The Red Sea under the Caliphal Dynasties, c. 639–1171

Students of world history will be familiar with the Red Sea as a strategic communications corridor linking the Mediterranean to the Indian Ocean. This paper examines the Red Sea region between the seventh and twelfth centuries, when it was ruled by a succession of Islamic caliphal dynasties, namely, the Umayyads, ʿAbbāsids, and Fāṭimids. It first sets out a sketch of the political history of the Red Sea and its constituent hinterland polities, including particularly Egypt, Sudan, al‐Ḥijāz, and Yemen, drawing attention to episodes and processes in which the Red Sea was significant. A section on Africa and Arabia explores the Red Sea as a zone of economic and social interaction; another section deals with the historic shift of Indian Ocean trade from the ʿAbbāsid Persian Gulf to the Fāṭimid Red Sea. Finally, the impact of the Red Sea on its constituent hinterland polities and the wider sweep of Islamic history is considered

Colonizing while migrating: How do individual enteric neural crest cells behave?

Background Directed cell migration is essential for normal development. In most of the migratory cell populations that have been analysed in detail to date, all of the cells migrate as a collective from one location to another. However, there are also migratory cell populations that must populate the areas through which they migrate, and thus some cells get left behind while others advance. Very little is known about how individual cells behave to achieve concomitant directional migration and population of the migratory route. We examined the behavior of enteric neural crest-derived cells (ENCCs), which must both advance caudally to reach the anal end and populate each gut region. Results The behaviour of individual ENCCs was examined using live imaging and mice in which ENCCs express a photoconvertible protein. We show that individual ENCCs exhibit very variable directionalities and speed; as the migratory wavefront of ENCCs advances caudally, each gut region is populated primarily by some ENCCs migrating non-directionally. After populating each region, ENCCs remain migratory for at least 24 hours. Endothelin receptor type B (EDNRB) signaling is known to be essential for the normal advance of the ENCC population. We now show that perturbation of EDNRB principally affects individual ENCC speed rather than directionality. The trajectories of solitary ENCCs, which occur transiently at the wavefront, were consistent with an unbiased random walk and so cell-cell contact is essential for directional migration. ENCCs migrate in close association with neurites. We showed that although ENCCs often use neurites as substrates, ENCCs lead the way, neurites are not required for chain formation and neurite growth is more directional than the migration of ENCCs as a whole. Conclusions Each gut region is initially populated by sub-populations of ENCCs migrating non-directionally, rather than stopping. This might provide a mechanism for ensuring a uniform density of ENCCs along the growing gut