Abstract. We isolated a mouse cDNA, zag1 (zygotic gene activation-associated gene 1), that has an open reading frame of 1,728-bp encoding a protein of 66.2 kDa including both a bipartite nuclear targeting sequence and a P-loop motif containing nucleoside triphosphate hydrolase motifs. Northern blot analysis of mouse tissues showed that zag1 was widely expressed but was especially prominent in the ovary and testis. RT-PCR analysis of in vitro fertilized embryos showed that the abundance of zag1 transcripts in oocytes decreased after fertilization, and zag1 mRNA was detected at 15 h post insemination (hpi) in fertilized embryos indicating that the gene was expressed at the start of zygotic gene activation at the mouse 1-cell stage. The nuclear-localization of ZAG1 protein in mouse preimplantation embryos at 15 hpi was confirmed by both subcellular analysis of enhanced green fluorescent protein (EGFP)-tagged ZAG1 and immunocytochemical analysis with anti-ZAG1 antibody. Subsequently, using yeast two-hybrid screening, we identified U2 small nuclear ribonucleoprotein B (U2B"), which is associated with pre-mRNA splicing, as a putative interacting partner of ZAG1 protein. Furthermore, knockdown of zag1 expression by an antisense DNA plasmid induced arrest and/or delay of embryonic development in injected 1-cell embryos. These results suggest that ZAG1 may be closely associated with zygotic gene expression in mouse preimplantation embryos. Key words: Embryonic gene activation (EGA), Gene expression, Maternal, Mouse, Preimplantation embryo, Zygotic gene activation (ZGA) (J. Reprod. Dev. 54 : 192-197, 2008) he development of preimplantation embryos is dependent on stored maternal factors in oocytes [1][2][3]. During meiosis in both male and female germ cells, transcriptional genome activation does not occur. In the mouse, minor zygotic gene activation (ZGA) first occurs during the latter stage of mouse 1-cell embryo development followed by major ZGA during the 2-cell stage [4]. Thus, ZGA depends on transcripts and proteins derived from maternaleffect genes. Several maternal-effect genes have been identified, including Stella [12,13], Hsf1 [14] and Formin2 [15]. Moreover, transcriptome analyses have revealed that maternal-effect genes are involved in oocyte maturation, maintenenance of meiotic arrest at the MII stage, fertilization and/or early embryonic development [16][17][18][19].The precise regulation of ZGA is considered to be essential for normal development of the preimplantation embryo because appropriate ZGA results in establishment of the totipotency of the fertilized egg and each blastomere of the embryo at the subsequent cleavage stage. However, the molecular mechanisms by which the nuclear reprogramming event at ZGA is regulated remain unclear. Recently, Brg1, a new member of the maternal-effect gene class, was shown to regulate ZGA in the mouse [20].To understand the molecular basis for regulation of ZGA, we focused on identification and functional characterization of genes activated in the late 1-cell stag...

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It was revealed from the crystal structure analysis of S-ovalbumin (S-OVA) formed by alkaline treatment that Ser164, Ser236, and Ser320 take the D-amino acid residue configuration (Yamasaki et al., J Biol Chem 2003; 278:35524-35530). To address the implications of a D-configuration for these Ser residues in S-OVA formation, three mutant OVAs (S164A, S236A, and S320A) were generated to compare their thermostabilities before and after alkaline treatment. Following alkaline treatment, S236A showed a marked increase in melting temperature similar to the wild type (DT m , 19°C) which corresponded to the formation of S-OVA, whereas the increment in T m for both S164A and S320A was only 4.5°C. Furthermore, the T m value of the double mutant S164/320A remained unchanged after alkaline treatment, supporting the relevance of Ser164 and Ser320 for thermostabilization of OVA. As Arg142 was predicted to interact with D-Ser164 upon S-OVA formation, it was substituted to Ala to generate R142A. The resulting increment in T m of mutant R142A after alkaline treatment was 5.8°C. The double mutant R142/S320A was therefore prepared to eliminate the participation of Ser320 in thermostabilization, and its T m value was compared before and after alkaline treatment. As expected, the increase in T m for the double mutant was only 1.2°C. Taken together, the data suggest that D-configuration of Ser164 caused by alkaline treatment favors interaction with Arg142 through conformational changes of the side chain. These results strongly supported the participation of the configurational inversion of both Ser164 and Ser320 residues in the formation of S-OVA.

Chicken ovalbumin (OVA) exists as mono-N-glycosylated form with a carbohydrate chain on Asn-292 in egg white, despite the possession of two potential N-glycosylation sites. To investigate the roles of N-glycosylation of OVA, we constructed a series of N-glycosylation mutants deleted N-glycosylation site and compared the secretion level of the mutants in Pichia pastoris. N292Q and N292/311Q mutants resulted in greater lowering of the secretion level as compared with wild-type, whereas N311Q mutant was secreted in approximately equal amounts to wild-type. However, secretion of wild-type and N311Q mutant was inhibited completely by tunicamycin treatment. All the N-glycosylation mutants have been expressed in the cells, as well as wild-type. Circular dichroism and fluorescence spectra of secreted N311Q mutant were almost identical to those of wild-type, while those of N292Q and N292/311Q mutants were different from wild-type; and, N292Q and N292/311Q mutants showed considerably lower denaturation temperature than wild-type. The results indicate that N-glycosylation at Asn-292 of OVA is required for the folding and secretion.