Apical cell adhesion molecule, trophinin, localizes to the nuclear envelope

A role for BYN-1/bystin in cellular uptake and clearance of residual bodies in the Caenorhabditis elegans germline

GLH/Vasa/DDX4 helicases are core germ-granule proteins that promote germline development and fertility. A yeast-two-hybrid screen using Caenorhabditis elegans GLH-1 as bait identified BYN-1, the homolog of human bystin/BYSL. In humans, bystin promotes cell adhesion and invasion in gliomas, and, with its binding partner trophinin, triggers embryonic implantation into the uterine wall. C. elegans embryos do not implant and lack a homolog of trophinin, but both trophinin and GLH-1 contain unique decapeptide phenylalanine-glycine (FG)-repeat domains. In germ cells, we find endogenous BYN-1 in the nucleolus, partitioned away from cytoplasmic germ granules. However, BYN-1 enters the cytoplasm during spermatogenesis to colocalize with GLH-1. Both proteins become deposited in residual bodies (RBs), which are then engulfed and cleared by the somatic gonad. We show that BYN-1 acts upstream of CED-1 to drive RB engulfment, and that removal of the FG-repeat domains from GLH-1 and GLH-2 can partially phenocopy byn-1 defects in RB clearance. These results point to an evolutionarily conserved pathway whereby cellular uptake is triggered by the cytoplasmic mobilization of bystin/BYN-1 to interact with proteins harboring FG-repeats.

[Novel Tyrosine Phosphorylation Signals in the Nucleus and on Mitotic Spindle Fibers and Lysosomes Revealed by Strong Inhibition of Tyrosine Dephosphorylation]

Protein-tyrosine phosphorylation is one of the posttranslational modifications and plays critical roles in regulating a wide variety of cellular processes, such as cell proliferation, differentiation, adhesion, migration, survival, and apoptosis. Protein-tyrosine phosphorylation is reversibly regulated by protein-tyrosine kinases and protein-tyrosine phosphatases. Strong inhibition of protein-tyrosine phosphatase activities is required to undoubtedly detect tyrosine phosphorylation. Our extremely careful usage of Na₃VO₄, a potent protein-tyrosine phosphatase inhibitor, has revealed not only the different intracellular trafficking pathways of Src-family tyrosine kinase members but also novel tyrosine phosphorylation signals in the nucleus and on mitotic spindle fibers and lysosomes. Furthermore, despite that the first identified oncogene product v-Src is generally believed to induce transformation through continuous stimulation of proliferation signaling by its strong tyrosine kinase activity, v-Src-driven transformation was found to be caused not by continuous proliferation signaling but by v-Src tyrosine kinase activity-dependent stochastic genome alterations. Here, I summarize our findings regarding novel tyrosine phosphorylation signaling in a spatiotemporal sense and highlight the significance of the roles of tyrosine phosphorylation in transcriptional regulation inside the nucleus and chromosome dynamics.

Expression of trophinin and dipeptidyl peptidase IV in endometrial co-culture in the presence of an embryo: A comparative immunocytochemical study

Recurrent implantation failure leads to a reduced pregnancy rate. The expression patterns of trophinin and dipeptidyl peptidase IV (CD26) indicate the involvement of embryo implantation and early placental development. The purpose of the present study was to evaluate endometrial co‑culture cells in the presence of embryo with trophinin and CD26 immunofluorescence staining. Patients with recurrent implantation failure were enrolled in the present study. The patients were aged between 26 and 36 years. Co‑cultures were prepared from endometrial biopsies for each patient. Controlled ovarian hyperstimulation was performed on each of the patients. Certain embryos were maintained in a conventional culture environment (n=80), and others in an endometrial co‑culture environment (n=25). Following embryo transfer, the co‑culture cells were examined under an inverted wide‑field fluorescence microscope. The ratio of a successful pregnancy was 0.38 in the present study (n=5/13 pregnancies). The average age of the successful group (28±3.54 years) was younger compared with the unsuccessful (32.67±2.81) group (P≤0.05). The number of trophinin (+) endometrial cells in the presence of an embryo was significantly lower (P=0.046) in the successful group on the first day. No significant difference between the groups was observed in terms of the number of CD26 (+) cells on the first to the fourth days (P≤0.05). Trophinin and CD26 immunostaining is important in the early period of pregnancy, and it will be beneficial in terms of providing the deficit of conventional culture medium in performed studies with the endometrial co‑culture medium. The co‑culture may be important, particularly in the early period, in patients with recurrent implantation failure in terms of enabling a connection between the cells belonging to the endometrium and the embryo.

P granules extend the nuclear pore complex environment in the C. elegans germ line

The immortal and totipotent properties of the germ line depend on determinants within the germ plasm. A common characteristic of germ plasm across phyla is the presence of germ granules, including P granules in Caenorhabditis elegans, which are typically associated with the nuclear periphery. In C. elegans, nuclear pore complex (NPC)-like FG repeat domains are found in the VASA-related P-granule proteins GLH-1, GLH-2, and GLH-4 and other P-granule components. We demonstrate that P granules, like NPCs, are held together by weak hydrophobic interactions and establish a size-exclusion barrier. Our analysis of intestine-expressed proteins revealed that GLH-1 and its FG domain are not sufficient to form granules, but require factors like PGL-1 to nucleate the localized concentration of GLH proteins. GLH-1 is necessary but not sufficient for the perinuclear location of granules in the intestine. Our results suggest that P granules extend the NPC environment in the germ line and provide insights into the roles of the PGL and GLH family proteins.

Nuclear localization of magphinins, alternative splicing products of the human trophinin gene

Human magphinin proteins are translation products of differentially spliced transcripts from the 5' region of the human trophinin gene (TRO), whose 3' region encodes trophinin, a unique cell adhesion molecule involved in human embryo implantation. Magphinins belong to the MAGE (melanoma-associated antigen) family, and a previous study of mouse magphinins showed their expression in male and female germ cells, suggesting a role in germ cell development. Here, we characterized the structure and subcellular localization of human magphinins. Confocal microscopy analysis of ectopically expressed magphinins revealed that magphinin-alpha and -beta localize in the cytoplasm, whereas magphinin-gamma lacking the peptide encoded by exon-3 is nuclear. Following Triton X-100 extraction, DNA digestion, and high salt extraction magphinin-gamma remained nuclear, suggesting strong association with the nuclear matrix. A series of magphinin-gamma deletion mutants were generated and assayed for localization, which showed that the N-terminal region of the MAGE homology domain is necessary for nuclear localization. When magphinin-gamma was expressed in NIH3T3 cells, cells underwent G1 arrest. These results suggest that human magphinin-gamma inhibits cell cycle progression through nuclear activity.

Differential mitotic activation of endogenous c-Src, c-Yes, and Lyn in HeLa cells

Src-family tyrosine kinases (SFKs) play an important role in mitosis. Despite overlapping expression of multiple SFK members, little is known about how individual SFK members are activated in M phase. Here, we examined mitotic activation of endogenous c-Src, c-Yes, and Lyn, which are co-expressed in HeLa cells. c-Src, c-Yes, and Lyn were activated at different levels in M phase, and the activation was inhibited by Cdc2 inactivation. Mitotic c-Src and c-Yes exhibited normal- and retarded-electrophoretic-mobility forms on SDS-polyacrylamide gels, whereas Lyn did not show mobility retardation. Like c-Src, the retardation of electrophoretic mobility of c-Yes was caused by Cdc2-mediated phosphorylation. The normal- and retarded-mobility forms of c-Src were comparably activated, but activation of the retarded-mobility form of c-Yes was higher than that of the normal-mobility form of c-Yes. Thus, these results suggest that endogenous c-Src, c-Yes, and Lyn are differentially activated through Cdc2 activation during M phase.

Crucial role of Bysl in mammalian preimplantation development as an integral factor for 40S ribosome biogenesis

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.