Centrosome inheritance after fertilization and nuclear transfer in mammals

Centrosomes, the main microrubule organizing centers in a cell, are nonmembrane-bound semi-conservative organelles consisting of numerous centrosome proteins that typically surround a pair of perpendicularly oriented cylindrical centrioles. Centrosome matrix is therefore oftentimes referred to as pericentriolar material (PCM). Through their microtubule organizing functions centrosomes are also crucial for transport and distribution of cell organelles such as mitochondria and macromolecular complexes. Centrosomes undergo cell cycle-specific reorganizations and dynamics. Many of the centrosome-associated proteins are transient and cell cycle-specific while others, such as y-tubulin, are permanently associated with centrosome structure. During gametogenesis, the spermatozoon retains its proximal centriole while losing most of the PCM, whereas the oocyte degenerates centrioles while retaining centrosomal proteins. In most mammals including humans, the spermatozoon contributes the proximal centriole during fertilization. Biparental centrosome contributions to the zygote are typical for most species with some exceptions such as the mouse in which centrosomes are maternally inherited and centrioles are assembled de novo during the blastocyst stage. After nuclear transfer in reconstructed embryos, the donor cell centrosome complex is responsible for carrying out functions that are typically fulfilled by the sperm centrosome complex during normal fertilization, including spindle organization, cell cycle progression and development. In rodents, donor cell centrioles are degraded after nuclear transfer, and centrosomal proteins from both donor cell and recipient oocytes contribute to mitotic spindle assembly. However, questions remain about the faithful reprogramming of centrosomes in cloned mammals and its consequences for embryo development. The molecular dynamics of donor cell centrosomes in nuclear transfer eggs need further analysis. The fate and functions of centrosome components in nuclear transfer embryos are being investigated by using molecular imaging of centrosome proteins labeled with specific markers including, but not limited to, green fluorescent protein (GFP).