Outlining the nascent nervous system of Branchiostoma floridae (amphioxus) by the pan-neural marker AmphiElav.

The cephalochordate amphioxus is the closest living relative of the vertebrates. The anatomy and development of the amphioxus nervous system is giving insights into the basic chordate neural organisation, prior to the increase in neural complexity that characterised the origin of vertebrates. We have analysed the expression of the pan-neural marker AmphiElav in the Florida lancelet (Branchiostoma floridae) through development and up to larval stages. AmphiElav is expressed in the developing neural tube with particular temporal and spatial dynamics that correlate with neuronal differentiation. In addition, AmphiElav is expressed in isolated epidermal cells from mid-neurula embryos. This epidermal expression probably corresponds to precursors of sensory neurons. Together with data from other neural markers, we discuss the evolutionary relevance of these neural precursors to the origin of some of the most dramatic vertebrate inventions, neural crests and placodes.

Preliminary observations on the spawning conditions of the European amphioxus (Branchiostoma lanceolatum) in captivity.

Members of the subphylum Cephalochordata, which include the genus Branchiostoma (i.e. amphioxus), represent the closest living invertebrate relatives of the vertebrates. To date, developmental studies have been carried out on three amphioxus species (the European Branchiostoma lanceolatum, the East Asian B. belcheri, and Floridian-Caribbean B. floridae). In most instances, adult animals have been collected from the field during their ripe season and allowed (or stimulated) to spawn in the laboratory. In any given year, dates of laboratory pawning have been limited by two factors. First, natural populations of these three most studied species of amphioxus are ripe, at most, for only a couple of months each year and, second, even when apparently ripe, animals spawn only at unpredictable intervals of every several days. This limited supply of living material hinders the development of amphioxus as a model system because this limitation makes it more difficult to work out protocols for new laboratory techniques. Therefore we are developing laboratory methods for increasing the number of amphioxus spawning dates per year. The present study found that a Mediterranean population of B. lanceolatum living near the Franco-Spanish border spawned naturally at the end of May and again at the end of June in 2003. Re-feeding experiments in the laboratory demonstrated that the gonads emptied at the end of May refilled with gametes by the end of June. We also found that animals with large gonads (both, obtained from the field and kept and fed at the laboratory during several weeks) could be induced to spawn in the laboratory out of phase with the field population if they were temperature shocked (spawning occurred 36 hours after a sustained increase in water temperature from 19 degrees C to 25 degrees C).