Patterning along the limb bud requires signals from many sources.

The limb bud is a structure formed early in limb development.

All limb buds must rely on other signaling factors to obtain their identity.

Determines where limb buds will form, and what limbs will develop there.

Within the limb bud, expression also varies as a function of the position along the anterior-posterior axis.

Cell division is seen throughout the limb bud.

The eyes and limb buds also are forming.

By the sixth week, limb buds had appeared.

Eventually, the limb bud develops into bones, tendons, muscles and joints.

We tested this by grafting the tip of a limb bud to the flank of the embryo.