Study of the origin and differentiation of the pharynx during regeneration in Eisenia foetida (Annelida)

A study has been made in Eisenia foetida of the regeneration of the pharynx, a complex organ with an epithelium, muscular fibres and glandular cells. We have investigated the origin of these constituents and analysed the ultrastructural aspects of their differentiation.

The epithelium derives from oesophageal endoderm and not from stomodeal ectoderm as during embryogenesis. Muscular fibres form from myoblasts which result from dedifferentiation of the muscular coats of the alimentary canal and dorsal vessel. Glandular elements come from the peritoneal coat of the dorsal vessel, and in particular from stem cells of chlora-gogen cells.

Each of these cellular classes synthesizes specific substances but this differentiation is always preceded by a period in which all the three cell types undergo similar modifications. They change shape to the adult form, then the electron density of the cytoplasm diminishes considerably.

A general hypothesis is formulated to try to explain these preliminary phenomena of differentiation. An inducer would determine a modification in the cell surface which would become permeable to enzymes. These enzymes would be able to hydrolyse the ‘coat’ of inactive mRNA pre-existing in the cells. Then the mRNA would control the synthesis of specific proteins.

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