Issues

Cover: Consistent left-right patterning of the heart and viscera is a crucial part of embryogenesis. The cover shows a ventral view of the Xenopus tadpole, with pseudocolouring that reveals the asymmetric positions and morphogenesis of the gut (yellow), heart (pink) and gall bladder (green); the embryo on the left is normal, whereas its mirror image on the right depicts one with situs inversus. Xenopus is an important model organism for the study of developmental asymmetries because work in this system has most clearly revealed the molecular pathways that align the left-right axis shortly after fertilisation. Because errors of laterality form a common class of birth defects, understanding the mechanisms and timing at which left-right asymmetry is initiated is essential for human health. See article by Vandenberg et al. on page 261.