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^*

Knopf John L

(Last)

(First)

(Middle)

128 SIDNEY STREET

(Street)

CAMBRIDGE

02199

(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)

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

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

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

X	Form filed by One Reporting Person
	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	221,500	D

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)
Option to Purchase Common Stock	⁽¹⁾	11/13/2022	Common Stock	37,500	$5.28	D
Option to Purchase Common Stock	⁽¹⁾	11/13/2022	Common Stock	37,500	$5.28	D
Option to Purchase Common Stock	⁽¹⁾	11/13/2022	Common Stock	37,500	$5.28	D
Option to Purchase Common Stock	⁽²⁾	11/13/2022	Common Stock	137,500	$5.28	D
Option to Purchase Common Stock	⁽²⁾	12/16/2021	Common Stock	50,000	$5.28	D
Option to Purchase Common Stock	⁽²⁾	12/02/2020	Common Stock	87,500	$3.88	D
Option to Purchase Common Stock	⁽²⁾	02/04/2020	Common Stock	50,000	$5.88	D
Option to Purchase Common Stock	⁽²⁾	03/27/2018	Common Stock	262,500	$5.08	D
Option to Purchase Common Stock	⁽²⁾	01/31/2017	Common Stock	100,000	$1.8	D
Option to Purchase Common Stock	⁽²⁾	03/29/2016	Common Stock	12,500	$0.4	D
Option to Purchase Common Stock	⁽³⁾	02/02/2015	Common Stock	12,500	$0.4	D

Explanation of Responses:

1. The options of registrants common stock vest over three years, with the first vesting three months after the achievement of the appropriate performance trigger. If the performance trigger is not achieved, the options vest on the forth year anniversary of the grant.

2. The options of registrants common stock vest in equal quarterly installments over the first four years after the grant.

3. The options of registrants common stock vested 25% on the first anniversary of the grant and in equal installments quarterly thereafter.

Remarks:

Exhibit List Exhibit 24 Power of Attorney

	/s/ Douglas Pagan, attorney in fact for John L. Knopf	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).
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.