Profilin and actin-related proteins regulate microfilament dynamics during early mammalian embryogenesis.

Background: Profilins are ubiquitous proteins widely distributed in animals, including humans. They regulate actin polymerization by sequestering actin monomers in association with other actin-related proteins (Arps). Actin remodelling is essential for oocyte maturation, fertilization and embryo development; yet the role of profilins in these events is not well understood. Here we investigate profilin distribution and function during bovine fertilization and early embryogenesis, and we examine profilin localization with respect to the co-distribution of other Arps.

Methods And Results: Western blotting, confocal microscopy with immunofluorescence and protein inhibition studies with antibodies were implemented. Profilin distributes inside interphase nuclei, throughout the cytoplasm and near the cell cortex at different stages of bovine oocyte maturation, fertilization and embryo development. Expression is detected through the blastocyst stage, where profilin localizes to the inner cell mass as well as trophectoderm. Profilin co-distributes with actin monomers and Arps vasodilator-stimulated phospho protein, p140mDia, Arp 3 and p80 coilin in pronucleate-stage zygotes. Antiprofilin antibodies inhibit normal embryo development by disrupting microfilaments, but not microtubules, and result in a higher concentration of profilin and p140mDia mislocalized to the cortex.

Conclusions: These findings demonstrate that profilin regulates actin dynamics both within the cytoplasm and inside the nuclei of developing mammalian embryos and that its function is essential during fertilization to ensure successful development.