We found a consistent arrangement and orientation in the apical region of larval flagellated cells.
Figure 6 shows glutinous granules of about 1-[micro]m diameter in the apical cytoplasm of flagellated cells.
Bottle cells are large (about 18 X 6 [micro]m) cells that are located between flagellated cells but have no flagellum themselves (Fig.
In most cases, a part of the cell is inserted between flagellated cells, but the greater part protrudes into a central cavity.
The brown staining of fragmented DNA produced by the TUNEL assay indicated that apoptosis was only located in the peripheral region of flagellated cells.
In summary, the results demonstrate that, in Microciona larvae, mannose is the only terminal, lectin-binding sugar on the surface of the flagellated cells as shown by con A staining.
We suggest that mannose receptors are present on the surface of phagocytes in the larvae (as shown in a variety of other organisms) (9) and that such receptors recognize and bind with mannose on apoptotic flagellated cells.
Our study supports the theory that peripheral flagellated cells in Microciona larvae are terminally differentiated; their fate is apoptosis and eventually phagocytosis.
Because larval flagellated cells change radically in morphology in the early stages of metamorphosis, it is almost impossible to follow their developmental fates unless the cells have some identification markers.
In this report, we show that larval flagellated cells transform into choanocytes during metamorphosis.
Flagellated cells make up the entire larval surface, except at the posterior end where many reddish brown pigment granules occur in the cytoplasm.
The larval surface region consists of a pseudostratified columnar epithelium of elongate flagellated cells; however, a basal lamina is absent [ILLUSTRATION FOR FIGURE 1 OMITTED].