Differences in blastomere totipotency in 2-cell mouse embryos are a maternal trait mediated by asymmetric mRNA distribution.

It is widely held that the first two blastomeres of mammalian embryos are equally totipotent and that this totipotency belongs to the group of regulative properties. However, this interpretation neglects an important aspect: evidence only came from successful monozygotic twins which can speak only for those pairs of half-embryos that are able to regulate in the first place. Are the frequently occurring incomplete pairs simply an artefact, or do they represent a real difference, be it in the imperfect blastomere's ability to regulate growth or in the distribution of any compound X that constrains regulation? Using the model system of mouse embryos bisected at the 2-cell stage after fertilization, we present evidence that the interblastomere differences evade regulation by external factors and are already latent in oocytes. Specifically, an interblastomere imbalance of epiblast production persists under the most diverse culture conditions and applies to the same extent in parthenogenetic counterparts. As a result, cases in which twin blastocysts continued to develop in only one member account for 65 and 57% of zygotic and parthenogenetic pairs, respectively. The interblastomere imbalance is related to the subcellular distribution of gene products, as documented for the epiblast-related gene Cops3, using mRNA FISH in super-resolution mode confocal microscopy. Blastomere patterns of Cops3 mRNA distribution are α-amanitin-resistant. Thus, the imbalance originates not from de novo transcription, but from influences which are effective before fertilisation. These data expose previously unrecognized limits of regulative capacities of 2-cell stage blastomeres and point to aspects of cytoplasmic organization of the mouse oocyte that segregate unequally to blastomeres during cleavage.

Retrospective analysis: reproducibility of interblastomere differences of mRNA expression in 2-cell stage mouse embryos is remarkably poor due to combinatorial mechanisms of blastomere diversification.

STUDY QUESTION: What is the prevalence, reproducibility and biological significance of transcriptomic differences between sister blastomeres of the mouse 2-cell embryo? SUMMARY ANSWER: Sister 2-cell stage blastomeres are distinguishable from each other by mRNA analysis, attesting to the fact that differentiation starts mostly early in the mouse embryo; however, the interblastomere differences are poorly reproducible and invoke the combinatorial effects of known and new mechanisms of blastomere diversification. WHAT IS KNOWN ALREADY: Transcriptomic datasets for single blastomeres in mice have been available for years but have never been systematically analysed together, although such an analysis may shed light onto some unclarified topics of early mammalian development. Two unknowns that remain are at which stage embryonic blastomeres start to diversify from each other and what is the molecular origin of that difference. At the earliest postzygotic stage, the 2-cell stage, opinions differ regarding the answer to these questions; one group claims that the first zygotic division yields two equal blastomeres capable of forming a full organism (totipotency) and another group claims evidence for interblastomere differences reminiscent of the prepatterning found in embryos of lower taxa. Regarding the molecular origin of interblastomere differences, there are four prevalent models which invoke (1) oocyte anisotropy, (2) sperm entry point, (3) partition errors of the transcript pool and (4) asynchronous embryonic genome activation in the two blastomeres. STUDY DESIGN, SIZE, DURATION: Seven transcriptomic studies published between 2011 and 2017 were eligible for retrospective analysis, since both blastomeres of the mouse 2-cell embryo had been analysed individually regarding the original pair associations and since the datasets were made available in public repositories. Five of these studies, encompassing a total of 43 pairs of sister blastomeres, were selected for further analyses based on high interblastomere correlations of mRNA levels. A double cut-off was used to select mRNAs that had robust interblastomere differences both within and between embryos (hits). The hits of each study were compared and contrasted with the hits of the other studies using Venn diagrams. The hits shared by at least four of five studies were analysed further by bioinformatics. PARTICIPANTS/MATERIALS, SETTING, METHODS: PubMed was systematically examined for mRNA expression profiles of single 2-cell stage blastomeres in addition to publicly available microarray datasets (GEO, ArrayExpress). Based on the original normalizations, data from seven studies were screened for pairwise sample correlation at the gene level (Spearman), and the top five datasets with the highest correlation were subjected to hierarchical cluster analysis. Interblastomere differences of gene expression were expressed as a ratio of the higher to the lower mRNA level for each pair of blastomeres. A double cut-off was used to make the call of interblastomere difference, accepting genes with mRNA ratios above 2 when observed in at least 50% of the pairs, and discarding the other genes. The proportion of interblastomere differences common to at least four of the five datasets was calculated. Finally, the corresponding gene, pathway and enrichment analyses were performed utilizing PANTHER and GORILLA platforms. MAIN RESULTS AND THE ROLE OF CHANCE: An average of 17% of genes within the datasets are differently expressed between sister blastomeres, a proportion which falls to 1% when considering the differences that are common to at least four of the five studies. Housekeeping mRNAs were not included in the 17% and 1% gene lists, suggesting that the interblastomere differences do not occur simply by chance. The 1% of shared interblastomere differences comprise 100 genes, of which 35 are consistent with at least one of the four prevalent models of sister blastomere diversification. Bioinformatics analysis of the remaining 65 genes that are not consistent with the four models suggests that at least one more mechanism is at play, potentially related to the endomembrane system. Although there are many dimensions to the issue of reproducibility (biological, experimental, analytical), we consider that the sister blastomeres are poised to escape high interblastomere correlations of mRNA levels, because at least five sources of diversity superimpose on each other, accounting for at least 25 = 32 different states. As a result, interblastomere mRNA differences of a given 2-cell embryo are necessarily difficult to reproduce in another 2-cell embryo. LARGE SCALE DATA: Data were as provided by the original studies (GSE21688, GSE22182, GSE27396, GSE45719, GSE57249, E-MTAB-3321, GSE94050). LIMITATIONS, REASONS FOR CAUTION: The original studies present similarities (e.g. fertilization in vivo after ovarian stimulation) as well as differences (e.g. mouse strains, method and timing of blastomere separation). We identified robust mRNA differences between the sister blastomeres, but these differences are underestimated because our double cut-off method works with thresholds and affords more protection against false positives than false negatives. Regarding the false negatives, transcriptome analysis may have captured only part of the interblastomere differences due to: (1) the 2-fold cut-off not being sensitive enough to detect the remaining part of the interblastomere differences, (2) the detection limit of the transcriptomic methods not being sufficient, or (3) interblastomere differences being oblivious to transcriptomic identification because transcriptional changes are oscillatory or because differences are mediated non-transcriptionally or post-transcriptionally. Regarding the false positives, it seems unlikely that a difference was found just by chance for the same group of transcripts due to the same technical error, given that different laboratories produced the data. WIDER IMPLICATIONS OF THE FINDINGS: It is clear that the sister blastomeres are distinguishable from each other by mRNA analysis even at the 2-cell stage; however, efforts to identify large stable patterns may be in vain. This elicits thoughts about the wisdom of adding new transcriptomic datasets to the ones that already exist; if all transcriptomic datasets produced so far show a reproducibility of 1%, then any future study would probably face the same issue again. Possibly, a solid identification of the 'large stable pattern that should be there but was not found' requires an even larger dataset than the sum of the seven datasets considered here. Conversely, small stable patterns may be easier to identify, but their biological relevance is less obvious. Alternatively, interblastomere differences may not be mediated by nucleic acids but by other cellular components. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the Deutsche Forschungsgemeinschaft (grant DFG BO 2540-4-3 to M.B. and grant NO 413/3-3 to V.N.). The authors declare that they have no competing financial interests.

Totipotency segregates between the sister blastomeres of two-cell stage mouse embryos.

Following fertilization in mammals, it is generally accepted that totipotent cells are exclusive to the zygote and to each of the two blastomeres originating from the first mitotic division. This model of totipotency was inferred from a minority of cases in which blastomeres produced monozygotic twins in mice. Was this due to experimental limitation or biological constraint? Here we removed experimental obstacles and achieved reliable quantification of the prevalence of dual totipotency among mouse two-cell stage blastomeres. We separated the blastomeres of 1,252 two-cell embryos, preserving 1,210 of the pairs. Two classes of monozygotic twins became apparent at the blastocyst stage: 27% formed a functional epiblast in both members (concordant), and 73% did so in only one member of the pair (discordant) - a partition that proved insensitive to oocyte quality, sperm-entry point, culture environment and pattern of cleavage. In intact two-cell embryos, the ability of sister blastomeres to generate epiblast was also skewed. Class discovery clustering of the individual blastomeres' and blastocysts' transcriptomes points to an innate origin of concordance and discordance rather than developmental acquisition. Our data place constraints on the commonly accepted idea that totipotency is allocated equally between the two-cell stage blastomeres in mice.

Treatment strategies for severe oligoasthenoteratozoospermia (OAT) (<0.1 million/mL) patients.

Intracytoplasmic sperm injection (ICSI) using spermatozoa from patients with severe oligoasthenoteratozoospermia is still a challenge. Although spermatozoa are available, lower fertilisation rates as well as compromised pregnancy rates are observed after ICSI. We aimed at identifying respective parameters in the pre-values of ejaculate samples used for couple counselling. The clinical pre-values of 121 patients and their corresponding 228 ICSI cycles performed between 2002 and 2010 were retrospectively analysed. Patients were divided into three groups: (i) group 1 (G1, n = 51) where all patients showed at least once <0.1 million/mL and ICSI was performed using ejaculate alone; (ii) group 2 (G2, n = 14) patients had once <0.1 Mill/mL or azoospermia and a testicular biopsy before start of ICSI; (iii) group 3 (G3, n = 56) patients were azoospermic and directed immediately to testicular sperm extraction (TESE). The pre-values of G2 differed significantly from G1 in terms of volume and motility. Lutenizing hormone (LH) and follicle-stimulating hormone (FSH) values were equal in G1 and G2, but showed significant differences in comparison to G3. Testis volume was significantly higher in G3. In the corresponding ICSI cycles, the percentage of cancelled embryo transfers was highest in G3. We did not find any correlations of hormonal markers or sperm pre-values with the success rates of ICSI. In our patient cohort, spermatozoa retrieved either from ejaculate or testicular biopsies have nearly identical chances in achieving pregnancies. Patients in need of TESE before ICSI have significantly lower sperm counts. However, it is not possible to calculate threshold values as indicator for TESE.

How to select immotile but viable spermatozoa on the day of intracytoplasmic sperm injection? An embryologist's view.

A viable spermatozoon is the prerequisite for initiating fertilization in intracytoplasmic sperm injection. Usually motility is the primary sign used to determine a sperm's viability. However, in every in vitro fertilization (IVF) laboratory cases are observed in which none or only few spermatozoa are motile. This can occur in treatment cycles involving ejaculated samples but is most common in cases where surgically extracted testicular spermatozoa are used. To aid in selection, several techniques have been developed to identify viable spermatozoa from the immotile fraction. Amongst the more commonly used approaches are (i) the hypo-osmotic swelling test (ii) chemical substances for induction of tail movements (iii) the sperm tail flexibility test and (iv) laser-assisted immotile sperm selection. All can be used routinely in an IVF laboratory with each having both strengths and weaknesses. It is the purpose of this short review to focus on the technical issues involved in the performance of each of these techniques and to highlight the advantages and disadvantages of each approach.

MicroRNA miR-513a-3p acts as a co-regulator of luteinizing hormone/chorionic gonadotropin receptor gene expression in human granulosa cells.

The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is essential for normal male and female reproductive processes. The spatial and temporal LHCGR gene expression is controlled by a complex system of regulatory mechanisms which are crucial for normal physiological function, especially during the female cycle. In this study, we aimed to elucidate whether microRNAs are involved in this network and play a role in regulating LHCGR expression. Computational analysis predicted that miR-513a-3p interacts with the LHCGR mRNA via three binding sites located in the 3'UTR region, enabling a synergistic action. Moreover, using a luciferase-based reporter assay we found that miR-513a-3p targets the LHCGR, resulting in a significant down-regulation of its expression. In human primary granulosa cell cultures we detected a dynamic, inversely associated expression pattern of miR-513a-3p and the LHCGR. In addition, transfection with miR-513a-3p or its specific inhibitor led to a down- or up-regulation at the LHCGR mRNA level, respectively. An increased amount of miR-513a-3p resulted in the down-regulation of the LHCGR mRNA, reflected by the attenuation of cAMP synthesis after hormonal stimulation. In conclusion, these data demonstrate that miR-513a-3p is involved in the control of the LHCGR expression by an inversely regulated mechanism at the post-transcriptional level and show for the first time that this kind of post-transcriptional process contributes to the multifaceted system of the human LHCGR regulation.

Optimizing TESE-ICSI by laser-assisted selection of immotile spermatozoa and polarization microscopy for selection of oocytes.

For most azoospermic men testicular sperm extraction (TESE) is the only treatment, however it presents challenges for the ART laboratory, as the retrieval of motile spermatozoa is difficult. In the absence of sperm movement no unequivocal distinction can be made between either dead or immotile, but vital spermatozoa. However, a single laser shot directed to the tip of the tail allows recognition of viability because the flagellum coils at the area of impact. To rank the quality and the maturity of oocytes, polarization microscopy can be used. The zona score and the visualization of the meiotic spindle correlate with implantation and pregnancy rates. We compared 65 TESE-ICSI cycles of the years 2007 and 2008 (Group 1, G1) with 58 TESE-ICSI cycles of the years 2009 and 2010 (Group 2, G2). Testicular spermatozoa were injected according to motility and morphology into selected oocytes. In G1 both, oocyte and spermatozoa were rated using light microscopy only, whereas in G2 the laser was used for sperm selection and the oocytes were rated by light and polarization microscopy. In G2 we enhanced our fertilization rate (FR) significantly in comparison to G1 (G1 42.1% vs. G2 52.7%, p < 0.001). The fertilization rate with immotile, but vital spermatozoa improved significantly when applying laser-based selection (p = 0.006). The laser selection of immotile spermatozoa and the use of polarization microscopy can enhance the FR of TESE-ICSI. No negative effect of the laser was seen on birth rates. The FR with immotile, but vital spermatozoa clearly benefits from laser selection and is a non-hazardous and safe method for the selection of viable but immotile sperm. To our knowledge this is the first report using new technology creating novel endpoints for the analysis of spermatozoa and oocytes in TESE-ICSI.

Coiled sperm from infertile patients: characteristics, associated factors and biological implication.

BACKGROUND: There is no systematic study on coiled sperm in semen, although they are commonly observed. This work characterizes coiled sperm in infertile men to understand the clinical implications and investigate the possible cause by osmotic swelling. METHODS: Coiled sperm in semen from 439 infertile patients were quantified and their ultrastructure examined by electron microscopy. Hypo-osmotic swelling (HOS) and demembranation tests were performed to elucidate the nature of the coiling. RESULTS: Semen from patients contained overall 3% of sperm with head-in-coil (HIC) and 8% other coiled forms, with 12% of patients having 20% or more such sperm. The percentage of coiled sperm (but not HIC) was correlated with age (R = 0.26, P = 0.003) and the epididymal secretory marker neutral alpha-glucosidase (R = 0.16, P < 0.001), and associated with heavy smoking and varicocele. Electron microscopy revealed coiling of tail filaments within the plasma membrane, resembling HOS. Some seminal coiled sperm and most sperm freshly coiled upon HOS could be opened by demembranation, while those that could not be opened were probably fixed in position by oxidation, which occurred more frequently in patients than semen donors. CONCLUSIONS: Sperm coiling in semen is common and independent of sperm quantity or hormonal status. Whereas HIC may have a genetic background, other coiled forms may be associated with a hostile endogenous milieu in the epididymis that causes swelling.

Comparative analysis of human, bovine, and murine Oct-4 upstream promoter sequences.

The Oct-4 gene encodes a transcription factor that is specifically expressed in embryonic stem cells and germ cells of the mouse embryo. Cells that differentiate into somatic tissues lose Oct-4 expression. Regulation of Oct-4 gene transcription involves a TATA-less minimal promoter and two upstream elements: the proximal (PE) and distal enhancers (DE). We report here the nucleotide sequence of the 5' upstream regulatory regions of the human and murine Oct-4 genes. A comparative alignment analysis between these regions and those of the bovine Oct-4 ortholog reveals four conserved regions of homology (CR 1 to 4) between these species (66-94% conservation). The 1A sequence within the mouse PE is located approximately half-way between CR 2 and CR 3. A putative Sp1/Sp3 binding site and the overlapping hormone responsive element (HRE) in CR1 are identical in all three species. A high number of CCC(A/T)CCC motifs exhibit various levels of homology in these upstream regions. We discuss the importance of these and other sequences and present candidate factors that may bind and regulate Oct-4 gene expression.

Constitutively active mutations of G protein-coupled receptors: the case of the human luteinizing hormone and follicle-stimulating hormone receptors.

Activating mutations of the luteinizing hormone receptor (LHR) and the follicle-stimulating hormone receptor (FSHR) have been known for several years. These activating mutations permanently stimulate, in the absence of their cognate ligand, the receptor signaling pathways. In the case of the LHR, the induced chronic stimulation causes sporadic and familial pseudoprecocious puberty, a phenotype observed only in males. The absence of a female phenotype is probably due to the requirement for FSH in the induction of LHR expression. For the FSHR, one activating mutation was found in a patient with normal spermatogenesis without detectable gonadotropins. Whether activating mutations of the gonadotropin receptors are involved in tumor development is not yet clear. Activating mutations of the FSHR were supposedly involved but not found in ovarian tumors. For the LHR, only one patient with a seminoma and an activating mutation was described. The different occurrence of activating mutations of the LHR compared to the FSHR is surprising, since the two genes are adjacently located on chromosome 2 and should therefore be affected by a similar mutation rate. It might well be that mutations occur with the same frequency, but that activating mutations of the FSHR do not result in any particular phenotype.

A mutation in the first transmembrane domain of the lutropin receptor causes male precocious puberty.

We describe a patient with onset of puberty at the age of 5 yr. characterized by accelerated growth, enlargement of genitalia, pubarche, and serum hormone levels compatible with noncentral precocious puberty. Exon 11 of the LH receptor gene was amplified from genomic DNA by PCR and directly sequenced. We identified a heterozygous C to T base change at nucleotide position 1126, exchanging codon 373 from Ala to Val in the first transmembrane domain. The LH receptor sequence of the parents was normal. The mutated receptor displayed an up to 7.5-fold increase in basal cAMP production compared to that of the wild-type receptor in transiently transfected COS-7 cells. Treatment of the patient with ketoconazole resulted in inconsistent suppression of serum testosterone levels. At the age of 9.1 yr, central activation of the hypothalamic-pituitary-gonadal axis occurred. Additional treatment with a GnRH agonist led to complete suppression of testosterone secretion. This is the first description of constitutive activation of the LH receptor in the first transmembrane segment. It suggests the involvement of the first transmembrane helix in signal transduction and provides further insight into the structural organization of the seven transmembrane domains of the glycoprotein hormone receptor proteins.

Expression of the gene for the retinal protein peripherin in the pineal gland of humans and Djungarian hamsters (Phodopus sungorus).

This study investigated whether the gene for peripherin, a protein previously considered to play only a role in the retina, may also be expressed in the pineal gland of both Djungarian hamsters (Phodopus sungorus) and humans. After extraction of mRNA from pooled pineal glands of hamsters and from one human pineal gland, mRNA was transcribed into cDNA followed by PCR amplification with specific primers. Clear signals were obtained at the expected sizes of the PCR products. An additional experiment in hamsters revealed that the peripherin gene is expressed throughout the entire 24-h period. Since peripherin is an important protein in the retina stabilizing the photoreceptor discs it is speculated that this protein might also play a structural role in the pineal gland.

Functional and clinical consequences of mutations in the FSH receptor.

The follicle-stimulating hormone (FSH) is essential for normal gametogenesis. In females FSH is required for ovarian development and follicle maturation whereas in males FSH determines Sertoli cell number and quantitatively and qualitatively normal spermatogenesis. FSH action is mediated by a G-protein coupled receptor expressed solely in granulosa and Sertoli cells. The FSH-receptor (FSHR) gene is localized on chromosome 2 p21 and spans a region of 54 kb. It consists of ten exons; exon one to nine encode the large extracellular domain and the transmembrane domain is comprised of exon ten. Mutations in the FSHR gene could severely affect gametogenesis and result in infertility. Therefore screening programs have been initiated, in which patients with disturbed fertility were searched for mutations in the FSHR gene. Several Finnish families were identified displaying an inherited pattern of ovarian dysgenesis, a disease leading to streaky underdeveloped ovaries and primary amenorrhea. By genetic linkage the locus of the genetic defect was confined to chromosome 2 p21. Analysis of the FSHR gene resulted in the identification of a mutation (Ala189Val) homozygous in all affected females. Functional studies revealed that the mutation affects the proper protein folding and thereby inactivates the receptor. In a male patient hypophysectomized because of a pituitary tumor, who despite undetectable serum gonadotropins had normal semen parameters, we hypothesized an activating mutation of the FSHR. Screening of exon ten of the FSHR gene resulted in the identification of a Asp567Gly transition in the third intracytoplasmatic loop. Functional studies resulted in a 1.5-fold increase in basal cAMP production compared to wild type FSHR, indicating that the heterozygous mutation leads to a ligand-independent constitutive activation of the FSHR. This patient provides an exceptional model of nature defining the role of FSH in human spermatogenesis. Mutations of the FSHR might have differential effects in each gender. For example activating mutations have not been described in women, therefore it is not clear whether the constitutive activity of the receptor could disturb normal follicular development resulting in certain infertility.

Larval and imaginal pathways in early development of Drosophila.

In holometabolous development, higher insects have two different life forms, the larva and the imago. Both larval and imaginal cells are derived from cells of the blastoderm stage. After the final embryonic wave of mitosis, however, only the imaginal cells remain diploid, proliferate massively and do not differentiate until metamorphosis. The separation of these two pathways was described by many authors as a fundamental process that must take place at a very early stage of development, most probably the blastoderm stage. Mainly by using single cell transplantations at the blastoderm or early gastrula stages, respectively, we found common cell lineages between larval and imaginal structures by clones overlapping in the ectoderm (i.e. larval epidermal cells and imaginal discs within a segment, or larval and imaginal salivary gland cells), the mesoderm (i.e. larval somatic muscles and adepithelial cells), and the endoderm (i.e. larval and imaginal midgut cells). From these findings we conclude that it seems to be a principle in Drosophila embryogenesis that the separation of larval and imaginal pathways is postponed to a later developmental stage.