The tumor suppressor protein, p53, is central to the pathways that monitor the stress, DNA damage repair, cell cycle, aging, and cancer. Highly complex p53 networks involving its upstream sensors and regulators, downstream effectors and regulatory feedback loops have been identified. CARF (Collaborator of ARF) was shown to enhance ARF-dependent and -independent wild-type p53 function. Here we report that (i) CARF overexpression causes premature senescence of human fibroblasts, (ii) it is vital for replicative and stress-induced senescence, and (iii) the lack of CARF function causes aneuploidy and apoptosis. We provide evidence that CARF plays a dual role in regulating p53-mediated senescence and apoptosis, the two major tumor suppressor mechanisms.The tumor suppressor protein, p53, is the most frequently inactivated protein in human cancers that symbolizes deregulation of genomic stability, cell cycle, senescence, and stress damage-repair response of cells (1-5). p53 signaling has been established as a complex network comprised of (i) upstream components consisting of stress signals and sensor proteins including kinases, transferases, methyalses, ligases, and others that regulate its activity either by post-translational modifications or by subcellular localization, (ii) core regulators including an upstream positive regulator (alternative reading frame, ARF) 4 protein that blocks its downstream effector and antagonist human double minute-2 (HDM2) protein, and (iii) the downstream effectors that determine the fate of cells by instigation of growth arrest, senescence, or apoptosis, the three potent tumor suppressor mechanisms. In addition to the fact that the initiation of DNA damage-induced senescence and establishment of growth arrest require p53 activation (4), a large number of studies have shown that the persistent inactivation of p53 is required for tumor maintenance. Cancer cells undergo either growth arrest or apoptosis with restoration of wild-type p53 function in vitro and in vivo (6 -8). These studies have prioritized further understanding of p53 signaling and regulation that would have major impact in cancer drug development.It is yet to be resolved how functional restoration of p53 culminates to growth arrest/senescence in some cells and apoptosis in others. Is it driven by the level of p53 expression, modulating partner proteins or its upstream regulators? Among the large number of p53-binding proteins that influence its activities, ARF and HDM2 have been demonstrated as its major regulators. HDM2 (an E3 ubiquitin ligase) is transcriptionally activated by p53 and acts to degrade p53 in turn; thus, executing a negative feedback loop on p53 activity. ARF has been shown to bind and inhibit HDM2 activity resulting in the activation of p53 pathway (9). CARF (Collaborator of ARF) protein was initially cloned as an ARF-binding protein by yeast two-hybrid screening and was shown to activate ARF-dependent and -independent p53 functions (10 -13). CARF interacts not only with ARF but also with p53 and HDM2, an...

Cell surfaces of biflagellate gametes and their morphological changes during fertilization of Bryopsis maxima Okamura were observed using a high-resolution field emission scanning electron microscope. Male gametes have broad and narrow faces, which are divided into at least five morphologically distinct regions: 1) the apical plate is a plate-like structure that is approximately 380-530 nm long and approximately 190 nm wide, in the center of the papilla and slightly protruded from the plasma membrane; 2) strips are smooth materials on ridges that originate from the basal part of the papilla and extend downward; 3) the lateral belt is a belt-shaped structure on the center of the narrower faces; 4) the flagellar surface; and 5) the other region of the cell body has a fine-grained appearance. In contrast, the entire female gamete surface is rough because of many granular or amorphous cell coats on the plasma membrane. When both gametes were mixed together, the initial fusion proceeded between the broader face of the male gamete and the anterior side of the female one near the basal bodies. Morphology of the male gamete's cell surface changed gradually as fusion proceeded and was covered by the granular materials; that surface closely resembled those of female gametes except for the apical plate. It was present until the planozygote attached itself to the substrate by the papilla. It finally disappeared after settlement. Therefore, these results indicate that gametes of B. maxima have sex-specific surface structures that change their morphology during fertilization and settlement.

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The intracellular behavior of human FCHO1 protein was investigated by live-cell imaging microscopy. The fluorescence intensity of green fluorescent protein (GFP)-FCHO1 fluctuated periodically in a perinuclear region approximately every 100 s, reminding us of the periodic fluctuations of clathrin reported in our recent work. The periodicity of FCHO1 was temporally correlated with that of clathrin, suggesting that FCHO1 is involved in clathrin-coated vesicle formation.

Swimming behavior of the sperm of Lygodium japonicum (Pteridophyta) and the associated ultrastructure of the flagellar apparatus were studied by video microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The sperm has approximately 70 flagella that emerge from a sinistrallycoiled flagellar apparatus, and swims forward by ciliary beat of these flagella. Backward swimming was not observed even after sperm collided with obstacles. Video microscopy showed that the flagella of the swimming sperm are oriented laterally and oblique-anteriorly. TEM and SEM observations revealed that the basal bodies of these flagella are arranged in at least two rows and oriented in the same directions as observed by video microscopy. These basal bodies (flagella) are categorized into two types according to their orientation: group I (laterally directed) and group II (oblique-anteriorly directed). The directionality of the basal bodies appears to be fixed by electron-dense material around their base. The outer dynein arms of the flagellar axoneme are entirely absent. These morphological characteristics of basal bodies (flagella) may relate to the lack of backward swimming behavior of the sperm. Based on these results, the evolution of swimming behavior in the archegoniates is discussed in connection with lack of backward swimming in a distantly related green alga, Mesostigma viride, and the Streptophyta.