cultural, political, etc.

enter, hit, join, reach
cut sb/sth off from, exclude sb/sth from
These teachers have been cut off from the mainstream of educational activity.

in the mainstream, within the mainstream
He was in the mainstream of British contemporary music.

into the mainstream
This technology was designed for specialists but is now starting to move into the mainstream.

out of the mainstream, outside the mainstream
He drifted out of the mainstream of society.

part of the mainstream
This style of drama is not part of the cultural mainstream.

Mainstream is used with these nouns:
acceptance, appeal, audience, cinema, culture, curriculum, economics, economist, establishment, feminism, fiction, film, institution, journalism, journalist, magazine, media, movie, music, Muslim, newspaper, politics, pop, press, publication, publisher, religion, rock, school, schooling, society, sociology, sport