Priapulid worms model early embryonic development
All animals originate from a single cell that multiplies and gives rise to anatomical structures during embryogenesis. It involves the separation of an undifferentiated mass of cells into three major layers: the ectoderm, the endoderm, and the mesoderm. Each of these germ layers form a set of differentiated tissues and organs. Ecdysozoa represent a group of diverse animals that includes insects, spiders, velvet worms and round worms. Priapulid worms, commonly referred to as 'penis worms', were among the most abundant animals in the Cambrian, when they were already morphologically like the known extant species. The recent morphological study of the embryonic development of the worm Priapulus caudatus demonstrated that it forms the primary germ layers in a similar manner to the ancestor of all bilaterally symmetrical animals. The goal of the EU-funded PEMDEEV (Priapulid endomesoderm development and ecdysozoan body plan evolution) project was to advance knowledge of the earliest events of embryonic development with a focus on the specification and differentiation of the endoderm. Project investigation resulted in a detailed morphological description of the process of endoderm formation and differentiation. Genetic analysis helped characterise the expression domains of a broad set of endo- and mesodermal-related genes. Researchers demonstrated that the digestive system forms from a small population of cells located at the posterior pole of the embryo before gastrulation. Importantly, the development of the endoderm into a functional digestive tract involved molecular patterning like the one observed in other ecdysozoans. The achievements of the project contributed to the establishment of priapulid worms as a tractable organism for developmental and evolutionary studies. It also underscored the importance of comparative analysis in the evolution of the Ecdysozoa.
Keywords
Priapulid worms, embryonic development, differentiation, Ecdysozoa, PEMDEEV
