Cell differentiation is the process by which genetically identical cells of an embryo become specialized or the process by which stable differences arise between cells of the embryo.
Molecular mechanism behind cell differentiation:
Cell differentiation is achieved by one of the following mechanisms:
a) Transcriptional control: Transcription of a particular gene in a specific cell is tissue specific. Genes that are not needed will remain inactive and are prevented from transcription.
b) Translational control: In Xenopus oocytes, mRNAs for heat shock proteins are masked and these are translated only after fertilization. Here protein synthesis is blocked for a certain period.
c) Gene amplification: Here specific genes are selectively amplified to attain higher rate of expression. In Oocytes of Amphibians, rRNA gene amplification occurs their by increasing the copy of that particular gene.
d) Gene rearrangement: A classic example is differentiation process of mature B-cell into plasma cell and memory cell. Here IgGs against different antigens are generated by gene rearrangement.
e) Transposition: sometimes under certain stimulus transfer of gene within a genome can occur which result in a stable change in the pattern of expression. At first the gene may be in a silent site and upon transposition it has reached in an expression site. This phenomenon of variation in gene expression depending on its position in the genome is referred as position effect.
Eg: Surface antigens in yeast and trypanosomes.
Whatever be the organism, whatever is the status, big or small, all had a humble beginning from a very very small microscopic cell, the zygote.