Re: How do cells 'know' how to form a blastula?

How do cells “know” how to form a blastula?

You’re asking the million dollar question of embryology. What initiates, 
regulates and differentiates the process of growth? Nobody knows the 
answers to these questions, and there are a lot of really smart people 
trying to figure it out.

The blastula is the name for the stage of development just before 
implantation into the uterus. First comes the fertilized egg cell – the 
zygote. This undergoes cleavage divisions to become the morula, which is 
sort of a solid ball of cells. The morula then transforms into the 
blastula, which is a larger hollow ball of cells. The blastula is also 
the first stage in development where the growing conceptus demonstrates 
recognizably different cells types – embryoblasts, which will develop 
into the embryo; and trophoblasts, which will develop into support 
structures. Of course how, and why this happens is very much a mystery. 

I could give you a long discussion of fate maps (working out which cell 
develops into which tissue type) or hox genes (genes that appear to 
control timing issues), but the bottom line is that nobody really knows 
how this works.

I’m sorry that I do not have the reference, but a few weeks ago there was 
an article in Science or Nature (I cannot remember which one) that sort 
of addresses your question. In that paper the authors report that there 
are proteins in the oocyte – pre-fertilization – that determine which end 
of the blastula will be the embryonic pole (the part where the embryo 
will develop) versus the vegetative pole (the part that will become 
placenta and other support structures).