A Collection of Holy Grails and Riddles of the Sphinx    About Embryology

Which is most surprising? Which most tantalizing?

Solving which ones would most help solve other(s)?

I) How can a single cell gradually convert itself into an animal?

II) How can separated 2 or 4 cells also form a scale model body?
(is the mechanism the same as in Dictyostelium slugs?)

("Embryonic regulation")
(The Driesch Phenomenon; I would call this, but nobody else does)

III) What differences cause mammal and urchin embryos to regulate, but cause embryos of Nematode worms and Drosophila flies NOT to be able to regulate (in other words, to have mosaic development?)

IV) Why does regulation not occur if early cells are killed rather than removed?
(The Roux Phenomenon; I would call this, but nobody else does)
In fact, Roux didn't claim cells were killed; just slowed very much;
So what would happed if you really did kill cells of early embryos?.

V) Why do geometric rearrangements of cells (gastrulation, neurulation) accompany branching of cell fates?
Are movements or forces part of the cell type reassignment process?

VI) Development is about half rearrangement of differentiated cells, and about half assignment to differentiate, according to location.

VII) In sponges, anatomy is entirely produced by cell rearrangement.
Locations of differentiated cells have absolutely nothing to do with the places where each cell type originally differentiated.

This is also true in Hydra. (Should we regard this as regulation?)

VIII) Why do Hox genes get transcribed in geometric patterns that look like diffusion gradients? (they are too big to get through membranes)

IX) Why do the spatial locations of Hox gene transciption (anterior-posterior) match the relative locations of these genes on chromosomes.

X) How do hox genes control formation of anatomical patterns?


    The (in my opinion) false synthesis:

1&2) Diffusion gradients control cell differentiation. (French flag)

3&4) "Pay no attention to the man behind the curtain"

5&6) Cell rearrangements are caused by adhesion gradients.

7 ) "Pay no attention..."

8) By diffusion gradients, à la French Flag.

9) Colinearity.

10) Turning on different genes to cause differentiation.


back to index page