Table of Contents

Volume 6, Issue 1

  January/February/March 2012

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EDITOR'S PREVIEW

Open Access Article

In this issue of Fly

Barbara Rattner
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EXTRA VIEWS

Open Access Article

The evolution of multiple mating: Costs and benefits of polyandry to females and polygyny to males

Patricia Adair Gowaty
Abstract | PDF

Polyandry is a paradox:  why do females mate multiple times when a single ejaculate often provides enough sperm for lifetime egg production? Gowaty et al. (2010) addressed explanations for polyandry in Drosophila pseudoobscura from the perspective of hypotheses based on sex differences in costs of reproduction (CoR). Contrary to CoR, Gowaty et al. (2010) showed that (1) a single ejaculate was inadequate for lifetime egg production; (2) polyandry provided fitness benefits to females beyond provision of adequate sperm; and (3) fitness benefits of polyandry were not offset by costs.  Here, I discuss predictions of the ad hoc hypotheses of CoR and three alternative hypotheses to CoR to facilitate a discussion and further development of a strong inference approach to experiments on the adaptive significance of polyandry for females.  Each of the hypotheses makes testable predictions; simultaneous tests of the predictions will provide a strong inference approach to understanding the adaptive significance of multiple mating.  I describe a sex-symmetric experiment meant to evaluate variation in fitness among lifelong virgin (V), monogamous females and males with one copulation (M_OC), monogamous females and males with multiple copulations (M_MC), P_AND, polyandrous females;  and P_GYN, polygynous males. Last, I recommend study of many different species, while taking care in choice of study species and attention to the assumptions of specific hypotheses.  I particularly urge study of many more Drosophila species both in laboratory and the wild to understand the “nature of flies in nature," where opportunities and constraints mold evolutionary responses. 

Microtubules cut loose at the cell cortex

David J. Sharp, Brian O'Rourke and Dong Zhang
Abstract | PDF

The ability of the microtubule cystoskeleton to rapidly and locally reorganize itself in response to intra- and extracellular signals is essential to its wide range of functions.  A site of tightly regulated microtubule dynamics—and the major interface between the microtubule cytoskeleton and the extracellular environment—is the cell cortex, where the selective stabilization and destabilization of microtubule plus-ends is required for normal cell division, morphogenesis and migration.  In a recent study, we found that the cortex of Drosophila S2 and D17 cells is coated with the microtubule severing enzyme and plus-end depolymerase, Kat-60, which actively suppresses microtubule growth and stability along the cell edge.  We have proposed that cortical Kat-60 functions by uncapping plus-ends thereby activating another microtubule depolymerase, KLP10A, preloaded onto the end.  The localized destruction of microtubule plus-ends at specific cortical could feed into larger regulatory pathways, such as those in control of the actin cytoskeleton, to influence cell polarization and motility.

The length scale of selection in protein evolution

Benjamin J. Callahan
Abstract | PDF

Central to the study of molecular evolution, and an area of long-standing debate, is the appropriate model for the fitness landscape of proteins. Much of this debate has focused on the strength and frequency of positive and purifying selection, but the form and frequency of selective correlations is also a vital element. The constituent amino acids within a protein generically interact and share selective pressures in predictable ways, which conflicts with the selective independence assumed by common caricatures of the fitness landscape. Here, I discuss a recent study by myself and coauthors that used whole-genome comparisons of orthologous molecular sequences from closely related Drosophilids to explore the form of the selective correlations and selective interactions (epistasis) between the amino acids within a protein. I outline our results and highlight our finding of a selective length scale of ten amino acids within which individual amino acids are substantially and generically more likely to both share selective pressures and interact epistatically. I then focus on the evidence presented in our study supporting a substantial role for epistasis in the process of molecular evolution, and discuss further the implications of this widespread epistasis on the overdispersion of the molecular clock and the efficacy of common tests for positive selection.

Phagocytosis of bacterial pathogens

Yoon-Suk Alexander Chung and Christine Kocks
Abstract | PDF

Phagocytosis is an evolutionarily ancient, receptor-driven process, by which phagocytic cells recognize invading microbes and destroy them after internalization. The phagocytosis receptor Eater is expressed exclusively on Drosophila phagocytes and is required for the survival of bacterial infections. In a recent study, we explored how Eater can defend fruit flies against different kinds of bacteria. We discovered that Eater bound to certain types of bacteria directly, while for others bacterial binding was dependent on prior disruption of the bacterial envelope. Similar to phagocytes, antimicrobial peptides and lysozymes are ancient components of animal immune systems. Our results suggest that cationic antimicrobial peptides, as well as lysozymes, can facilitate Eater binding to live Gram-negative bacteria. Both types of molecules promote surface-exposure of bacterial ligands that otherwise would remain buried and hidden under an outer membrane. We propose that unmasking ligands for phagocytic receptors may be a conserved mechanism operating in many animals, including humans. Thus, studying a Drosophila phagocytosis receptor may advance our understanding of innate immunity in general.

Balancing sex chromosome expression and satisfying the sexes

Jamila I. Horabin
Abstract | Full Text | PDF

Equalizing sex chromosome expression between the sexes when they have largely differing gene content appears to be necessary, and across species, is accomplished in a variety of ways. Even in birds, where the process is less than complete,¹ a mechanism to reduce the difference in gene dose between the sexes exists. In early development, while the dosage difference is unregulated and still in flux, it is frequently exploited by sex determination mechanisms. The Drosophila female sex determination process is one clear example, determining the sexes based on X chromosome dose. Recent data show that in Drosophila, the female sex not only reads this gene balance difference, but at the same time usurps the moment. Taking advantage of the transient default state of male dosage compensation, the sex determination master-switch Sex-lethal which resides on the X, has its expression levels enhanced before it works to correct the gene imbalance.² Intriguingly, key developmental genes which could create developmental havoc if their levels were unbalanced show more exquisite regulation,³ suggesting nature distinguishes them and ensures their expression is kept in the desirable range.




REVIEWS

The ADAM family: Insights into Notch proteolysis

Laura Christian
Abstract | Full Text | PDF

Notch signaling is integral to a large number of developmental and homeostasis events, and either gain or loss of Notch signaling results in a wide range of defects. Notch must be processed by several proteases, including a member of the ADAM (a disintegrin and metalloprotease) family to mediate downstream signaling. Until recently, interactions of Notch with specific ADAMs in different contexts were unclear. ADAM10 is now known to be specifically essential for development and homeostasis of mouse epidermis and cardiovascular structures, and ADAM17 may not be able to fully replace ADAM10 in these contexts. However, Notch from T-cell acute lymphoblastic leukemia (T-ALL) patients can be cleaved by both ADAMs 10 and 17. Studies have revealed that ADAM10 is necessary for Notch processing when Notch is activated by a ligand, while ADAM17 is the major protease for processing Notch that is activated independently of ligand in both flies and mammals.

Open Access Article

Genetics and neurobiology of aggression in Drosophila

Liesbeth Zwarts, Marijke Versteven and Patrick Callaerts
Abstract | PDF

Aggressive behavior is widely present throughout the animal kingdom and is crucial to ensure survival and reproduction. Aggressive actions serve to acquire territory, food, or mates and in defense against predators or rivals; while in some species these behaviors are involved in establishing a social hierarchy. Aggression is a complex behavior, influenced by a broad range of genetic and environmental factors. Recent studies in Drosophila provide insight into the genetic basis and control of aggression. The state of the art on aggression in Drosophila and the many opportunities provided by this model organism to unravel the genetic and neurobiological basis of aggression are reviewed.




METHODS AND TECHNICAL ADVANCES

A novel genetic tool for clonal analysis of fourth chromosome mutations

Rui Sousa-Neves and Joseph M. Schinaman
Abstract | PDF

The fourth chromosome of Drosophila remains one of the most intractable regions of the fly genome to genetic analysis. The main difficulty posed to the genetic analyses of mutations on this chromosome arises from the fact that it does not undergo meiotic recombination, which makes recombination mapping impossible, and also prevents clonal analysis of mutations, a technique which relies on recombination to introduce the prerequisite recessive markers and FLP-recombinase recognition targets (FRT). Here we introduce a method that overcomes these limitations and allows for the generation of single Minute haplo-4 clones of any fourth chromosome mutant gene in tissues of developing and adult flies.




RESEARCH PAPER

Effect of sodium channel abundance on Drosophila development, reproductive capacity and aging

Graham Garber, Lee Ann Smith, Robert Reenan and Blanka Rogina
Abstract | PDF

The voltage-gated Na+ channels (VGSC) are complex membrane proteins responsible for generation and propagation of the electrical signals through the brain, the skeletal muscle and the heart. The levels of sodium channels affect behavior and physical activity. This is illustrated by the maleless mutant allele (mlenapts) in Drosophila, where the decreased levels of voltage-gated Na+ channels cause temperature-sensitive paralysis.

Here, we report that mlenapts mutant flies exhibit developmental lethality, decreased fecundity and increased neurodegeneration. The negative effect of decreased levels of Na+ channels on development and ts-paralysis was more pronounced at 18 and 29°C than at 25°C, suggesting particular sensitivity of the mlenapts flies to temperatures above and below normal environmental conditions. Similarly, longevity of mlenapts flies was unexpectedly short at 18 and 29°C compared with flies heterozygous for the mlenapts mutation. Developmental lethality and neurodegeneration of mlenapts flies was partially rescued by increasing the dosage of para, confirming a vital role of Na+ channels in development, longevity and neurodegeneration of flies and their adaptation to temperatures.