MCRS1 is essential for epiblast development during early mouse embryogenesis

Loss of KANSL3 leads to defective inner cell mass and early embryonic lethality

e-Lysine acetylation is a prominent histone mark found at transcriptionally active loci. Among many lysine acetyl transferases, nonspecific lethal complex (NSL) members are known to mediate the modification of histone H4. In addition to histone modifications, the KAT8 regulatory complex subunit 3 gene (Kansl3), a core member of NSL complex, has been shown to be involved in several other cellular processes such as mitosis and mitochondrial activity. Although functional studies have been performed on NSL complex members, none of the four core proteins, including Kansl3, have been studied during early mouse development. Here we show that homozygous knockout Kansl3 embryos are lethal at peri-implantation stages, failing to hatch out of the zona pellucida. When the zona pellucida is removed in vitro, Kansl3 null embryos form an abnormal outgrowth with significantly disrupted inner cell mass (ICM) morphology. We document lineage-specific defects at the blastocyst stage with significantly reduced ICM cell number but no difference in trophectoderm cell numbers. Both epiblast and primitive endoderm lineages are altered with reduced cell numbers in null mutants. These results show that Kansl3 is indispensable during early mouse embryonic development and with defects in both ICM and trophectoderm lineages.

Omics Views of Mechanisms for Cell Fate Determination in Early Mammalian Development

During mammalian preimplantation development, a totipotent zygote undergoes several cell cleavages and two rounds of cell fate determination, ultimately forming a mature blastocyst. Along with compaction, the establishment of apicobasal cell polarity breaks the symmetry of an embryo and guides subsequent cell fate choice. Although the lineage segregation of the inner cell mass (ICM) and trophectoderm (TE) is the first symbol of cell differentiation, several molecules have been shown to bias the early cell fate through their inter-cellular variations at much earlier stages, including the 2- and 4-cell stages. The underlying mechanisms of early cell fate determination have long been an important research topic. In this review, we summarize the molecular events that occur during early embryogenesis, as well as the current understanding of their regulatory roles in cell fate decisions. Moreover, as powerful tools for early embryogenesis research, single-cell omics techniques have been applied to both mouse and human preimplantation embryos and have contributed to the discovery of cell fate regulators. Here, we summarize their applications in the research of preimplantation embryos, and provide new insights and perspectives on cell fate regulation.

Unreprogrammed H3K9me3 prevents minor zygotic genome activation and lineage commitment in SCNT embryos

Somatic cell nuclear transfer (SCNT) can be used to reprogram differentiated somatic cells to a totipotent state but has poor efficiency in supporting full-term development. H3K9me3 is considered to be an epigenetic barrier to zygotic genomic activation in 2-cell SCNT embryos. However, the mechanism underlying the failure of H3K9me3 reprogramming during SCNT embryo development remains elusive. Here, we perform genome-wide profiling of H3K9me3 in cumulus cell-derived SCNT embryos. We find redundant H3K9me3 marks are closely related to defective minor zygotic genome activation. Moreover, SCNT blastocysts show severely indistinct lineage-specific H3K9me3 deposition. We identify MAX and MCRS1 as potential H3K9me3-related transcription factors and are essential for early embryogenesis. Overexpression of Max and Mcrs1 significantly benefits SCNT embryo development. Notably, MCRS1 partially rescues lineage-specific H3K9me3 allocation, and further improves the efficiency of full-term development. Importantly, our data confirm the conservation of deficient H3K9me3 differentiation in Sertoli cell-derived SCNT embryos, which may be regulated by alternative mechanisms.

Mcrs1 regulates G2/M transition and spindle assembly during mouse oocyte meiosis

Microspherule protein 1 (Mcrs1) is a component of the nonspecific lethal (NSL) complex and the chromatin remodeling INO80 complex, which participates in transcriptional regulation during mitosis. Here, we investigate the roles of Mcrs1 during female meiosis in mice. We demonstrate that Mcrs1 is a novel regulator of the meiotic G2/M transition and spindle assembly in mouse oocytes. Mcrs1 is present in the nucleus and associates with spindle poles and chromosomes of oocytes during meiosis I. Depletion of Mcrs1 alters HDAC2-mediated H4K16ac, H3K4me2, and H3K9me2 levels in nonsurrounded nucleolus (NSN)-type oocytes, and reduces CDK1 activity and cyclin B1 accumulation, leading to G2/M transition delay. Furthermore, Mcrs1 depletion results in abnormal spindle assembly due to reduced Aurora kinase (Aurka and Aurkc) and Kif2A activities, suggesting that Mcrs1 also plays a transcription-independent role in regulation of metaphase I oocytes. Taken together, our results demonstrate that the transcription factor Mcrs1 has important roles in cell cycle regulation and spindle assembly in mouse oocyte meiosis.

Species-specific molecular differentiation of embryonic inner cell mass and trophectoderm: A systematic review

A wide-ranging review study regarding the molecular characterization of the first cell lineages of the developmental embryo is lacking, especially for the primary events during earliest differentiation which leads to the determination of cellular fate. Here, a systematic review and meta-analysis were conducted according to PRISMA guidelines. MEDLINE-PubMed was searched based on an established search strategy through April 2021. Thirty-six studies fulfilling the inclusion criteria were subjected to qualitative and quantitative analysis. Among the studies, 50 % (18/36) used mice as an animal model, 22.2 % (8/36) pigs, 16.7 % (6/36) cattle, 5.5 % (2/36) humans, and 2.8 % (1/36) goats as well as 2.8 % (1/36) equine. Our results demonstrated that each of the first cell lineages of embryos requires a certain pattern of expression to establish the cellular determination of fate. Moreover, these patterns are shared by many species, particularly for those molecules that have already been identified in the literature as biomarkers. In conclusion, the present study integrated carefully chosen studies regarding embryonic development and first cellular decisions in mammalian species and summarized the information about the differential characterization of the first cell lineages and their possible relationship with specific gene expression.

The molecular characteristics and functional roles of microspherule protein 1 (MCRS1) in gene expression, cell proliferation, and organismic development

Accurate spatial and temporal regulation of cell cycle progression is essential for cell proliferation and organismic development. This review demonstrates the role of microspherule protein 58kD, commonly known as MCRS1, as a key cell cycle regulator of higher eukaryotic organisms. We discuss the isoforms and functional domains of MCRS1 as well as their subcellular localization at specific stages of the cell cycle. These molecular characteristics reveal MCRS1's dynamic regulatory role in gene expression, genome stability, cell proliferation, and organismic development. Furthermore, we discuss the molecular details of its seemingly opposite, tumor-suppressive or tumor-promoting, role in different types of cancer.

Early embryonic lethality of mice lacking POLD2

As a highly conserved DNA polymerase (Pol), Pol δ plays crucial roles in chromosomal DNA synthesis and various DNA repair pathways. However, the function of POLD2, the second small subunit of DNA Pol δ (p50 subunit), has not been characterized in vivo during mammalian development. Here, we report for the first time, the essential role of subunit POLD2 during early murine embryogenesis. Although Pold2 mutant mouse embryos exhibit normal morphology at E3.5 blastocyst stage, they cannot be recovered at gastrulation stages. Outgrowth assays reveal that mutant blastocysts cannot hatch from the zona pellucida, indicating impaired blastocyst function. Notably, these phenotypes can be recapitulated by small interfering RNA (siRNA)-mediated knockdown, which also exhibit slowed cellular proliferation together with skewed primitive endoderm and epiblast allocation during the second cell lineage specification. In summary, our study demonstrates that POLD2 is essential for the earliest steps of mammalian development, and the retarded proliferation and embryogenesis may also alter the following cell lineage specifications in the mouse blastocyst embryos.

Mcrs1 is required for branchial arch and cranial cartilage development

Mcrs1 is a multifunctional protein that is critical for many cellular processes in a wide range of cell types. Previously, we showed that Mcrs1 binds to the Six1 transcription factor and reduces the ability of the Six1-Eya1 complex to upregulate transcription, and that Mcrs1 loss-of-function leads to the expansion of several neural plate genes, reduction of neural border and pre-placodal ectoderm (PPR) genes, and pleiotropic effects on various neural crest (NC) genes. Because the affected embryonic structures give rise to several of the cranial tissues affected in Branchio-otic/Branchio-oto-renal (BOR) syndrome, herein we tested whether these gene expression changes subsequently alter the development of the proximate precursors of BOR affected structures - the otic vesicles (OV) and branchial arches (BA). We found that Mcrs1 is required for the expression of several OV genes involved in inner ear formation, patterning and otic capsule cartilage formation. Mcrs1 knockdown also reduced the expression domains of many genes expressed in the larval BA, derived from either NC or PPR, except for emx2, which was expanded. Reduced Mcrs1 also diminished the length of the expression domain of tbx1 in BA1 and BA2 and interfered with cranial NC migration from the dorsal neural tube; this subsequently resulted in defects in the morphology of lower jaw cartilages derived from BA1 and BA2, including the infrarostral, Meckel's, and ceratohyal as well as the otic capsule. These results demonstrate that Mcrs1 plays an important role in processes that lead to the formation of craniofacial cartilages and its loss results in phenotypes consistent with reduced Six1 activity associated with BOR.

MCRS1 Expression Regulates Tumor Activity and Affects Survival Probability of Patients with Gastric Cancer

Gastric cancer is the fifth most common cancer worldwide and the third most common cause of cancer-related deaths. Surgery remains the first-choice treatment. Chemotherapy is considered in the middle and advanced stages, but has limited success. Microspherule protein 1 (MCRS1, also known as MSP58) is a protein originally identified in the nucleus and cytoplasm that is involved in the cell cycle. High expression of MCRS1 increases tumor growth, invasiveness, and metastasis. The mechanistic relationships between MCSR1 and proliferation, apoptosis, angiogenesis, and epithelial–mesenchymal transition (EMT) remain to be elucidated. We clarified these relationships using immunostaining of tumor tissues and normal tissues from patients with gastric cancer. High MCRS1 expression in gastric cancer positively correlated with Ki-67, Caspase3, CD31, Fibronectin, pAKT, and pAMPK. The hazard ratio of high MCRS1 expression was 2.44 times that of low MCRS1 expression, negatively impacting patient survival.

Berberine alleviates LPS-induced apoptosis, oxidation, and skewed lineages during mouse preimplantation development†

Female infertility is a heterogeneous disorder with a variety of complex causes, including inflammation and oxidative stress, which are also closely associated with the pathogenesis of polycystic ovary syndrome (PCOS). As a new treatment for PCOS, berberine (BER), a natural compound from Berberis, has been clinically applied recently. However, the mechanisms underlying the association between BER and embryogenesis are still largely unknown. In this study, effects of BER on preimplantation development were evaluated under both normal and inflammatory culture conditions induced by lipopolysaccharide (LPS) in mice. Our data first suggest that BER itself (25 nM) does not affect embryo quality or future developmental potency; however, it can effectively alleviate LPS-induced embryo damage by mitigating apoptosis via reactive oxygen species (ROS)-/caspase-3-dependent pathways and by suppressing proinflammatory cytokines via inhibition of the NF-κB signaling pathway during preimplantation embryonic development. In addition, skewed cell lineage specification in the inner cell mass (ICM) and primitive endoderm (PE) caused by LPS can also be successfully rescued with BER. In summary, these findings for the first time demonstrate the nontoxicity of low doses of BER and its antiapoptotic and antioxidative properties on embryonic cells during mammalian preimplantation development.

Loss of RBBP4 results in defective inner cell mass, severe apoptosis, hyperacetylated histones and preimplantation lethality in mice†

Retinoblastoma-binding protein 4 (RBBP4) (also known as chromatin-remodeling factor RBAP48) is an evolutionarily conserved protein that has been involved in various biological processes. Although a variety of functions have been attributed to RBBP4 in vitro, mammalian RBBP4 has not been studied in vivo. Here we report that RBBP4 is essential during early mouse embryo development. Although Rbbp4 mutant embryos exhibit normal morphology at E3.5 blastocyst stage, they cannot be recovered at E7.5 early post-gastrulation stage, suggesting an implantation failure. Outgrowth (OG) assays reveal that mutant blastocysts cannot hatch from the zona or can hatch but then arrest without further development. We find that while there is no change in proliferation or levels of reactive oxygen species, both apoptosis and histone acetylation are significantly increased in mutant blastocysts. Analysis of lineage specification reveals that while the trophoblast is properly specified, both epiblast and primitive endoderm lineages are compromised with severe reductions in cell number and/or specification. In summary, these findings demonstrate the essential role of RBBP4 during early mammalian embryogenesis.

Functional roles of the chromatin remodeler SMARCA5 in mouse and bovine preimplantation embryos†

Upon fertilization, extensive chromatin reprogramming occurs during preimplantation development. Growing evidence reveals species-dependent regulations of this process in mammals. ATP-dependent chromatin remodeling factor SMARCA5 (also known as SNF2H) is required for peri-implantation development in mice. However, the specific functional role of SMARCA5 in preimplantation development and if it is conserved among species remain unclear. Herein, comparative analysis of public RNA-seq datasets reveals that SMARCA5 is universally expressed during oocyte maturation and preimplantation development in mice, cattle, humans, and pigs with species-specific patterns. Immunostaining analysis further describes the temporal and spatial changes of SMARCA5 in both mouse and bovine models. siRNA-mediated SMARCA5 depletion reduces the developmental capability and compromises the specification and differentiation of inner cell mass in mouse preimplantation embryos. Indeed, OCT4 is not restricted into the inner cell mass and the formation of epiblast and primitive endoderm disturbed with reduced NANOG and SOX17 in SMARCA5-deficient blastocysts. RNA-seq analysis shows SMARCA5 depletion causes limited effects on the transcriptomics at the morula stage, however, dysregulates 402 genes, including genes involved in transcription regulation and cell proliferation at the blastocyst stage in mice. By comparison, SMARCA5 depletion does not affect the development through the blastocyst stage but significantly compromises the blastocyst quality in cattle. Primitive endoderm formation is greatly disrupted with reduced GATA6 in bovine blastocysts. Overall, our studies demonstrate the importance of SMARCA5 in fostering the preimplantation development in mice and cattle while there are species-specific effects.

Genetic causes of preimplantation embryo developmental failure

Embryo development requires orchestrated events, finely regulated at the molecular and cellular level by mechanisms which are progressively emerging from animal studies. With progress in genetic technologies-such as genome editing and single-cell RNA analysis-we can now assess embryo gene expression with increased precision and gain new insights into complex processes until recently difficult to explore. Multiple genes and regulative pathways have been identified for each developmental stage. We have learned that embryos with undisturbed and timely gene expression have higher chances of successful development. For example, selected genes are highly expressed during the first stages, being involved in cell adhesion, cell cycle, and regulation of transcription; other genes are instead crucial for lineage specification and therefore expressed at later stages. Due to ethical constraints, studies on human embryos remain scarce, mainly descriptive, and unable to provide functional evidence. This highlights the importance of animal studies as basic knowledge to test and appraise in a clinical context. In this review, we report on preimplantation development with a focus on genes whose impairment leads to developmental arrest. Preconceptional genetic screening could identify loss-of-function mutations of these genes; thereby, novel biomarkers of embryo quality could be adopted to improve diagnosis and treatment of infertility.

Epithelial-Mesenchymal Transition Drives Three-Dimensional Morphogenesis in Mammalian Early Development

From fertilization to onset of gastrulation, a mammalian embryo goes through several rounds of cellular morphogenesis resembling phenomena of epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), collectively referred to as EMTs. How these EMT events play a role in shaping the three-dimensional (3-D) architecture of the developing embryo is not well-understood. In this review, we present a model in which cellular morphogenesis, represented primarily by dynamic changes in its epithelialization status, is the driving force of embryonic 3-D organization. This is achieved through the integration of three key components of mammalian early development, the pluripotency regulation, morphogenetic signaling, and biomechanical force anisotropy. Although cells in an early embryo do not exhibit full mesenchymal characteristics, our model underscores the importance of investigating molecular regulation of epithelial cell polarity and partial EMT/MET in understanding mammalian early development.

ZC3H4-a novel Cys-Cys-Cys-His-type zinc finger protein-is essential for early embryogenesis in mice†

Zinc finger domains of the Cys-Cys-Cys-His (CCCH) class are evolutionarily conserved proteins that bind nucleic acids and are involved in various biological processes. Nearly 60 CCCH-type zinc finger proteins have been identified in humans and mice, most have not been functionally characterized. Here, we provide the first in vivo functional characterization of ZC3H4-a novel CCCH-type zinc finger protein. Our results show that although Zc3h4 mutant embryos exhibit normal morphology at E3.5 blastocyst stage, they cannot be recovered at E7.5 early post-gastrulation stage, suggesting implantation failure. Outgrowth assays reveal that mutant blastocysts either fail to hatch from the zona pellucida, or can hatch but do not form a typical inner cell mass colony, the source of embryonic stem cells (ESCs). Although there is no change in levels of reactive oxygen species, Zc3h4 mutants display severe DNA breaks and reduced cell proliferation. Analysis of lineage specification reveals that both epiblast and primitive endoderm lineages are compromised with severe reductions in cell number and/or specification in the mutant blastocysts. In summary, these findings demonstrate the essential role of ZC3H4 during early mammalian embryogenesis.

Mcrs1 interacts with Six1 to influence early craniofacial and otic development

The Six1 transcription factor plays a major role in craniofacial development. Mutations in SIX1 and its co-factor, EYA1, are causative for about 50% of Branchio-otic/Branchio-oto-renal syndrome (BOR) patients, who are characterized by variable craniofacial, otic and renal malformations. We previously screened for other proteins that might interact with Six1 to identify additional genes that may play a role in BOR, and herein characterize the developmental role of one of them, Microspherule protein 1 (Mcrs1). We found that in cultured cells, Mcrs1 bound to Six1 and in both cultured cells and embryonic ectoderm reduced Six1-Eya1 transcriptional activation. Knock-down of Mcrs1 in embryos caused an expansion of the domains of neural plate genes and two genes expressed in both the neural plate and neural crest (zic1, zic2). In contrast, two other genes expressed in pre-migratory neural crest (foxd3, sox9) were primarily reduced. Cranial placode genes showed a mixture of expanded and diminished expression domains. At larval stages, loss of Mcrs1 resulted in a significant reduction of otic vesicle gene expression concomitant with a smaller otic vesicle volume. Experimentally increasing Mcrs1 above endogenous levels favored the expansion of neural border and neural crest gene domains over cranial placode genes; it also reduced otic vesicle gene expression but not otic vesicle volume. Co-expression of Mcrs1 and Six1 as well as double knock-down and rescue experiments establish a functional interaction between Mcrs1 and Six1 in the embryo, and demonstrate that this interaction has an important role in the development of craniofacial tissues including the otic vesicle.

Advantages of the outgrowth model for evaluating the implantation competence of blastocysts

The implantation process is highly complex and difficult to mimic in vitro, and a reliable experimental model of implantation has yet to be established. Many researchers have used embryo transfer (ET) to assess implantation potential; however, ET with pseudopregnant mice requires expert surgical skills and numerous sacrificial animals. To overcome those economic and ethical problems, several researchers have tried to use outgrowth models to evaluate the implantation potential of embryos. Many previous studies, as well as our experiments, have found significant correlations between blastocyst outgrowth in vitro and implantation in utero by ET. This review proposes the blastocyst outgrowth model as a possible alternative to animal experimentation involving ET in utero. In particular, the outgrowth model might be a cost- and time-effective alternative method to ET for evaluating the effectiveness of culture conditions or treatments. An advanced outgrowth model and further culture of outgrowth embryos could provide a subtle research model of peri- and postimplantation development, excluding maternal effects, and thereby could facilitate progress in assisted reproductive technologies. Recently, we found that outgrowth embryos secreted extracellular vesicles containing specific microRNAs. The function of microRNAs from outgrowth embryos should be elucidated in further researches.