X0306 4 2016-12-21 0 0001280600 ACCELERON PHARMA INC XLRN 0001117003 MCGUIRE TERRANCE ONE MARINA PARK DRIVE, SUITE 1100 BOSTON MA 02210 1 0 0 0 Common Stock 2016-12-21 4 J 0 747127 0.00 D 0 I See Footnote Common Stock 2016-12-21 4 J 0 2190 0.00 A 3814 D Represents a pro rata distribution, and not a purchase or sale, without additional consideration by Polaris Venture Partners IV, L.P. ("PVP IV") and Polaris Venture Partners Entrepreneurs' Fund IV, L.P. ("PVPE IV" and, together with PVP IV, the "Funds") to their respective limited partners and general partner, Polaris Venture Management Co. IV, L.L.C. ("PVM IV"). Represents 725,005 shares distributed by PVP IV to its limited partners, 12,708 shares distributed by PVPE IV to its limited partners and 9,414 shares distributed by PVM IV to its members, including the Reporting Person. In connection with the foregoing distributions by the Funds, the Funds distributed an aggregate of 7,419 shares to PVM IV, which merely constituted a change of the form of beneficial ownership of the shares. These distributions were effected in accordance with the terms of the governing documents of each of PVP IV, PVPE IV and PVM IV. The Reporting Person is a managing member of PVM IV, the general partner of each of PVP IV and PVPE IV. The Reporting Person disclaims beneficial ownership of the Funds' and PVM IV's securities and this report shall not be deemed an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their pecuniary interest, if any, therein. /s/ Mary Blair, Attorney in-Fact for Terrance McGuire 2016-12-22