Description of Securities Registered Pursuant to Section 12 of the Securities Exchange Act of 1934

The following description of our common stock is a summary and does not purport to be complete. It is subject to and qualified in its entirety by reference to our Amended and Restated Certificate of Incorporation (“Certificate of Incorporation”) and our Amended and Restated Bylaws (“Bylaws”), each of which are incorporated by reference as an exhibit to the Annual Report on Form 10-K of which this Exhibit 4.3 is a part, and by applicable law. We encourage you to read our Certificate of Incorporation, our Bylaws and the applicable provisions of the Delaware General Corporation Law for additional information.

Our authorized capital stock consists of 150,000,000 shares of common stock, par value $0.001 per share (the “common stock”), and 10,000,000 shares of preferred stock, par value $0.001 per share (the “preferred stock”), all of which shares of preferred stock are undesignated.

We may issue shares of our common stock from time to time. The holders of shares of our common stock are entitled to one vote for each share held of record on all matters to be voted on by stockholders and do not have cumulative voting rights. Subject to the rights of holders of any future series of undesignated preferred stock which may be designated, each share of the outstanding common stock is entitled to participate ratably in any distribution of net assets made to the stockholders in the event of our liquidation, dissolution or winding up and is entitled to participate equally in dividends if and when declared by our board of directors. There are no redemption, sinking fund, conversion or preemptive rights with respect to shares of common stock. All shares of common stock have equal rights and preferences.

Our common stock is listed on the Nasdaq Global Select Market under the trading symbol “NTGN.”

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.

Our board of directors will have the authority, without further action by our stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting, or the designation of, such series, any or all of which may be greater than the rights of common stock. The issuance of our preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon our liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change in control of our company or other corporate action. No shares of convertible preferred stock are outstanding, and we have no present plan to issue any shares of convertible preferred stock.

No shares of preferred stock are outstanding as of the date of our Annual Report on Form 10-K with which this Exhibit 4.3 is filed as an exhibit.

Pursuant to the terms of our investors’ rights agreement, dated as of December 28, 2016, certain of our stockholders are entitled to rights with respect to the registration of their shares under the Securities Act until the earliest of (a) the fifth anniversary of our initial public offering, (b) a deemed liquidation event, as defined in the investors’ rights agreement, or (c) at

such time after the initial public offering when the holders’ shares may be sold without restriction pursuant to Rule 144 within a three-month period without registration. We refer to these shares collectively as registrable securities.

Pursuant to the investors’ rights agreement, the holders of shares of our common stock who are parties to the investors’ rights agreement are entitled to demand registration rights. Under the terms of the investors’ rights agreement, we will be required, upon the written request of the holders of at least 25% of our outstanding registrable securities, as defined in the investors’ rights agreement, that would result in an anticipated aggregate offering price of at least $3.0 million, to file a registration statement and use commercially reasonable efforts to effect the registration of all or a portion of these shares for public resale.

Pursuant to the investors’ rights agreement, if we are eligible to file a registration statement on Form S-3, upon the written request of at least 10% of the holders of registrable securities to sell registrable securities at an aggregate offering amount, net of selling expenses, of at least $1.0 million, we will be required to use commercially reasonable efforts to effect a registration of those shares.

Pursuant to the investors’ rights agreement, if we register any of our securities either for our own account or for the account of other security holders, the holders of the registrable securities are entitled to include their shares in the registration.

Our Certificate of Incorporation and our Bylaws include a number of provisions that may have the effect of delaying, deferring or preventing another party from acquiring control of us and encouraging persons considering unsolicited tender offers or other unilateral takeover proposals to negotiate with our board of directors rather than pursue non-negotiated takeover attempts. These provisions include the items described below.

In accordance with our Certificate of Incorporation, our board is divided into three classes serving staggered three-year terms, with one class being elected each year. Our Certificate of Incorporation also provides that directors may be removed only for cause and then only by the affirmative vote of the holders of at least two thirds (2/3) of the shares then entitled to vote at an election of directors. Furthermore, any vacancy on our board of directors, however occurring, including a vacancy resulting from an increase in the size of our board, may only be filled by the affirmative vote of a majority of our directors then in office even if less than a quorum. The classification of directors, together with the limitations on removal of directors and treatment of vacancies, has the effect of making it more difficult for stockholders to change the composition of our board of directors.

Our Certificate of Incorporation provides that all stockholder actions are required to be taken by a vote of the stockholders at an annual or special meeting and that stockholders may not take any action by written consent in lieu of a meeting. This requirement may lengthen the amount of time required to take stockholder actions and would prevent the amendment of our bylaws or removal of directors by our stockholders without holding a meeting of stockholders.

Our Certificate of Incorporation and Bylaws provide that only a majority of the members of our board of directors then in office may call special meetings of stockholders and only those matters set forth in the notice of the special meeting may be considered or acted upon at a special meeting of stockholders. Our bylaws limit the business that may be conducted at an annual meeting of stockholders to those matters properly brought before the meeting.

Advance Notice Requirements.

Our Bylaws establish advance notice procedures with regard to stockholder proposals relating to the nomination of candidates for election as directors or new business to be brought before meetings of our stockholders. These procedures provide that notice of stockholder proposals must be timely given in writing to our corporate secretary prior to the meeting at

which the action is to be taken. Generally, to be timely, notice must be received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the annual meeting for the preceding year. Our Bylaws specify the requirements as to form and content of all stockholders’ notices. These requirements may preclude stockholders from bringing matters before the stockholders at an annual or special meeting.

Any amendment of our Certificate of Incorporation must first be approved by a majority of our board of directors, and if required by law, must thereafter be approved by a majority of the outstanding shares entitled to vote on the amendment and a majority of the outstanding shares of each class entitled to vote thereon as a class. Our Bylaws may be amended by the affirmative vote of a majority of the directors then in office, subject to any limitations set forth in the Bylaws; and may also be amended by the affirmative vote of the holders of not less than two thirds (2/3) of the outstanding shares entitled to vote on such amendment, or at any special meeting of stockholders called for such purpose in accordance with our Bylaws.

Our Bylaws provide that, unless we consent in writing to an alternative forum, the Court of Chancery of the State of Delaware will be the sole and exclusive forum for certain state law claims, including derivative actions brought on our behalf, actions asserting breach of fiduciary duty claims, actions asserting claims arising under the Delaware General Corporation Law, and actions governed by the internal affairs doctrine, and the United States District Court for the District of Massachusetts will be the exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act. In addition, our Bylaws provide that any person or entity purchasing or otherwise acquiring any interest in shares of our common stock is deemed to have notice of and consented to the foregoing provisions.

On December 19, 2018 the Court of Chancery of the State of Delaware issued a decision declaring that federal forum selection provisions purporting to require claims under the Securities Act be brought in federal court are ineffective and invalid under Delaware law. On August 5, 2019, the decision was appealed to the Delaware Supreme Court and the appeal remains pending.  As a result, we may incur additional costs, which could have an adverse effect on our business, financial condition or results of operations.  In addition, our forum selection provisions impose additional litigation costs on stockholders and may limit their ability to bring a claim in a judicial forum that they find favorable for disputes with us. The Court of Chancery of the State of Delaware and the United States District Court for the District of Massachusetts may also reach different judgments or results than would other courts that may be more or less favorable to us than our stockholders.

We are subject to the provisions of Section 203 of the Delaware General Corporation Law. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a three-year period following the time that this stockholder becomes an interested stockholder, unless the business combination is approved in a prescribed manner. Under Section 203, a business combination between a corporation and an interested stockholder is prohibited unless it satisfies one of the following conditions:

 Section 203 defines a business combination to include:

In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation and any entity or person affiliated with or controlling or controlled by the entity or person.