Sec Form 4 Filing - MCGUIRE TERRANCE @ ACCELERON PHARMA INC - 2014-05-05

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person MCGUIRE TERRANCE 2. Issuer Name and Ticker or Trading Symbol ACCELERON PHARMA INC [ XLRN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O POLARIS VENTURE PARTNERS, 1000 WINTER STREET SUITE 3350 3. Date of Earliest Transaction (MM/DD/YY) 05/05/2014 (Street) WALTHAM, MA02451 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/05/2014 S 313,491 ( 1 ) ( 2 ) D $ 42.86 2,819,743 ( 3 ) I ( 3 ) See footnote ( 3 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MCGUIRE TERRANCE C/O POLARIS VENTURE PARTNERS 1000 WINTER STREET SUITE 3350 WALTHAM, MA02451 X Signatures /s/ Terrance McGuire 05/06/2014 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 307,893 shares and 5,598 shares that were held directly 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"), respectively. Polaris Venture Management Co. IV, L.L.C. ("PVM IV") is the general partner of the Funds. PVM IV disclaims beneficial ownership of these securities and this report shall not be deemed an admission that PVM IV is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of its pecuniary interest, if any, therein. ( 2 )(Continued from footnote 1) Each of Jonathan A. Flint, Terrance G. McGuire and Alan G. Spoon are the managing members of PVM IV. Each of Messrs. Flint, McGuire and Spoon disclaims beneficial ownership of these 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. ( 3 )Represents 2,769,495 shares and 50,248 shares that are held directly by PVP IV and PVPE IV, respectively. PVM IV disclaims beneficial ownership of these securities and this report shall not be deemed an admission that PVM IV is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of its pecuniary interest, if any, therein. Each of Jonathan A. Flint, Terrance G. McGuire and Alan G. Spoon are the managing members of PVM IV. Each of Messrs. Flint, McGuire and Spoon disclaims beneficial ownership of these 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.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.