Cell to cell contacts mediating mating‐type dependent recognition(s) during the preconjugant cell interactions of Oxytricha bifaria (ciliata, hypotrichida)

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Abstract
The direct conjugant interactions leading to pair formation (“Visible Reaction”) of Oxytricha bifaria were studied by means of enzymes acting on the cell surface. They are able to interrupt at successive stages the cell interactions occurring during the Visible Reaction. The results show that: 1) mating type specific cell recognition occurs during the Visible Reaction; 2) this recognition is a prerequisite for pair formation; and 3) cell to cell contacts leading to membrane fusion play a critical role in such a recognition.The system of the preconjugant interactions in O. bifaria is composed of, at least, two successive and distinct stages, each playing separate roles in the general strategy of conjugation: A) a waiting period and B) a Visible Reaction. During the waiting period, complementary cells interact from a distance by means of mating type specific soluble factors (gamones) (Esposito et al., '76), and become “ready” to contact other similarly “ready” cells. By means of direct interactionsmediated by mating type specific cell‐to‐cell contacts during the Visible Reaction, a cell can recognize the contacted potential partner as belonging either to a complementary mating type (“go ahead”), or to its own mating type (“interrupt the conjugation program”). A general model of preconjugant interactions in ciliates is briefly discussed.
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