1. Studies of morphogenetic interactions between primary sensory axons and target tissues during development and regeneration of peripheral mechanoreceptors. The role of neural versus non-neural factors is analysed by electron or light microscopy and histo- or immunocytochemistry.

2. A new research field focuses on an analysis of intrinsic - myogenic, and extrinsic - mainly neurogenic and hormonal influences regulating the expression of muscle phenotype. Ultrastructure and expression of myosin heavy chain (MHC) isoforms during development and regeneration of extrafusal and intrafusal muscle fibres is studied using electron microscopic, histochemical and immunocytochemical methods and techniques of molecular biology.

Main results

1. We have confirmed that sensory innervation plays a key role in the induction of typical morphological characteristics and in the expression of specific MHC isoforms in intrafusal muscle fibres, whereas motor innervation contributes to the diversity in the expression and distribution of different MHC isoforms along the length of intrafusal fibres. We have shown that one type of intrafusal satellite cells give rise to myotubes capable, if innervated by sensory axons, to differentiate into a special intrafusal phenotype. This part of our research is covered in the invited review published in Microscop. Res. Tech. (Soukup et al. Microscop Res Tech 30: 390407, 1995).

2. The current experiments are based on our own model of heterochronous isotransplantation. We have shown that after isotransplantation, the intrafusal satellite cells retain a great plasticity as they are able to differentiate into fibres with extrafusal fast or slow phenotype, when reinnervated solely by extrafusal motor axons. Furthermore, this model enables us to compare the contribution of genetic factors, nerve impulse frequency and thyroid hormone levels to the differentiation of muscle phenotype. This topic is summarized by the review published in Physiological Research.

The first results on differentiation of muscle fibre types in hypo- eu- and hyperthyroid rats demonstrate that the grafted, genetically predetermined, slow muscle reinnervated by fast nerve differentiates as fast muscle, but the percentage of 2B, 2X/D, 2A and type 1 fibres varies depending on to the thyroid status. 

Publications