graviperception in each system. We describe the key sensory structures in each class of organism and present what is known about the genetic control of development of these structures and the molecular signaling pathways operating in the mature organs. We also discuss the role of large genetic screens in identifying specific genes with roles in mechanosensation and graviperception.

E pluribus unum, ex uno plura: quantitative and single-gene perspectives on the study of behavior

Genetic studies of behavior have traditionally come in two flavors: quantitative genetic studies of natural variants and single-gene studies of induced mutants. Each employed different techniques and methods of analysis toward the common, ultimate goal of understanding how genes influence behavior. With the advent of new genomic technologies, and also the realization that mechanisms underlying behavior involve a considerable degree of complex gene interaction, the traditionally separate strands of behavior genetics are merging into a single, synthetic strategy.

Drosophila melanogaster and the future of 'evo-devo' biology in space. Challenges and problems in the path of an eventual colonization project outside the earth

Space exploration, especially its future phase involving the International Space Station (ISS) makes possible the study of the effects on living systems of long-term expositions to such a strange environment. This phase is being initiated when Biological Sciences are crossing a no-return line into a new territory where the connection between phenotype and genotype may be finally made. We briefly review the paradoxical results obtained in Space experiments performed during the last third of the XX Century. They reveal that simple unicellular systems sense the absence of gravity changing their cytoskeletal organization and the signal transduction pathways, while animal development proceeds unaltered in these conditions, in spite of the fact that these processes are heavily involved in embryogenesis. Longer-term experiments possible in the ISS may solve this apparent contradiction. On the other hand, the current constraints on the scientific use of the ISS makes necessary the development of new hardware and the modification of current techniques to start taking advantage of this extraordinary technological facility. We discuss our advances in this direction using one of the current key biological model systems, Drosophila melanogaster. In addition, the future phase of Space exploration, possibly leading to the exploration and, may be, the colonization of another planet, will provide the means of performing interesting evolutionary experiments, studying how the terrestrial biological systems will change in their long-term adaptation to new, very different environments. In this way, Biological Research in Space may contribute to the advancement of the new Biology, in particular to the branch known as "Evo-Devo". On the other hand, as much as the Space Adventure will continue involving human beings as the main actors in the play, long-term multi-generation experiments using a fast reproducing species, such as Drosophila melanogaster, capable of producing more than 300 generations in 15 years, the useful life foreseen for ISS, will be important. Among other useful information, they will help in detecting the possible changes that a biological species may undergo in such an environment, preventing the uncontrolled occurrence of irreversible deleterious effects with catastrophic consequences on the living beings participating in this endeavour.

Y-chromosome effects on Drosophila geotaxis interact with genetic or cytoplasmic background

Previously, all of the major fruit fly, Drosophila melanogaster, chromosomes (I, II and III) have been shown to be associated with geotaxis, but the Y chromosome has not. Using two methods (back-crossing and chromosome substitution), Y chromosomes from lines that have evolved stable, extreme expressions of geotaxis were placed into different genetic and cytoplasmic backgrounds to test the resulting males for geotaxis. The results of the back-crossing do not support the interpretation of Y-chromosome effects on geotaxis. These tests do not have sufficient statistical power, however, to detect small genetic effects. In the chromosome substitution experiment, the geotaxis-line Y chromosomes were placed into high- and low-selected lines, Canton-S and Champaign wild-type backgrounds. The results of the chromosome substitution experiment provide evidence for a Y-chromosome effect on geotaxis in selected geotaxis lines, but not in wild-type stock, backgrounds. These results suggest that the Y chromosome has a small effect on geotaxis, whose detection depends on genetic and/or cytoplasmic background. The implications of these results are discussed for behaviour genetic analysis of D. melanogaster and for issues of statistical power in detecting small genetic effects.

A biometrical genetic approach to chromosome analysis in Drosophila: detection of epistatic interactions in geotaxis

Chromosome analysis has been widely used as a first step in elucidating the genetic architecture of several behaviors of Drosophila melanogaster. These chromosome studies have generally used incomplete designs or fairly simple statistical analyses. Here I reanalyze two data sets on geotaxis from Pyle (1978) and Ksander (1966) using a biometrical genetic design. Results from the biometrical genetic reanalysis suggest that individual differences in geotaxis might be due to genes on all three major chromosomes which show extensive epistatic interactions.

Genetic basis for remating in Drosophila melanogaster. IV. A chromosome substitution analysis

Drosophila melanogaster lines previously selected for fast and slow return of female receptivity were subjected to a chromosome substitution analysis. Chromosomal effects on direct response to selection were distinctively different between selection lines derived from two different base populations. All three chromosomes tested affect the trait in the JEFFERS selection lines. In contrast, only chromosome II was found to have a main effect in the COMP selection lines. Significant interactions between chromosome II and the other chromosomes were also found in both of the selection lines. All of the components of virgin fly mating behavior measured were affected by chromosome II.

Biometrical and chromosome analyses of lines of Drosophila melanogaster selected for central excitation

Lines of Drosophila melanogaster, bidirectionally selected for extreme and opposite expression of central excitatory state (CES), were subjected first to biometrical and then to chromosome analysis. The analyses revealed that low CES expression is partially dominant to high, at least two chromosomes (II and III) are correlated with CES expression, for the low line, both chromosomes, II and III, are necessary for low expression, cytoplasmic factors are involved with CES expression, and loci of minor effect on the X and Y chromosomes are correlated with CES expression.

Divergent selection on locomotor activity in Drosophila melanogaster. III. Genetic analysis

Divergent directional selection produced three pairs of lines each consisting of a line with high and a line with low locomotor activity. Reciprocal crosses between the high and low lines of one of these pairs showed that a considerable part of the activity differences was contributed by differences between the X chromosomes. This was confirmed by a substitution of the three large chromosomes, between the low and the high lines. The two large autosomal chromosomes had only minor effects. Interactions between chromosomes were sometimes significant. Low-activity alleles tended to be dominant over alleles for high activity.

A chromosome substitution analysis of geotactic maze behavior in Drosophila melanogaster

Positive and negative geotactic maze behaviors were selected in strains of Drosophila melanogaster, for over 40 generations on 15-unit classification mazes. A chromosome substition analysis of these behaviors was undertaken to determine which of the three major chromosomes is most important in causing the differences in geotactic maze behavior between the divergent strains. By following the appropriate mating scheme, every possible homozygous chromosomal combination of the X, II, and III chromosomes from the geopositive and geonegative strain was produced. Heterozygous combinations were also produced to test for dominance and interchromosomal interactions. The results indicate that all three chromosomes are involved in geotactic behavior. The order of importance was II greater than III greater than X. Dominance effects were found in females of the X chromosome from the geopositive strain and for the III chromosome from the geonegative strain. No evidence for interchromosomal interactions was uncovered.

Selection for geotaxis in Drosophila melanogaster: heritability, degree of dominance, and correlated responses to selection

Selection for geotaxis was carried out with flies from a natural population of Drosophila melanogaster; geotactic behavior was measured by means of a Hirsch classification maze. The population was initally almost neutral to gravity, and it responded to both positive (downward) and negative (upward) selection with a realized heritability of about 0.13. Stabilizing selection toward neutral gravity was carried out simultaneously. At generations 6, 9, and 10, all possibly hybrid crosses between pairs of the selected populations were generated and tested. The geotactic scores of hybrids in generations 6 and 9 were not significantly different from the midparent values, while the scores of hybrids in generation 10 deviated significantly from the midparent values in the direction of positive geotaxis. The frequencies of polymorphic inversions declined in every population during selection, but the population under neutral selection seemed to maintain a higher chromosomal polymorphism than those under positive or negative selection. There was no significant depression of productivity, measured as number of progeny, in any population during nine generations of selection.