When Anna Kushnir was kind enough during her stint at Nature to invite me to be a part of the club of Nature Network bloggers, I was – and still am – extraordinarily flattered. Since last summer, I have not carried out my self-imposed mission very much, which was to discuss my interest in developmental biology from time to time.
Perusing this week’s Nature table of contents online, I finally noticed (sorry!) the (the_) online Journal clubrichardson.html. Sponsored by Nature, Naturally. I got to browsing, and then to commenting. It did feel a bit like shooting the breeze at a journal club, except that I would maintain that the barrier to entry is a bit higher. Any stupid comments one might make will be recorded for posterity.
I was drawn to Michael Richardson’s discussion of an article by Leucht et al. in Development (135, 2845–2854; 2008) last year. As I answered the survey I received tonight from Nature Reports Stem Cells, I am not really one for timeliness. I want timelessness in my great science. And I hardly have time to keep up on all the breaking news in all the disciplines that interest me.
Anyhow, the theme was the difference between an adult stem cell with a certain theoretical potential, and the restricted potential it actually does have in vivo. Richardson wrote that the authors demonstrated that “They validate the concept of non-equivalence — seemingly identical cells differ if they come from different places in the embryo — first enunciated by Julian Lewis and Lewis Wolpert in the 1970s, and show that it holds in the adult.”
My probably-too-technical-for-a-blog response:
“There are, however, equivalence groups among progenitor populations. Transplanting cells derived from the calvarium can and does repair/reconstruct the jaw (both neural crest-derived and populations originally expressing few if any Hox gene members); from the tibia, one might in theory expect the cells to be able to repair the femur, but also perhaps the more anterior, mesodermally-derived bone in the clavicle.
However, ribs and iliac bone are regularly used for mandibular reconstruction. And apparently, vascularized grafts are becoming all the rage because of a more successful outcome. This is not simply cartilage in the place of the jaw (eg. the femur used in Benlidayi 2009 PMID: 19446201).
The other observation I would like to make is that Hox-expressing trunk-level neural crest cells, after a while in culture, will discontinue Hox expression. While normally unable to make cartilage and bone, they can then do so, like their cranial counterparts (Abzhanov et al. 2003 PMID: 12925584).
Leucht et al. were rather dismissive of both the paper and concept, which is surprising, given that Abzhanov has published with Helms in the past. And Couly et al. 1998 (PMID: 9693148) had shown a decade earlier that neural crest cells within a Hox+ or Hox- equivalence group can form appropriate skeletal structures, and outside of that equivalence group, keep their Hox expression status when grafted heterotopically. However, one could imagine that it is possible to apply exogenous influences not available in the normal tissue environment to alter Hox (or other master transcriptional regulator) gene expression status. And thereby, cell potential and eventual fate."
In any case, if I can’t post again in the immediate future, I thought I would try to leave the current post as something related to the blog’s true Nature rather than generic flower/cat photos or calls to vaguely political action.
