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Mitinori Saitou

Publications and source records attributed to Mitinori Saitou.

13 recordsLinked to original sources
PubMed2006

Blimp1 defines a progenitor population that governs cellular input to the sebaceous gland.

Epidermal lineage commitment occurs when multipotent stem cells are specified to three lineages: the epidermis, the hair follicle, and the sebaceous gland (SG). How and when a lineage becomes specified remains unknown. Here, we report the existence of a population of unipotent progenitor cells that reside in the SG and express the transcriptional repressor Blimp1. Using cell-culture studies and genetic lineage tracing, we demonstrate that Blimp1-expressing cells are upstream from other cells of the SG lineage. Blimp1 appears to govern cellular input into the gland since its loss leads to elevated c-myc expression, augmented cell proliferation, and SG hyperplasia. Finally, BrdU labeling experiments demonstrate that the SG defects associated with loss of Blimp1 lead to enhanced bulge stem cell activity, suggesting that when normal SG homeostasis is perturbed, multipotent stem cells in the bulge can be mobilized to correct this imbalance.

Animals↗
PubMed2006

Gene expression dynamics during germline specification in mice identified by quantitative single-cell gene expression profiling.

Germ cell fate in mice is induced in proximal epiblast cells at Embryonic Day (E) 6.5 by signaling molecules. Prdm1(also known as Blimp1)-positive lineage-restricted precursors of primordial germ cells (PGCs) initiate the formation of a cluster that differentiates into Dppa3 (also known as stella)-positive PGCs from around E7.0 onwards in the extra-embryonic mesoderm. Around E7.5, these PGCs begin migrating towards the definitive endoderm, with concomitant extensive epigenetic reprogramming. To gain a more precise insight into the mechanism of PGC specification and its subsequent development, we exploited quantitative, single-cell, gene expression profiling to explore gene expression dynamics during the 36 h of PGC differentiation from E6.75 to E8.25, in comparison with the corresponding profiles of somatic neighbors. This analysis revealed that the transitions from Prdm1-positive PGC precursors to Dppa3-positive PGCs and to more advanced migrating PGCs involve a highly dynamic, stage-dependent transcriptional orchestration that begins with the regaining of the pluripotency-associated gene network, followed by stepwise activation of PGC-specific genes, differential repression of the somatic mesodermal program, as well as potential modulations of signal transduction capacities and unique control of epigenetic regulators. The information presented here regarding the cascade of events involved in PGC development should serve as a basis for detailed functional analyses of the gene products associated with this process, as well as for appropriate reconstitution of PGCs and their descendant cells in culture.

Animals↗
PubMed2006

An improved single-cell cDNA amplification method for efficient high-density oligonucleotide microarray analysis.

A systems-level understanding of a small but essential population of cells in development or adulthood (e.g. somatic stem cells) requires accurate quantitative monitoring of genome-wide gene expression, ideally from single cells. We report here a strategy to globally amplify mRNAs from single cells for highly quantitative high-density oligonucleotide microarray analysis that combines a small number of directional PCR cycles with subsequent linear amplification. Using this strategy, both the representation of gene expression profiles and reproducibility between individual experiments are unambiguously improved from the original method, along with high coverage and accuracy. The immediate application of this method to single cells in the undifferentiated inner cell masses of mouse blastocysts at embryonic day (E) 3.5 revealed the presence of two populations of cells, one with primitive endoderm (PE) expression and the other with pluripotent epiblast-like gene expression. The genes expressed differentially between these two populations were well preserved in morphologically differentiated PE and epiblast in the embryos one day later (E4.5), demonstrating that the method successfully detects subtle but essential differences in gene expression at the single-cell level among seemingly homogeneous cell populations. This study provides a strategy to analyze biophysical events in medicine as well as in neural, stem cell and developmental biology, where small numbers of distinctive or diseased cells play critical roles.

Animals↗
PubMed2006

Generation of stella-GFP transgenic mice: a novel tool to study germ cell development.

The relationship between germ cells and pluripotent embryonic stem (ES) cells is of particular interest, together with approaches to generate primordial germ cell (PGCs) from ES cells. A critical requirement in these experiments is the ability to unambiguously detect PGCs with the use of, for example, reporter genes. The currently available transgenic reporters do not show exclusive expression in PGCs at their earliest developmental stages. Here we describe the use of germline-restricted expression of stella, which is currently the best marker gene for PGCs. We generated two stella-GFP reporters and show that both transgenes surpass other reporters in terms of timing and specificity of expression in PGCs. Additionally, we demonstrate the usefulness of stella-GFP during the derivation of PGCs from ES cells.

Animals↗
PubMed2005

Blimp1 and the emergence of the germ line during development in the mouse.

To elucidate the mechanism for the specification of primordial germ cells (PGCs) in mice, we have developed and exploited the methods of single cell analysis. Based on these studies, we proposed a molecular program associated with this process, a key event of which is the repression of homeobox genes that are, without exception, upregulated in somatic neighbors. We have now identified Blimp1, a potent transcriptional repressor of a histone methyltransferase subfamily, as a key regulator of PGC specification. Indeed, the unexpected early onset of Blimp1 expression in a few cells at the most proximal-posterior epiblast cells marks the origin of the germ cell lineage. Disruption of Blimp1 function resulted in aberrant PGC-like cells with a deregulated intrinsic gene expression program at a very early stage, which demonstrates that Blimp1 is a critical determinant of the germ line in mice.

Animals↗
PubMed2005

Analysis of Esg1 expression in pluripotent cells and the germline reveals similarities with Oct4 and Sox2 and differences between human pluripotent cell lines.

Establishment of pluripotent epiblast cells is a critical event during early mammalian development because all somatic lineages and the primordial germ cells (PGCs) are derived from them. The epiblast and PGCs are in turn the precursors of pluripotent embryonic stem cells and embryonic germ cells, respectively. Although PGCs are specialized cells, they express several key pluripotency-related genes, such as Oct4 and Sox2. We have analyzed Esg1 expression in mouse and human cells and shown that in the mouse the gene is specifically expressed in preimplantation embryos, stem cells, and the germline. Moreover, Esg1 coexpresses with Oct4 and Sox2, confirming its identity as a marker of the pluripotent cycle. Esg1 is also expressed with Oct4 and Sox2 by human embryonic stem cells and in germ cell carcinoma tissue but not by all human embryonal carcinoma cell lines. These data suggest that together with Oct4 and Sox2, Esg1 plays a conserved role in the pluripotent pathway of mouse and human stem and germ cells.

Animals↗
PubMed2005

Blimp1 is a critical determinant of the germ cell lineage in mice.

Germ cell fate in mice is induced in pluripotent epiblast cells in response to signals from extraembryonic tissues. The specification of approximately 40 founder primordial germ cells and their segregation from somatic neighbours are important events in early development. We have proposed that a critical event during this specification includes repression of a somatic programme that is adopted by neighbouring cells. Here we show that Blimp1 (also known as Prdm1), a known transcriptional repressor, has a critical role in the foundation of the mouse germ cell lineage, as its disruption causes a block early in the process of primordial germ cell formation. Blimp1-deficient mutant embryos form a tight cluster of about 20 primordial germ cell-like cells, which fail to show the characteristic migration, proliferation and consistent repression of homeobox genes that normally accompany specification of primordial germ cells. Furthermore, our genetic lineage-tracing experiments indicate that the Blimp1-positive cells originating from the proximal posterior epiblast cells are indeed the lineage-restricted primordial germ cell precursors.

Animals↗
PubMed2005

Extensive and orderly reprogramming of genome-wide chromatin modifications associated with specification and early development of germ cells in mice.

Induction of mouse germ cells occurs from the proximal epiblast at around embryonic day (E) 7.0. These germ cells then migrate to, and enter the gonads at about E10.5 after which they undergo epigenetic reprogramming including erasure of parental imprints. However, the epigenetic properties acquired by nascent germ cells and the potential remodeling of these epigenetic marks in the subsequent migratory period have been largely unexplored. Here we have used immunohistochemistry to examine several genome-wide epigenetic modifications occurring in germ cells from their specification to their colonization of the genital ridges. We show that at around E8.0, germ cells concomitantly and significantly reduce H3-K9 dimethylation and DNA methylation, two major repressive modifications for gene expression. These events are preceded by the transient loss of all the DNA methyltransferases from their nuclei. By contrast, germ cells substantially increase the levels of H3-K27 trimethylation, another repressive modification with more plasticity, at E8.5-9.0 and maintain this state until at least E12.5. H3-K4 methylation and H3-K9 acetylation, modifications associated with transcriptionally permissive/active chromatin, are similar in germ and surrounding somatic cells but germ cells transiently increase these marks sharply upon their entry into the genital ridge. H3-K9 trimethylation, a hallmark of centromeric heterochromatin, is kept relatively constant during the periods examined. We suggest that this orderly and extensive epigenetic reprogramming in premigratory and migratory germ cells might be necessary for their reacquisition of underlying totipotency, for subsequent specific epigenetic remodeling, including the resetting of parental imprints, and for the production of gametes with an appropriate epigenotype for supporting normal development.

Animals↗
PubMed2003

Stella is a maternal effect gene required for normal early development in mice.

stella is a novel gene specifically expressed in primordial germ cells, oocytes, preimplantation embryos, and pluripotent cells. It encodes a protein with a SAP-like domain and a splicing factor motif-like structure, suggesting possible roles in chromosomal organization or RNA processing. Here, we have investigated the effects of a targeted mutation of stella in mice. We show that while matings between heterozygous animals resulted in the birth of apparently normal stella null offspring, stella-deficient females displayed severely reduced fertility due to a lack of maternally inherited Stella-protein in their oocytes. Indeed, we demonstrate that embryos without Stella are compromised in preimplantation development and rarely reach the blastocyst stage. stella is thus one of few known mammalian maternal effect genes, as the phenotypic effect on embryonic development is mainly a consequence of the maternal stella mutant genotype. Furthermore, we show that STELLA that is expressed in human oocytes is also expressed in human pluripotent cells and in germ cell tumors. Interestingly, human chromosome 12p, which harbours STELLA, is consistently overrepresented in these tumors. These findings suggest a similar role for STELLA during early human development as in mice and a potential involvement in germ cell tumors.

Amino Acid Sequence↗
PubMed2003

Specification of germ cell fate in mice.

An early fundamental event during development is the segregation of germ cells from somatic cells. In many organisms, this is accomplished by the inheritance of preformed germ plasm, which apparently imposes transcriptional repression to prevent somatic cell fate. However, in mammals, pluripotent epiblast cells acquire germ cell fate in response to signalling molecules. We have used single cell analysis to study how epiblast cells acquire germ cell competence and undergo specification. Germ cell competent cells express Fragilis and initially progress towards a somatic mesodermal fate. However, a subset of these cells, the future primordial germ cells (PGCs), then shows rapid upregulation of Fragilis with concomitant transcriptional repression of a number of genes, including Hox and Smad genes. This repression may be a key event associated with germ cell specification. Furthermore, PGCs express Stella and other genes, such as Oct-4 that are associated with pluripotency. While these molecules are also detected in mature oocytes as maternally inherited factors, their early role is to regulate development and maintain pluripotency, and they do not serve the role of classical germline determinants.

Animals↗
PubMed2002

A molecular programme for the specification of germ cell fate in mice.

Germ cell fate in mice is induced in proximal epiblast cells by the extra-embryonic ectoderm, and is not acquired through the inheritance of any preformed germ plasm. To determine precisely how germ cells are specified, we performed a genetic screen between single nascent germ cells and their somatic neighbours that share common ancestry. Here we show that fragilis, an interferon-inducible transmembrane protein, marks the onset of germ cell competence, and we propose that through homotypic association, it demarcates germ cells from somatic neighbours. Using single-cell gene expression profiles, we also show that only those cells with the highest expression of fragilis subsequently express stella, a gene that we detected exclusively in lineage-restricted germ cells. The stella positive nascent germ cells exhibit repression of homeobox genes, which may explain their escape from a somatic cell fate and the retention of pluripotency.

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