The Nikkei stock index jumped over 2 percent Monday morning, as export-oriented issues were boosted by the yen’s weakness against the U.S. dollar and investors hunted bargains after sharp losses last week. The 225-issue Nikkei Stock Average rose 813.79 points, or 2.10 percent, from Friday to 39,521.43. The broader Topix index was up 40.35 points, or 1.51 percent, at 2,711.15. The dollar stayed firm around the 149 yen line on expectations that the Bank of Japan is likely to maintain an accommodative monetary stance even if it moves to end its negative interest rate policy at its two-day meeting…