Fig. 5. Test of the hypothesis that two permanent stem cell systems produce epaxial and hypaxial clones. (A,B) Hypothetical clones that would be obtained with two permanent stem cell systems. The dermomyotome (green), and the myotome (blue) are represented at three stages of their mediolateral growth. Stem cells are represented by closed circles and the myocytes by open circles. The clones that would result from the labelling of a stem cell are represented by thin horizontal lines below. (A) Model of two stem cell systems located in the edges of the dermomyotome. (B) Model of two stem cell systems located in the center of the dermomyotome. (C) Mediolateral extension of epaxial (closed diamonds) and hypaxial (open rectangles) monosegmented clones in function of their medial (epaxial clones) or lateral border (hypaxial clones). (D) Clonal complexity of the myotome along the mediolateral axis. The mediolateral axis is divided into 20 parts of equal length, and the number of contributing monosegmented clones is shown. Insets: (a,b) expected graphs for the two opposing stem cell systems hypothesized, respectively, in A and in B. m, medial; l, lateral.