Tokyo stocks opened higher Friday on buying spurred by overnight gains on Wall Street, with the U.S. Dow Jones index extending its winning streak to seven days. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 515.92 points, or 1.36 percent, from Thursday to 38,589.90. The broader Topix index was up 27.71 points, or 1.02 percent, at 2,741.17. On the top-tier Prime Market, gainers were led by oil and coal, marine transportation and metal product issues. At 9 a.m., the U.S. dollar fetched 155.39-42 yen compared with 155.42-52 yen in New York and 155.82-84 yen in Tokyo …