During teleostean fin regeneration the actinotrichia, rods of a collagen-like protein, the elastoidin, are immersed in the blastema, maintaining their apical position. In this epimorphic event the latter fact might be achieved by either a cellular carriage or a continuous turn-over of these hyperpolimerized fibrils. By means of a3H-proline pulse and radioautographic chase experiment of the isolated actinotrichia we have found a turn-over of collagen within the structure. From these and additional morphometric results, we present in this work an operational hypothesis of how gradually differentiating blastemal cells and an appropriately shaped basal lamina, can control the number and distribution of actinotrichia which might be under the balanced control of their synthesis and degradation.
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