Genomic analysis of immunity in a Urochordate
and the emergence of the verterate immune system: "waiting for Godot".
Ascidians are members of the subphylum urochordates
, which is a group of the phylum chordates along with cephalochordates and vertebrates (Satoh, 2003).
Originally identified in mammalian tissues, NO has been identified in the signaling cascades of many invertebrates such as coelenterates, platyhelminths, nematodes, annelids, molluscs, arthropods, echinoderms, and urochordates
(Martinez, 1995; Midler, 1997).
The pelagobenthic life cycle is by far the most common life cycle in the ocean, and is shared by almost all marine invertebrate phyla, from sponges to echinoderms and urochordates
. It is characterized by a planktonic larval dispersal phase that ends with settlement onto the substratum and metamorphosis into the benthic adult form.
1 A), and both phyla make up the sister group of the chordate phylum, which includes urochordates
, cephalochordates, and vertebrates (Castresana et al., 1998; Bromham and Degnan, 1999; Cameron et al., 2000; Furlong and Holland, 2002; Smith et al., 2004; Bourlat et al., 2006).
In contrast to urochordates
, cephalochordates have retained many features of the basal chordate body plan and are likely to approximate the ancestor of both urochordates
have become popular model organisms in the effort to deduce information about the common chordate ancestor.
It is present in urochordates
, cephalochordates, and larval lampreys, and its function is secretion of a mucous net to retain particles during feeding (Olsson, 1965; Deibel and Powell, 1987; Hiruta et al., 2005).
First, while some interspecific comparisons have found a relationship between offspring size and development time in species with non-feeding larvae (e.g., ascidians [2, 12]), others have found no significant relationship in urochordates
or echinoderms (14) (although the number of replicates was low in both groups).
Bi- versus multichimerism in colonial urochordates
: a hypothesis for links between natural tissue transplantation, allogenetics and evolutionary ecology.
with muscular locomotion provide a fifth independent divergence in locomotory structure.
To date, orthologs of mammalian [CB.sub.1] or [CB.sub.2] receptors have also not been identified in any invertebrate deuterostomes (e.g., cephalochordates, urochordates
, hemichordates, and echinoderms); but complete genome sequences have not yet been obtained for species representative of these phyla.