Translational control plays a crucial role during gametogenesis and early embryogenesis in organisms as different as worms and mammals as highlighted by the essential function of genes for many RNA-binding proteins in knock-out models. We have investigated the expression and function during mammalian meiosis and early embryogenesis of Sam68, an RNA-binding protein implicated in several aspects of RNA metabolism. Sam68 expression and localization within the cells is stage specific: it is expressed in the nucleus of mitotic germ cells, it disappears at the onset of meiosis (leptotene/zygotene stages), and it accumulates again in the nucleus of pachytene spermatocytes and oocytes. During the meiotic divisions, Sam68 translocates to the cytoplasm where it is found associated with the polysomes. Translocation correlates with serine/threonine phosphorylation and it is blocked by inhibitors of the mitogen activated protein kinases ERK1/2 and of the maturation promoting factor cyclinB-cdc2 complex. Both kinases associate with Sam68 in pachytene spermatocytes and phosphorylate the regulatory regions upstream and downstream of the Sam68 RNA-binding motif. Molecular cloning of the mRNAs associated with Sam68 in mouse spermatocytes reveals a subset of genes that might be post-transcriptionally regulated by this RNA-binding protein during spermatogenesis. We have demonstrated that Sam68 shuttles between the nucleus and the cytoplasm in secondary spermatocytes, suggesting that it may promote translation of specific RNA targets during the meiotic divisions. Moreover, RNAi-mediated knock-down of Sam68 in fertilized embryos strongly affects pre-implantation development, with reduced rate of blastocyst formation and profound alteration of the trophoblast layer. Since translational activation of dormant mRNAs in the oocyte is essential to set in motion the molecular mechanisms of development, we suggest that Sam68 post-transcriptionally regulates the expression of genes required for the acquisition of totipotency at the onset of embryogenesis.
Sam68 in germ cells and early embryogenesis
Paronetto MP;
2006-01-01
Abstract
Translational control plays a crucial role during gametogenesis and early embryogenesis in organisms as different as worms and mammals as highlighted by the essential function of genes for many RNA-binding proteins in knock-out models. We have investigated the expression and function during mammalian meiosis and early embryogenesis of Sam68, an RNA-binding protein implicated in several aspects of RNA metabolism. Sam68 expression and localization within the cells is stage specific: it is expressed in the nucleus of mitotic germ cells, it disappears at the onset of meiosis (leptotene/zygotene stages), and it accumulates again in the nucleus of pachytene spermatocytes and oocytes. During the meiotic divisions, Sam68 translocates to the cytoplasm where it is found associated with the polysomes. Translocation correlates with serine/threonine phosphorylation and it is blocked by inhibitors of the mitogen activated protein kinases ERK1/2 and of the maturation promoting factor cyclinB-cdc2 complex. Both kinases associate with Sam68 in pachytene spermatocytes and phosphorylate the regulatory regions upstream and downstream of the Sam68 RNA-binding motif. Molecular cloning of the mRNAs associated with Sam68 in mouse spermatocytes reveals a subset of genes that might be post-transcriptionally regulated by this RNA-binding protein during spermatogenesis. We have demonstrated that Sam68 shuttles between the nucleus and the cytoplasm in secondary spermatocytes, suggesting that it may promote translation of specific RNA targets during the meiotic divisions. Moreover, RNAi-mediated knock-down of Sam68 in fertilized embryos strongly affects pre-implantation development, with reduced rate of blastocyst formation and profound alteration of the trophoblast layer. Since translational activation of dormant mRNAs in the oocyte is essential to set in motion the molecular mechanisms of development, we suggest that Sam68 post-transcriptionally regulates the expression of genes required for the acquisition of totipotency at the onset of embryogenesis.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
