Annie Baker and Julianne Nicholson bought their first bras at the same J.C. Penney.

Call it cinematic destiny. The two were somewhat acquainted through New York theater circles, but it wasn’t until they were sitting together in Washington Square Park, reminiscing about their respective childhoods in Western Massachusetts, that they realized just how much they have in common. Their shared agent suggested they meet to see whether Nicholson would be a fit for the title role of “Janet Planet,” Baker’s mother-daughter tale that takes place in the 1990s near her hometown of Amherst.

Nicholson, who spent much of her youth less than 15 miles away in Montague, knew the setting intimately..