Possible Role of ZPAC,Zygote-specific Proteasome Assembly Chaperone,During Spermatogenesis in the Mouse

In the mammalian testis, the ubiquitin-proteasome system plays important roles in the process that promotes the formation of mature sperm. We recently identified zygote-specific proteasome assembly phaperone (ZPAC), which is specifically expressed in the mouse gonads and zygote. ZPAC mediates a unique proteasome assembly pathway in the zygote, but the expression profile and function of ZPAC in the testis is not fully understood. In this study, we investigated the possible role of ZPAC during mouse spermatogenesis. First, we analyzed the expression of ZPAC and 20S proteasome subunit α4/PSMA7 in the adult mouse testis. ZPAC and α4 were expressed in spermatogonia, spermatocytes, and round spermatids. In elongating spermatids, ZPAC was expressed until step 10, whereas expression of α4 persisted until step 12. We then examined the expression profile of ZPAC and α4 in a mouse model of experimental unilateral cryptorchidism. Consistent with appearance of morphologically impaired germ cells following cryptorchidism, the ZPAC protein level was significantly decreased at 4 days post induction of experimental cryptorchidism (D4) compared with the intact testis, although the amount of α4 protein persisted at least until D10. Moreover, intense ZPAC staining was co-localized with staining of annexin V, an early indicator of apoptosis in mammalian cells, in germ cells of cryptorchid testis, but ZPAC was also expressed in germ cells showing no detectable expression of annexin V. These results suggest that ZPAC plays a role during spermatogenesis and raises the possibility that 20S proteasome mediated by ZPAC may be involved in the regulation of germ cell survival during spermatogenesis.     

Molecular and Evolutionary Analysis of the Hd6 Photoperiod Sensitivity Gene Within Genus Oryza

Heading date determines rice’s adaptation to its area and cropping season. We analyzed the molecular evolution of the Hd6 quantitative trait locus for photoperiod sensitivity in a total of 20 cultivated varieties and wild rice species and found 74 polymorphic sites within its coding region (1,002 bp), of which five were nonsynonymous substitutions. Thus, natural mutations and modifications of the coding region of Hd6 within the genus Oryza have been suppressed during its evolution; this is supported by low Ka (≤0.003) and Ka/Ks (≤0.576) values between species, indicating purifying selection for a protein-coding gene. A nonsynonymous substitution detected in the japonica variety “Nipponbare” (a premature stop codon and nonfunctional allele) was found within only some local Japanese japonica varieties, which suggests that this point mutation happened recently, probably after the introduction of Chinese rice to Japan, and is likely involved in rice adaptation to high latitudes. Phylogenetic analysis and genome divergence using the entire Hd6 genomic region confirmed the current taxonomic sections of Oryza and supported the hypothesis of independent domestication of indica and japonica rice.     

Mobilization of the active transposon mPing in interspecific hybrid rice between Oryza sativa and O. glaberrima

Miniature Ping (mPing) is the first active miniature inverted-repeat transposable element to be identified in rice, and its mobilization is activated by stress treatments. We have examined the mobilization of mPing in four NERICA (New Rice for Africa) lines and 13 interspecific lines. All 17 lines are inbred progenies derived from crosses between Oryza sativa variety WAB56-104 as the recurrent parent and the O. glaberrima variety CG14 as the donor parent. We found that 16 of the 17 lines studied inherited mPing together with its autonomous partner, Pong, from WAB56-104. Transposon display of mPing disclosed polymorphic banding patterns among these lines. Most importantly, seven of the lines displayed clear polymorphic banding patterns for mPing, indicating that mPing might have been mobilized in these lines. Locus-specific PCR analysis also confirmed the mobilization of mPing. These results signify that interspecific hybridization may activate the transposition of mPing. Based on these results, we discuss the potential use of the mPing system as an efficient tool for gene tagging in interspecific hybrid rice.