Potential applications of pulsating joint loading in sports medicine.

Because bone is responsive to mechanical loading, pulsating joint loading (PJL), which laterally applies oscillatory mechanical loads to joints, can be explored for preventive conditioning and therapeutic treatments. Herein, the general features of PJL are reviewed, and its potential usage for sports medicine is discussed.

Amphibian in vitro heart induction: a simple and reliable model for the study of vertebrate cardiac development.

Amphibian embryos are an excellent model system for analyzing the mechanisms of vertebrate cardiogenesis. Studies of heart development in Xenopus have, for example, revealed that the inductive interaction of the heart primordia with the adjacent underlying endoderm and dorsal lip starts at the early stages of gastrulation. However, the molecular basis of those early inductive events and the genes expressed during the early phases of heart differentiation remain largely unknown.

Future opportunities for life science programs in space.

Most space-related life science programs are expensive and time-consuming, requiring international cooperation and resources with trans-disciplinary expertise. A comprehensive future program in "life sciences in space" needs, therefore, well-defined research goals and strategies as well as a sound ground-based program. The first half of this review will describe four key aspects such as the environment in space, previous accomplishments in space (primarily focusing on amphibian embryogenesis), available resources, and recent advances in bioinformatics and biotechnology, whose clear understanding is imperative for defining future directions.

Student-oriented learning: an inquiry-based developmental biology lecture course.

In this junior-level undergraduate course, developmental life cycles exhibited by various organisms are reviewed, with special attention--where relevant--to the human embryo. Morphological features and processes are described and recent insights into the molecular biology of gene expression are discussed. Ways are studied in which model systems, including marine invertebrates, amphibia, fruit flies and other laboratory species are employed to elucidate general principles which apply to fertilization, cleavage, gastrulation and organogenesis.

Promoter competition assay for analyzing gene regulation in joint tissue engineering.

We describe a new biochemical technique, "promoter competition assay," for examining the role of cis-acting DNA elements in tissue cultures. Recent advances in tissue engineering permit the culture of a variety of cells. Many tissues are engineered, however, without an appropriate understanding of molecular machinery that regulates gene expression and cellular growth.

Work in progress: the renaissance in amphibian embryology.

Various historical eras in the distant as well as the recent past of amphibian embryology are briefly reviewed. The concepts which emerged from the early years matured, then were laid to rest for several decades. A resurgence, driven by key discoveries with peptide growth factors, and fueled by modern molecular biology methods, is underway.

In vitro control of organogenesis and body patterning by activin during early amphibian development.

In the process of amphibian development, an embryonic body plan is established through cell division, sequential gene expression, morphogenesis and cell differentiation. The mechanism of body patterning is complex and includes multiple induction events. Activin, a TGF-beta family protein, can induce several kinds of mesodermal and endodermal tissues in animal cap explants in a dose-dependent manner.

Role of activin and other peptide growth factors in body patterning in the early amphibian embryo.

The amphibian body plan is established as the result of a series of inductive interactions. During early cleavage stages cells in the vegetal hemisphere induce overlying animal hemisphere cells to form mesoderm. The interaction represents the first major body-patterning event and is mediated by peptide growth factors.

Peptide growth factors in amphibian embryogenesis: intersection of modern molecular approaches with traditional inductive interaction paradigms.

Recent discoveries of the role peptide growth factors (PGFs) play in regulating embryonic patterning and differentiation have profoundly influenced research on the molecular biology of early amphibian embryogenesis. Several PGFs have been recognized to be present as endogenous components of amphibian eggs and early embryos, while other PGFs -- which are known from heterologous systems (e.g.

An essay on the similarities and differences between inductive interactions in anuran and urodele embryos.

As a first step towards providing a conceptual approach to understanding similarities and differences in the mechanisms which guide inductive interactions among related organisms (e.g. various amphibia), a set of five principles is offered here.

Activin treated urodele ectoderm: a model experimental system for cardiogenesis.

The tissue interactions which comprise the inductive phenomena associated with urodele heart morphogenesis are relatively well understood. In order to take full advantage of the experimental potential of this system formulation of an in vitro tissue culture system would be very helpful. Herein are described conditions for culturing Cynops pyrrhogaster early gastrula ectoderm tissue in the presence of the peptide growth factor activin.

Expression of the axolotl homologue of mouse chaperonin t-complex protein-1 during early development.

Molecular chaperones assist in the folding of proteins, but their role during development is not well understood. Here we report the temporal and spatial expression pattern of the axolotl homologue of mouse chaperonin TCP-1 during normal amphibian embryogenesis and in several models of abnormal embryogenesis. A partial axolotl TCP-1 cDNA (646 bp; 519 coding bp) isolated by 3' RACE PCR shows considerable homology to mouse TCP-1.

Cloning and expression of the axolotl proto-oncogene ski.

In vitro and in vivo overexpression studies have demonstrated that the c-ski proto-oncogene can influence proliferation, morphological transformation and myogenic differentiation. We report the isolation and expression of an axolotl (Ambystoma mexicanum) c-ski (aski) gene. Sequence analysis revealed a high degree of nucleotide and predicted amino acid (AA) homology with mammalian and anuran c-ski, showing the highest conservation to Xenopus laevis c-ski (74% nucleotide and 87% AA).

Overexpression of XMyoD or XMyf5 in Xenopus embryos induces the formation of enlarged myotomes through recruitment of cells of nonsomitic lineage.

The myogenic regulatory factors (MRFs) MyoD and Myf5 are the earliest described muscle-specific genes to be expressed in Xenopus development. To study the in vivo effects of overexpressing Xenopus MyoD and Myf5, synthetic RNAs were microinjected into single blastomeres of 2- to 32-cell stage Xenopus embryos. In vivo overexpression of these MRFs initiates the precocious and ectopic expression of actin and myosin.

The location of the third cleavage plane of Xenopus embryos partitions morphogenetic information in animal quartets.

Analysis of the developmental potential of animal quartets (the set of four animal blastomeres isolated from the 8-cell stage Xenopus embryo) provided insight into the manner in which morphogenetic information is distributed along the animal-vegetal axis. Gravity treatments were employed to alter the partitioning plane. Animal quartets isolated from embryos exposed to simulated weightlessness had larger animal blastomeres, and they formed structures such as a groove and a protrusion more often than 1g-control animal quartets.

Early development of Xenopus embryos is affected by simulated gravity.

Early amphibian (Xenopus laevis) development under clinostat-simulated weightlessness and centrifuge-simulated hypergravity was studied. The results revealed significant effects on (i) "morphological patterning" such as the cleavage furrow pattern in the vegetal hemisphere at the eight-cell stage and the shape of the dorsal lip in early gastrulae and (ii) "the timing of embryonic events" such as the third cleavage furrow completion and the dorsal lip appearance. Substantial variations in sensitivity to simulated force fields were observed, which should be considered in interpreting spaceflight data.

Early amphibian (anuran) morphogenesis is sensitive to novel gravitational fields.

Anuran amphibian embryos (Xenopus laevis and Rana dybowskii) are sensitive to novel gravitational fields. Under simulated weightlessness, (i) the location of the first horizontal cleavage furrow was shifted toward the vegetal pole at the eight-cell stage; (ii) the position of the blastocoel was more centered, and the number of cell layers in the blastocoel roof was increased at the blastula stage; (iii) the dorsal lip appeared closer to the vegetal pole at the gastrula stage; and (iv) head and eye dimensions were enlarged at the hatching tadpole stage. Effects of simulated hypergravity were opposite to those of simulated weightlessness, except that hypergravity, unlike simulated weightlessness, reduced the number of primordial germ cells in feeding tadpoles.

Altering the position of the first horizontal cleavage furrow of the amphibian (Xenopus) egg reduces embryonic survival.

The animal/vegetal cleavage ratio (AVCR), defined as the ratio of the height of the animal blastomere to the height of the Xenopus embryo at the 8 cell stage, can be shifted by placing embryos in novel gravitational fields: clinostating (microgravity simulation) increases AVCR, and centrifugation (hypergravity simulation) reduces AVCR. This report contributes to an understanding of the subcellular mechanism responsible for the furrow relocation and assesses its significance. Embryo inversion and D2O immersion were found to increase AVCR, and cold shock was found to reduce AVCR.

Understanding the organization of the amphibian egg cytoplasm: gravitational force as a probe.

A combination of hypergravity (centrifugation) and hypogravity (clinostat) studies have been carried out on amphibian (frog, Xenopus) eggs. The results reveal that the twinning caused by centrifugation exhibits substantial spawning to spawning variation. That variation can be attributed to the apparent viscosity of the egg's internal cytoplasm.

Bifurcation of the amphibian embryo's axis: analysis of variation in response to egg centrifugation.

Xenopus embryos have been reported to vary widely in their developmental response to centrifugation. Variation in response to centrifugation, as measured by embryo survival and twinning of axial structures, was monitored different spawnings of Xenopus laevis eggs. A convenient method for quantifying the egg cytoplasm's potential for displacement in a centrifugal field was employed.