The firm, Revolution, plans to raise up to $100 million for that
fund's investment, it disclosed ___ in a filing with the Securities
and Exchange Commission.
It doesn't require a heavy punctuation mark like a semicolon or a full stop since what follows the mark is not an independent clause. A comma is required, though, to mark the boundary of the content of disclosure.
The verb “disclosed” normally requires a complement like a direct object or, as is the case here, a complement clause. Here, the complement is missing and is represent by the gap notation “___”.
Gap obtains its core meaning anaphorically from the preceding verb phrase “plans to raise up to $100 million for that fund's investment”, from which was can deduce that the salient interpretation of gap is “(that) it plans to raise up to $100 million for that fund's investment”, i.e. a declarative content clause.