RTRS: Yen tumbles to multi-year lows as BOJ begins buying bonds
* Dollar near four-year high vs yen, poised to break 100 level
* BOJ begins buying longer-dated government bonds
* Euro shrugs off Portugal worry as Spain, Italy yields fall
By Wanfeng Zhou
NEW YORK, April 8 (Reuters) - The yen slumped to a near four-year low against the dollar and a three-year trough against the euro on Monday after the Bank of Japan kicked off its aggressive monetary easing program in an attempt to beat persistent deflation.
