A crane towers over an office-lab tower under construction at 10-50 Prospect St. in Somerville's Union Square on March 20, 2022. Photo by James Sanna | Banker & Tradesman Staff

The MBTA inaugurated its first new transit line in 20 years on Monday morning when the Green Line Extension’s first phase opened in Somerville’s Union Square.

The subway line’s imminent arrival has spurred a rapid boom in life science real estate developments as developers race to capitalize on the equally rapid explosion in the local biotech industry spilling over from nearby Kendall Square.

Some of these projects were already completed long before the Green Line trains arrived. A joint venture of Leggatt McCall Properties and DLJ Real Estate Partners completed the first in a planned trio of speculative lab towers last year, signing a major anchor lease for 208,000 square feet with Flagship, a biotech incubator. The partnership is seeking to expand its footprint further with a 242,000-square-foot lab building a few blocks away on the Somerville-Cambridge line.

Perhaps the most drastic change spurred by the Green Line Extension, however, will be a massive, 2.4 million-square-foot remake of Union Square by master developer US2, a joint venture between Magellan Development, RAS Development LLC, Cypress Equity Investments and USAA Real Estate.

The development’s first phase, a 194,000-square-foot office-lab building, a 450-unit apartment tower and 271 parking spaces and 10-50 Prospect St., broke ground last July and is currently under construction.