Essential genes for myoblast fusion in Drosophila embryogenesis.

In Drosophila, as in vertebrates, each muscle is a syncytium and arises from mesodermal cells by successive fusion. This requires cell-cell recognition, alignment, formation of prefusion complexes, followed by electron-dense plaques and membrane breakdown. Because muscle development in Drosophila is rapid and well-documented, it has been possible to identify several genes essential for fusion. Molecular analysis of two of these genes revealed the importance of cytoplasmic components. One of these, Myoblast city, is expressed in several tissues and is homologous to the mammalian protein DOCK180. Myoblast city is presumably involved in cell recognition and cell adhesion. Blown fuse, the second cytoplasmic component, is selectively expressed in the mesoderm and essential in order to proceed from the prefusion complex to electron-dense plaques at opposed membranes between adjacent myoblasts. The rolling stone gene is transiently expressed during myoblast fusion. The Rost protein is located in the membrane and thus might be a key component for cell recognition. The molecular characterization of further genes relevant for fusion such as singles bar and sticks and stones will help to elucidate the mechanism of myoblast fusion in Drosophila.     

Expression of evolutionarily conserved eye specification genes during Drosophila embryogenesis

Eye specification in Drosophila is thought be controlled by a set of seven nuclear factors that includes the Pax6 homolog, Eyeless. This group of genes is conserved throughout evolution and has been repeatedly recruited for eye specification. Several of these genes are expressed within the developing eyes of vertebrates and mutations in several mouse and human orthologs are the underlying causes of retinal disease syndromes. Ectopic expression in Drosophila of any one of these genes is capable of inducing retinal development, while loss-of-function mutations delete the developing eye. These nuclear factors comprise a complex regulatory network and it is thought that their combined activities are required for the formation of the eye. We examined the expression patterns of four eye specification genes, eyeless (ey), sine oculis (so), eyes absent (eya), and dachshund (dac) throughout all time points of embryogenesis and show that only eyeless is expressed within the embryonic eye anlagen. This is consistent with a recently proposed model in which the eye primordium acquires its competence to become retinal tissue over several time points of development. We also compare the expression of Ey with that of a putative antennal specifying gene Distal-less (Dll). The expression patterns described here are quite intriguing and raise the possibility that these genes have even earlier and wide ranging roles in establishing the head and visual field.     

Spatial and temporal expression patterns of selenoprotein genes during embryogenesis in zebrafish

Selenium is important for embryogenesis in vertebrates but little is known about the expression patterns and biological functions of most selenoprotein genes. Taking advantage of the zebrafish model, systematic analysis of selenoprotein gene expression was performed by in situ hybridization on whole-mount embryos at different developmental stages. Twenty-one selenoprotein mRNAs were analyzed and all of them exhibited expression patterns restricted to specific tissues. Moreover, we demonstrated that highly similar selenoprotein paralogs were expressed within distinct territories. Therefore, tissue- and development-specific expression patterns provided new information for selenoproteins of unknown function.     

Maternal-effect genes as the recording genes of Turing-Child patterns: sequential compartmentalization in Drosophila

The early embryo is often a two-dimensional surface. The fate map is the subdivision of this surface into regions which give rise to parts of the phenotype. It is shown for Drosophila that the fate map is generated by the spontaneous and sequential formation of Turing-Child (TC) eigenfunction patterns. These patterns are recorded by the maternal-effect genes. The addition of the nodal lines of the TC patterns yields the correct number, positions, sequences and symmetries of regional boundaries. A simplest nontrivial 'homeotic transformation' is suggested and explained. A single mutation converts a region in one end of the fate map to a mirror-symmetric image of a nonadjacent region in the other end of the fate map, and this is attributed to the geometry of the TC patterns. This geometry also determines the initial shape of the zygotic gene expression. The vision of William Bateson that biological form is shaped like Chladni's patterns in acoustics and music is justified. A similar sequence of TC patterns occurs in the normal development of all organisms, and it is suggested that artificial intervention which completes the full sequence of TC patterns can be useful in the context of regenerative medicine and this is illustrated with the sea urchin.     

Exploring spatiotemporal patterns in early stages of primary succession on former lignite mining sites

Questions: 1. Does random colonization predominate in early stages of primary succession? 2. Do pioneer species facilitate the establishment of later arriving species? 3. Does an initially random distribution change to an aggregated pattern with ongoing succession? Location: Lignite mining region of Lower Lusatia, eastern Germany. Methods: Individual plants were mapped along a 2 m × 28 m transect during three successive years and classified into two groups (1) the pioneer Corynephorus canescens and (2)‘all other species’. Using the pair‐correlation function, univariate point pattern analysis was carried out by applying a heterogeneous Poisson process as null model. Bivariate analysis and a toroidal shift null model were applied to test for independence between the spatial patterns of the two groups separately for each year, as well by exploring spatiotemporal patterns from different years. Results: In the first year Corynephorus and ‘all other species’ showed an aggregated pattern on a spatial scale > 40 cm and in the second and third years a significant attraction for distances between 4 and 12 cm, with an increasing radius in the third year. The analyses of interspecific spatiotemporal dynamics revealed a change from independence to attraction between distances of 4 cm and 16 cm when using Corynephorus as focal species. However, applying ‘all other species’ as focal points results in a significant attraction at distances up to 60 cm in the first year and a diminishing attraction in the second and third years with distances ≤ 6 cm. Conclusions: Facilitative species‐species interactions are present in early stages of primary succession, resulting mainly from pioneer species acting as physical barriers and their ability to capture diaspores being drifted by secondary dispersal along the substrate surface. However, due to gradual establishment of perennial species and their ability of lateral extension by vegetative dispersal, facilitation may influence spatial pattern formation predominantly on short temporal and fine spatial scales.     

Rapid evolution and gene-specific patterns of selection for three genes of spermatogenesis in Drosophila

Hybrid males resulting from crosses between closely related species of Drosophila are sterile. The F1 hybrid sterility phenotype is mainly due to defects occurring during late stages of development that relate to sperm individualization, and so genes controlling sperm development may have been subjected to selective diversification between species. It is also possible that genes of spermatogenesis experience selective constraints given their role in a developmental pathway. We analyzed the molecular evolution of three genes playing a role during the sperm developmental pathway in Drosophila at an early (bam), a mid (aly), and a late (dj) stage. The complete coding region of these genes was sequenced in different strains of Drosophila melanogaster and Drosophila simulans. All three genes showed rapid divergence between species, with larger numbers of nonsynonymous to synonymous differences between species than polymorphisms. Although this could be interpreted as evidence for positive selection at all three genes, formal tests of selection do not support such a conclusion. Departures from neutrality were detected only for dj and bam but not aly. The role played by selection is unique and determined by gene-specific characteristics rather than site of expression. In dj, the departure was due to a high proportion of neutral synonymous polymorphisms in D. simulans, and there was evidence of purifying selection maintaining a high lysine amino acid protein content that is characteristic of other DNA-binding proteins. The earliest spermatogenesis gene surveyed, which plays a role in both male and female gametogenesis, was bam, and its significant departure from neutrality was due to an excess of nonsynonymous substitutions between species. Bam is degraded at the end of mitosis, and rapid evolutionary changes among species might be a characteristic shared with other degradable transient proteins. However, the large number of nonsynonymous changes between D. melanogaster and D. simulans and a phylogenetic comparative analysis among species confirms evidence of positive selection driving the evolution of Bam and suggests an yet unknown germ cell line developmental adaptive change between these two species.     

黒腹果蝇中嵌合新基因的进化命运和表达模式

新基因的起源和进化对基因组多样性的产生具有重要的贡献.新基因起源常常通过外显子重排而形成嵌合的基因结构,以产生具有新功能的蛋白质.该文调查了在黒腹果蝇中的14个新起源的嵌合基因在群体中的多态性,发现其中8个在群体中的核苷酸多态性会引起提前终止子,而其他6个在群体中编码框都完整且其中4个受到负选择.研究结果表明,嵌合新基因起源后可能存在两种命运:积累提前终止子突变而假基因化,或者表现出一定功能而受自然选择固定下来.基因表达的数据显示,与RNA介导外显子重排(逆转座)形成的新基因不一样,这些由DNA水平外显子重排产生的新基因没有精巢或者雄性特异性表达模式,而是表现出更为多样性的时空表达模式,这提示尽管通过DNA水平外显子重排产生的新基因可能正在变成假基因或者非蛋白质编码的RNA基因,但它们依然可能具有进化出广泛的生物学功能的潜力.     

The spatiotemporal learning rule and its efficiency in separating spatiotemporal patterns

The hippocampus plays an important role in the course of establishing long-term memory, i.e., to make short-term memory of spatially and temporally associated input information. In 1996 (Tsukada et al. 1996), the spatiotemporal learning rule was proposed based on differences observed in hippocampal long-term potentiation (LTP) induced by various spatiotemporal pattern stimuli. One essential point of this learning rule is that the change of synaptic weight depends on both spatial coincidence and the temporal summation of input pulses. We applied this rule to a single-layered neural network and compared its ability to separate spatiotemporal patterns with that of other rules, including the Hebbian learning rule and its extended rules. The simulated results showed that the spatiotemporal learning rule had the highest efficiency in discriminating spatiotemporal pattern sequences, while the Hebbian learning rule (including its extended rules) was sensitive to differences in spatial patterns.     

Evolutionary fate and expression patterns of chimeric new genes in Drosophila melanogaster

Origin and evolution of new genes contribute a lot to genome diversity. New genes usually form chimeric gene structures through DNA-based exon shuffling and generate proteins with novel functions. We investigated polymorphism of 14 chimeric new genes in Drosophila melanogaster populations and found that eight have premature stop codons in some individuals while six are intact in the population, four of which are under negative selection, suggesting the two evolutionary fates of new chimeric genes after origination: accumulate premature stop codons and pseudolize, or acquire functions and get fixed by natural selection. Different from new genes originated through RNA-based duplication (retroposition) which are usually testis-specific or male-specific expressed, the expression patterns of these new genes through DNA-based exon shuffling are temporally and spatially diverse, implying that they may have the potential to evolve various biological functions despite that they may become pseudogenes or non-protein-coding RNA genes.