A morphomechanical aspect of epigenesis

Epigenesis in classical embryology is regarded as self-complication of spatial organization of the embryo during its development. The reality of the phenomenon of self-complication at the cellular and supracellular levels has been demonstrated by classical experimental embryology. Today, in light of studies of cell differentiation mechanisms, this problem acquired a molecular aspect. However, the attempt to solve it within the limits of molecular level leads to the paradox of "unreducible complexity". The discovery of a physical factor that concurrently would influence the processes of supracellular and molecular levels would be the best way to solve the problem of self-complication. The mechanical tension in cells and tissues of a developing organism may play the role of such factor. The paper considers facts on the role of mechanical stresses in morphogenesis and gene expression.     

Craniofacial development and the evolution of the vertebrates: the old problems on a new background

Based on recent advances in experimental embryology and molecular genetics, the morphogenetic program for the vertebrate cranium is summarized and several unanswered classical problems are reviewed. In particular, the presence of mesodermal segmentation in the head, the homology of the trabecular cartilage, and the origin of the dermal skull roof are discussed. The discovery of the neural-crest-derived ectomesenchyme and the roles of the homeobox genes have allowed the classical concept of head segmentation unchanged since Goethe to be re-interpreted in terms of developmental mechanisms at the molecular and cellular levels. In the context of evolutionary developmental biology, the importance of generative constraints is stressed as the developmental factor that generates the homologous morphological patterns apparent in various groups of vertebrates. Furthermore, a modern version of the germ-layer theory is defined in terms of the conserved differentiation of cell lineages, which is again questioned from the vantage of evolutionary developmental biology.     

Contribution of the Belgian school of embryology to the concept of neural induction by the organizer

Albert BRACHET, founder of the Brussels School of embryology, conducted delicate experiments in which he selectively destroyed zones of the grey crescent with heated needles. This allowed him to observe, in 1923, that the median region of the grey crescent of the blastula is a area of spontaneous differentiation and that this "primary self-differentiation centre" organizes the axial organs in anurans. It is thus fair to say that A. BRACHET contributed significantly to the emergence of the organizer concept. Albert DALCQ and Jean PASTEELS, successors of A. BRACHET, trying to solve the problem of the organizer's determination, proposed their famous quantitative theory of embryonic development resulting in the concept of morphogenetic potential, which increases with the CV concentration, a combination of a cortical constituent C and a vegetal substance V. Jean BRACHET, the younger son of A. BRACHET and one of the founding father of molecular biology and embryology, was soon convinced that the organizer owes its inducing power to a chemical substance. Being the first to suggest the role of RNA in protein synthesis, he first imagined that RNA could be the active substance in induction but became convinced afterwards that the inducer must have a proteic nature. His interest in the molecular aspects of induction stimulated research that was to make chemical embryology molecular.     

Modern evolutional developmental biology: Mechanical and molecular genetic or phenotypic approaches?

Heightened interest in the evolutionary problems of developmental biology in the 1980s was due to the success of molecular genetics and disappointment in the synthetic theory of evolution, where the chapters of embryology and developmental biology seem to have been left out. Modern evo-devo, which turned out to be antipodean to the methodology of the synthetic theory of evolution, propagandized in the development of evolutionary problems only the mechanical and molecular genetic approach to the evolution of ontogenesis, based on cellular and intercellular interactions. The phonotypical approach to the evaluation of evolutionary occurrences in ontogenesis, which aids in the joining of the genetic and epigenetic levels of research, the theory of natural selection, the nomogenetic conception, and the problem of the wholeness of the organism in onto- and phylogenesis may be against this. The phenotypic approach to ontogenesis is methodologically the most perspective for evolutionary developmental biology.     

Mechanotransduction pathways in skeletal muscle hypertrophy

In the last decade, molecular biology has contributed to define some of the cellular events that trigger skeletal muscle hypertrophy. Recent evidence shows that insulin like growth factor 1/phosphatidyl inositol 3-kinase/protein kinase B (IGF-1/PI3K/Akt) signaling is not the main pathway towards load-induced skeletal muscle hypertrophy. During load-induced skeletal muscle hypertrophy process, activation of mTORC1 does not require classical growth factor signaling. One potential mechanism that would activate mTORC1 is increased synthesis of phosphatidic acid (PA). Despite the huge progress in this field, it is still early to affirm which molecular event induces hypertrophy in response to mechanical overload. Until now, it seems that mTORC1 is the key regulator of load-induced skeletal muscle hypertrophy. On the other hand, how mTORC1 is activated by PA is unclear, and therefore these mechanisms have to be determined in the following years. The understanding of these molecular events may result in promising therapies for the treatment of muscle-wasting diseases. For now, the best approach is a good regime of resistance exercise training. The objective of this point-of-view paper is to highlight mechanotransduction events, with focus on the mechanisms of mTORC1 and PA activation, and the role of IGF-1 on hypertrophy process.     

Mechanotransduction pathways in skeletal muscle hypertrophy

In the last decade, molecular biology has contributed to define some of the cellular events that trigger skeletal muscle hypertrophy. Recent evidence shows that insulin like growth factor 1/phosphatidyl inositol 3-kinase/protein kinase B (IGF-1/PI3K/Akt) signaling is not the main pathway towards load-induced skeletal muscle hypertrophy. During load-induced skeletal muscle hypertrophy process, activation of mTORC1 does not require classical growth factor signaling. One potential mechanism that would activate mTORC1 is increased synthesis of phosphatidic acid (PA). Despite the huge progress in this field, it is still early to affirm which molecular event induces hypertrophy in response to mechanical overload. Until now, it seems that mTORC1 is the key regulator of load-induced skeletal muscle hypertrophy. On the other hand, how mTORC1 is activated by PA is unclear, and therefore these mechanisms have to be determined in the following years. The understanding of these molecular events may result in promising therapies for the treatment of muscle-wasting diseases. For now, the best approach is a good regime of resistance exercise training. The objective of this point-of-view paper is to highlight mechanotransduction events, with focus on the mechanisms of mTORC1 and PA activation, and the role of IGF-1 on hypertrophy process.     

Endoderm development: from patterning to organogenesis

Although the ectoderm and mesoderm have been the focus of intensive work in the recent era of studies on the molecular control of vertebrate development, the endoderm has received less attention. Because signaling must occur between germ layers in order to achieve a properly organized body, our understanding of the coordinated development of all organs requires a more thorough consideration of the endoderm and its derivatives. This review focuses on present knowledge and perspectives concerning endoderm patterning and organogenesis. Some of the classical embryology of the endoderm is discussed and the progress and deficiencies in cellular and molecular studies are noted.     

Sclerotome development and morphogenesis: when experimental embryology meets genetics

The vertebra develops from the ventral part of the somite, the sclerotome. Sclerotome progenitors are subject to multiple signaling molecules secreted by the adjacent tissues that control their fate. The aim of this article is to discuss the mechanisms of sclerotome induction, chondrogenesis and morphogenesis. By integrating the results from classical studies and recent molecular advances, this will illustrate how the powerful combination of experimental embryology and genetic approaches has recently illuminated the multiple steps of vertebra formation.     

A Multilevel Probabilistic Beam Search Algorithm for the Shortest Common Supersequence Problem

The shortest common supersequence problem is a classical problem with many applications in different fields such as planning, Artificial Intelligence and especially in Bioinformatics. Due to its NP-hardness, we can not expect to efficiently solve this problem using conventional exact techniques. This paper presents a heuristic to tackle this problem based on the use at different levels of a probabilistic variant of a classical heuristic known as Beam Search. The proposed algorithm is empirically analysed and compared to current approaches in the literature. Experiments show that it provides better quality solutions in a reasonable time for medium and large instances of the problem. For very large instances, our heuristic also provides better solutions, but required execution times may increase considerably.     

From field to gel blot: teaching a holistic view of developmental phenomena to undergraduate biology students at the University of Tokyo

We present here an outline of the lectures and laboratory exercises for undergraduate developmental biology students at the University of Tokyo. The main aim of our course is to help students fill the gap between natural history, classical embryology and molecular developmental biology. To achieve this aim, we take up various topics in the lectures, from fertilization and early development to developmental engineering. Our laboratory exercises begin with an introduction to the natural history of the organism. The entire class and the instructors collect newts in the field and discuss features of their mating behavior and so on. In the laboratory, students are absorbed by exercises such as a lampbrush chromosome preparation and an in vitro beating heart induction. After that, students choose their own research projects for which they will employ both classical embryological and modern molecular biological techniques. At the end of our course, the connectivity principle from field to gel blot will be part of the students' understanding.     

Somatic transgenesis in the avian model system

The chick embryo is a versatile model system, in which classical embryology can be combined with modern molecular approaches. In the last two decades, several efficient methods have been developed to introduce exogenous genes into the chick embryo. These techniques allow alteration of gene expression levels in a spatially and temporally restricted manner, thereby circumventing embryonic lethality and/or eliminating secondary effects in other tissues. Here, we present the current status of avian somatic transgenic techniques, focusing on electroporation and retrovirus-mediated gene transfer. Electroporation allows quick and efficient gain-of-function studies based on transient misexpression of genes. Retroviral vectors, which are capable of integrating exogenous genes into the host chromosome, permit analysis of long-term effects of gene misexpression. The variety of methods available for somatic transgenesis, along with the recent completion of the chicken genome, are transforming the chick embryo into one of the most attractive model systems to examine function of genes that are important for embryonic development.     

Genetic disorders of the skeleton: a developmental approach

Although disorders of the skeleton are individually rare, they are of clinical relevance because of their overall frequency. Many attempts have been made in the past to identify disease groups in order to facilitate diagnosis and to draw conclusions about possible underlying pathomechanisms. Traditionally, skeletal disorders have been subdivided into dysostoses, defined as malformations of individual bones or groups of bones, and osteochondrodysplasias, defined as developmental disorders of chondro-osseous tissue. In light of the recent advances in molecular genetics, however, many phenotypically similar skeletal diseases comprising the classical categories turned out not to be based on defects in common genes or physiological pathways. In this article, we present a classification based on a combination of molecular pathology and embryology, taking into account the importance of development for the understanding of bone diseases.     

The Impact of Molecular Methods on the Systematics of Angiosperms

A comparison is made between the systematics of selected orders and families based on morphology and other “classical” characters on the one hand, and the results of molecular methods on the other hand. It can be shown that taxa defined by a broad array of characters from morphology, anatomy, embryology and phytochemistry usually are confirmed by molecular results. On the other hand a family like the Saxifragaceae s.l. delimited solely on the basis of floral morphology has been shown to be grossly polyphyletic. Some quite surprising results of the molecular analyses usually agree with some embryological or phytochemical characters, and sometimes even with characters of vegetative morphology and anatomy. As a special case “unequal ancient splits” are discussed, where one clade contains few genera and species usually retaining many primitive characters, and the other shows great diversity and contains the more advanced members.     

Alpheus Spring Packard and cave fauna in the evolution debate

Conclusion Packard attempted to incorporate cave fauna into a general theory of evolution that would be consistent with the principle of recapitulation, and would have as the primary mechanism the inheritance of the effects of the environment. Beyond this, he also attempted to demonstrate that the evolution of cave fauna was consistent with progressive evolution. The use he made of comparative anatomy and embryology places him within the tradition of classical morphology that was dominant through much of the last half of the nineteenth century, but of waning importance by the time of Packard's death in 1905. The importance Packard gave to cave fauna as evidence for Lamarckian evolution stimulated interest in the phenomenon; this interest, and references to cave fauna in the scientific literature, declined after his death. Since then, the importance of cave fauna in evolutionary theory has declined from their status as the star evidence in Packard's theory to their present status as a difficult anomaly within the modern synthetic theory.     

The calcium signal for Balb/MK keratinocyte terminal differentiation induces sustained alterations in phosphoinositide metabolism without detectable protein kinase C activation

Balb/MK keratinocytes require epidermal growth factor for proliferation and terminally differentiate in response to elevated extracellular Ca2+ concentrations. The molecular pathways controlling cell differentiation in this system have yet to be established. We show that a dramatic and sustained activation of phosphoinositide metabolism is produced upon addition of Ca2+ to Balb/MK cultures. The pattern of inositol trisphosphate isomers released in response to Ca2+ challenge appeared to be atypical. Inositol 1,3,4-trisphosphate release was observed by 30s and was produced earlier than any alteration in inositol 1,4,5-trisphosphate levels. Concomitant with the liberation of inositol phosphates, an increased production of diacylglycerol was observed. Despite a 3-fold increase in diacylglycerol levels detected even at 12 h after Ca2+ addition, no evidence of functional activation or down-regulation of protein kinase C was found. This was established by measuring p80 phosphorylation, epidermal growth factor binding, and protein kinase C levels by immunoblotting. Analysis of the diacylglycerol generated following Ca2+ addition to Balb/MK cells revealed that a significant proportion of that lipid was an alkyl ether glyceride molecular species. Therefore, it is possible that this diacylglycerol molecular species may play a role in the Ca2+-induced differentiation program of Balb/MK cells through mechanisms other than stimulation of classical protein kinase C.