Here’s one for PZ, since it’s more on developmental than cell biology. And, oh yeah, it’s about a cephalopod!
Published online last Friday in Development Genes and Evolution was a paper by Baratte and colleagues, on Engrailed in cephalopods: a key gene related to the emergence of morphological novelties. They looked at a cuttlefish, Sepia officinalis, and showed that the transcription factor engrailed is expressed in the shell-forming cells in the early stages of organogenesis, supporting the role of engrailed in molluscan shell formation to organisms with an internal shell. In the context of evolution of the metazoan body plan, engrailed is used in various ways throughout a variety of taxa to establish compartment boundaries during development, and facilitate morphological novelties, such as the internalization of calcified structures in cephalopods.
For additional background perspective, from the paper’s introduction:
Among those genes, engrailed is one of the most relevant example demonstrating the evolvability and plasticity of gene function during evolution. This transcription factor was first shown in Drosophila to be a key gene in the establishment of segment polarity (Kornberg 1981; Fjose et al. 1985), in neurogenesis (Patel et al. 1989), and in appendage development (Raftery et al. 1991). Highly conserved in protostomes and deuterostomes, engrailed orthologues show similar roles in other arthropods (Patel et al. 1989; Abzhanov and Kaufman 2000), in annelids (Wedeen and Weisblat 1991; Seaver and Kaneshige 2006), in echinoderms (Lowe and Wray 1997; Byrne et al. 2005; Yaguchi et al. 2006), and in chordates (Joyner 1996; Holland et al. 1997). Extensive comparisons among taxa suggest that neurogenesis is likely the ancestral function of engrailed and that subsequent recruitments have increased engrailed contributions (Patel et al. 1989; Gibert 2002). In molluscs, however, there is no strong data for the involvement of engrailed in neural development. Instead, engrailed is expressed in cells at the margin of the future shell (protoconch) in a wide range of molluscs: in a bivalve (Transenella tantilla, Jacobs et al. 2000), in gastropods (Ilyanassa obsoleta, Moshel et al. 1998; Patella vulgata, Nederbragt et al. 2002), in a scaphopod (Antalis entalis, Wanninger and Haszprunar 2001), and in a polyplacophoran (Lepidochitona caverna, Jacobs et al. 2000). From engrailed role during shell development in molluscs, Nederbragt et al. (2002) proposed that its ancestral function is the formation of a compartment boundary as an alternative to the neurogenic hypothesis.
As a cell biologist though, I find myself asking however, “How does engrailed get turned on or off, and how does it coordinate the formation of segment boundary with surrounding cells?”
- Baratte S, Andouche A, Bonnaud L. Engrailed in cephalopods: a key gene related to the emergence of morphological novelties. Dev Genes Evol. 2007 (Published online March 30). Pubmed