Aseries of questions and suspicions have challenged the validity of a scientific paper that reported that body cells taken from mice could be reprogrammed into stem cells — immature cells that can develop into all types of body tissues — by simply exposing them to low-pH (acidic) liquids.

The paper, published in Nature magazine on Jan. 29 by a group of scientists led by Dr. Haruko Obokata at the government-backed Riken's Center for Developmental Biology in Kobe, attracted global attention as a groundbreaking stem cell study.

Riken must carry out a rigorous investigation, then issue a report that squarely answers each question and suspicion.