MALDI mass spectrometry imaging shows a gradual change in the proteome landscape during mouse ovarian folliculogenesis

Follicular fluid exosome-derived miR-339-5p enhances in vitro maturation of porcine oocytes via targeting SFPQ, a regulator of the ERK1/2 pathway

In this study, we aimed to investigate cytoplasmic maturation and miRNA expression of mature oocytes cultured in porcine follicular fluid exosomes. We also examined the effect of miR-339-5p on oocyte maturation. Twenty eight differentially expressed miRNAs were detected using miRNA-seq. We then transfected cumulus oocyte complexes with miR-339-5p mimics and inhibitor during culture. The results showed that exosomes increased endoplasmic reticulum levels and the amount of lipid droplets, and decreased ROS levels, lipid droplet size, and percentage of oocytes with abnormal cortical granule distribution. Overexpressing miR-339-5p significantly decreased cumulus expansion genes, oocyte maturation-related genes, target gene proline/glutamine-rich splicing factor (SFPQ), ERK1/2 phosphorylation levels, oocyte maturation rate, blastocyst rate, and lipid droplet number, but increased lipid droplet size and the ratio of oocytes with abnormal cortical granule distribution. Inhibiting miR-339-5p reversed the decrease observed during overexpression. Mitochondrial membrane potential and ROS levels did not differ significantly between groups. In summary, exosomes promote oocyte cytoplasmic maturation and miR-339-5p regulating ERK1/2 activity through SFPQ expression, thereby elevating oocyte maturation and blastocyst formation rate in vitro.

Extracellular vesicles secreted by cumulus cells contain microRNAs that are potential regulatory factors of mouse oocyte developmental competence

The role of cumulus cells (CCs) in the acquisition of oocyte developmental competence is not yet fully understood. In a previous study, we matured cumulus-denuded fully-grown mouse oocytes to metaphase II (MII) on a feeder layer of CCs (FL-CCs) isolated from developmentally competent (FL-SN-CCs) or incompetent (FL-NSN-CCs) SN (surrounded nucleolus) or NSN (not surrounding nucleolus) oocytes, respectively. We observed that oocytes cultured on the former could develop into blastocysts, while those matured on the latter arrested at the 2-cell stage. To investigate the CC factors contributing to oocyte developmental competence, here we focused on the CCs' release into the medium of extracellular vesicles (EVs) and on their miRNA content. We found that, during the 15-h transition to MII, both FL-SN-CCs and FL-NSN-CCs release EVs that can be detected, by confocal microscopy, inside the zona pellucida (ZP) or the ooplasm. The majority of EVs are <200 nm in size, which is compatible with their ability to cross the ZP. Next-generation sequencing of the miRNome of FL-SN-CC versus FL-NSN-CC EVs highlighted 74 differentially expressed miRNAs, with 43 up- and 31 down-regulated. Although most of these miRNAs do not have known roles in the ovary, in silico functional analysis showed that seven of these miRNAs regulate 71 target genes with specific roles in meiosis resumption (N = 24), follicle growth (N = 23), fertilization (N = 1), and the acquisition of oocyte developmental competence (N = 23). Overall, our results indicate CC EVs as emerging candidates of the CC-to-oocyte communication axis and uncover a group of miRNAs as potential regulatory factors.

Quantitative mass spectrometry imaging: therapeutics & biomolecules

Mass spectrometry imaging (MSI) has become increasingly utilized in the analysis of biological molecules. MSI grants the ability to spatially map thousands of molecules within one experimental run in a label-free manner. While MSI is considered by most to be a qualitative method, recent advancements in instrumentation, sample preparation, and development of standards has made quantitative MSI (qMSI) more common. In this feature article, we present a tailored review of recent advancements in qMSI of therapeutics and biomolecules such as lipids and peptides/proteins. We also provide detailed experimental considerations for conducting qMSI studies on biological samples, aiming to advance the methodology.

Sample Preparation Method for MALDI Mass Spectrometry Imaging of Fresh-Frozen Spines

Technologies assessing the lipidomics, genomics, epigenomics, transcriptomics, and proteomics of tissue samples at single-cell resolution have deepened our understanding of physiology and pathophysiology at an unprecedented level of detail. However, the study of single-cell spatial metabolomics in undecalcified bones faces several significant challenges, such as the fragility of bone, which often requires decalcification or fixation leading to the degradation or removal of lipids and other molecules. As such, we describe a method for performing mass spectrometry imaging on undecalcified spine that is compatible with other spatial omics measurements. In brief, we use fresh-frozen rat spines and a system of carboxyl methylcellulose embedding, cryofilm, and polytetrafluoroethylene rollers to maintain tissue integrity while avoiding signal loss from variations in laser focus and artifacts from traditional tissue processing. This reveals various tissue types and lipidomic profiles of spinal regions at 10 μm spatial resolutions using matrix-assisted laser desorption/ionization mass spectrometry imaging. We expect this method to be adapted and applied to the analysis of the spinal cord, shedding light on the mechanistic aspects of cellular heterogeneity, development, and disease pathogenesis underlying different bone-related conditions and diseases. This study furthers the methodology for high spatial metabolomics of spines and adds to the collective efforts to achieve a holistic understanding of diseases via single-cell spatial multiomics.

Spatial lipidomics of fresh-frozen spines

Technologies assessing the lipidomics, genomics, epigenomics, transcriptomics, and proteomics of tissue samples at single-cell resolution have deepened our understanding of physiology and pathophysiology at an unprecedented level of detail. However, the study of single-cell spatial metabolomics in undecalcified bones faces several significant challenges, such as the fragility of bone which often requires decalcification or fixation leading to the degradation or removal of lipids and other molecules and. As such, we describe a method for performing mass spectrometry imaging on undecalcified spine that is compatible with other spatial omics measurements. In brief, we use fresh-freeze rat spines and a system of carboxyl methylcellulose embedding, cryofilm, and polytetrafluoroethylene rollers to maintain tissue integrity, while avoiding signal loss from variations in laser focus and artifacts from traditional tissue processing. This reveals various tissue types and lipidomic profiles of spinal regions at 10 μm spatial resolutions using matrix-assisted laser desorption/ionization mass spectrometry imaging. We expect this method to be adapted and applied to the analysis of spinal cord, shedding light on the mechanistic aspects of cellular heterogeneity, development, and disease pathogenesis underlying different bone-related conditions and diseases. This study furthers the methodology for high spatial metabolomics of spines, as well as adds to the collective efforts to achieve a holistic understanding of diseases via single-cell spatial multi-omics.

Recent advances in mass spectrometry imaging of single cells

Mass spectrometry imaging (MSI) is a sensitive, specific, label-free imaging analysis technique that can simultaneously obtain the spatial distribution, relative content, and structural information of hundreds of biomolecules in cells and tissues, such as lipids, small drug molecules, peptides, proteins, and other compounds. The study of molecular mapping of single cells can reveal major scientific issues such as the activity pattern of living organisms, disease pathogenesis, drug-targeted therapy, and cellular heterogeneity. Applying MSI technology to the molecular mapping of single cells can provide new insights and ideas for the study of single-cell metabolomics. This review aims to provide an informative resource for those in the MSI community who are interested in single-cell imaging. Particularly, we discuss advances in imaging schemes and sample preparation, instrumentation improvements, data processing and analysis, and 3D MSI over the past few years that have allowed MSI to emerge as a powerful technique in the molecular imaging of single cells. Also, we highlight some of the most cutting-edge studies in single-cell MSI, demonstrating the future potential of single-cell MSI. Visualizing molecular distribution at the single-cell or even sub-cellular level can provide us with richer cell information, which strongly contributes to advancing research fields such as biomedicine, life sciences, pharmacodynamic testing, and metabolomics. At the end of the review, we summarize the current development of single-cell MSI technology and look into the future of this technology.