Post on 18-Dec-2015
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Signals in frog embryos
How can we identify developmental signaling pathways?
How do other vertebrate embryos develop?
Developmental biology jargon
Cell fate – the normal future identity of a cell (muscle, skin, etc.). A fate map represents future cell fates.
Specification – the process by which a cell acquires a particular fate. Specified cells could still switch to some other fate in response to extracellular signals. A specification map represents the identities that cells have acquired at a particular stage.
Determination – the process by which cells fix their fate stably. Determined cells do not change fate even if they receive new signals.
Differentiation – the process by which cells actually change to take on a particular identity (e.g. express muscle-specific genes).
What experimental results demonstrate that a particular signal induces a response?
Location – The signal must be present in the right place and at the right time.
Sufficiency – The signal must be able to induce the response (perhaps outside normal context).
Necessity – When the signal is removed or blocked, the response is also blocked.
Using these logical criteria to discover and test signals that might regulate a response.
Location – Find molecules that are present in the right place and at the right time.
Separate mRNA or proteins from different places, look for differences.
Sufficiency – Identify potential signaling molecules that can induce the response (perhaps outside its normal context).
Inject mRNAs or proteins corresponding to putative signals. Use gain-of-function mutations or transgenes.
Necessity – Remove or block the signal, test whether the response still occurs or not.
Loss-of-function mutationsInhibitors of particular pathwaysRNA interference
TGF- receptors activate gene regulatory proteins at the membrane
The TGF- family includesVg1, nodal, Xnr, activin, BMPs.
Some of these are localized to the vegetal region.
The TGF- family includesVg1, nodal, Xnr, activin, BMPs.
Some of these are localized to the vegetal region.
Maternal VegT (transcription factor, vegetally localized) activates zygotic Xnr (Xenopus Nodal-related) genes on vegetal side.
(VegT also specifies endoderm.)
Activin can induce different genes at different concentrations
General mesoderm
Dorsal mesoderm (organizer)
TGF- receptors activate gene regulatory proteins at the membrane
The TGF- family includesVg1, nodal, Xnr, activin, BMPs.
Some of these are localized to the vegetal region.
Another important pathway in inducing dorsal mesoderm-catenin immunolocalizations:
dorsal side ventral side
-catenin is a transcription factor
TGF- receptors activate gene regulatory proteins at the membrane
The TGF- family includesVg1, nodal, Xnr, activin, BMPs.
BMP4 acts in ventral mesoderm.
Maternal patterning signals set up zygotic gene expression
Brachyury and Goosecoid are transcription factors
Activin can induce different genes at different concentrations
General mesoderm
Dorsal mesoderm (organizer)
Injection of goosecoid mRNA into ventral vegetal cells of 16-cell embryo
Control embryos (not injected)