Comparison of normal (left) and mutant (right) gut configurations in mouse embryo

A normal mouse embryo (left) has guts with a different configuration than those of an embyro (right) lacking an enzyme that modifies the molecule hyularonan. Credit: A. Sivakumar et al./Dev. Cell

Developmental biology

Why the developing gut does the twist

The intestines get their ‘bowl-of-spaghetti’ look with help from a molecule that helps to rotate the embyronic gut.

A molecule found in connective tissue helps to twist the developing gut into its final, familiar form.

Rotation of the embryonic midgut — which gives rise to most of the large and small intestines in an adult human — is a key early step in forming the gut’s convoluted and asymmetrical shape. But relatively little is known about how the gut makes this crucial, counterclockwise turn.

Natasza Kurpios at Cornell University in Ithaca, New York, and her colleagues discovered that in chick and mouse embryos, the connective-tissue molecule hyaluronan becomes decorated with amino-acid chains, but only on the right side of the gut. An accumulation of modified hyaluronan causes the right side of the gut to expand significantly, tilting the organ leftward and triggering rotation.

A protein found on the embryo’s left side was long thought to be the major regulator of left–right asymmetry in organ development. But the authors say that hyaluronan on the right side of the gut plays an unexpected part in controlling intestinal asymmetry.