PhD thesis

Introduction
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muscular remodeling during metamorphosis using the following species: Joania
cordata (previously Argyrotheca cordata), Argyrotheca cistellula, Novocrania
anomala, and Terebratalia transversa.
Gene expression
Data on the molecular processes that regulate animal development have
greatly expanded within recent years (Carroll 2005). The investigation of gene
families that encode signaling molecules with roles in the control of cell fate
specification, proliferation, movement, and segment polarity has considerably
improved our understanding of metazoan ontogeny (Davidson and Levine
2008). So far, only few sequences of developmental genes have been
identified in brachiopods, such as members of the Wnt gene family (Holland
et al. 1991) and Hox genes (de Rosa et al. 1999), but nothing has so far been
published on the expression of these genes during ontogeny. This might not
be too surprising, since marine animals as little accessible as brachiopods are
unlikely to be favored as candidate model organisms for this kind of studies
(Sommer 2009). However, since the bauplan of some brachiopods has not
changed significantly since the Early Cambrian, gene expression data from this
phylum are very interesting because they may shed light on gene functions in
the brachiopod ancestor. This information might contribute to understand the
evolution of early bilaterian animals. In this study, the expression patterns of
the developmental homeobox genes Not and Cdx were investigated in larvae
of the rhynchonelliform brachiopod Terebratalia transversa. This was done in
order to reveal the functions of these genes in Brachiopoda and to assess their
ancestral function in animal development.
Not is a homeobox gene and representatives of its family play an important role
during notochord formation in vertebrates (Abdelkhalek et al. 2004). Its role in
invertebrate development is not well known (Martinelli and Spring 2004). Cdx
is a homeobox gene that is expressed in posterior tissues of almost all phyla
investigated so far (Hejnol and Martindale 2008). In addition to the posterior
tissues it was found to be expressed in mesoderm, gut, brain, and the central
nervous system of mice, lancelets, and annelids, as well as in the gut of
Drosophila and the mesoderm of Artemia (Macdonald and Struhl 1986; Duprey
et al. 1988; Brooke et al. 1998; Copf et al. 2004; Fröbius and Seaver 2006). The
gene expression patterns presented in this thesis are the first of their kind for
the phylum Brachiopoda.