Abstract. Mammalian preimplantation embryos enter the S phase immediately after the end of the M phase; their cell cycle lacks a substantial G1 phase. Previously, we suggested that the absence of the G1 phase was attributable to a loss of retinoblastoma protein (RB) function, which is required for suppression of S phase entrance and that this loss of RB function in turn was attributable to the low RB expression level during preimplantation development in mouse embryos. The present study aimed to examine whether or not RB inhibition by CDK4/6-cyclin D-dependent phosphorylation is involved in the loss of RB function in preimplantation mouse embryos by the expression of p16INK4a , a potent endogenous inhibitor of CDK4/6-cyclin D. First, the decrease in RB expression between the four-cell and morula stages was confirmed in in vivo-derived mouse embryos. We then examined the efficiency of the p16 INK4a expression vector in inhibiting RB phosphorylation and cell cycle progression using NIH-3T3 cells and obtained gradual RB dephosphorylation and a significantly lower proliferation rate in p16 INK4a-transfected cells than in control cells. This indicated the successful p16INK4a effects on cell-cycle progression by the vector used. On the other hand, the development rate of mouse embryos injected with the p16INK4a expression vector was the same as that of the control embryos, although p16INK4a expression was detected at mRNA and protein levels in the former group but not in the control group. These results suggest that RB phosphorylation is not involved in RB dysfunction or in the lack of a G1 phase in mouse embryos and that the decrease in RB expression is important for preimplantation-embryo-specific cellcycle regulation. Moreover, the present study indicates the similarity between preimplantation embryos and cancer cells, which p16INK4a expression does not arrest at the G1 phase. Key words: Mouse embryo, p16 INK4a, Retinoblastoma protein (J. Reprod. Dev. 57: [492][493][494][495][496][497][498][499] 2011) he cell cycle of a mammalian preimplantation embryo substantially lacks a G1 phase; the embryo enters the S phase immediately after the end of the M phase [1][2][3]. This substantive absence of the G1 phase would be related to the characteristics of early embryo cleavage, such as a shortened cell cycle, mitogen independence and a lack of embryo growth.In somatic cells, the transcription of DNA replication factors is necessary for progression to the S phase, and inhibition of this transcription protects cells from deregulated proliferation [4][5][6]. Retinoblastoma protein (RB), a well-known tumor-suppressor gene product, plays principal roles in this transcriptive inhibition. During the G1 phase, RB binds to and represses E2F, a transcriptional regulator, which can transactivate genes that are important for S phase entry [7,8]. When RB is inactivated by phosphorylation by the CDK4/6-cyclin D complex [9,10], the genes required for the G1/S transition are highly transcribed by activated E2F, and the cells enter the S...

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The present paper introduces a near-future perception system called Previewed Reality. In a coexistence environment of a human and a robot, unexpected collisions between the human and the robot must be avoided to the extent possible. In many cases, the robot is controlled carefully so as not to collide with a human. However, it is almost impossible to perfectly predict human behavior in advance. On the other hand, if a user can determine the motion of a robot in advance, he/she can avoid a hazardous situation and exist safely with the robot. In order to ensure that a user perceives future events naturally, we developed a near-future perception system named Previewed Reality. Previewed Reality consists of an informationally structured environment, a VR display or an AR display, and a dynamics simulator. A number of sensors are embedded in an informationally structured environment, and information such as the position of furniture, objects, humans, and robots, is sensed and stored structurally in a database. Therefore, we can forecast possible subsequent events using a robot motion planner and a dynamics simulator and can synthesize virtual images from the viewpoint of the user, which will actually occur in the near future. The viewpoint of the user, which is the position and orientation of a VR display or an AR display, is also tracked by an optical tracking system in the informationally structured environment, or the SLAM technique on an AR display. The synthesized images are presented to the user by overlaying these images on a real scene using the VR display or the AR display. This system provides human-friendly communication between a human and a robotic system, and a human and a robot can coexist safely by intuitively showing the human possible hazardous situations in advance.

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