Drosophila

Abstract Abstract. The highly conserved basic helix-loop-helix transcription factor Hand plays a crucial role in cardiogenesis, limb formation and other developmental processes of vertebrates. Humans, mice and other higher vertebrates have two related genes, dHand (also known as Hand2, Hed, Thing2) and eHand (also known as Hand1, Hxt, Thing1), whereas fish and Drosophila have only a single hand gene. We cloned Drosophila hand and studied the embryonic expression in detail by using various tissue-specific markers that allowed us to analyze the identity of hand-expressing cells. We found hand to be expressed in the entire heart, including all cardioblasts and pericardial cells, in the progenitors of the circular visceral muscles, the lymph gland and garland cells, and in a few cells in the CNS. The expression of Drosophila hand starts after the inductive activity of the early regulators in these tissues, e.g. Tinman and Bagpipe, suggesting a role of Hand in differentiation rather than in tissue determination. In many aspects the expression pattern of Drosophila hand resembles the patterns of its vertebrates orthologues, for instance in cardiac tissues. We assume that Hand proteins might play a highly conserved role throughout evolution. Electronic Supplementary Material is available if you access this article at http://dx.doi.org/10.1007/s00427-002-0268-6. On that page (frame on the left side), a link takes you directly to the supplementary material.

The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have higher transposon density (25%-50%) than euchromatic reference regions (3%-11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% versus 11%-27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density ...

Ageing is widely believed to be a non-adaptive process that results from a decline in the force of natural selection. However, recent studies in Saccharomyces cerevisiae are consistent with the existence of a programme of altruistic ageing and death. We suggest that the similarities between the molecular pathways that regulate ageing in yeast, worms, flies and mice, together with evidence that is consistent with programmed death in salmon and other organisms, raise the possibility that programmed ageing or death can also occur in higher eukaryotes.

Numerous field and laboratory experiments have shown that many species have the capacity for social learning, including mate choice decisions that can be influenced by witnessing the mating decisions of others. Here we develop a numerical model of mate choice copying that follows the population genetics tradition, consisting in tracking allele frequencies in a population over time under various scenarios. In contrast to previous evolutionary models, we consider both positive social information and negative social information because many mating systems are driven by males in pursuit of a mate and female refusal of copulation may provide negative social information. The inclusion of negative social information to mate choice copying helps the spread of a novel trait, even if female innate mate choice preference is biased toward the common male type. We argue that the presence or absence of copying might simply mirror the associated cost-benefit relationship of the mating system of a ...

Polarized cell behaviors drive axis elongation in animal embryos, but the mechanisms underlying elongation of many tissues remain unknown. Eggs of Drosophila undergo elongation from a sphere to an ellipsoid during oogenesis. We used live imaging of follicles (developing eggs) to elucidate the cellular basis of egg elongation. We find that elongating follicles undergo repeated rounds of circumferential rotation around their long axes. Follicle epithelia mutant for integrin or collagen IV fail to rotate and elongate, which results in round eggs. We present evidence that polarized rotation is required to build a polarized, fibrillar extracellular matrix (ECM) that constrains tissue shape. Thus, global tissue rotation is a morphogenetic behavior that uses planar polarity information in the ECM to control tissue elongation.

Classical work on germ cells in fishes has dealt with three main issues; their embryonic origin, the proliferation, and migration pathway during embryonic and larval development. Until recently, primordial germ cells (PGCs) have been studied in a number of fishes using morphological criteria only. The identification of the Drosophila vasa homolog gene of zebrafish now allows comparison of these morphological data with vasa RNA expression patterns in zebrafish. Teleost PGCs can be distinguished from somatic cells by their distinct morphology, at the earliest during gastrulation, and in most fishes their number varies between 10 and 30 during pregonial development. Mitosis is generally not observed in PGCs at extragonadal locations, whereas they are mitotically active once at the gonadal ridges. During gastrulation, PGCs appear to translocate from the epiblast to the hypoblast and during somitogenesis they are found associated with the most peripheral yolk syncitial layer (YSL). From the peripheral YSL they migrate through the median mesoderm into the dorsal mesoderm and then to the dorsal mesentery, where they establish the gonad primordia with mesenchymal cells. Vasa RNA positive cells, the PGCs of the zebrafish conform to these general observations. Interestingly, classical descriptive and experimental data can now be reevaluated using vasa as a molecular marker of the fish germ line. The power of zebrafish genetics together with possibilities of experimental embryology should accelerate research on aspects of vertebrate germ line development such as PGC migration, division and apoptosis, as well as (in) fertility. The present review summarizes some of the classical data on germ line development in fishes in relation to recent data on vasa expression in zebrafish and compares these findings, where appropriate, with those in other model organisms. Special emphasis is placed on vasa gene expression as a potential universal germ line marker and suggestions are made for novel, zebrafish specific approaches to investigate the vertebrate germ line.

A simple mathematical method is developed to estimate the number of nucleotide substitutions per site between two DNA sequences, by extending Kimura's (1980) two-parameter method to the case where a G+C-content bias exists. This method will be useful when there are strong transition-transversion and G+C-content biases, as in the case of Drosophila mitochondrial DNA.

For many astronomers, the progressive development of life has been seen as a natural occurrence given proper environmental conditions on a planet: even though such beings would not be identical to humans, there would be significant parallels. A striking contrast is seen in writings of nonphysical scientists, who have held more widely differing views. But within this diversity, reasons for differences become more apparent when we see how views about extraterrestrials can be related to the differential emphasis placed on modern evolutionary theory by scientists of various disciplines. One clue to understanding the differences between the biologists, paleontologists, and anthropologists who speculated on extraterrestrials is suggested by noting who wrote on the subject. Given the relatively small number of commentators on the topic, it seems more than coincidental that four of the major contributors to the evolutionary synthesis in the 1930s and 1940s are among them. Upon closer examination it is evident that the exobiological arguments of Theodosius Dobzhansky and George Gaylord Simpson and, less directly, of H. J. Muller and Ernst Mayr are all related to their earlier work in formulating synthetic evolution. By examining the variety of views held by nonphysical scientists, we can see that there were significant disagreements between them about evolution into the 1960s. By the mid-1980s, many believed that “higher” life, particularly intelligent life, probably occurs quite infrequently in the universe; nevertheless, some held out the possibility that convergence of intelligence could occur across worlds. Regardless of the final conclusions these scientists reached about the likely prevalence of extraterrestrial intelligence, the use of evolutionary arguments to support their positions became increasingly common.

Worldwide, an important aspect of invasive insect pest management is more effective, safer detection and control systems. Phenyl propanoids are attractive to numerous species of Dacinae fruit flies. Methyl eugenol (ME) (4-allyl-1, 2-dimethoxybenzene-carboxylate), cue-lure (C-L) (4-(p-acetoxyphenyl)-2-butanone), and raspberry ketone (RK) (4-(p-hydroxyphenyl)-2-butanone) are powerful male-specific lures. Most evidence suggests a role of ME and C-L/RK in pheromone synthesis and mate attraction. ME and C-L/RK are used in current fruit fly programs for detection, monitoring, and control. During the Hawaii Area-Wide Pest Management Program in the interest of worker safety and convenience, liquid C-L/ME and insecticide (i.e., naled and malathion) mixtures were replaced with solid lures and insecticides. Similarly, Male Annihilation Technique (MAT) with a sprayable Specialized Pheromone and Lure Application Technology (SPLAT), in combination with ME (against Bactrocera dorsalis, oriental fruit fly) or C-L/RK (against B. cucurbitae, melon fly), and the reduced-risk insecticide, spinosad, was developed for area-wide suppression of fruit flies. The nontarget effects of ME and C-L/RK to native invertebrates were examined. Although weak attractiveness was recorded to flower-visiting insects, including bees and syrphid flies, by ME, effects to native Drosophila and other Hawaiian endemics were found to be minimal. These results suggested that the majority of previously published records, including those of endemic Drosophilidae, were actually for attraction to dead flies inside fruit fly traps. Endemic insect attraction was not an issue with C-L/RK, because B. cucurbitae were rarely found in endemic environments.