SEC FORM 3

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person^*

Polaris Venture Management Co IV LLC

(Last)

(First)

(Middle)

C/O POLARIS VENTURE PARTNERS

1000 WINTER STREET SUITE 3350

(Street)

WALTHAM

02451

(City)

(State)

(Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
09/18/2013

3. Issuer Name and Ticker or Trading Symbol
ACCELERON PHARMA INC [ XLRN ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

Director	X	10% Owner
Officer (give title below)		Other (specify below)

5. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	12,070	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
1. Title of Derivative Security (Instr. 4)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
Series A Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	1,706,532	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Series B Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	629,499	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Series C Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	363,495	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Series D Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	48,577	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Series E Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	277,520	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Series F Convertible Preferred Stock	⁽⁵⁾	⁽⁵⁾	Common Stock	95,541	⁽⁵⁾	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾
Warrants to Purchase Common Stock	⁽⁶⁾	⁽⁶⁾	Common Stock	183,902	$5.88	D⁽¹⁾⁽²⁾⁽³⁾⁽⁴⁾

1. Name and Address of Reporting Person^*

Polaris Venture Management Co IV LLC

(Last)

(First)

(Middle)

C/O POLARIS VENTURE PARTNERS

1000 WINTER STREET SUITE 3350

(Street)

WALTHAM

02451

(City)

(State)

(Zip)

Relationship of Reporting Person(s) to Issuer

Director	X	10% Owner
Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

POLARIS VENTURE PARTNERS ENTREPRENEURS FUND IV LP

(Last)

(First)

(Middle)

C/O POLARIS VENTURE PARTNERS

1000 WINTER STREET SUITE 3350

(Street)

WALTHAM

02451

(City)

(State)

(Zip)

Relationship of Reporting Person(s) to Issuer

Director	X	10% Owner
Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

POLARIS VENTURE PARTNERS IV LP

(Last)

(First)

(Middle)

C/O POLARIS VENTURE PARTNERS

1000 WINTER STREET SUITE 3350

(Street)

WALTHAM

02451

(City)

(State)

(Zip)

Relationship of Reporting Person(s) to Issuer

Director	X	10% Owner
Officer (give title below)		Other (specify below)

Explanation of Responses:

1. 222 shares of common stock, 3,384 warrants to purchase common stock, 29,594 shares of Series A Convertible Preferred Stock, 11,584 shares of Series B Convertible Preferred Stock, 6,689 shares of Series C Convertible Preferred Stock, 894 shares of Series D Convertible Preferred Stock, 3,168 shares of Series E Convertible Preferred Stock and 1,758 shares of Series F Convertible Preferred Stock of the registrant are owned directly by Polaris Venture Partners Entrepreneurs Fund IV, L.P. (PVPE IV).

2. Polaris Venture Management Co. IV, L.L.C. (PVM IV) is the general partner of PVPE IV. 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 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 therein.

3. 11,848 shares of common stock, 180,518 warrants to purchase common stock, 1,676,938 shares of Series A Convertible Preferred Stock, 617,915 shares of Series B Convertible Preferred Stock, 356,806 shares of Series C Convertible Preferred Stock, 47,683 shares of Series D Convertible Preferred Stock, 169,020 shares of Series E Convertible Preferred Stock and 93,783 shares of Series F Convertible Preferred Stock of the registrant are owned directly by Polaris Venture Partners IV, L.P. (PVP IV)

4. PVM IV is the general partner of PVP IV. 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 therein. Each of Messrs. Flint, McGuire and 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 therein.

5. The Series A Convertible Preferred Stock, Series B Convertible Preferred Stock, Series C Convertible Preferred Stock, Series D Convertible Preferred Stock, Series E Convertible Preferred Stock and Series F Convertible Preferred Stock are each convertible into Common Stock at any time at the holder's election and upon the consummation of a qualified public offering of the registrant. There is no expiration date for any series of convertible preferred stock.

6. The warrants to purchase Common Stock are exercisable at any time at the holders election, and have an expiration date on the ten year anniversary of the warrant issue date.

Remarks:

Exhibit List Exhibit 24 - Power of Attorney

	/s/ Douglas Pagan, attorney-in-fact for Polaris Venture Management Co. IV, L.L.C.	09/18/2013
	/s/ Douglas Pagan, attorney-in-fact for Polaris Venture Partners IV, L.P.	09/18/2013
	/s/ Douglas Pagan, attorney-in-fact for Polaris Venture Partners Entrepreneurs Fund IV, L.P.	09/18/2013
	** Signature of Reporting Person	Date
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 5 (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).
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