Sioban Sen Gupta

Purpose: Oocyte quality declines with age and metabolic stress, largely due to mitochondrial dysfunction and NAD⁺ depletion. Nicotinamide mononucleotide (NMN), a precursor of NAD⁺, has emerged as a potential intervention to restore cellular energy metabolism. This study systematically reviews preclinical evidence on NMN supplementation and integrates transcriptomic analysis of human oocytes to assess its relevance in human fertility. Methods: A systematic review was conducted following PRISMA guidelines across Medline, Embase, and Scopus (January 2015–October 2024). Seven high-quality original studies were included after screening and bias assessment. Data were synthesised through thematic analysis and pathway annotation. Additionally, single-oocyte RNA sequencing was performed on 46 human oocytes at germinal vesicle, metaphase I, and metaphase II stages to profile NAD⁺-related gene expression. Results: Across animal models, NMN supplementation has been shown to improve mitochondrial regulation, reduce oxidative stress, and modulate apoptotic and inflammatory pathways in response to metabolic, environmental, and ageing stress. Transcriptomic analysis identified 900 differentially expressed genes between germinal vesicle and metaphase II oocytes, with significant changes in mitochondrial and oxidative stress–related genes (i.e. SIRT3, DNM1L, SOD1), aligned with NMN’s known mechanisms of action. Conclusions: NMN supplementation shows improvements for oocyte function across diverse preclinical models. Human transcriptomic data further highlight mitochondrial and oxidative pathways as key regulatory points during oocyte maturation. Standardised protocols and clinical trials are needed to evaluate NMN’s translational potential in the context of human reproduction.

Purpose: Utilising non-invasive imaging parameters to assess human oocyte fertilisation, development and implantation; and their influence on transcriptomic profiles. Methods: A ranking tool was designed using imaging data from 957 metaphase II stage oocytes retrieved from 102 patients undergoing ART. Hoffman modulation contrast microscopy was conducted with an Olympus IX53 microscope. Images were acquired prior to ICSI and processed using ImageJ for optical density and grey-level co-occurrence matrices texture analysis. Single-cell RNA sequencing of twenty-three mature oocytes classified according to their competence was performed. Result(s): Overall fertilisation, blastulation and implantation rates were 73.0%, 62.6% and 50.8%, respectively. Three different algorithms were produced using binary logistic regression methods based on “optimal” quartiles, resulting in an accuracy of prediction of 76.6%, 67% and 80.7% for fertilisation, blastulation and implantation. Optical density, gradient, inverse difference moment (homogeneity) and entropy (structural complexity) were the parameters with highest predictive properties. The ranking tool showed high sensitivity (68.9–90.8%) but with limited specificity (26.5–62.5%) for outcome prediction. Furthermore, five differentially expressed genes were identified when comparing “good” versus “poor” competent oocytes. Conclusion(s): Imaging properties can be used as a tool to assess differences in the ooplasm and predict laboratory and clinical outcomes. Transcriptomic analysis suggested that oocytes with lower competence may have compromised cell cycle either by non-reparable DNA damage or insufficient ooplasmic maturation. Further development of algorithms based on image parameters is encouraged, with an increased balanced cohort and validated prospectively in multicentric studies.

The biggest cell in the human body, the oocyte, encloses almost the complete machinery to start life. Despite all the research performed to date, defining oocyte quality is still a major goal of reproductive science. It is the consensus that mature oocytes are transcriptionally silent although, during their growth, the cell goes through stages of active transcription and translation, which will endow the oocyte with the competence to undergo nuclear maturation, and the oocyte and embryo to initiate timely translation before the embryonic genome is fully activated (cytoplasmic maturation). A systematic search was conducted across three electronic databases and the literature was critically appraised using the KMET score system. The aim was to identify quantitative differences in transcriptome of human oocytes that may link to patient demographics that could affect oocyte competence. Data was analysed following the principles of thematic analysis. Differences in the transcriptome were identified with respect to age or pathological conditions and affected chromosome mis segregation, perturbations of the nuclear envelope, premature maturation, and alterations in metabolic pathways—amongst others—in human oocytes.

Autosomal aneuploidy is the leading cause of embryonic and foetal death in humans. This arises mainly from errors in meiosis I or II of oogenesis. A largely ignored source of error stems from germinal mosaicism, which leads to premeiotic aneuploidy. Molecular cytogenetic studies employing metaphase fluorescence in situ hybridization and comparative genomic hybridisation suggest that premeiotic aneuploidy may affect 10–20% of oocytes overall. Such studies have been criticised on technical grounds. We report here an independent study carried out on unmanipulated oocytes that have been analysed using next generation sequencing (NGS). This study confirms that the incidence of premeiotic aneuploidy in an unselected series of oocytes exceeds 10%. A total of 140 oocytes donated by 42 women gave conclusive results; of these, 124 (88.5%) were euploid. Sixteen out of 140 (11.4%) provided evidence of premeiotic aneuploidy. Of the 140, 112 oocytes were immature (germinal vesicle or metaphase I), of which 10 were aneuploid (8.93%); the remaining 28 were intact metaphase II - first polar body complexes, and six of these were aneuploid (21.4%). Of the 16 aneuploid cells, half contained simple errors (one or two abnormal chromosomes) and half contained complex errors. We conclude that germinal mosaicism leading to premeiotic aneuploidy is a consistent finding affecting at least 10% of unselected oocytes from women undergoing egg collection for a variety of reasons. The importance of premeiotic aneuploidy lies in the fact that, for individual oocytes, it greatly increases the risk of an aneuploid mature oocyte irrespective of maternal age. As such, this may account for some cases of aneuploid conceptions in very young women.

The original article unfortunately contained a mistake. In the online version of the paper, the words "MII (metaphase II)–PB1 (1st polar body) complex (MII-PB1 complex)” in table 1 are incorrectly...

Purpose: Molecular cytogenetic analysis has confirmed that a proportion of apparently meiotic aneuploidy may be present in the germ cells prior to the onset of meiosis, but there is no clear perception of its frequency. The aim of this review is to assess the evidence for premeiotic aneuploidy from a variety of sources to arrive at an estimate of its overall contribution to oocyte aneuploidy in humans. Methods: Relevant scientific literature was covered from 1985 to 2018 by searching PubMed databases with search terms: gonadal/germinal mosaicism, ovarian mosaicism, premeiotic aneuploidy, meiosis and trisomy 21. Additionally, a key reference from 1966 was included. Results: Data from over 9000 cases of Down syndrome showed a bimodal maternal age distribution curve, indicating two overlapping distributions. One of these matched the pattern for the control population, with a peak at about 28 years and included all cases that had occurred independently of maternal age, including those due to germinal mosaicism, about 40% of the cohort. The first cytological proof of germinal mosaicism was obtained by fluorescence in situ hybridisation analysis. Comparative genomic hybridisation analysis of oocyte chromosomes suggests an incidence of up to 15% in premeiotic oocytes. Direct investigation of fetal ovarian cells led to variable results for chromosome 21 mosaicism. Conclusions: Oocytes with premeiotic errors will significantly contribute to the high level of preimplantation and prenatal death. Data so far available suggests that, depending upon the maternal age, up to 40% of aneuploidy that is present in oocytes at the end of meiosis I may be due to germinal mosaicism.

Reciprocal Y autosome translocations are rare but frequently associated with male infertility. We report on the meiotic outcome in embryos fathered by two males with the karyotypes 46,X,t(Y;4)(q12;p15.32) and 46,X,t(Y;16)(q12;q13). The two couples underwent preimplantation genetic diagnosis (PGD) enabling determination of the segregation types that were compatible with fertilization and preimplantation embryo development. Both PGD and follow up analysis were carried out via fluorescence in situ hybridization (FISH) or array comparative genomic hybridization (aCGH) allowing the meiotic segregation types to be determined in a total of 27 embryos. Interestingly, it was seen that the number of female embryos resulting from alternate segregation with the chromosome combination of X and the autosome from the carrier gamete differed from the corresponding balanced males with derivative Y and the derivative autosome by a ratio of 7:1 in each case (P = 0.003) while from the adjacent-1 mode of segregation, the unbalanced male embryos with the combination of der Y and the autosome were seen in all embryos from couple A and in couple B with the exception of one embryo only that had the other chromosome combination of X and derivative autosome (P = 0.011). In both cases the deficit groups have in common the der autosome chromosome that includes the segment Yq12 to qter. The most likely explanation may be that this chromosome is associated with the X chromosome at PAR2 (pseudoautosomal region 2) in the sex-body leading to inactivation of genes on the autosomal segment that are required for the meiotic process and that this has led to degeneration of this class of spermatocytes during meiosis.