Lack of transcriptional coordination between mitochondrial and nuclear oxidative phosphorylation genes in the presence of two divergent mitochondrial genomes

In most eukaryotes,oxidative phosphorylation(OXPHOS)is the main energy production process and it involves both mitochondrial and nuclear genomes.The close interaction between the two genomes is critical for the coordinated function of the OXPHOS process.Some bivalves show doubly uniparental inheritance(DUI)of mitochondria,where two highly divergent mitochondrial genomes,one inherited through eggs(F-type)and the other through sperm(M-type),coexist in the same individual.However,it remains a puzzle how nuclear OXPHOS genes coordinate with two divergent mitochondrial genomes in DUI species.In this study,we compared transcription,polymorphism,and synonymous codon usage in the mitochondrial and nuclear OXPHOS genes of the DUI species Ruditapes philippinarum using sex-and tissue-specific transcriptomes.Mitochondrial and nuclear OXPHOS genes showed different transcription profiles.Strong co-transcription signal was observed within mitochondrial(separate for F-and M-type)and within nuclear OXPHOS genes but the signal was weak or absent between mitochondrial and nuclear OXPHOS genes,suggesting that the coordination between mitochondrial and nuclear OXPHOS subunits is not achieved transcriptionally.McDonald-Kreitman and frequency-spectrum based tests indicated that M-type OXPHOS genes deviated significantly from neutrality,and that F-type and M-type OXPHOS genes undergo different selection patterns.Codon usage analysis revealed that mutation bias and translational selection were the major factors affecting the codon usage bias in different OXPHOS genes,nevertheless,translational selection in mitochondrial OXPHOS genes appears to be less efficient than nuclear OXPHOS genes.Therefore,we speculate that the coordination between OXPHOS genes may involve post-transcriptional/translational regulation.

Single Nucleotide Polymorphism-Based Chromosomal Microarray Evaluation of Hydatidiform Moles: A US National Reference Laboratory Experience

Objectives: This retrospective study evaluated 1) benefits of single nucleotide polymorphism (SNP)-based chromosomal microarrays (CMAs) in the diagnosis of complete hydatidiform mole (CHM) and partial HM (PHM) in products of conception (POC) and amniotic fluid (AF) specimens, and 2) frequency of whole-genome uniparental disomy (wgUPD) and triploidy in POC and AF specimens received at a US national reference laboratory. Methods: We reviewed consecutive 2138 POC and 3230 AF specimens and identified the cases with wgUPD and triploidy which are associated with molar pregnancy. Results: Of 2138 consecutive POC specimens tested, SNP-based CMA detected wgUPD in 10 (0.47%) and triploidy in 84 (3.93%). Of the 10 wgUPD cases, 9 (90%) were confirmed as CHM. Of 3230 consecutive AF specimens, the array detected wgUPD in 1 case (0.03%) and triploidy in 11 (0.34%). Conclusions: SNP-based microarray allows detection of wgUPD in POC and AF specimens at a US national reference laboratory. Correctly diagnosing HM and differentiating CHM from PHM are important for clinical management. The effective SNP-based CMA detection of wgUPD in CHM may enable physicians to monitor patients at risk for gestational trophoblastic disease and neoplasm. Conventional chromosome analysis of POC has a high failure rate, cannot be performed on formalin-fixed paraffin embedded samples, and cannot detect wgUPD. Further multi-institutional collaborative assessmen on accuracy, cost-effectiveness, and adequate access to SNP-based CMA, may lead this testing platform to be considered as the first-tier analysis tool for POC specimens, including those showing PHM or CHM.

Competitive Expression of Endogenous Wheat CENH3 May Lead to Suppression of Alien ZmCENH3 in Transgenic Wheat × Maize Hybrids

Uniparental chromosome elimination in wheat × maize hybrid embryos is widely used in double haploid production of wheat. Several explanations have been proposed for this phenomenon, one of which is that the lack of cross-species CENH3 incorporation may act as a barrier to interspecies hybridization. However, it is unknown if this mechanism applies universally. To study the role of CENH3 in maize chromosome elimination of wheat x maize hybrid embryos,？cos, maize ZmCENH3 and wheat aTaCENH3-B driven by the constitutive CaMV35S promoter were transformed into wheat variety Yangmai 158. Five transgenic lines for ZmCENH3 and six transgenic lines for ctTaCENH3-B were identified. RT-PCP analysis showed that the transgene could be transcribed at a low level in all ZmCENH3 transgenic lines, whereas transcription of endogenous wheat CENH3 was significantly up-regulated. Interestingly, the expression levels of both wheat CENH3 and ZmCENH3 in the ZmCENH3 transgenic wheat × maize hybrid embryos were higher than those in the non-transformed Yangmai 158 × maize hybrid embryos. This indicates that the alien ZmCENH3 in wheat may induce competitive expression of endogenous wheat CENH3, leading to suppression of ZmCENH3 over-expression. Eliminations of maize chromosomes in hybrid embryos of ZmCENH3 transgenic wheat ×maize and Yangmai 158 x maize were compared by observations on micronuelei presence, by marker analysis using maize SSRs （simple sequence repeats）, and by FISH （fluorescence in situ hybridization） using 45S rDNA as a probe. The results indicate that maize chromosome elimination events in the two crosses are not sigmficantly different. Fusion protein ZmCENH3- YFP could not be detected in ZmCENH3 transgenic wheat by either Western blotting or immnunostaining, whereas accumulation and loading of the αTaCENH3-B-GFP fusion protein was normal in aTaCENH3-B transgenic lines. As ZmCENH3-YFP did not accumulate after AM114 treatment, we speculate that low levels of ZmCENH3 protein in transgenic wheat may be one of the factors that lead to failure of suppression of maize chromatin elimination in ZmCENH3 transgenic wheat × maize hybrids.