Teruaki Takasaki et al. (2002) Japanese Worm Meeting "MRG-1, a mortality factor-related protein, is required maternally for primordial germ cells to initiate mitotic proliferation in C. elegans"

Masaki Fujita, Hiroshi Sakamoto, Taizo Kawano, Noboru Nakajima, Yoshiro Shimura, Teruaki Takasaki

[Japanese Worm Meeting, 2002]

In the course of study on cellular senescence, MRG15 has been identified as a human mortality factor 4 (MORF4)-related gene. Since it is highly conserved among a wide range of organisms, MRG15 is thought to have a fundamental function. Although MORF4 was known to induce a senescence-like phenotype in immortal cell lines, the function of MRG15 is still unknown. To investigate the physiological function of MRG15, we are using C. elegans as a model for multicellular organisms. RNA-mediated interference of mrg-1 , a nematode homologous gene of MRG15, resulted in a complete absence of the germline. Examination of the expression of PGL-1, a component of P granules, revealed that two primordial germ cells, Z2 and Z3, couldnt undergo mitotic proliferation in mrg-1 (RNAi) animals. It has been known that Z2 and Z3, which are generated from P4 cell at about 100-cell stage, do not divide further throughout embryogenesis. Our data suggest that MRG-1 is required for Z2 and Z3 to resume proliferation during post-embryonic development. Zygotic RNAi experiments using rde-1 , an RNAi-deficient mutant strain, demonstrated that MRG-1 functions maternally. Moreover, immunoblot analysis using mutant animals with germline deficiencies indicated that MRG-1 is expressed predominantly in oocyte. This expression pattern strongly supports that MRG-1 is a maternal protein. In immunoblot analysis, MRG-1 was clearly detected in embryo, L1 larvae and adult hermaphrodites, whereas it decreases drastically between the L2 and L4 larval stages. Recent studies in vitro, we found that MRG-1 protein is unstable in larval cell extracts. These results imply that some protease regulates the level of MRG-1 in different stages by a degradation mechanism.

Teruaki Takasaki et al. (2003) International Worm Meeting "MRG-1, a member of the mortality factor-related gene family, is required for primordial germ cells to initiate mitotic proliferation"

Hiroshi Sakamoto, Teruaki Takasaki, Masaki Fujita, Noboru Nakajima, Yoshiro Shimura, Taizo Kawano

[International Worm Meeting, 2003]

MRG15, an evolutionally conserved chromodomain protein, is a member of human mortality factor 4 (MORF4)-related gene family. MORF4 is known to induce a senescence-like phenotype to a subset of immortal human cell lines such as HeLa cells. Although MRG15 is nearly identical to MORF4, it does not exhibit the senescence-inducing activity. Intriguingly, MRG15, but not MORF 4, has a chromatin organization modifier domain (chromodomain), a motif found in proteins associated with higher-order chromatin structure such as heterochromatin protein HP-1 and polycomb group (PcG) proteins. Members of MORF4-related gene family (MRGs) contain several predicted protein motifs, including a nuclear localization signal, a helix-loop-helix, and a leucine zipper. These motifs are often found in transcription factors, suggesting that MRGs may function as a transcriptional regulator. Recent studies of human MRG15 revealed that MRG15 regulates the transcription from some promoters in vitro. However the in vivo function(s) of MRG15 is still unknown. To investigate the in vivo function of MRG15, we utilized a Caenorhabditis elegans as a model organism. Here we show that MRG-1, a C. elegans homolog of MRG15, is essential for germ-line development. MRG-1 is expressed in the germ-line, and abundant in almost all cells in embryo. RNA-mediated interference (RNAi) of mrg-1 resulted in sterility caused by complete absence of germ cells. Examination of the expression of PGL-1, a component of germ-line specific P granules, revealed that two primordial germ cells (PGCs) are normally produced during embryogenesis in mrg-1(RNAi) animals, but these PGCs cannot undergo mitotic proliferation. To analyze the function of MRG-1 in post-embryonic germ-line development, we performed post-embryonic RNAi. The resultant larvae were able to produce fertile germ cells normally, but their F1 progeny lacked the germ cells. These results indicate that MRG-1 is required for PGCs to initiate mitotic proliferation, not to maintain germ cell proliferation.

Toshiaki Suzuki et al. (2003) International Worm Meeting "Analysis of Ce-PARKIN in C. elegans"

Nobutaka Hattori, Toshiaki Suzuki, Keiji Tanaka, Yoshikuni Mizuno, Shohei MItani, Noriyuki Matsuda, Hideki Yashiroda, Toshiaki Kitami, Keiko Gengyo-Ando

[International Worm Meeting, 2003]

Autosomal recessive juvenile parkinsonism (AR-JP) is one of the most common forms of familial parkinsons disease characterized by selective loss of dopaminergic neurons in substantia nigra and the locus coeruleus. parkin is the causative gene of AR-JP. The human parkin gene encodes 465 amino acids with a ubiquitin-like domain in the amino-terminus and two RING finger motifs in the carboxy terminus. So far, various deletion mutations and point mutations have been discovered in patients of AR-JP, suggesting that the loss of function of Parkin is the cause of AR-JP. Recently we and others showed that Parkin has a ubiquitin-protein ligase activity and therefore suggested that the defect of protein degradation in the neurons of AR-JP patients (Shimura H. et al. Nat. Genet. 25, 302-5, 2000). To investigate the function of Parkin in vivo, we began to analyze the Ce-PARKIN of C. elegans. Two deletion mutations in parkin genes show no defect in their viabilities. The expression of Ce-PARKIN seems to be specific to subset of neurons. Therefore, we focused on the function of Ce-PARKIN in the neurons and the analysis is underway.