Generation of mitochondrial replacement monkeys by female pronucleus transfer

Mitochondrial replacement techniques to resolve mitochondrial dysfunction and ooplasmic deficiencies: where are we now?

Mitochondria are the powerhouses of cell and play crucial roles in proper oocyte competence, fertilization, and early embryo development. Maternally inherited mitochondrial DNA (mtDNA) mutations can have serious implications for individuals, leading to life-threatening disorders and contribute to ovarian ageing and female infertility due to poor oocyte quality. Mitochondrial replacement techniques (MRTs) have emerged as a promising approach not only to replace defective maternal mitochondria in patients carrying mtDNA mutations, but also to enhance oocyte quality and optimize IVF outcomes for individuals experiencing infertility. There are two main categories of MRT based on the source of mitochondria. In the heterologous approach, mitochondria from a healthy donor are transferred to the recipient's oocyte. This approach includes several methodologies such as germinal vesicle, pronuclear, maternal spindle, and polar body transfer. However, ethical concerns have been raised regarding the potential inheritance of third-party genetic material and the development of heteroplasmy. An alternative approach to avoid these issues is the autologous method. One promising autologous technique was the autologous germline mitochondrial energy transfer (AUGMENT), which involved isolating oogonial precursor cells from the patient, extracting their mitochondria, and then injecting them during ICSI. However, the efficacy of AUGMENT has been debated following the results of a randomized clinical trial (RCT) that demonstrated no significant benefit over conventional IVF. Recent developments have focused on novel approaches based on autologous, non-invasively derived stem cells to address infertility. While these techniques show promising results, further RCTs are necessary to establish their effectiveness and safety for clinical use. Only after robust evidence becomes available could MRT potentially become a viable treatment option for overcoming infertility and enabling patients to have genetically related embryos. This review aims to provide an overview of the current state of MRTs in addressing low oocyte quality due to mitochondrial dysfunction.

Selection Increases Mitonuclear DNA Discordance but Reconciles Incompatibility in African Cattle

Mitochondrial function relies on the coordinated interactions between genes in the mitochondrial DNA and nuclear genomes. Imperfect interactions following mitonuclear incompatibility may lead to reduced fitness. Mitochondrial DNA introgressions across species and populations are common and well documented. Various strategies may be expected to reconcile mitonuclear incompatibility in hybrids or admixed individuals. African admixed cattle (Bos taurus × B. indicus) show sex-biased admixture, with taurine (B. taurus) mitochondrial DNA and a nuclear genome predominantly of humped zebu (B. indicus). Here, we leveraged local ancestry inference approaches to identify the ancestry and distribution patterns of nuclear functional genes associated with the mitochondrial oxidative phosphorylation process in the genomes of African admixed cattle. We show that most of the nuclear genes involved in mitonuclear interactions are under selection and of humped zebu ancestry. Variations in mitochondrial DNA copy number may have contributed to the recovery of optimal mitochondrial function following admixture with the regulation of gene expression, alleviating or nullifying mitochondrial dysfunction. Interestingly, some nuclear mitochondrial genes with enrichment in taurine ancestry may have originated from ancient African aurochs (B. primigenius africanus) introgression. They may have contributed to the local adaptation of African cattle to pathogen burdens. Our study provides further support and new evidence showing that the successful settlement of cattle across the continent was a complex mechanism involving adaptive introgression, mitochondrial DNA copy number variation, regulation of gene expression, and selection of ancestral mitochondria-related genes.

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

Comparative analysis of superovulated versus uterine-embryo synchronized recipients for embryo transfer in cynomolgus monkeys (Macaca fascicularis)

Introduction

Assisted reproductive technologies (ARTs), such as intracytoplasmic sperm injection and embryo transfer, are essential for generating genetically edited monkeys. Despite their importance, ARTs face challenges in recipient selection in terms of time and the number of animals required. The potential of superovulated monkeys, commonly used as oocyte donors, to serve as surrogate mothers, remains underexplored. The study aimed to compare the efficacy of superovulated and uterine-embryo synchronized recipients of embryo transfer in cynomolgus monkeys (Macaca fascicularis).

Methods

This study involved 23 cynomolgus monkeys divided into two groups-12 superovulated recipients and 11 synchronized recipients. The evaluation criteria included measuring endometrial thickness on the day of embryo transfer and calculating pregnancy and implantation rates to compare outcomes between groups.

Results

The study found no statistically significant differences in endometrial thickness (superovulated: 4.48 ± 1.36 mm, synchronized: 5.15 ± 1.58 mm), pregnancy rates (superovulated: 30.8%, synchronized: 41.7%), and implantation rates (superovulated: 14.3%, synchronized: 21.9%) between the groups (p > 0.05).

Conclusion

The observations indicate that superovulated recipients are as effective as synchronized recipients for embryo transfer in cynomolgus monkeys. This suggests that superovulated recipients can serve as viable options, offering an efficient and practical approach to facilitate the generation of gene-edited models in this species.