Histogenesis as exemplified by striated musculature
The first indication of the beginning myogenesis is the lengthening of the premyoblasts. Responsible for this are several genes on chromosome 11. They belong to the myogenic regulatory factors (MRF) family and activate the transcription of muscle-specific genes.
From premyoblasts to the myotubes
Premyoblasts are the first specific and determining cells of myogenesis. At the place where muscles are being generated they transform themselves into myoblasts and begin to synthesize the actin and myosin myofilaments.
Very soon the myoblasts begin to divide and several cells merge to form multi-cellular myotubes (stages 18 - 20) in which the myofibers are still arranged around the cell nucleus.
At the end of the embryonic period the cell nuclei move to the periphery and slowly lengthen. One can now clearly recognize the striations.