The pre-birth section of human life is something which is mostly glossed over in the GCSE and most of the A level courses, even though it is a very important and interesting time in life. At GCSE the entire process was called "fertilisation period" and at A level the most detail we go into is just that the embryo grows from a ball of cells into a foetus and then a neonate. Dr Keenan's talk explained some of the processes behind making you from two haploid cells.
Gastrulation is the period of fertilisation following the blastula where the entire embryo is a "hollow cup" shaped structure with three layers of cells; the outer layer (ectoderm) will later be formed into the central nervous system, the middle layer (endoderm) will mainly consist of muscle tissue and the inner layer will form vital organs.
This is also the time that the embryo forms it's body axes (cranial, dorsal, ventral, proximal, distal etc) with a particular family of genes controlling the process.
The embryo then plays a molecular "pass the parcel" as Dr Keenan put it, using an analogy of retailers and large companies distributing goods to model the way genes are first expressed to signal growth and begin to form a foetus: the customer orders online from a large company like Amazon, requesting a package. Amazon is an online retailer which models the signalling proteins BMP Shh FGF and Wnt, in organisers in the cell.
left: FGF protein, used in embryonic formation and also used to heal wounds, because both processes need to form new cells.
To get to the customer, the package must travel on roads which are signalling pathways in the embryo. The package itself is a phosphate group (PO₄) transported by a kinase- an enzyme which catalyses the transfer of this phosphate group like a courier. To enter the correct part of the body the courier must press the "doorbell" which is a transcription factor in the targeted cell, delivering it to the customer, a gene.
The talk by Dr Keenan made me realise how important this stage of life really is, that without it we would still be just a ball of cells in complete disorder, and that this tells our body where to grow muscle, bone, skin and organs. I found it very interesting to learn more than the A level course offers, and in particular this links to the chapters we have completed on protein synthesis so far, how complex and specific they are to perform these certain functions.
