Mating-Type Substances

Abstract

Conjugation in Paramecium is initiated by a highly specific cell-cell recognition and adhesion event referred to as the mating reaction (Sonneborn 1937). The term “mating-type substances” was first introduced by Metz (1946, 1948, 1954) to define substances or molecular configurations on the cell surface that mediate the mating reaction. Even after 50 years of research on mating problems in Paramecium, there is still no convincing evidence that substances secreted from cells are involved in the mating reaction. This fact strongly confirms the supposition that sexual interactions of Paramecium are strictly cell surface events between complementary mating-type substances, although the existence of the latter still remains hypothetical. Thus, the mating reaction provides a simple and excellent system for studies on membrane-membrane interactions in general.