Comparison of spore proteins among species of the cellular slime moulds Dictyostelium and Polysphondylium as examined by immunological cross-reactivity

Spore proteins of six cellular slime mould species, Dictyostelium discoideum, D. mucoroides, D. purpureum, D. lacteum, Polysphondylium violaceum, and P. pallidum were studied. The spore proteins were cross-reacted with four different polyclonal antibodies produced against D. mucoroides spores and D. discoideum major spore coat proteins SP96, SP70, and SP60 by SDS polyacrylamide gel electrophoresis and immunoblotting. The spore proteins of D. discoideum and D. mucoroides showed the strongest cross-reactivity with all the antisera and also produced many common protein bands, thus reflecting their morphological similarities. Polysphondylium violaceum, which is quite distinct in morphology from D. discoideum and D. mucoroides, produced the second strongest cross-reactivity. In contrast, the proteins of D. purpureum showed little cross-reactivity, although morphologically it closely resembles D. mucoroides. The developmental changes of these spore proteins were investigated by cross-reacting the antisera against vegetative and slug cell proteins. In the cases of D. discoideum and D. mucoroides, the band patterns of slug proteins coincided with those of spores, which suggested that most of the spore proteins had already accumulated at the slug stage. However, this was not the case with P. violaceum, which suggested that spore proteins of this species cross-reactive with the antisera were synthesized or modified at the culmination stage.