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Molecular and Cellular Biology, March 2007, p. 2202-2214, Vol. 27, No. 6
0270-7306/07/$08.00+0     doi:10.1128/MCB.01908-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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*

Center for Experimental Medicine,¹ Fine Morphology Laboratory, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan²

Received 9 October 2006/ Returned for modification 15 November 2006/ Accepted 4 January 2007

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.

Published ahead of print on 22 January 2007.

Supplemental material for this article may be found at http://mcb.asm.org/.

Present address: Oregon Health and Science University, Portland, OR.