Evolutionary conservation of the placodal transcriptional network during sexual and asexual development in chordates.

Background: An important question behind vertebrate evolution is whether the cranial placodes originated de novo, or if their precursors were present in the ancestor of chordates. In this respect, tunicates are of particular interest as they are considered the closest relatives to vertebrates. They are also the only chordate group possessing species that reproduce both sexually and asexually, allowing both types of development to be studied to address whether embryonic pathways have been co-opted during budding to build the same structures.

Differentiation of papillae and rostral sensory neurons in the larva of the ascidian Botryllus schlosseri (Tunicata).

During the metamorphosis of tunicate ascidians, the swimming larva uses its three anterior papillae to detect the substrate for settlement, reabsorbs its chordate-like tail, and becomes a sessile oozooid. In view of the crucial role played by the anterior structures and their nerve relations, we applied electron microscopy and immunocytochemistry to study the larva of the colonial ascidian Botryllus schlosseri, following differentiation of the anterior epidermis during late embryogenesis, the larval stage, and the onset of metamorphosis. Rudiments of the papillae appear in the early tail-bud stage as ectodermic protrusions, the apexes of which differentiate into central and peripheral bipolar neurons.

Muscle differentiation in a colonial ascidian: organisation, gene expression and evolutionary considerations.

Background: Ascidians are tunicates, the taxon recently proposed as sister group to the vertebrates. They possess a chordate-like swimming larva, which metamorphoses into a sessile adult. Several ascidian species form colonies of clonal individuals by asexual reproduction.

Does hair cell differentiation predate the vertebrate appearance?

It is generally accepted that the three main chordate groups (tunicates, cephalochordates and vertebrates) originated from a common ancestor having the basic features of the chordate body plan, i.e. a neural tube and a notochord flanked by striated musculature.

Properties of primary mouse myoblasts expanded in culture.

Implantation of myoblasts is a strategy used to enhance the regeneration of skeletal muscle tissue in vivo. In mouse models, myogenic cell lines and primary cells have been employed with different yields of adult muscle tissue formed. The present work is a study of some developmental features of expanded primary mouse myoblasts (i28), which have been shown to form muscle tissue.