Three Dimensional Pattern Formation Of Muscle

Background and PurposePatterns are orders embedded in randomness in nature. In the biological world, the process which generates this ordering was termed pattern formation. Scientists are always puzzled with the mechanism of it. The question of how to build a well organized organ from a group of homogeneous stem cells is poorly understood. For the muscle tissue, it always exists as a group of muscles, within which many muscle bundles interweave into a complicated3-Dimensional pattern. So far, there are few studies on the mechanism of muscle3-D pattern formation, and there is no unanimous conclusion.Feather muscle is one special kind of smooth muscle, which locate within the dermis and interconnect feather follicles into a net. Feather muscles beneath every follicle can be divided into two kinds--depressor muscle and erector muscle. These muscle bundles form the sophisticated3-D pattern. This pattern has been built well when it is still an embryo. However, so far, the investigation on the feather muscle was limited within anatomy on the adult. The embryonic pattern and the process of pattern formation are still unknown.The purpose of this research is to find out the3-D pattern formation of feather muscle, to clarify the mechanism of pattern formation, and to summarize the general rule which can provide the guidance for the studies of other kinds of muscle and organs.MethodsFirst, the method of immunohistochemistry was used to observe the whole developmental process of feather muscle; then, the experiments of feather bud re-allignment, recombination and reconstitution were done to clarify the relationship between muscle pattern formation and the surrounding environment; the culture system, skin culture system on collagen gel was invented and with its help, extra force was exerted on the skin, and it was proved that the biomechanical force played an important role in the muscle pattern formation; last, Integrin beta-1was found to be expressed on the muscle cells with immunohistochemistry method and Integrin beta-1was proved to have function of mediating the attachment of muscle cells to tendon cells from the result of antibody neutralized experiment.Results and Conclusions1. Muscle bundles use feather buds as reference points and get connection. The muscle patterns differ among different tracts. Tenascin-C (TN-C) is expressed in the attachment sites of muscle cells (tendon tissue). After the whole process of3-D pattern formation is observed, many rules of pattern formation are found:1) There are4main tenascin domains beneath each feather bud connecting with muscles. The emergence of these domains are always earlier than the muscle cells;2) From every domain, muscle fibers radiate out, reaching for nearest neighboring buds. In the beginning, the direction of muscle bundle is not determined until the first connection is built;3) Muscle bundles from TN-C domains radiate out at different time. The time sequence helps to build the3-Dimensional muscle structure and to prevent the wrong connections.2. The immunohistochemistry results show that feather muscles can continue to develop and form pattern in the skin explant system. The bud realignment and recombination experiments show that feather muscles always get connection with the feather buds nearby. The relative positions among feather buds determine the muscle pattern. Feather muscle network can be divided into many units. One unit is the muscle group related with one feather bud. Single unit has its own direction and polarity which is consistent with those of the feather bud. Feather muscles emerge in the reconstitution skin and the muscle pattern also regenerate. The new formed pattern is not pre-determined, but adapts to the feather bud pattern. The identities of feather muscles may not differ in nature, although they may have various functions. To summarize, the feather muscle pattern formation adapts to the surrounding environment.3. Chicken embryonic skin can be cultured on the collagen gel skin culture system, and then the force-exerting system is developed. Both systems are the excellent research modles. The embryonic skin is inclined to contract. The fact of skin expanding during development depends on the banlance between the contracting and the extra forces. This balance influences the differentiation and pattern formation of feather muscle. The extra force exerting on the skin guides the direction of feather muscle. The tension lines existing in the skin influence the macro-pattern of feather muscle. The pattern of TN-C is also regulated by the biomechanical force. The TN-C domains provide the anchoring positions for the muscle cells. The biomechanical force is the key factor influencing the adaptive muscle pattern formation.4. Integrin beta-1is expressed on the feather muscle cells and it functions as the receptor for the TN-C. It may play an important role during muscle cells anchoring to tendon cells. When its function is inhibited, the patterns of TN-C and muscle change tremendously and muscle connection is also inhibited.