Posted by: Dan | April 3, 2007

Engrailed and Evolution of Cephalopod Morphology

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

Responses

  1. Check this out. It is absolutely mind-boggling.

  2. If evolutionists want to end the arguments all they need do is, get their brilliant heads together and assemble a ‘simple’ living cell. This should be possible, because today they certainly have a very great amount of knowledge about the contents of the so-called ‘simple’ cell.

    After all, shouldn’t all the combined Intelligence of all the worlds scientist be able the do what chance encounters with random chemicals, without a set of instructions, accomplished about 4 billion years ago, ‘according to the evolutionists,’ and having no intelligence at all available to help them along in their quest to become a living entity. Surely the evolutionists scientists of today should be able to make us a ‘simple’ cell.

    If it weren’t so pitiful it would be humorous, that intelligent people have swallowed the evolution mythology.

    Beyond doubt, the main reason people believe in evolution is that sources they admire, say it is so. It would pay for these people to do a thorough examination of all the evidence CONTRARY to evolution that is readily available: Try answersingenesis.org. The evolutionists should honestly examine the SUPPOSED evidence ‘FOR’ evolution for THEMSELVES.

    Build us a cell, from scratch, with the required raw material, that is with NO cell material, just the ‘raw’ stuff, and the argument is over. But if the scientists are unsuccessful, perhaps they should try Mother Earth’s recipe, you know, the one they claim worked the first time about 4 billion years ago, so they say. All they need to do is to gather all the chemicals that we know are essential for life, pour them into a large clay pot and stir vigorously for a few billion years, and Walla, LIFE!

    Oh, you don’t believe the ‘original’ Mother Earth recipe will work? You are NOT alone, Neither do I, and MILLIONS of others!

  3. After all, shouldn’t all the combined Intelligence of all the worlds scientist be able the do what chance encounters with random chemicals, without a set of instructions, accomplished about 4 billion years ago, ‘according to the evolutionists,’ and having no intelligence at all available to help them along in their quest to become a living entity.

    No, actually – there’s nothing saying that all the worlds’ scientists can recreate a situation with unknown conditions. Could you recreate, say, the formation of carbon nanotubes in a lab without a protocol? No, I don’t think so.

    Beyond doubt, the main reason people believe in evolution is that sources they admire, say it is so. It would pay for these people to do a thorough examination of all the evidence CONTRARY to evolution that is readily available: Try answersingenesis.org. The evolutionists should honestly examine the SUPPOSED evidence ‘FOR’ evolution for THEMSELVES.

    LOL! Thanks for the laugh, and you’re getting sent to the Stupid Bin for that one.

  4. […] That quote is actually a comment left today by Jim. […]


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