Today: Redwood City biotech company Versartis soars 48 percent after raking in $126 million in IPO; San Jose's A10 Networks raises $187.5 million but struggles in trading, with gains just shy of 6 percent. Also, Gilead falls as lawmakers question drug's cost, and Netflix drops as CEO Reed Hastings rips the state of net neutrality.

The lead: A10 Networks and Versartis keep Silicon Valley IPO train rolling

San Jose's A10 Networks and Redwood City's Versartis both made their public debuts on Wall Street on Friday, but while posting gains, neither company reached the sky-high stock surges that have become commonplace among recent Silicon Valley IPOs.

Software maker A10 Networks raised $187.5 million in its IPO after pricing 12.5 million shares at $15, on the high end of its expected $13 to $15 range. It got off to a rocky start though, opening at $13.75 and slipping even further in early trading. After dipping as low as $13.59, A10 recovered as the day went on, reaching a high of $16.50 before closing at $15.88, up 5.87 percent.

"This is an incredibly proud and exciting day for our company," A10 founder and CEO Lee Chen wrote in a blog post. "It is also just the beginning as we continue to grow A10 into a lasting company."

A10 has posted losses in the past two years, and has been in long-term patent litigation with one of its top competitors, Seattle-based F5 Networks. But revenue has steadily risen, with A10 posting 18 percent growth last year.

Versartis also priced its initial shares at the top of its range, at $21 for its 6 million shares, raising $126 million. The biotech drugmaker raised $55 million in venture funding last month, giving it a $181 million boost as it pushes its growth-hormone deficiency drug to market, which it foresees as growing to a $4 billion market by 2018. Shares surged out of the gate Friday, peaking at $36.30 before settling down to $31.18 at the closing bell, up 48 percent.

Thanks to a perfect storm of expiring drug patents and the new federal health care law, Wall Street has discovered an insatiable appetite for biotech companies, as the Merc's Peter Delevett wrote earlier this month. Bay Area biotech companies have been in the center of it all -- Versartis is the ninth to go public in the past year.

SV150 market report: Gilead's drug costs questioned, Hastings calls for net neutrality

Versartis was one of the few big gainers on the day, as the markets' early morning rally faded and the major indexes ended the day with losses.

The biotech sector was bit particularly hard, as lawmakers questioned the hefty price of Gilead Science's new anti-hepatitis C drug, Sovaldi. The Foster City company fell $3.46, or 4.6 percent, to $72.07, on worries that the government and insurers would balk at paying for expensive new treatments. "Our concern is that a treatment will not cure patients if they cannot afford it," Democrats on the House Energy and Commerce Committee wrote in a letter to Gilead CEO John Martin.

Elsewhere in Silicon Valley, Netflix fell $18.28, or 4.3 percent, to $405.99, after CEO Reed Hastings criticized the lack of net neutrality laws. Netflix reached a deal with Comcast recently to ensure smooth broadband delivery of its content, but in an open letter, Hastings said such a deal proves there's a problem. "While in the short term Netflix will in cases reluctantly pay large ISPs to ensure a high quality member experience, we will continue to fight for the Internet the world needs and deserves," Hastings wrote.

LinkedIn shares dropped $7.70, or 3.8 percent, to $196.72, despite CEO Jeff Weiner being named the nation's top CEO in an employee survey by Glassdoor. Twitter gained 80 cents, or 1.6 percent, to $50.92 after a Turkish attempt to muzzle the social network backfired, as tech-savvy Turks used Google's free DNS service to circumvent the ban. And Apple rose $4.17, or 0.8 percent, to $532.87, after Billboard reported the Cupertino tech giant may launch a streaming music service to rival Spotify and Oakland-based Pandora, and offer an iTunes app for Android phones.

Up: Apple, HP, Yahoo, Facebook, Twitter

Down: Google, Oracle, Intel, Cisco, eBay, VMware, Juniper, Zynga, LinkedIn, Tesla

The SV150 index of Silicon Valley's biggest companies: Down 15.34, or 0.99 percent, to 1,541.38.

The tech-heavy Nasdaq composite index: Down 42.50, or 0.98 percent, to 4,276.79.

The blue chip Dow Jones industrial average: Down 28.28, or 0.17 percent, to 16,302.77.

And the widely watched Standard & Poor's 500 index: Down 5.49, or 0.29 percent, to 1,866.52.

Check in weekday afternoons for the 60-Second Business Break, a summary of news from Mercury News staff writers, The Associated Press, Bloomberg News and other wire services.