The Developmental Basis of Quantitative Craniofacial Variation in Humans and Mice

The human skull is a complex and highly integrated structure that has long held the fascination of anthropologists and evolutionary biologists. Recent studies of the genetics of craniofacial variation reveal a very complex and multifactorial picture. These findings contrast with older ideas that posit much simpler developmental bases for variation in cranial morphology such as the growth of the brain or the growth of the chondrocranium relative to the dermatocranium. Such processes have been shown to have major effects on cranial morphology in mice. It is not known, however, whether they are relevant to explaining normal phenotypic variation in humans. To answer this question, we obtained vectors of shape change from mutant mouse models in which the developmental basis for the craniofacial phenotype is known to varying degrees, and compared these to a homologous dataset constructed from human crania obtained from a single population with a known genealogy. Our results show that the shape vectors associated with perturbations to chondrocranial growth, brain growth, and body size in mice do largely correspond to axes of covariation in humans. This finding supports the view that the developmental basis for craniofacial variation funnels down to a relatively small number of key developmental processes that are similar across mice and humans. Understanding these processes and how they influence craniofacial shape provides fundamental insights into the developmental basis for evolutionary change in the human skull as well as the developmental-genetic basis for normal phenotypic variation in craniofacial form.     

Developmental programming of reproduction and fertility: what is the evidence?

The concept of the foetal/developmental origins of adult disease has been around for ~20 years and from the original epidemiological studies in human populations much more evidence has accumulated from the many studies in animal models. The majority of these have focused upon the role of early dietary intake before conception, through gestation and/or lactation and subsequent interactions with the postnatal environment, e.g. dietary and physical activity exposures. Whilst a number of theoretical models have been proposed to place the experimental data into a biological context, the underlying phenomena remain the same; developmental deficits (of single (micro) nutrients) during critical or sensitive periods of tissue growth alter the developmental pathway to ultimately constrain later functional capacity when the individual is adult. Ageing, without exception, exacerbates any programmed sequelae. Thus, adult phenotypes that have been relatively easy to characterise (e.g. blood pressure, insulin sensitivity, body fat mass) have received most attention in the literature. To date, relatively few studies have considered the effect of differential early environmental exposures on reproductive function and fecundity in predominantly mono-ovular species such as the sheep, cow and human. The available evidence suggests that prenatal insults, undernutrition for example, have little effect on lifetime reproductive capacity despite subtle effects on the hypothalamic-pituitary-gonadal axis and gonadal progenitor cell complement. The postnatal environment is clearly important, however, since neonatal/adolescent growth acceleration (itself not independent from prenatal experience) has been shown to significantly influence fecundity in farm animals. The present paper will expand these interesting areas of investigation and review the available evidence regarding developmental programming of reproduction and fertility. However, it appears there is little strong evidence to indicate that offspring fertility and reproductive senescence in the human and in farm animal species are overtly affected by prenatal nutrient exposure. Nevertheless, it is clear that the developing gonad is sensitive to its immediate environment but more detailed investigation is required to specifically test the long-term consequences of nutritional perturbations during pregnancy on adult reproductive well-being.     

Zebrafish Models of p53 Functions

Zebrafish models have significantly contributed to our understanding of vertebrate development and, more recently, human disease. The growing number of genetic tools available in zebrafish research has resulted in the identification of many genes involved in developmental and disease processes. In particular, studies in the zebrafish have clarified roles of the p53 tumor suppressor in the formation of specific tumor types, as well as roles of p53 family members during embryonic development. The zebrafish has also been instrumental in identifying novel mechanisms of p53 regulation and highlighting the importance of these mechanisms in vivo. This article will summarize how zebrafish models have been used to reveal numerous, important aspects of p53 function.The zebrafish, Danio rerio, is a small model organism that has long been used to study vertebrate development. Zebrafish embryos are optically clear and develop externally to the mother, facilitating the study of early developmental processes. In addition, zebrafish have increasingly been used in modeling human diseases, including a number of cancers. The availability of forward and reverse genetic tools in the zebrafish has resulted in the identification and characterization of many genes involved in development and disease. One gene that has been extensively studied is the p53 tumor suppressor gene, which is structurally and functionally conserved in the zebrafish. This article will discuss how studies in the zebrafish have increased our understanding of how p53 contributes to the formation of specific tumor types, resulted in the identification of novel mechanisms of p53 regulation, and showed how p53 and p53 family members are involved in embryonic development.     

The Golgi apparatus: Lessons from Drosophila

Historically, Drosophila has been a model organism for studying molecular and developmental biology leading to many important discoveries in this field. More recently, the fruit fly has started to be used to address cell biology issues including studies of the secretory pathway, and more specifically on the functional integrity of the Golgi apparatus. A number of advances have been made that are reviewed below. Furthermore, with the development of RNAi technology, Drosophila tissue culture cells have been used to perform genome-wide screens addressing similar issues. Last, the Golgi function has been involved in specific developmental processes, thus shedding new light on the functions of a number of Golgi proteins.     

Analysis of trinomial responses from reproductive and developmental toxicity experiments.

This paper presents a Dirichlet-trinomial distribution for modelling data obtained from reproductive and developmental studies. The common endpoints for the evaluation of reproductive and developmental toxic effects are the number of dead fetuses, the number of malformed fetuses, and the number of normal fetuses for each litter. With current statistical methods for the evaluation of reproductive and developmental effects, the effect on the number of deaths and the effect on the number of malformations are analyzed separately. The Dirichlet-trinomial model provides a procedure for the analysis of multiple endpoints simultaneously. This proposed Dirichlet-trinomial model is a generalization of the beta-binomial model that has been used for handling the litter effect in reproductive and developmental experiments. Likelihood ratio tests for differences in the number of deaths, the number of malformations, and the number of normals among dosed and control groups are derived. The proposed test procedure based on the Dirichlet-trinomial model is compared with that based on the beta-binomial model with an application to a real data set.     

Species comparison of anatomical and functional immune system development

The components of the immune system have not been traditionally emphasized as potential target organs in standard developmental and reproductive toxicity (DART) protocols. A number of workshops have been organized in recent years to examine scientific questions that underlie developmental immunotoxicity tests, and the interpretation of results as they relate to human risk assessment. A key question that must be addressed is to determine the most appropriate species and strains to model the developing human immune system. The objective of this review is to compare the anatomical and functional development of the immune system in several species important to either preclinical studies for drug development or safety assessments for chemicals, with what is known in humans. The development of the immune system in humans will be compared to what is known in mice, rats, dogs and nonhuman primates.     

Phenotypic Plasticity in Embryonic Development of Reptiles:Recent Research and Research Opportunities in China

Adaptive developmental plasticity can enable an organism to modify its phenotype rapidly, in response to local(and perhaps, unpredictable) conditions, by altering reaction norms during development. Previous studies on this topic have been dominated by western scientists, employing western study systems and approaches. Recently, the expansion of Chinese ecological research has seen a broadening of studies taxonomically(phylogenetically). Here, we briefly summarize research that has been conducted on developmental plasticity in Chinese reptiles over the past two decades, and suggest productive directions for future studies in this field. There are exciting research opportunities in this field in China, and we call for increased collaboration between western and eastern scientists to elucidate the role of developmental plasticity in evolutionary responses of organisms to environmental changes. As human activities increase the intensity and frequency of such changes, the need to understand responses of biological systems becomes an increasingly urgent priority.     

Postnatal Cranial Development in Papionin Primates: An Alternative Model for Hominin Evolutionary Development

The evolution of hominin growth and life history has long been a subject of intensive research, but it is only recently that paleoanthropologists have considered the ontogenetic basis of human morphological evolution. To date, most human EvoDevo studies have focused on developmental patterns in extant African apes and humans. However, the Old World monkey tribe Papionini, a diverse clade whose members resemble hominins in their ecology and population structure, has been proposed as an alternative model for human craniofacial evolution. This paper reviews prior studies of papionin development and socioecology and presents new analyses of juvenile shape variation and ontogeny to address fundamental questions concerning primate cranial development, including: (1) When are cranial shape differences between species established? (2) How do epigenetic influences modulate early-arising pattern differences? (3) How much do postnatal developmental trajectories vary? (4) What is the impact of developmental variation on adult cranial shape? and, (5) What role do environmental factors play in establishing adult cranial form? Results of this inquiry suggest that species differences in cranial morphology arise during prenatal or earliest postnatal development. This is true even for late-arising features that develop under the influence of epigenetic factors such as mechanical loading. Papionins largely retain a shared, ancestral pattern of ontogenetic shape change, but large size and sexual dimorphism are associated with divergent developmental trajectories, suggesting differences in cranial integration. Developmental simulation studies indicate that postnatal ontogenetic variation has a limited influence on adult cranial morphology, leaving early morphogenesis as the primary determinant of cranial shape. The ability of social factors to influence craniofacial development in Mandrillus suggests a possible role for phentotypic plasticity in the diversification of primate cranial form. The implications of these findings for taxonomic attribution of juvenile fossils, the developmental basis of early hominin characters, and hominin cranial diversity are discussed.     

Trichloroethylene and dichloroethylene: a critical review of teratogenicity

Trichloroethylene (TCE) and dichloroethylene (DCE) are high-volume industrial chemicals frequently found as contaminants in public drinking water supplies. The developmental toxicity of both chemicals has been evaluated in laboratory and epidemiologic studies. It has been suggested that TCE and DCE are specific cardiac teratogens and that drinking water contaminated with them increases the risk of congenital heart defects in exposed human populations. In contrast, other laboratory and epidemiologic studies do not find an increase in developmental effects, either in general or specifically affecting the heart. This laboratory and epidemiologic base was reviewed to evaluate the strengths and weaknesses of the conflicting published reports. We conclude that the weight of experimental and epidemiologic evidence does not support the hypothesis that TCE or DCE is a selective developmental toxicant in general or a cardiac teratogen specifically.     

Cyclosporine A: Review of genotoxicity and potential for adverse human reproductive and developmental effects: Report of a working group on the genotoxicity of cyclosporine A,August 18, 1993

Cyclosporine is an important therapeutic agent for transplant recipients and for a growing number of autoimmune diseases. Experimental animal and human data has indicated that cyclosporine is unlikely to be genotoxic. In contrast, azathioprine, an agent often given with cyclosporine, is considered to be genotoxic making the assessment of the independent effects of cyclosporine difficult. Cyclosporine does appear to be related to the development of tumors, primarily lymphomas, in animals and humans, but the basis of its potential carcinogenicity is not completely understood. In terms of reproductive and developmental toxicity, cyclosporine produces some adverse effects in both experimental animals and humans. In animals, the effects are seen at high doses sufficient to cause maternal toxicity. In humans, outcomes such as growth retardation have been noted, but the confounding effects of renal toxicity and resultant pregnancy complications cloud the interpretation. An increase in congenital anomalies and genetic disease have not been found reported in human studies that are limited in sample size.     

斑马鱼模型在药物筛选中的应用

斑马鱼具有子代数量多、体外受精、胚胎透明、可以做大规模遗传突变筛选等生物学特性, 因此成为一种良好的脊椎动物模式生物。随着研究的深入, 斑马鱼不仅应用于遗传学和发育生物学研究, 而且拓展和延伸到疾病模型和药物筛选领域。作为一种整体动物模型, 斑马鱼能够全面地检测评估化合物的活性和副作用, 实现高内涵筛选。近年来, 科学家们不断地发展出新的斑马鱼疾病模型和新的筛选技术, 并找到了一批活性化合物。这些化合物大多数在哺乳动物模型中也有相似的效果, 其中前列腺素E2(dmPGE2)和来氟米特(Leflunomide)已经进入临床实验, 分别用来促进脐带血细胞移植后的增殖和治疗黑素瘤。这些成果显示了斑马鱼模型很适合用于药物筛选。文章概括介绍了斑马鱼模型的特点和近年来在疾病模型和药物筛选方面的进展, 希望能够帮助人们了解斑马鱼在新药研发中的应用, 并开展基于斑马鱼模型的药物筛选。     

Evolutionary and developmental studies of unifacial leaves in monocots: Juncus as a model system

An important objective in evolutionary developmental biology is to understand the molecular genetic mechanisms that have given rise to morphological diversity. Leaves in angiosperms generally develop as a flattened structure with clear adaxial–abaxial polarity. In monocots, however, a unifacial leaf has evolved in a number of divergent species, in which leaf blades consist of only the abaxial identity. The mechanism of unifacial leaf development has long been a matter of debate for comparative morphologists. However, the underlying molecular genetic mechanism remains unknown. Unifacial leaves would be useful materials for developmental studies of leaf-polarity specification. Moreover, these leaves offer unique opportunities to investigate important phenomena in evolutionary biology, such as repeated evolution or convergent evolution of similar morphological traits. Here we describe the potential of unifacial leaves for evolutionary developmental studies and present our recent approaches to understanding the mechanisms of unifacial leaf development and evolution using Juncus as a model system.     

Mosaic pattern and lineage analysis in chimeras

Mammalian chimeras have been used in a number of developmental studies over the years. A major limitation in these studies has been the lack of in situ procedures for establishing mosaic pattern in the tissues of these animals. Recently, a number of procedures have become available for the histochemical demonstration of mosaicism in chimeras. These include the elucidation of various enzymes, receptors, or surface antigens, which have variant expression between strains. The observation of pattern in organs of mosaic animals can suggest possible modes of organogenesis and organ maintenance. Experimentation with such animals can be used to establish some mechanisms of pathogenesis as well.     

Transmission ratio distortion: review of concept and implications for genetic association studies

Transmission ratio distortion (TRD) occurs when one of the two alleles from either parent is preferentially transmitted to the offspring. This leads to a statistical departure from the Mendelian law of inheritance, which states that each of the two parental alleles is transmitted to offspring with a probability of 0.5. A number of mechanisms are thought to induce TRD such as meiotic drive, gametic competition, and embryo lethality. TRD has been extensively studied in animals, but the prevalence of TRD in humans remains largely unknown. Nevertheless, understanding the TRD phenomenon and taking it into consideration in many aspects of human genetics has potential benefits that have not been sufficiently emphasized in the current literature. In this review, we discuss the importance of TRD in three distinct but related fields of genetics: developmental genetics which studies the genetic abnormalities in zygotic and embryonic development, statistical genetics/genetic epidemiology which utilizes population study designs and statistical models to interpret the role of genes in human health, and population genetics which is concerned with genetic diversity in populations in an evolutionary context. From the perspective of developmental genetics, studying TRD leads to the identification of the processes and mechanisms for differential survival observed in embryos. As a result, it is a genetic force which affects allele frequency at the population, as well as, at the organismal level. Therefore, it has implications on genetic diversity of the population over time. From the perspective of genetic epidemiology, the TRD influence on a marker locus is a confounding factor which has to be adequately dealt with to correctly interpret linkage or association study results. These aspects are developed in this review. In addition to these theoretical notions, a brief summary of the empirical evidence of the TRD phenomenon in human and mouse studies is provided. The objective of our paper is to show the potentially important role of TRD in many areas of genetics, and to create an incentive for future research.     

Developmental mechanisms and experimental models to understand forebrain malformative diseases

The development of the central nervous system can be divided into a number of phases, each of which can be subject of genetic or epigenetic alterations that may originate particular developmental disorders. In recent years, much progress has been made in elucidating the molecular and cellular mechanisms by which the vertebrate forebrain develops. Therefore, our understanding of major developmental brain disorders such as cortical malformations and neuronal migration disorders has significantly increased. In this review, we will describe the major stages in forebrain morphogenesis and regionalization, with special emphasis on developmental molecular mechanisms derailing telencephalic development with subsequent damage to cortical function. Because animal models, mainly mouse, have been fundamental for this progress, we will also describe some characteristic mouse models that have been capital to explore these molecular mechanisms of malformative diseases of the human brain. Although most of the genes involved in the regulation of basic developmental processes are conserved among vertebrates, the extrapolation of mouse data to corresponding gene expression and function in humans needs careful individual analysis in each functional system.     

Developmental mechanisms and experimental models to understand forebrain malformative diseases

The development of the central nervous system can be divided into a number of phases, each of which can be subject of genetic or epigenetic alterations that may originate particular developmental disorders. In recent years, much progress has been made in elucidating the molecular and cellular mechanisms by which the vertebrate forebrain develops. Therefore, our understanding of major developmental brain disorders such as cortical malformations and neuronal migration disorders has significantly increased. In this review, we will describe the major stages in forebrain morphogenesis and regionalization, with special emphasis on developmental molecular mechanisms derailing telencephalic development with subsequent damage to cortical function. Because animal models, mainly mouse, have been fundamental for this progress, we will also describe some characteristic mouse models that have been capital to explore these molecular mechanisms of malformative diseases of the human brain. Although most of the genes involved in the regulation of basic developmental processes are conserved among vertebrates, the extrapolation of mouse data to corresponding gene expression and function in humans needs careful individual analysis in each functional system.     

Ethylene's role in phosphate starvation signaling: more than just a root growth regulator

Phosphate (Pi) is a common limiter of plant growth due to its low availability in most soils. Plants have evolved elaborate mechanisms for sensing Pi deficiency and for initiating adaptive responses to low Pi conditions. Pi signaling pathways are modulated by both local and long-distance, or systemic, sensing mechanisms. Local sensing of low Pi initiates major root developmental changes aimed at enhancing Pi acquisition, whereas systemic sensing governs pathways that modulate expression of numerous genes encoding factors involved in Pi transport and distribution. The gaseous phytohormone ethylene has been shown to play an integral role in regulating local, root developmental responses to Pi deficiency. Comparatively, a role for ethylene in systemic Pi signaling has been more circumstantial. However, recent studies have revealed that ethylene acts to modulate a number of systemically controlled Pi starvation responses. Herein we highlight the findings from these studies and offer a model for how ethylene biosynthesis and responsiveness are integrated into both local and systemic Pi signaling pathways.