Development of the nematocyte junctional complex in hydra tentacles in relation to cellular recognition and...

Formation of the nematocyte-battery cell-mesoglea (NBM) junctional complex of hydra was studied. Normal animals were grafted to nematocyte-free animals and the tentacles of the repopulating host were examined by transmission electron microscopy. Migrating nematocytes extend cytoplasmic processes between battery cell myonemes to contact the mesoglea. Tufts of extracellular filaments radiate from the base of the battery cell adjacent to some of these regions of contact. The fascial desmosome of the NBM complex develops from a lateral fusion of macular desmosomes which often lie near a condensation of extracellular filaments. Microtubules within the intervening battery cell process become oriented perpendicularly to form the apposing half of the desmosomal junction and connect it with the hemidesmosomal portion of the NBM complex. These findings suggest that a migrating nematocyte receives environmental cues associated with the mesoglea-battery cell interface which may serve to direct the nematocyte to its definitive position and induce the subsequent formation of the complete NBM complex.