3 posts · 2,561 views
Sharing both life experiences and my interest in developmental biology, with a common theme loosely tied to the passage of time.
Heather Etchevers
3 posts
Sort by: Latest Post, Most Popular
View by: Condensed, Full
- December 1, 2008
- 05:16 AM
- 1,100 views
Realize your potential!
by Heather Etchevers in A Developing Passion
Be all you can be!
This morning brought notification of yet another delightful editorial by Gerald Weissmann in the FASEB Journal (which I don’t otherwise read much), entitled, Fashions in Science: From Philosophers’ Camp to Epigenetics.1
The idea that there are fashions in science is nothing new whatsoever. Who among us has not lamented the fact that one’s subject of predilection is not the easy sell and draw for money and personnel that we might have believed anything “-omics”, related to human disease-causing viruses, or string theory is?
Many interesting debates about how organisms develop and acquire form and function seem to revolve around an artificial, easy dichotomy between nature and nurture, and Weissmann exposed them for the specious simplifications they are.
Aristotle proposed that humans developed from the interplay of nature, or “preformation,” and nurture, which he called “epigenesis.” Once genetics became a science, and “evo” joined “devo,” nature and nurture were revived in the guise of Mendelian vs. non-Mendelian heredity; Weismann’s immortal germ plasm vs. mortal protoplasm; and Mayr’s “soft” inheritance vs. the “hard” kind. More recently, Dawkins’ selfish gene (nature) has been countered by E. O. Wilson’s altruistic biology (nurture). Right now the epigenetic style is in high fashion with us and, like all high fashions, attracts the attractive. Dame Honor anticipated this sentiment in her presidential address to the First International Congress of Cell Biology in Paris:
Sartorially speaking we are probably not an outstandingly fashionable group, but where our research is concerned, we can be as fashion-conscious as the most elegant woman in this City. In science, as in the world of dress, fashions recur … .
I have few quibbles with following fashion. We scientists only heap scorn on it because it implies a certain passivity of thought, and an expenditure of limited energy on an apparently futile endeavor. (At least with respect to clothing, or to emulsions at the dinner table.) It’s not for me (well, clothes are, but not necessarily fashionable ones), yet I spend my time in other, arguably futile endeavors like writing blog entries, so I am ill-equipped to criticize.
It is de bon ton as well as relevant to cite Conrad Hal Waddington’s The Strategy of the Genes (Geo Allen & Unwin, London 1957) and the now-famous schematic describing fate acquisition in a progressively more restrictive environment, his “epigenetic landscape”. As Jonathan Slack explains the concept in his biography of Waddington 2,
…Up to a certain threshold, any genetic variation or environmental noise will be ‘buffered’ and not affect the pathway, but above this threshold, the cell would flip over into an adjacent pathway. By representing a pathway as a valley in a surface, Waddington provided a simple mechanical analogy for the rather complex biochemical-genetic buffering that occurs in organisms during development.
Weissmann’s summary of Waddington’s major insight is this:
Successive generations of the same phenotype will tend to seek the same path and the phenotype will become fixed regardless of the variability of its environment or genotype.
With a somatic mutation, for example, there can be enough impetus for a cell to roll out of one trough and enter another. The cell can react (or not) quite differently to its environment and its endogenous (epi)genetic state of affairs, which had “canalized” it so well until then. In the case of some cancers, it might go careening across the valleys as if the billiard ball had been given a hard lateral hit, and not really enter any of them for long.
During normal development, a cell will embark upon a path of differentiation that is progressively restricted over time. If you take it out of that context, as in innumerable experiments carried out by the legatees of Wilhelm Roux, Ethel Browne, Hans Spemann, Hilde Mangold, and Nicole Le Douarin, it often long retains the potential to go on and do other things, and that potential can wane over time at a variable rate depending on the cell type. Whether the potential is ever revealed is a matter of circumstance.
Which can apply to people, as well.
Insight that has brought us to another scientific fashionable concept in which I happily participate, stem cells. But woe be to anyone who tried to define a stem cell once and for all! Like the term’s object, “stem cell” is context-dependent.
I wish Weissmann did not reserve his insights for his readers at FASEB J but also opened up the editorials, at least, to Open Access and eventually to comments, such that they could double as blog posts. I am sure the discussions would be fascinating.... Read more »
Gerald Weissmann. (2008) Fashions in Science: From Philosophers’ Camp to Epigenetics. FASEB J, 4033-4037. DOI: http://www.fasebj.org/cgi/content/full/22/12/4033
Jonathan M. W. Slack. (2002) Timeline: Conrad Hal Waddington: the last Renaissance biologist?. Nature Reviews Genetics, 3(11), 889-895. DOI: 10.1038/nrg933
- May 22, 2009
- 05:19 AM
- 858 views
Genealogical links from early primates to Moors to you
by Heather Etchevers in A Developing Passion
Brian Clegg brought up an interesting and somewhat confounding point in Henry Gee’s recent post on Missing Links.
Let’s say one does want to take an anthropocentric point of view, and trace a representative human genealogy over time.
Let’s say that one is not particularly interested in the fact that we are cousins with a particular species of coral reef alga. Just like the fact that we are all related here on Nature Network. These family ties are not relevant to how we interact or feel about one another, as they are too distant and tenuous to hold our interest or imagination for long. As an aside, when I understood that another NN member has worked on a similar subject to me at one point, I immediately did feel that sort of tender family connection with her – a scientific genealogy – and this concept has been explored by others, elsewhere.
Now, that last view is an interesting one, because it is linear. That is, if you take the flattened tree view of genealogy, Mr. Badger has done a lot of pruning to focus on the one branch that leads to him. This is a common representation, and I don’t want to criticize it as much as, or as elegantly, as Eric Michael Johnson did. Suffice it to say that such a focus is easily mistaken for implying that each individual is a link in a chain, or a rung on a ladder, that has a destination.
I am going to play devil’s advocate, and say that I do see the justification for this simple presentation, as long as it is understood that there is a multidimensional context, through which one can trace that one-dimensional path in time, between two points: some “ancestor” and yourself. And that there is no destination out there.
What are the parameters?
Time. Past, present, future. A unidirectional vector.
Direct ascendance/descendance. Parents, self, children. Siblings are descendants of one or two direct ascendants. Any cousin, no matter how distant, can be described in terms of a mating relationship linking him or her to direct ascendants or descendants. In a spatial coordinate system, ascendance and descendance already occupy three dimensions. I’m not sure if that is because the time component is already inherent, since it is not possible to have descendants before a certain period of time has elapsed in an individual’s life. And we can only make one or a few progeny at a time. Some mathematician should probably come along and set me straight on this.
Hypothetical situations. What if? The premise of speculative fiction. Go back to a branch point, and take the road less travelled.
When we think about what we have in common with Ida or with Lucy, it’s as easy to write what links us to them. We have a common ancestor, certainly. Where the term “missing link” is very misleading, is that the real genealogy from that faraway common ancestor to the closest organism (in time) with a proven direct ascendancy is entirely in the realm of hypothesis until a fossil is found that can collapse all possible alternative scenarios into the observation of one that really happened. Such a fossil can not be a missing link; it can only be a point from which we can deduce the existence of a branch node – perhaps a new one.
There is a nice, apparently open access discussion of trait evolution here, by David Baum. Notably: “Tree thinking teaches us that all living organisms are equally distant in time from the root of the tree of life and therefore all are equally advanced. Thus, in the eyes of evolution, a human and a bacterium are equally derived. Although one of these organisms is certainly more morphologically complex than the other, both organisms are remarkable in that they are the product of parents that successfully and repeatedly gave rise to offspring over an unimaginably long time span (at least 3 billion years).”
So, more recently, this article (not open access) sparked my imagination, as it began thus:
After the collapse of the Roman Empire in Europe, the Arab dominance across the Mediterranean was one of the most impressive historical events that occurred in this region. Arabs appeared on the southern shores of the Mediterranean in the early seventh century and quickly conquered North Africa. They spread their language and religion to the native Northwest (NW) African Berber populations, which represented the bulk of the Muslim army that later conquered southern Europe. Referred to either as Moors (in Iberia) or Saracens (in South Italy and Sicily), their arrival in Europe dates to 711 AD, rapidly subduing most of Iberia and Sicily (831 AD). Among European kingdoms their presence was seen as a constant danger, and only by the fifteenth century was the Iberian reconquest completed. In the thirteenth century Frederick II destroyed Arab rule in Sicily and between 1221 and 1226 he moved all the Arabs of Sicily to the city of Lucera, north of Apulia. Lucera was later destroyed by Charles II (1301) but an Arab community was recorded in Apulia in 1336. Guerrilla warfare was still conducted by Arabs in Sicily even after Frederick II’s actions.
Imagine what life was like for our common great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandmother, Mara (I’ve named her thus), in that little settlement in Sicily, in 787! Because that long ago, she was in nearly all of our families, among the vocal readership of this blog. Assuming a ripe generational length of 25 years is perhaps a little optimistic when facing a nubile young woman in a conquered territory. The authors made reference to another publication in which the generational length was estimated at 31 years, and so only 40 generations away.)
To some probable relief, the authors found that among the populations studied, the southern Iberian peninsula and Sicily have the highest representation of Berber-like genotypes. It’s too bad they couldn’t have collaborated with French or Greek colleagues, or compared their results to similar calculations on an (eg.) Japanese population. But I am not a geneticist, I just hang around with a lot of them.
Anyhow, getting back to Mara – her particular existence is still only postulated, and will remain in that state of suspended animation until proper evidence allies her to someone who exists in the historical record either before or after her.
Should you go out looking for that evidence, and find the record of existence of a woman who lived at the right time in what is now Catania – well, who is to say that it was her progeny who survived and whose descendants were in your family? What if Mara was the half-sister who died in childbirth? Could you tell the difference based on the morphology of her third lumbar vertebra?
It would be impossible to say that Mara was a missing link in one branch of your genealogy until you had a hand on a lot more evidence. Much less the missing link. How much more impossible, then, to affirm that any sort of fossil is any sort of real “missing link”! At best, it can be compatible with a model – an existing one, or what is more fun, a new unifying one. It may rather be a childless cousin, and flesh out missing information on other branches of your family, but you won’t get a piece of the inheritance for all that. You may get a great boost to the imagination, though.
—... Read more »
Capelli, C., Onofri, V., Brisighelli, F., Boschi, I., Scarnicci, F., Masullo, M., Ferri, G., Tofanelli, S., Tagliabracci, A., Gusmao, L.... (2009) Moors and Saracens in Europe: estimating the medieval North African male legacy in southern Europe. European Journal of Human Genetics, 17(6), 848-852. DOI: 10.1038/ejhg.2008.258
- November 6, 2009
- 07:20 AM
- 603 views
Gene therapy can work!
by Heather Etchevers in A Developing Passion
I am basking in the reflected glory of working at an institution that has more or less successfully applied gene therapy to alleviate the suffering of children with incurable genetic diseases. And they’re fighting the good fight, because sometimes, they win. Here, I discuss how they did it, and why.... Read more »
Cartier, N., Hacein-Bey-Abina, S., Bartholomae, C., Veres, G., Schmidt, M., Kutschera, I., Vidaud, M., Abel, U., Dal-Cortivo, L., Caccavelli, L.... (2009) Hematopoietic Stem Cell Gene Therapy with a Lentiviral Vector in X-Linked Adrenoleukodystrophy. Science, 326(5954), 818-823. DOI: 10.1126/science.1171242
topics
join us!
Do you write about peer-reviewed research in your blog? Use ResearchBlogging.org to make it easy for your readers — and others from around the world — to find your serious posts about academic research.
If you don't have a blog, you can still use our site to learn about fascinating developments in cutting-edge research from around the world.
News
Editor's Selections: Programmed cell death in unicellular parasites, a novel gene transfer agent from Baronella, and full-contact herpes gladiatorum
Editor's Selections: Family medical histories, a grave in the Bahamas, medieval malaria, and macaques
Editor's Selections: Blood Tests for Depression, the Axolotl, Dopamine, and The Bachelor
