U.S. stock index futures were slightly lower Tuesday morning.At around 04:10 a.m. ET, Dow futures dipped 35 points, indicating a negative open of more than 34 points. Futures on the S&P and Nasdaq were both marginally lower.Market focus is largely attuned to global trade developments, with high-level negotiators from the U.S. and China poised to hold a fresh round of talks in Washington, D.C., on Thursday.The U.S. expanded its trade blacklist to include some of China’s top artificial intelligence firms on Monday, punishing Beijing for its treatment of predominantly Muslim ethnic minorities. The decision appeared likely to draw a sharp response from China, with investors worried it might harm the chances of a breakthrough later this week.The White House has scheduled an increase in U.S. tariffs on $250 billion worth of Chinese goods to 30% from 25% on October 15. President Donald Trump has said the tariff increase will take effect if no progress is made in bilateral trade negotiations.The world’s two largest economies have imposed tariffs on billions of dollars’ worth of one another’s goods since the start of 2018, battering financial markets and souring business and consumer sentiment.On the data front, the NFIB Small Business Optimism Index for September and producer price index (PPI) figures for September will both be released Tuesday morning.In corporate news, Domino’s Pizza and AZZ are scheduled to report earnings before the opening bell.Levi Strauss and Helen of Troy will both report their latest quarterly results after market close.