The reprogramming of sperm compared to somatic celi neclei. (360G-Wellcome-089613_Z_09_Z)

The sperm cell has a highly specialised developmental programme and gene expression profile. However, in order to allow embryo-specific gene expression, the paternal genome has to undergo reprogramming. Reprogramming is also crucial for a proper embryonic development during another process -somatic cell nuclear transfer (SCNT). Normally, a cell once differentiated, cannot de-differentiate. However, it has been shown that it is possible to de-differentiate a cell experimentally. When somatic cell nuclei of Xenopus laevis were transferred into enucleated eggs, healthy embryos were generated. However, in contrast to fertilization, SCNT seems to be significantly less efficient in embryo generation [1]. But can mechanisms of reprogramming after fertilisation be directly compared with those that follow SCNT? Probably not, as both processes occur differently. In order to investigate the comparative efficiency of fertilisation events and SCNT in offspring generation, I would treat the sperm in the same way as the somatic cell is treated in the SCNT procedure and examine the developmental capacity of such embryos. If the results prove that the sperm is indeed more efficient than a somatic cell nucleus in producing normal embryos, I would investigate what is so special about the sperm making it so efficient. This would lead to an identification of sperm-specific factors responsible for the efficiency of the reprogramming after fertilization. Ultimately, further characterisation of these factors and mechanisms of their action should shed light on similarities/differences between reprogramming after fertilization and SCNT. It would be a major contribution to understand what controls the ability, especially of nuclei from differentiated cells, to lead to normal embryo development.