Fibroblasts and other tissue cells in culture exhibit various social behaviours such as contact inhibition of movement and contact guidance. Fibrous network of the extracellular matrix containing collagen, fibronectin, laminin and proteoglycans is the substratum for cell migration in many occasions during embryogenesis, including neural crest cell migration, primordial germ cell migration, neurite extension and gastrulation in echinoderm, avian, mammalian and amphibian embryos. Studies on amphibian gastrulation revealed that each embryonic mesoderm cell moves by extending lamel-lipodia and filopodia which attach to the extracellular fibril network on the inner surface of the ectoderm layer. There have been accumulating pieces of evidence that the fibril network serves as an adequate substratum for the mesoderm cell migration, and provides guidance by the mechanism of contact guidance caused by the alignment of fibrils along the blastopore and animal pole axis. Contact inhibition of movement is another mechanism which causes cell movement away from the blastopore region. Immunostaining has shown that the extracellular fibrils contain fibronectin and laminin.
Muscle contraction takes place by relative sliding of myosin-containing thick filament and actin-containing thin filament. The mechanical energy of sliding is supplied from the chemical energy of ATP hydrolysed by the actomyosin system, and the chemomechanical energy transformation in contracting muscle is highly efficient. As crossbridges which extrude from thick filaments can bind with thin filaments and hydrolyse ATP, the secret of the chemomechanical energy transformation must reside in the specific way of molecular interaction between ATP-hydrolysing crossbridges and thin filaments. However, detailed molecular mechanism of the energy transfer process (and also that of the force generation process itself) has not been clarified. Only very recently several experimental results have been obtained which may be directly related with the energetic process associated with the elementary ATP splitting cycle in contracting muscle. In this review we will see the classical view of energetic process of muscle contraction, later experimental results which required the revision of the classical view, and then recent experimental approaches.
Electric spatial patterns are often observed in growth and regeneration Processes in biological systems. Characean algae develop alternating bands composed of acid and alkaline regions along their cell walls, accompanied with the circulating electric current. A theoretical analysis reveals that this state belongs to electric dissipative structures appearing far from equilibrium. A similar banding Pattern can also be found in multicellular systems as bean roots. It is suggested that the current flows to the root tip with the formation of several local current loops in the mature region. These kinds of spatio-temponal electric organization may play an essential role in the growth process.
In this review I have described our current view about antigen recognition structures on the membrane surfaces. I have focused particularly on those molecular events which occur at the early steps of the transmembrane signal transducation in the immune system. These are of special interest and I hope this kind of study will offer a fruitful suggestion for immunotherapy near future.