Functional canonical RNAi in mice expressing a truncated Dicer isoform and long dsRNA.

Canonical RNA interference (RNAi) is sequence-specific mRNA degradation guided by small interfering RNAs (siRNAs) made by RNase III Dicer from long double-stranded RNA (dsRNA). RNAi roles include gene regulation, antiviral immunity or defense against transposable elements. In mammals, RNAi is constrained by Dicer's adaptation to produce another small RNA class-microRNAs. However, a truncated Dicer isoform (ΔHEL1) supporting RNAi exists in mouse oocytes. A homozygous mutation to express only the truncated ΔHEL1 variant causes dysregulation of microRNAs and perinatal lethality in mice. Here, we report the phenotype and canonical RNAi activity in DicerΔHEL1/wt mice, which are viable, show minimal miRNome changes, but their endogenous siRNA levels are an order of magnitude higher. We show that siRNA production in vivo is limited by available dsRNA, but not by Protein kinase R, a dsRNA sensor of innate immunity. dsRNA expression from a transgene yields sufficient siRNA levels to induce efficient RNAi in heart and muscle. DicerΔHEL1/wt mice with enhanced canonical RNAi offer a platform for examining potential and limits of mammalian RNAi in vivo.

Pronuclear and blastocyst morphology are associated age-dependently with embryo ploidy in in vitro fertilization cycles.

This retrospective study aimed to assess the relationship between standard markers of embryo morphology, maternal age and blastocyst ploidy determined by trophectoderm (TE) biopsy and Next-generation Sequencing (NGS). A total of 774 oocytes and embryos from 288 PGT-A cycles were scored for pronuclear, cleavage stage and blastocyst morphology. Pronuclear oocytes aligned between the nuclei and presenting equal number of nucleolus precursor bodies (NPBs) were designated Z1, oocytes showing equal number of NPBs, but not aligned, as Z2 while Z3 oocytes had an unequal number of NBPs between the nuclei or NPBs aligned in one nucleus and non-aligned in the other. Pronuclear oocytes with unequal-sized or non-aligned nuclei were designated Z4. Blastocysts were graded as BL1 (AA, AB or BA), BL2 (BB or CB) and BL3 (BC or CC) based on the combination of inner cell mass (ICM) and TE scores. Pronuclear and blastocyst morphology were correlated with aneuploidy in a < 40-year-old group (p < 0.01 and p < 0.05, respectively), but not in those ≥40 years. Interestingly, BL3 blastocysts classified as Z1 or Z3-Z4 on day-1 had different aneuploidy rates (BL3/Z1 = 46.7% vs. BL3/Z3-Z4 = 90.0%, p < 0.05). In summary, our data showed that pronuclear and blastocyst morphology are associated with blastocyst ploidy in younger patients. This may help embryo selection for embryo transfer and decision-making on which blastocysts should be biopsied in PGT-A cycles.

Morphology-based selection from available euploid blastocysts induces male-skewed sex proportion in the offspring.

PURPOSE: To determine whether blastocyst morphology has an impact on sex proportion at pre-implantation and birth in PGT-A and non-PGT-A cycles. METHODS: A total of 1254 biopsied blastocysts from 466 PGT-A cycles were analyzed for sex proportion, day of biopsy, degree of expansion, inner cell mass (ICM), and trophectoderm (TE) morphology. From these, 197 frozen single embryo transfers (SET) were assessed for clinical outcomes and sex proportion of ongoing pregnancies and deliveries. In addition, we evaluated the day of vitrification/embryo transfer, degree of expansion, and TE morphology in a group of 229 births (217 cycles) from frozen or fresh transfers of non-biopsied blastocysts. RESULTS: Sex proportion was impacted by day of biopsy and TE morphology, but not by ICM morphology, in PGT-A cycles. Therefore, biopsy on day 5 and TE "A" shifted the sex proportion towards males. Interestingly, we noted that our morphology-based embryo selection for SET of euploid blastocysts has favored the choice for XY embryos, generating a 54.3% XY proportion at transfer and 56.1% XY proportion at ongoing pregnancy/delivery. Our models indicate a weaker association between blastocyst morphology parameters and sex proportion of babies in non-PGT-A cycles. CONCLUSION: Blastocyst features associated with a skewed sex proportion towards XY embryos, such as biopsy on day 5 and top quality TE, are also parameters used for selecting euploid embryos for SET. Therefore, our data suggest that morphology-based embryo selection represents a strong factor responsible for a skewed male sex proportion at birth in PGT-A cycles.