Seems like it may be it may be fund-specific, which would make sense. If a fund needed to invest $50M minimum, that would effect a company like POET enormously.

Still looking for more info...

Definition of 'Institutional Shares'

A class of mutual fund shares available for sale to investing institutions, either on a load or no-load basis. With sizable minimum investments, usually around $500,000 or more, funds will typically waive any front-end sales charges on these shares.

Investopedia Says
Investopedia explains 'Institutional Shares'

Institutions, such as large money managers, often buy a significant number of shares in mutual funds at any one time. Buyers of big blocks of mutual fund shares expect, and often receive, a break on commission charges. Because of the large investments required to receive these breaks, individual investors typically cannot afford these shares.

http://www.investopedia.com/terms/i/institutionalshares.asp

http://www.investopedia.com/articles/stocks/07/insitutional-owners.asp