Abstract

Crucial Role of Bysl in Mammalian Preimplantation Development as an Integral Factor for 40S Ribosome Biogenesis ▿ † Kenjiro Adachi 1 , Chie Soeta-Saneyoshi 1 , ‡ , Hiroshi Sagara 2 and Yoichiro Iwakura 1 , * 1 Center for Experimental Medicine 2 Fine Morphology Laboratory, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan ABSTRACT Blastocyst formation during mammalian preimplantation development is a unique developmental process that involves lineage segregation between the inner cell mass and the trophectoderm. To elucidate the molecular mechanisms underlying blastocyst formation, we have functionally screened a subset of preimplantation embryo-associated transcripts by using small interfering RNA (siRNA) and identified Bysl (bystin-like) as an essential gene for this process. The development of embryos injected with Bysl siRNA was arrested just prior to blastocyst formation, resulting in a defect in trophectoderm differentiation. Silencing of Bysl by using an episomal short hairpin RNA expression vector inhibited proliferation of embryonic stem cells. Exogenously expressed Bysl tagged with a fluorescent protein was concentrated in the nucleolus with a diffuse nucleoplasmic distribution. Furthermore, the loss of Bysl function by using RNA interference or dominant negative mutants caused defects in 40S ribosomal subunit biogenesis. These findings provide evidence for a crucial role of Bysl as an integral factor for ribosome biogenesis and suggest a critical dependence of blastocyst formation on active translation machinery.