activin-2 is required for regeneration of polarity on the planarian anterior-posterior axis.

Planarians are flatworms and can perform whole-body regeneration. This ability involves a mechanism to distinguish between anterior-facing wounds that require head regeneration and posterior-facing wounds that require tail regeneration. How this head-tail regeneration polarity decision is made is studied to identify principles underlying tissue-identity specification in regeneration.

Nuclear receptor NR4A is required for patterning at the ends of the planarian anterior-posterior axis.

Positional information is fundamental to animal regeneration and tissue turnover. In planarians, muscle cells express signaling molecules to promote positional identity. At the ends of the anterior-posterior (AP) axis, positional identity is determined by anterior and posterior poles, which are putative organizers.

Ethical issues in fetal diagnosis and treatment.

Fetal diagnosis has raised ethical issues since it was first developed in the 1940s and 1950s. Two controversial issues have predominated. First, when the techniques for prenatal diagnosis were invasive techniques, they created risks to the pregnant women.