eLife Assessment
This study reports the fundamental discovery of a novel structure in the developing gut that acts as a midline barrier between left and right asymmetries. Some of the evidence supporting the dynamics, composition, and function of this novel basement membrane in the chick is solid, some is even convincing, but investigation of its origin and impact on asymmetric organogenesis remains challenging and is not yet conclusive. This careful work is of broad relevance to patterning mechanisms, the importance of the extracellular matrix, and laterality disorders.