Modeling pattern formation: counting to two in the Drosophila egg

The EGF receptor pathway patterns the Drosophila egg and specifies the position of its dorsal appendages. A new mathematical analysis of this patterning network has highlighted its crucial features and provided novel insights into the spatial and temporal kinetics controlling patterning.     

Low-molecular-weight factors from colonial hydroids affect pattern formation

Summary Two morphogenetic factors have been isolated from tissue of colonial hydroids. Both exert strong effects on pattern formation during metamorphosis, regeneration and colony development. Polyp-inhibiting factor (PIF) is a bivalent inhibitor which strongly affects head and bud formation but acts weakly on stolon branching. Proportion-altering factor (PAF) is a distalizing factor. It counteracts the formation of stolon and promotes the formation of head structures during metamorphosis and regeneration. PIF and PAF antagonistically influence the spatial arrangement of polyps within a colony. They are capable of dislocating structures and thus appear to interfere with or are even part of the pattern-controlling mechanism. Both factors are of low molecular size (about 500 daltons), hydrophilic and probably not peptides.     

Pigmentation pattern formation on snakes

We consider a cell-chemotaxis model mechanism for generating some of the common, simple and complex, patterns found on the skin of snakes. By investigating the pattern generation potential of the model we show that many of the more complex patterns might result from growth of the integument during the pattern formation process. We suggest that many of the diverse elaborate patterns on snakes, and other species, can be generated by a single mechanism if the time scale of the pattern process is commensurate with the time scale associated with significant embryonic growth.     

昆虫内共生菌研究概况

内共生菌与昆虫形成互惠共生关系,在宿主昆虫的生长、生殖、传播植物病害以及探讨生命起源与进化等等方面都有很重要的意义。从昆虫内共生菌的特点、内共生菌在昆虫体内的分布、对昆虫的影响、获得少或缺内共生菌的方法及其研究内共生菌的潜在意义等方面进行了综述。     

The egg came first, of course! Anterior-posterior pattern formation in Drosophila embryogenesis and oogenesis

The anterior-posterior body pattern of the Drosophila embryo is initiated through the action of maternal gene products. In particular, three groups of maternally acting genes (the anterior, posterior and terminal groups) have been shown to direct the synthesis and spatial restriction of the three major organizing activities in the egg. The initial spatial localizations of the maternal organizing activities are established during oogenesis. After fertilization these activities regulate zygotic gene activity along the anterior-posterior axis of the egg.     

Roles of cell-extrinsic growth factors in vertebrate eye pattern formation and retinogenesis

Formation of the vertebrate visual system involves complex interplays of cell-extrinsic cues and cell-intrinsic determinants. Studies in several vertebrate species demonstrate that multiple classes of signaling molecules participate in pattern formation of the eye and neurogenesis of the retina. Certain signals, such as hedgehog, BMP, and FGF molecules, are repeatedly deployed at varying concentration thresholds and in different cellular contexts. Accumulating evidence reveals a striking conservation of molecular mechanisms regulating the neurogenic process between Drosophila and vertebrate retinas. The remaining challenge is to understand how these well-characterized signaling pathways are activated and integrated to impact eye morphogenesis and retinal progenitor cell fate determination.     

Dynamics of pattern formation

Experiments were designed to test the validity ofTuring's suggested pattern-forming mechanisms, which are initially capable of giving rise to only five to seven uniform structures.TheOregon-R (wild-type), mass-cultured strain ofDrosophila melanogaster was employed. Selection for the regular arrangement of microchaetac on the margin of the fourth abdominal sternite was practiced for twenty generations. In the L line, individuals with six uniformly spaced bristles were selected as parents of every generation. Due to the absence of nine bristles dividing the sternal margin uniformly, the progeny was raised in each generation in the H line from males and females with nine as equidistant bristles as possible. The whole experiment was performed at 25±0.50°C.Selection was effective in increasing the frequency of six regular bristles in the L line. But no progress in the desired direction was obtained in the H line, although the proportion of sternites with nine irregular structures was found to increase. The experimental results supportTuring's diffusion-reaction scheme of pattern formation in morphogenesis.Supported by grants GB-1388 and GB-3219 from the National Science Foundation.     

Lessons on pattern formation from planet WATOR

It is well known that if reacting species experience unequal diffusion rates, then dynamics that lead to a constant steady state in a "well-mixed" environment can in a spatial setting lead to interesting patterns. In this paper, we focus on complementary pattern formation mechanisms that operate even when the diffusion rates are equal. In particular, we can say that when the mean-field ODE has an attracting periodic orbit then the stochastic spatial model will have large-scale spatial structures in equilibrium. We explore this mechanism in depth through the dynamics of the simulator WATOR.     

Fingerprint pattern factors

Factor analysis was employed using the ulnar ridge count, radial ridge count, ridge count (the larger of the radial or ulnar count as generally used for calculating total ridge count), and pattern type for each finger in 720 twins. Pattern type and ulnar count displayed parallel factor loadings while loadings for radial and ridge count also paralleled each other. This relationship did not hold for the index finger, indicating the importance of pattern direction and greater pattern diversity for this digit. Total ridge count was most closely associated with a factor of ring and little finger radial and ridge count and only secondarily with an index finger factor. When radial and ulnar counts were deleted to make comparisons with earlier studies, the result was factors having groupings of variables identical with previous reports. It appears that factor analysis results in consistent extraction of identical or very similar factors from different populations, and the use of radial and ulnar counts adds more information than when only the larger of the two counts is considered.     

Problems and paradigms: Morphogens and pattern formation

Morphogen gradient theories have enjoyed considerable popularity since the beginning of this century, but conclusive evidence for a role of morphogens in controlling multicellular development has been elusive. Recently, work on three secreted signalling proteins, Activin in Xenopus, and Wingless and Dpp in Drosophila, has stongly suggested that these proteins function as morphogens. In order to define a factor as a morphogen, it is necessary to show firstly, that it has a direct effect on target cells and secondly, that it affects the development of target cells in a concentration-dependent manner. With these criteria in mind, the evidence available for a variety of proposed morphogens is discussed. While the evidence is not conclusive in most of the cases considered, there is a strong case in favour of the three proteins mentioned above, which suggests that morphogens are potentially of general importance in controlling the development of multicellular organisms.     

Advances in pattern formation: Signaling and transcription

The 49(th) Annual Drosophila Research Conference was held in the sunny confines of San Diego. As usual, large numbers of Drosophila scientists working in fields as different as immunology and evolution descended on the venue. The meeting showed that the fly community is still vibrant and diverse even with the funding crunch at the NIH and the renewed rumors that Drosophila may have outlived its usefulness. This short review will focus on one session of platform presentations detailing the recent advances in the field of pattern formation. This session offered a variety of topics reviewing the formation of pattern in various tissues through diverse mechanisms. I will focus on early embryonic patterning through pair-rule genes, specificity of FGF signaling, and tissue regeneration.     

Perspective: network-guided pattern formation of neural dynamics

The understanding of neural activity patterns is fundamentally linked to an understanding of how the brain''s network architecture shapes dynamical processes. Established approaches rely mostly on deviations of a given network from certain classes of random graphs. Hypotheses about the supposed role of prominent topological features (for instance, the roles of modularity, network motifs or hierarchical network organization) are derived from these deviations. An alternative strategy could be to study deviations of network architectures from regular graphs (rings and lattices) and consider the implications of such deviations for self-organized dynamic patterns on the network. Following this strategy, we draw on the theory of spatio-temporal pattern formation and propose a novel perspective for analysing dynamics on networks, by evaluating how the self-organized dynamics are confined by network architecture to a small set of permissible collective states. In particular, we discuss the role of prominent topological features of brain connectivity, such as hubs, modules and hierarchy, in shaping activity patterns. We illustrate the notion of network-guided pattern formation with numerical simulations and outline how it can facilitate the understanding of neural dynamics.     

Ultraviolet light inhibits grey crescent formation on the frog egg

Summary Work by others has shown that ultraviolet (UV) irradiation of the vegetal half of the uncleaved frog egg causes defects in neural development. We find that the earliest effect of irradiation ofRana pipiens eggs is to prevent grey crescent formation, the first indication of dorso-ventral polarization of the egg. The UV effect on the grey crescent and on neural development shows similarities in timing, dose-responses, and reversal by cold. We suggest that the UV effect on neural morphogenesis may be caused by the inhibition of cortical-cytoplasmic movement involved in grey crescent formation.     

One-dimensional daisyworld: spatial interactions and pattern formation

The zero-dimensional daisyworld model of Watson and Lovelock (1983) demonstrates that life can unconsciously regulate a global environment. Here that model is extended to one dimension, incorporating a distribution of incoming solar radiation and diffusion of heat consistent with a spherical planet. Global regulatory properties of the original model are retained. The daisy populations are initially restricted to hospitable regions of the surface but exert both global and local feedback to increase this habitable area, eventually colonizing the whole surface. The introduction of heat diffusion destabilizes the coexistence equilibrium of the two daisy types. In response, a striped pattern consisting of blocks of all black or all white daisies emerges. There are two mechanisms behind this pattern formation. Both are connected to the stability of the system and an overview of the mathematics involved is presented. Numerical experiments show that this pattern is globally determined. Perturbations in one region have an impact over the whole surface but the regulatory properties of the system are not compromised by transient perturbations. The relevance of these results to the Earth and the wider climate modelling field is discussed.     

Insect egg cortex isolated by microsurgery: Specific protein pattern and uridine incorporation

Summary Egg cortex material (ECM) containing the oolemma and adherent periplasm has been isolated from an insect egg by means of micromanipulation. Analysis of proteins by SDS-PAAG-electrophoresis demonstrated striking differences between the protein banding patterns of ECM and of whole eggs. ECM and whole eggs also differ clearly with respect to³H-uridine uptake; the ECM contains RNA labeled during the previtellogenetic period of oogenesis (probably in the germarium) but, in contrast to the central parts of the oocyte, is largely void of label taken up during the last stages of oogenesis.Supported by the Deutsche Forschungsgemeinschaft, SFB 46     

Temperature during egg formation and the effect of climate warming on egg size in a small songbird

The predicted effects of recent climate warming on egg size in birds are controversial, as only two long-term studies have been reported, with contrasting results. Long-term data on egg size variation are analyzed in relation to ambient temperatures in a southern European population of pied flycatchers where breeding phenology has not matched the spring advancement in the last decades. Cross-sectional, population analyses indicated that egg breadth, but not egg length, has decreased significantly along the 16-year period, leading to marginally non-significant decreases in egg volume. Longitudinal, individual analyses revealed that despite females consistently laying larger eggs when they experienced warmer temperatures during the prelaying and laying periods, there was an overall negative response – i.e. decreasing egg volume and breadth with increasing spring (May) average temperatures – across individuals. This trend is hypothesised to be caused by the mismatched breeding phenology, in relation to climate warming, of this population. Except in the unlikely cases of populations capable of perfectly synchronising their phenology to changes in their environment, maladjustments are likely for traits such as egg size, which depend strongly on female condition. Slight changes or absence thereof in breeding dates may be followed by mismatched dates, in terms of food abundance, for optimal egg formation, which would be reflected in smaller average egg size, contrary to early predictions on the effects of climate warming on bird egg size.