Lateral inhibition models of developmental processes

Most mathematical models for embryological pattern formation depend on the phenomenon of local autocatalysis with lateral inhibition (LALI). While the underlying physical and chemical mechanisms hypothesized by the models may be quite different, they all predict very similar kinds of spatial patterns. Therefore, since the underlying mechanism cannot in general be deduced from the pattern itself, other criteria must be applied in evaluating the usefulness of pattern formation models. The author points out how LALI is implemented in neural, chemical, and mechanical models of development, and suggests some general properties of LALI models that may impose limitations on organ shapes in ontogeny and phylogeny.     

Nonlinear analysis of some models for the evolution of dominance

For two different classes of models for the evolution of dominance modifiers a nonlinear analysis is performed. The first class arises from the classical model of R. A. Fisher by assuming that the modifiers under consideration are not neutral in their pleiotropic effects. The second class is based on a model of P. M. Sheppard for the evolution of dominance in mimicry. Again the derived models with non-neutral modifiers are analysed.     

GM plants as sources of im/possibility: a developmental systems view of stabilization

This paper generates a heuristic understanding of the stabilization dynamic of genetically modified plants. This heuristic, the paper argues, can provide a fruitful platform for studying the political dimensions embedded in GM plants. Focusing on stabilization is important, because outside laboratories a plant can have an intermediating role only as a cultivar; as something which has integrated into biological processes and human practices. The actual stabilizing entity is not just an object, but a dynamic analogous to what is called a developmental system. The empowering or suppressing consequences of GM plants depend significantly on the qualities of this spatio-temporal order stabilizing; on the “possibility space” it opens up. Moreover, stabilization connects and makes things possible, but it does not do so automatically, predictably – or for everyone. Centralized control may support stability, but it may also increase vulnerability by reducing local possibility space.     

A bifurcation model for developmental processes

I have constructed, for developmental processes, a qualitative model similar to the compartment hypothesis in Drosophila, and examined its relevance to vertebrate systems. In this model a polarized “cluster” of interacting cells will be the unit for “bifurcation” of the developmental pathway into two alternative states of “locon” which is the genetic unit controlling this process. The minimum size of the cluster critical for bifurcation and the size of the emerging subclusters will be dictated by the cognate locon. This will obviate the need for an extrinsically imposed threshold of some state variable for the boundary of the two subclusters. However, the orientation of bifurcation will be determined by the polarity of the cluster. A physiological factor of competence will impose a temporal constraint to bifurcation.Thus, combinatorial binary codes for a set of locons, like those originally devised by Kauffman (1973), can be assigned to developmental pathways. One of the clusters emerging from a sequence of bifurcations will have the same code as the mother cluster. It will represent the “developmental sink”, and will not recycle through the bifurcation series originating from the initial mother cluster, because of the difference in spatio-temporal factors incorporated in the size and competence of the individual clusters. If bifurcations are prevented, the mother cluster will be forced along the pathway of the developmental sink.I have applied the model to cases in vertebrate development where commitments to developmental pathways for aperiodic or periodic segmentations may follow a linear temporal sequence, producing, in turn, subclusters of uncommitted, or stem, cells towards the more intensely polarized end of the mother cluster. Such cases include limb, somite and tail formation and several stem cell systems with a finite lifespan. I have discussed some possible experimentation which emerges from the model.     

Explaining how and explaining why: developmental and evolutionary explanations of dominance

There have been two different schools of thought on the evolution of dominance. On the one hand, followers of Wright [Wright S. 1929. Am. Nat. 63: 274–279, Evolution: Selected Papers by Sewall Wright, University of Chicago Press, Chicago; 1934. Am. Nat. 68: 25–53, Evolution: Selected Papers by Sewall Wright, University of Chicago Press, Chicago; Haldane J.B.S. 1930. Am. Nat. 64: 87–90; 1939. J. Genet. 37: 365–374; Kacser H. and Burns J.A. 1981. Genetics 97: 639–666] have defended the view that dominance is a product of non-linearities in gene expression. On the other hand, followers of Fisher [Fisher R.A. 1928a. Am. Nat. 62: 15–126; 1928b. Am. Nat. 62: 571–574; Bürger R. 1983a. Math. Biosci. 67: 125–143; 1983b. J. Math. Biol. 16: 269–280; Wagner G. and Burger R. 1985. J. Theor. Biol. 113: 475–500; Mayo O. and Reinhard B. 1997. Biol. Rev. 72: 97–110] have argued that dominance evolved via selection on modifier genes. Some have called these “physiological” versus “selectionist,” or more recently [Falk R. 2001. Biol. Philos. 16: 285–323], “functional,” versus “structural” explanations of dominance. This paper argues, however, that one need not treat these explanations as exclusive. While one can disagree about the most likely evolutionary explanation of dominance, as Wright and Fisher did, offering a “physiological” or developmental explanation of dominance does not render dominance “epiphenomenal,” nor show that evolutionary considerations are irrelevant to the maintenance of dominance, as some [Kacser H. and Burns J.A. 1981. Genetics 97: 639–666] have argued. Recent work [Gilchrist M.A. and Nijhout H.F. 2001. Genetics 159: 423–432] illustrates how biological explanation is a multi-level task, requiring both a “top-down” approach to understanding how a pattern of inheritance or trait might be maintained in populations, as well as “bottom-up” modeling of the dynamics of gene expression.     

The canola microspore-derived embryo as a model system to study developmental processes in plants

The ability of microspores to undergo embryo development after a successful induction treatment provides a unique experimental system to study a variety of developmental processes in plants. Recent published results focus on the cellular and molecular aspects of the early induction process. In this review, besides summarizing the current findings, the advantages of using the MDE system to study other aspects of embryo development are emphasized. The continual improvement of culturing procedures, media components, and molecular methods guarantees exciting new findings in the near future.     

Lineus as a model for studying developmental processes in animals reconstructed from adult pieces

The difficulties that prevent reconstruction of animals by piecing together body fragments from several adults are overcome by using nemerteans of the genus Lineus. For 25 years I have managed to make viable composite worms by grafting body parts cut out of Lineus specimens either from the same clonal strain (syngeneically reconstructed worms) or from the same species (allogeneically reconstructed worms) or else from different species (xenogeneically reconstructed worms). Body reconstruction has usually been carried out orthotopically, i.e., the components of composite animals have been selected so as to be anatomically complementary. However, reconstruction has been made heterotopically when it was essential to obtain morphogenetic events in the adults. Here, I shall review some of the developmental processes that took place in such reconstructed animals. First, I shall report immune responses in composite worms derived from various combinations of body pieces grafted together. Second, I shall study sex differentiation during gonad development in growing or regenerating chimeric worms made by the grafting of male and female components. I shall refer also to gonadogenesis in the asexual progeny of bipartite chimeras derived from lateral body halves of both sexes fused together (clones of bilaterally allophenic worms). Third, I shall analyze regulative processes (regeneration, transgeneration) during localized morphogenesis occurring in heterotopically reconstructed worms. The data show how reconstructed Lineus may be exploited to increase our knowledge of developmental mechanisms, especially in the misunderstood field of organismal pattern homeostasis.     

Translational control in cellular and developmental processes

Growing evidence indicates that translational control of specific mRNAs contributes importantly to genetic regulation across the breadth of cellular and developmental processes. Synthesis of protein from a specific mRNA can be controlled by RNA-binding proteins at the level of translational initiation and elongation, and translational control is also sometimes coupled to mRNA localization mechanisms. Recent discoveries from invertebrate and vertebrate systems have uncovered novel modes of translational regulation, have provided new insights into how specific regulators target the general translational machinery and have identified several new links between translational control and human disease.     

How genomic and developmental dynamics affect evolutionary processes

Evolutionary genetics is concerned with natural selection and neutral drift, to the virtual exclusion of almost everything else. In its current focus on DNA variation, it reduces phenotypes to symbols. Varying phenotypes, however, are the units of evolution, and, if we want a comprehensive theory of evolution, we need to consider both the internal and external evolutionary forces that shape the development of phenotypes. Genetic systems are redundant, modular and subject to a variety of genomic mechanisms of "turnover" (transposition, gene conversion, unequal crossingover, slippage and so on). As such the construction and spread of novel combinations of modules by turnover, in particular within gene promoters, contributes significantly to the evolution of phenotypes. Furthermore, redundancy, turnover and modularity lead to ever more complex networks of genetic interactions and ever more functions for a given module. The significant interaction between genomic turnover and natural selection leads to a molecular coevolution between interacting modules and hence facilitates the establishment of biological novelties.     

Multiple developmental processes underlie sex differentiation in angiosperms

The production of unisexual flowers has evolved numerous times in dioecious and monoecious plant taxa. Based on repeated evolutionary origins, a great variety of developmental and genetic mechanisms underlying unisexual flower development is predicted. Here, we comprehensively review the modes of development of unisexual flowers, test potential correlations with sexual system, and end with a synthesis of the genetics and hormonal regulation of plant sex determination. We find that the stage of organ abortion in male and female flowers is temporally correlated within species and also confirm that the arrest of development does not tend to occur preferentially at a particular stage, or via a common process.     

The roles of epithelial-mesenchymal cell interactions in developmental processes

This review surveys some recent trends in the study of the developmental interactions between epithelial and mesenchymal cells. The influence of such interactions on cell differentiation is considered with reference to kidney development, limb bud development, chondrogenesis and osteogenesis, and tooth development. Effects on epithelial morphogenesis are discussed, using salivary gland development as an example. The roles of humoral factors (hormones or growth factors) are considered, and the evidence for the participation of cell adhesion molecules is examined.     

Flavonoids as developmental regulators

Flavonoids, usually regarded as dispensable phytochemicals derived from plant secondary metabolism, play important roles in the biology of plants by affecting several developmental processes. Bioactive flavonoids also signal to microbes, serve as allelochemicals and are important nutraceuticals in the animal diet. Despite the significant progress made in identifying flavonoid pathway genes and regulators, little is currently known about the protein targets of flavonoids in plant or animal cells. Recently, there have been advances in our understanding of the roles that flavonoids play in developmental processes of plants. The multiple cellular roles of flavonoids can reflect their chemical diversity, or might suggest the existence of cellular targets shared between many of these seemingly disparate processes.     

基于网络的昆虫发育进程自动模拟系统

为了有效的预测害虫的发生期,开发了昆虫发育自动模拟系统,该系统基于网络平台,应用PHP丰富的函数库和计算功能设计有效积温运算模块,通过公共气象信息系统建立了气象数据库,并根据实时及预报的公共气象信息,即逐日最高及最低气温,昆虫发育有效积温相关的生物学参数,运用正弦法计算每天的有效积温及一段时间的累计积温,自动模拟昆虫在不同时期的发育虫态和虫龄。服务器端基于Apache+PHP+MySQL架构,操作简单,调试和维护方便。经与2011年江苏通州烟粉虱Bemisia tabaci(Gennadius)、灰飞虱Laodelphax striatellus(Fallén)系统调查数据比对,符合实际发生情况,可在生产上推广应用。     

Prospects for exploring molecular developmental processes in Haemonchus contortus

Haemonchus contortus of small ruminants is a parasitic nematode of major socio-economic importance world-wide. While there is considerable knowledge of the morphological changes which take place during the life cycle of H. contortus, very little is understood about the molecular and biochemical processes which govern developmental changes in the parasite. Recent technological advances and the imminent genomic sequence for H. contortus provide unique opportunities to investigate the molecular basis of such processes in parasitic nematodes. This article reviews molecular and biochemical aspects of development in H. contortus, reports on some recent progress on signal transduction molecules in this parasite and emphasises the opportunities that new technologies and the free-living nematode, Caenorhabditis elegans, offer for investigating developmental aspects in H. contortus and related strongylid nematodes, also in relation to developing novel approaches for control.     

Interplay between microRNAs and RNA-binding proteins determines developmental processes

MicroRNAs (miRNAs) are genes involved in normal development and cancer. They inhibit gene expression by associating with 3'-Untranslated regions (3' UTRs) of messenger RNAs (mRNAs), and are thought to regulate a large proportion of protein coding genes. However, it is becoming apparent that miRNA activity is not necessarily always determined by its expression in the cell. MiRNA activity can be affected by RNA-binding proteins (RBPs). For example, the RNA-binding protein HuR associates with the 3'UTR of the CAT1 mRNA after stress, counteracting the effect of miR-122. Second, we found that the expression of an RNA-binding protein called Dead end (Dnd1) prohibits the function of several miRNAs by blocking the accessibility of target mRNAs. Dnd1 function is essential for proper development of primordial germ cells (PGCs) in zebrafish and mammals, indicating a crucial role for RBP/miRNA interplay on 3'UTRs of mRNAs in developmental decisions. In this perspective we discuss the interplay between RBPs and miRNAs in the context of germ cells and review current observations implicating RBPs in miRNA function.