Forced expression of the homeobox-containing gene Pem blocks differentiation of embryonic stem cells

Imprinted X-chromosome inactivation impacts primitive endoderm differentiation in mouse blastocysts

Epigenetic and transcriptome alterations are essential for lineage specification, represented by imprinted X-chromosome inactivation (iXCI) in female mouse preimplantation embryos. However, how various factors affect transcriptome states and lineage commitment remains unclear. We found that in vitro culture duration strongly influences transcriptional variation compared to iXCI loss. Single-cell analysis of the inner cell mass (ICM) for major transcription and epigenomic factors revealed that sex-specific differences in expression are diminished by loss of iXCI in the primitive endoderm (PrE) but not in the epiblast. Females had a higher proportion of ICM compared to that in males, and PrE development was affected by iXCI states in female embryos. Our findings provide insight into sex differences and iXCI function in lineage specification.

Stem Cell Therapies for Neurodegenerative Diseases

Stem cell therapies have been proposed as a treatment option for neurodegenerative diseases, but the best stem cell source and therapeutic efficacy for neuroregeneration remain uncertain. Embryonic stem cells (ESCs) and neural stem cells (NSCs), which can efficiently generate neural cells, could be good candidates but they pose ethical and practical issues. Not only difficult to find the good source of those cells but also they alway pose immunorejection problem since they may not be an autologous cells. Even if we overcome the immunorejection problem, it has also been reported that transplantation of ESCs develop teratoma. Although adult stem cells are more accessible, they have a limited developmental potential. We developed technologies to increase potency of mesenchymal stem cells, which allow them to develop into neural cells, by over expression of the ESC gene, nanog. We also developed a small molecule compound, which significantly increases endogenous NSCs by peripheral administration, eliminating even the necessity of stem cell injection to the brain. These novel technologies may offer neuroregenerative therapies for Alzheimers disease (AD). However, we found that AD pathological condition prevent neurogenesis from NSCs. This chapter discusses how to overcome the problem associated stem cell therapy under AD pathology and introduces exosome as a tool to improve the modification of adult stem cells. These new technologies may open a door for the new era for AD therapy.

DUSP9 Modulates DNA Hypomethylation in Female Mouse Pluripotent Stem Cells

Blastocyst-derived embryonic stem cells (ESCs) and gonad-derived embryonic germ cells (EGCs) represent two classic types of pluripotent cell lines, yet their molecular equivalence remains incompletely understood. Here, we compare genome-wide methylation patterns between isogenic ESC and EGC lines to define epigenetic similarities and differences. Surprisingly, we find that sex rather than cell type drives methylation patterns in ESCs and EGCs. Cell fusion experiments further reveal that the ratio of X chromosomes to autosomes dictates methylation levels, with female hybrids being hypomethylated and male hybrids being hypermethylated. We show that the X-linked MAPK phosphatase DUSP9 is upregulated in female compared to male ESCs, and its heterozygous loss in female ESCs leads to male-like methylation levels. However, male and female blastocysts are similarly hypomethylated, indicating that sex-specific methylation differences arise in culture. Collectively, our data demonstrate the epigenetic similarity of sex-matched ESCs and EGCs and identify DUSP9 as a regulator of female-specific hypomethylation.

Xist-dependent imprinted X inactivation and the early developmental consequences of its failure

The long noncoding RNA Xist is expressed from only the paternal X chromosome in mouse preimplantation female embryos and mediates transcriptional silencing of that chromosome. In females, absence of Xist leads to postimplantation lethality. Here, through single-cell RNA sequencing of early preimplantation mouse embryos, we found that the initiation of imprinted X-chromosome inactivation absolutely requires Xist. Lack of paternal Xist leads to genome-wide transcriptional misregulation in the early blastocyst and to failure to activate the extraembryonic pathway that is essential for postimplantation development. We also demonstrate that the expression dynamics of X-linked genes depends on the strain and parent of origin as well as on the location along the X chromosome, particularly at the first 'entry' sites of Xist. This study demonstrates that dosage-compensation failure has an effect as early as the blastocyst stage and reveals genetic and epigenetic contributions to orchestrating transcriptional silencing of the X chromosome during early embryogenesis.

Gene array analysis of neural crest cells identifies transcription factors necessary for direct conversion of embryonic fibroblasts into neural crest cells

Neural crest cells (NC cells) are multipotent cells that emerge from the edge of the neural folds and migrate throughout the developing embryo. Although the gene regulatory network for generation of NC cells has been elucidated in detail, it has not been revealed which of the factors in the network are pivotal to directing NC identity. In this study we analyzed the gene expression profile of a pure NC subpopulation isolated from Sox10-IRES-Venus mice and investigated whether these genes played a key role in the direct conversion of Sox10-IRES-Venus mouse embryonic fibroblasts (MEFs) into NC cells. The comparative molecular profiles of NC cells and neural tube cells in 9.5-day embryos revealed genes including transcription factors selectively expressed in developing trunk NC cells. Among 25 NC cell-specific transcription factor genes tested, SOX10 and SOX9 were capable of converting MEFs into SOX10-positive (SOX10+) cells. The SOX10+ cells were then shown to differentiate into neurons, glial cells, smooth muscle cells, adipocytes and osteoblasts. These SOX10+ cells also showed limited self-renewal ability, suggesting that SOX10 and SOX9 directly converted MEFs into NC cells. Conversely, the remaining transcription factors, including well-known NC cell specifiers, were unable to convert MEFs into SOX10+ NC cells. These results suggest that SOX10 and SOX9 are the key factors necessary for the direct conversion of MEFs into NC cells.

Summary: In this study, we identified the transcription factors specifically expressed in developing neural crest cells, and showed that SOX10 and SOX9 directly converted fibroblasts into neural crest cells.

Ex Uno Plures: Molecular Designs for Embryonic Pluripotency

Pluripotent cells in embryos are situated near the apex of the hierarchy of developmental potential. They are capable of generating all cell types of the mammalian body proper. Therefore, they are the exemplar of stem cells. In vivo, pluripotent cells exist transiently and become expended within a few days of their establishment. Yet, when explanted into artificial culture conditions, they can be indefinitely propagated in vitro as pluripotent stem cell lines. A host of transcription factors and regulatory genes are now known to underpin the pluripotent state. Nonetheless, how pluripotent cells are equipped with their vast multilineage differentiation potential remains elusive. Consensus holds that pluripotency transcription factors prevent differentiation by inhibiting the expression of differentiation genes. However, this does not explain the developmental potential of pluripotent cells. We have presented another emergent perspective, namely, that pluripotency factors function as lineage specifiers that enable pluripotent cells to differentiate into specific lineages, therefore endowing pluripotent cells with their multilineage potential. Here we provide a comprehensive overview of the developmental biology, transcription factors, and extrinsic signaling associated with pluripotent cells, and their accompanying subtypes, in vitro heterogeneity and chromatin states. Although much has been learned since the appreciation of mammalian pluripotency in the 1950s and the derivation of embryonic stem cell lines in 1981, we will specifically emphasize what currently remains unclear. However, the view that pluripotency factors capacitate differentiation, recently corroborated by experimental evidence, might perhaps address the long-standing question of how pluripotent cells are endowed with their multilineage differentiation potential.

Rhox in mammalian reproduction and development

Homeobox genes play essential roles in embryonic development and reproduction. Recently, a large cluster of homeobox genes, reproductive homeobox genes on the X chromosome (Rhox) genes, was discovered as three gene clusters, α, β, and γ in mice. It was found that Rhox genes were selectively expressed in reproduction-associated tissues, such as those of the testes, epididymis, ovaries, and placenta. Hence, it was proposed that Rhox genes are important for regulating various reproductive features, especially gametogenesis in male as well as in female mammals. It was first determined that 12 Rhox genes are clustered into α (Rhox1-4), β (Rhox5-9), and γ (Rhox10-12) subclusters, and recently Rhox13 has also been found. At present, 33 Rhox genes have been identified in the mouse genome, 11 in the rat, and three in the human. Rhox genes are also responsible for embryonic development, with considerable amounts of Rhox expression in trophoblasts, placenta tissue, embryonic stem cells, and primordial germ cells. In this article we summarized the current understanding of Rhox family genes involved in reproduction and embryonic development and elucidated a previously unreported cell-specific expression in ovarian cells.

LIF-dependent signaling: new pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.

Homeobox gene Rhox5 is regulated by epigenetic mechanisms in cancer and stem cells and promotes cancer growth

Background

Homeobox genes murine Rhox5 and human RHOXF1 are expressed in early embryonic stages and then mostly restricted to germline tissues in normal adult, yet they are aberrantly expressed in cancer cells in vitro and in vivo . Here we study the epigenetic regulation and potential functions of Rhox5 gene.

Findings

In Rhox5 -silenced or extremely low expresser cells, we observed low levels of active histone epigenetic marks (H3ac, H4ac and H3K4me2) and high levels of repressive mark H3K9me2 along with DNA hypermethylation in the promoter. In Rhox5 low expresser cells, we typically observed modest levels of both active and repressive histone marks along with moderate DNA methylation. In Rhox5 highly expressed CT26 cancer cells, we observed DNA hypomethylation along with high levels of both active and repressive histone marks. Epigenetic drugs (retinoic acid and MS-275) induced F9 cell differentiation with enhanced Rhox5 expression and dynamic changes of epigenetic marks. Finally, Rhox5 knockdown by small hairpin RNA (shRNA) in CT26 colon cancer decreased cell proliferation and migration in vitro and tumor growth in vivo .

Conclusions

Both DNA methylation and histone methylation/acetylation play key roles in modulating Rhox5 expression in various cell types. The stem cell-like "bivalent domain", an epigenetic feature originally identified in key differentiation genes within stem cells, exists in the Rhox5 gene promoter in not only embryonic stem cells but also cancer cells, cancer stem cells, and differentiated Sertoli cells. As Ras signaling-dependent Rhox5 expression promotes tumor growth, Rhox5 may be an ideal target for therapeutic intervention in cancer.

The Role of the Leukemia Inhibitory Factor (LIF) - Pathway in Derivation and Maintenance of Murine Pluripotent Stem Cells

Developmental biology, regenerative medicine and cancer biology are more and more interested in understanding the molecular mechanisms controlling pluripotency and self-renewal in stem cells. Pluripotency is maintained by a synergistic interplay between extrinsic stimuli and intrinsic circuitries, which allow sustainment of the undifferentiated and self-renewing state. Nevertheless, even though a lot of efforts have been made in the past years, the precise mechanisms regulating these processes remain unclear. One of the key extrinsic factors is leukemia inhibitory factor (LIF) that is largely used for the cultivation and derivation of mouse embryonic and induced pluripotent stem cells. LIF acts through the LIFR/gp130 receptor and activates STAT3, an important regulator of mouse embryonic stem cell self-renewal. STAT3 is known to inhibit differentiation into both mesoderm and endoderm lineages by preventing the activation of lineage-specific differentiation programs. However, LIF activates also parallel circuitries like the PI3K-pathway and the MEK/ERK-pathway, but its mechanisms of action remain to be better elucidated. This review article aims at summarizing the actual knowledge on the importance of LIF in the maintenance of pluripotency and self-renewal in embryonic and induced pluripotent stem cells.

The Rhox genes

Homeobox genes encode transcription factors that have crucial roles in embryogenesis. A recently discovered set of homeobox genes--the Rhox genes--are expressed during both embryogenesis and in adult reproductive tissues. The 33 known mouse Rhox genes are clustered together in a single region on the X chromosome, while likely descendents of the primodial Rhox cluster, Arx and Esx1, have moved to other positions on the X chromosome. Here, we summarize what is known about the regulation and function of Rhox cluster and Rhox-related genes during embryogenesis and gametogenesis. The founding member of the Rhox gene cluster--Rhox5 (previously known as Pem)--has been studied in the most depth and thus is the focus of this review. We also discuss the unusually rapid evolution of the Rhox gene cluster.

Smad4-dependent pathways control basement membrane deposition and endodermal cell migration at early stages of mouse development

Background

Smad4 mutant embryos arrest shortly after implantation and display a characteristic shortened proximodistal axis, a significantly reduced epiblast, as well as a thickened visceral endoderm layer. Conditional rescue experiments demonstrate that bypassing the primary requirement for Smad4 in the extra-embryonic endoderm allows the epiblast to gastrulate. Smad4-independent TGF-β signals are thus sufficient to promote mesoderm formation and patterning. To further analyse essential Smad4 activities contributed by the extra-embryonic tissues, and characterise Smad4 dependent pathways in the early embryo, here we performed transcriptional profiling of Smad4 null embryonic stem (ES) cells and day 4 embryoid bodies (EBs).

Results

Transcripts from wild-type versus Smad4 null ES cells and day 4 EBs were analysed using Illumina arrays. In addition to several known TGF-β/BMP target genes, we identified numerous Smad4-dependent transcripts that are mis-expressed in the mutants. As expected, mesodermal cell markers were dramatically down-regulated. We also observed an increase in non-canonical potency markers (Pramel7, Tbx3, Zscan4), germ cell markers (Aire, Tuba3a, Dnmt3l) as well as early endoderm markers (Dpp4, H19, Dcn). Additionally, expression of the extracellular matrix (ECM) remodelling enzymes Mmp14 and Mmp9 was decreased in Smad4 mutant ES and EB populations. These changes, in combination with increased levels of laminin alpha1, cause excessive basement membrane deposition. Similarly, in the context of the Smad4 null E6.5 embryos we observed an expanded basement membrane (BM) associated with the thickened endoderm layer.

Conclusion

Smad4 functional loss results in a dramatic shift in gene expression patterns and in the endodermal cell lineage causes an excess deposition of, or an inability to breakdown and remodel, the underlying BM layer. These structural abnormalities probably disrupt reciprocal signalling between the epiblast and overlying visceral endoderm required for gastrulation.

Stem cell pluripotency: a cellular trait that depends on transcription factors, chromatin state and a checkpoint deficient cell cycle

Embryonic stem (ES) and induced pluripotent stem (iPS) cells self-renew and are pluripotent. Differentiation of these cells can yield over 200 somatic cell types, making pluripotent cells an obvious source for regenerative medicine. Before the potential of these cells can be maximally harnessed for clinical applications, it will be necessary to understand the processes that maintain pluripotentiality and signal differentiation. Currently, three unique molecular properties distinguish pluripotent stem cells from somatic cells. These include a unique transcriptional hierarchy that sustains the pluripotent state during the process of self-renewal; a poised epigenetic state that maintains chromatin in a form ready for rapid cell fate decisions; and a cell cycle characterized by an extremely short gap 1 (G1) phase and the near absence of normal somatic cell checkpoint controls. Recently, B-MYB (MYBL2) was implicated in the gene regulation of two pluripotency factors and normal cell cycle progression. In this article, the three pluripotency properties and the potential role of B-Myb to regulate these processes will be discussed.

Genes and signals regulating murine trophoblast cell development

A fundamental step in embryonic development is cell differentiation whereby highly specialised cell types are developed from a single undifferentiated, fertilised egg. One of the earliest lineages to form in the mammalian conceptus is the trophoblast, which contributes exclusively to the extraembryonic structures that form the placenta. Trophoblast giant cells (TGCs) in the rodent placenta form the outermost layer of the extraembryonic compartment, establish direct contact with maternal cells, and produce a number of pregnancy-specific cytokine hormones. Giant cells differentiate from proliferative trophoblasts as they exit the cell cycle and enter a genome-amplifying endocycle. Normal differentiation of secondary TGCs is a critical step toward the formation of the placenta and normal embryonic development. Trophoblast development is also of particular interest to the developmental biologist and immunobiologist, as these cells constitute the immediate cellular boundary between the embryonic and maternal tissues. Abnormalities in the development of secondary TGCs results in severe malfunction of the placenta. Herein we review new information that has been accumulated recently regarding the molecular and cellular regulation of trophoblast and placenta development. In particular, we discuss the molecular aspects of murine TGC differentiation. We also focus on the role of growth and transcription factors in TGC development.

Thymus-specific deletion of insulin induces autoimmune diabetes

Insulin expression in the thymus has been implicated in regulating the negative selection of autoreactive T cells and in mediating the central immune tolerance towards pancreatic beta-cells. To further explore the function of this ectopic insulin expression, we knocked out the mouse Ins2 gene specifically in the Aire-expressing medullary thymic epithelial cells (mTECs), without affecting its expression in the beta-cells. When further crossed to the Ins1 knockout background, both male and female pups (designated as ID-TEC mice for insulin-deleted mTEC) developed diabetes spontaneously around 3 weeks after birth. beta-cell-specific autoimmune destruction was observed, as well as islet-specific T cell infiltration. The presence of insulin-specific effector T cells was shown using ELISPOT assays and adoptive T cell transfer experiments. Results from thymus transplantation experiments proved further that depletion of Ins2 expression in mTECs was sufficient to break central tolerance and induce anti-insulin autoimmunity. Our observations may explain the rare cases of type 1 diabetes onset in very young children carrying diabetes-resistant HLA class II alleles. ID-TEC mice could serve as a new model for studying this pathology.

Liver-specific deletion of the growth hormone receptor reveals essential role of growth hormone signaling in hepatic lipid metabolism

Growth hormone (GH) plays a pivotal role in growth and metabolism, with growth promotion mostly attributed to generation of insulin-like growth factor I (IGF-I) in liver or at local sites of GH action, whereas the metabolic effects of GH are considered to be intrinsic to GH itself. To distinguish the effects of GH from those of IGF-I, we developed a Cre-lox-mediated model of tissue-specific deletion of the growth hormone receptor (GHR). Near total deletion of the GHR in liver (GHRLD) had no effect on total body or bone linear growth despite a >90% suppression of circulating IGF-I; however, total bone density was significantly reduced. Circulating GH was increased 4-fold, and GHRLD displayed insulin resistance, glucose intolerance, and increased circulating free fatty acids. Livers displayed marked steatosis, the result of increased triglyceride synthesis and decreased efflux; reconstitution of hepatic GHR signaling via adenoviral expression of GHR restored triglyceride output to normal, whereas IGF-I infusion did not correct steatosis despite restoration of circulating GH to normal. Thus, with near total absence of circulating IGF-I, GH action at the growth plate, directly and via locally generated IGF-I, can regulate bone growth, but at the expense of diabetogenic, lipolytic, and hepatosteatotic consequences. Our results indicate that IGF-I is essential for bone mineral density, whereas hepatic GH signaling is essential to regulate intrahepatic lipid metabolism. We propose that circulating IGF-I serves to amplify the growth-promoting effects of GH, while simultaneously dampening the catabolic effects of GH.

Identification of prosaposin as a novel interaction partner for Rhox5

Prosaposin (Psap) has multiple cellular functions. It is involved in the development of the reproductive system, nervous system, and prostate cancer as well as in the regulation of sphingolipid catabolism by activating several lysosomal hydrolases involved in the metabolism of various sphingolipids. In this research, it was found to be a novel interaction partner for Rhox5 using yeast two-hybrid screening. The interaction between Rhox5 and the full-length prosapsoin (the transcript without exon 8) as well as the C-terminal domain of prosaposin, was further confirmed in both yeast two hybrid analysis and in vitro assay. It suggested that the C-terminal domain of prosaposin may be critical for the Rhox5-prosaposin interaction. Given the important roles played by both Rhox5 and prosaposin in maintaining the differentiation of male reproductive organs, spermatogenesis, and fertilization, the interaction between Rhox5 and prosaposin might regulate the development of male reproductive organs dynamically.

Characterization and transformation potential of "Synthetic" astrocytes differentiated from murine embryonic stem cells

Our objective was to determine if murine embryonic stem (ES) cells, which are readily available from repositories, could be developed as a model of gliomagenesis, recognizing the difficulty in obtaining and transforming somatic astrocytes. Using a stringently controlled sequential differentiation procedure on wild type (wt) and p53+/- ES cells, we established GFAP+A2B5-synthetic astrocytes with high efficiency (>90%). The synthetic astrocytes stably express several differentiated astrocyte associated structural proteins and biochemical markers, but lacked expression of differentiated neurons and oligodendrocytes. However, in contrast to somatic differentiated astrocytes, the synthetic astrocytes expressed stem cell markers, with a transcriptome profile similar to astrocytes differentiated from neural stem cells (NSC) and somatic astrocyte cultures established from E13.5-Cortex and P4-hippocampus. In addition, the synthetic astrocytes demonstrated plasticity, with ability to dedifferentiate into neuronal and oligodendrocyte lineages. Intracranial injection of postnatal differentiated somatic astrocytes or synthetic astrocytes of either wt or p53+/- background did not grow tumors, unlike corresponding ES cells that develop teratomas. In contrast, retroviral transduction of either wt or p53+/- synthetic astrocytes and not the postnatal somatic astrocytes, with relevant oncogenes found in human malignant astrocytomas (MDM2, myr-AKT, V12H-RAS), led to intracranial high-grade undifferentiated gliomas. This study demonstrates utilization of readily available ES cells of varying genetic backgrounds to model and further our understanding of gliomagenesis. Large numbers of replenishable derivative synthetic glial lineage cells retain genetic and phenotypic characteristics of progenitor cells and thereby are more amenable to transformation by genetic aberrations involved in gliomagenesis.

Expression profiling in transgenic FVB/N embryonic stem cells overexpressing STAT3

Background

The transcription factor STAT3 is a downstream target of the LIF signalling cascade. LIF signalling or activation is sufficient to maintain embryonic stem (ES) cells in an undifferentiated and pluripotent state. To further investigate the importance of STAT3 in the establishment of ES cells we have in a first step derived stable pluripotent embryonic stem cells from transgenic FVB mice expressing a conditional tamoxifen dependent STAT3-MER fusion protein. In a second step, STAT3-MER overexpressing cells were used to identify STAT3 pathway-related genes by expression profiling in order to identify new key-players involved in maintenance of pluripotency in ES cells.

Results

Transgenic STAT3-MER blastocysts yielded pluripotent germline-competent ES cells at a high frequency in the absence of LIF when established in tamoxifen-containing medium. Expression profiling of tamoxifen-induced transgenic FVB ES cell lines revealed a set of 26 genes that were markedly up- or down-regulated when compared with wild type cells. The expression of four of the up-regulated genes (Hexokinase II, Lefty2, Pramel7, PP1rs15B) was shown to be restricted to the inner cell mass (ICM) of the blastocysts. These differentially expressed genes represent potential candidates for the maintenance of pluripotency of ES cells. We finally overexpressed two candidate genes, Pem/Rhox5 and Pramel7, in ES cells and demonstrated that their overexpression is sufficient for the maintenance of expression of ES cell markers as well as of the typical morphology of pluripotent ES cells in absence of LIF.

Conclusion

Overexpression of STAT3-MER in the inner cell mass of blastocyst facilitates the establishment of ES cells and induces the upregulation of potential candidate genes involved in the maintenance of pluripotency. Two of them, Pem/Rhox5 and Pramel7, when overexpressed in ES cells are able to maintain the embryonic stem cells in a pluripotent state in a LIF independent manner as STAT3 or Nanog.

Pluripotency of embryonic stem cells

Embryonic stem (ES) cells derived from pre-implantation embryos have the potential to differentiate into any cell type derived from the three germ layers of ectoderm (epidermal tissues and nerves), mesoderm (muscle, bone, blood), and endoderm (liver, pancreas, gastrointestinal tract, lungs), including fetal and adult cells. Alone, these cells do not develop into a viable fetus or adult animal because they do not retain the potential to contribute to extraembryonic tissue, and in vitro, they lack spatial and temporal signaling cues essential to normal in vivo development. The basis of pluripotentiality resides in conserved regulatory networks composed of numerous transcription factors and multiple signaling cascades. Together, these regulatory networks maintain ES cells in a pluripotent and undifferentiated form; however, alterations in the stoichiometry of these signals promote differentiation. By taking advantage of this differentiation capacity in vitro, ES cells have clearly been shown to possess the potential to generate multipotent stem and progenitor cells capable of differentiating into a limited number of cell fates. These latter types of cells may prove to be therapeutically viable, but perhaps more importantly, the studies of these cells have led to a greater understanding of mammalian development.

Stem cell gene expression changes induced specifically by mutated K-ras

K-Ras proteins transduce signals from membrane-bound receptors via multiple downstream effector pathways and thereby regulate fundamental stem cell processes that affect neoplasia, including proliferation, apoptosis, and differentiation, but their contribution to tumourigenesis is unclear. Because cancers develop from stem cells, we set out to determine the characteristic changes in gene expression brought about by mutated K-ras (without interference from normal K-ras) in otherwise normal stem cells. cDNA microarrays were used to analyze gene expression profiles comparing wild-type murine embryonic stem (ES) cells with K-ras(Val12) expressing ES cells (previously made null for both endogenous K-ras alleles and transfected with K-ras(Val12), with valine for glycine at codon 12). K-ras(Val12) was expressed at 1.2-fold normal K-ras levels and produced transcripts for both activated K-Ras4A and 4B isoforms. The array expression data were confirmed by real-time quantitative PCR analysis of selected genes expressed both in the K-ras(Val12) expressing ES cells (R = 0.91 with array data) and in the normal intestinal tissues of K-ras(Val12) transgenic mice (R = 0.91 with array data). Changes in gene expression were correlated with the effects of K-ras(Val12) expression on ES cells of enhancing self-renewal in an undifferentiated state, increasing susceptibility to DNA damage-induced apoptosis, and increased proliferation. These expression data may explain, at least in part, some neoplasia-related aspects of the phenotypic changes brought about in this ES cell line by mutated K-ras, in that upregulation of cell growth-related proteins and DNA-associated proteins is consistent with increased proliferation; upregulation of certain apoptosis-related proteins is consistent with a greater susceptibility to DNA damage-induced apoptosis; and downregulation of structural proteins, extracellular matrix components, secretory proteins and receptors is consistent with a less differentiated phenotype.

DNA methylation regulates long-range gene silencing of an X-linked homeobox gene cluster in a lineage-specific manner

DNA methylation is a major epigenetic mechanism that has been suggested to control developmental gene regulation during embryogenesis, but its regulatory mechanisms remain unclear. In this report, we show that CpG islands associated with the X-linked homeobox gene cluster Rhox, which is highly expressed in the extraembryonic trophectoderm, are differentially methylated in a stage- and lineage-specific manner during the post-implantation development of mice. Inactivation of both Dnmt3a and Dnmt3b, DNA methyltransferases essential for the initiation of de novo DNA methylation, abolished the establishment of DNA methylation and the silencing of Rhox cluster genes in the embryo proper. The Dnmt3-dependent CpG-island methylation at the Rhox locus extended for a large genomic region ( approximately 1 Mb) containing the Rhox cluster and surrounding genes. Complementation experiments using embryonic stem (ES) cells deficient in the DNA methyltransferases suggested that the CpG-island methylation by Dnmt3a and Dnmt3b was restricted within this large genomic region, and did not affect the neighboring genes outside it, implicating the existence of region-specific boundaries. Our results suggest that DNA methylation plays important roles in both long-range gene silencing and lineage-specific silencing in embryogenesis.

Aberrant profile of gene expression in cloned mouse embryos derived from donor cumulus nuclei

Somatic cell nuclear transfer has successfully been used to clone several mammalian species including the mouse, albeit with extremely low efficiency. This study investigated gene expression in cloned mouse embryos derived from cumulus cell donor nuclei, in comparison with in vivo fertilized mouse embryos, at progressive developmental stages. Enucleation was carried out by the conventional puncture method rather than by the piezo-actuated technique, whereas nuclear transfer was achieved by direct cumulus nuclear injection. Embryonic development was monitored from chemically induced activation on day 0 until the blastocyst stage on day 4. Poor developmental competence of cloned embryos was observed, which was confirmed by lower cell counts in cloned blastocysts, compared with the in vivo fertilized controls. Subsequently, real-time polymerase chain reaction was used to analyze and compare embryonic gene expression at the 2-cell, 4-cell, and blastocyst stages, between the experimental and control groups. The results showed reduced expression of the candidate genes in cloned 2-cell stage embryos, as manifested by poor developmental competence, compared with expression in the in vivo fertilized controls. Cloned 4-cell embryos and blastocysts, which had overcome the developmental block at the 2-cell stage, also showed up-regulated and down-regulated expression of several genes, strongly suggesting incomplete nuclear reprogramming. We have therefore demonstrated that aberrant embryonic gene expression is associated with low developmental competence of cloned mouse embryos. To improve the efficiency of somatic cell nuclear transfer, strategies to rectify aberrant gene expression in cloned embryos should be investigated.

Regulatory networks in embryo-derived pluripotent stem cells

Mammalian development requires the specification of over 200 cell types from a single totipotent cell. Investigation of the regulatory networks that are responsible for pluripotency in embryo-derived stem cells is fundamental to understanding mammalian development and realizing therapeutic potential. Extracellular signals and second messengers modulate cell-autonomous regulators such as OCT4, SOX2 and Nanog in a combinatorial complexity. Knowledge of this circuitry might reveal how to achieve phenotypic changes without the genetic manipulation of Oct4, Nanog and other toti/pluripotency-associated genes.

Interaction of mouse Pem protein and cell division cycle 37 homolog

Mouse Pem, a homeobox gene, encodes a protein consisting of 210 amino acid residues. To study the function of mouse Pem protein, we used the yeast two-hybrid system to screen the library of 7-day mouse embryo with full-length mouse Pem cDNA. Fifty-two colonies were obtained after 1.57 x 10(8) colonies were screened by nutrition limitation and beta-galactosidase assay. Seven individual insert fragments were obtained from the library, and three of them were identified, one of which was confirmed to be the cell division cycle 37 (Cdc37) homolog gene by sequencing. The interaction between mouse Pem and Cdc37 homolog was then confirmed by glutathione S-transferase pull-down assay, and the possible interaction model was suggested.

EMP-1 is a junctional protein in a liver stem cell line and in the liver

In an attempt to discover cell markers for liver stem cells, a cDNA microarray analysis was carried out to compare the gene expression profiles between an adult liver stem cell line, Lig-8, and mature hepatocytes. Several genes in the categories of extracellular matrix, cell membrane, cell adhesion, transcription factor, signal molecule, transporter, and metabolic enzyme were shown to be differentially expressed in Lig-8 cells. Among them, epithelial membrane protein (EMP)-1 has been previously implicated with stem cell phenotypes. Antiserum to EMP-1 was produced to localize its expression. On monolayers of Lig-8 cells, EMP-1 was expressed along the intercellular border. In the liver harboring proliferating oval cells, the liver progenitors, EMP-1 was localized as ribbon bands, a staining pattern for epithelial junctions, all the way through bile duct epithelia, oval cell ductules, and into peri-hepatocytic regions. These peri-hepatocytic regions were proved to be bile canaliculi by co-localization of EMP-1 and dipeptidyl peptidase IV, an enzyme located on bile canaliculi. This report is the first to indicate EMP-1 to be a junctional protein in the liver.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Gene Regulation in Spermatogenesis

Mammalian spermatogenesis is a complex hormone-dependent developmental program in which a myriad of events must take place to ensure that germ cells reach their proper stage of development at the proper time. Many of these events are controlled by cell type- and stage-specific transcription factors. The regulatory mechanisms involved provide an intriguing paradigm for the field of developmental biology and may lead to the development of new contraceptives an and innovative routs to treat male infertility. In this review, we address three aspects of the genetic regulatory mechanism that drive spermatogenesis. First, we detail what is known about how steroid hormones (both androgens and estrogens) and their cognate receptors initiate and maintain mammalian spermatogenesis. Steroids act through three mechanistic routes: (i) direct activation of genes through hormone-dependent promoter elements, (ii) secondary transcriptional responses through activation of hormone-dependent transcription factors, and (iii) rapid, transcription-independent (nonclassical) events induced by steroid hormones. Second, we provide a survey of transcription factors that function in mammalian spermatogenesis, including homeobox, zinc-finger, heat-shock, and cAMP-response family members. Our survey is not intended to cover all examples but to give a flavor for the gamut of biological roles conferred by transcription factors in the testis, particularly those defined in knockout mice. Third, we address how testis-specific transcription is achieved. In particular, we cover the evidence for and against the idea that some testis-specific genes are transcriptionally silent in somatic tissues as a result of DNA methylation.

Technical Assessment of the First 20 Years of Research Using Mouse Embryonic Stem Cell Lines

This review assesses the effect that mouse embryonic stem (ES) cells have had on biomedical research during the 20 years that followed their isolation in 1981. Notable scientific discoveries enabled by these cell lines--including insights into cell cycle regulation, spatial and temporal relationships during development, and the roles of transcription factors and homeobox genes in developmental pathways--are discussed. The acceleration of basic discovery of gene function and the genetic basis of disease using a breakthrough technology (homologous recombination between modified gene constructs and the ES cell genome) became the principal enabling method to establish transgenic laboratory animals with single targeted genetic change. This review also examines the widespread influence of mouse ES cells as an enabling technology by highlighting their effect on drug development paradigms, directed differentiation to treat specific diseases, nuclear transfer protocols used in cloning, and establishment of methodologies for isolating non-rodent ES cells. This review concludes with a brief analysis of the most influential mouse ES cell lines of the first 20 years as viewed within the twin contexts of human disease application and contributions to the primary literature.

Conserved and divergent paths that regulate self-renewal in mouse and human embryonic stem cells

The past few years have seen remarkable progress in our understanding of embryonic stem cell (ES cell) biology. The necessity of examining human ES cells in culture, coupled with the wealth of genomic data and the multiplicity of cell lines available, has enabled researchers to identify critical conserved pathways regulating self-renewal and identify markers that tightly correlate with the ES cell state. Comparison across species has suggested additional pathways likely to be important in long-term self-renewal of ES cells including heterochronic genes, microRNAs, genes involved in telomeric regulation, and polycomb repressors. In this review, we have discussed information on molecules known to be important in ES cell self-renewal or blastocyst development and highlighted known differences between mouse and human ES cells. We suggest that several additional pathways required for self-renewal remain to be discovered and these likely include genes involved in antisense regulation, microRNAs, as well as additional global repressive pathways and novel genes. We suggest that cross species comparisons using large-scale genomic analysis tools are likely to reveal conserved and divergent paths required for ES cell self-renewal and will allow us to derive ES lines from species and strains where this has been difficult.

Kinetics of senescence-associated changes of gene expression in an epithelial, temperature-sensitive SV40 large T antigen model

Replicative senescence limits the number of times primary cells can divide and is therefore regarded as a potential checkpoint for cancer progression. The majority of studies examining changes of gene expression upon senescence have been made with stationary senescent cells. We wanted to study the transition from normal growth to senescence in detail and identify early regulators of senescence by analyzing early changes in global gene expression, using Affymetrix microarrays. For this purpose, we used a murine epithelial senescence model, where senescence is abrogated by SV40 large T antigen and can be induced by using a temperature-sensitive form of SV40 large T antigen (SV40ts58). Comparisons were made to wild-type SV40 large T antigen-expressing cells and to cells expressing SV40ts58 large T antigen grown to confluence. After removal of genes that are similarly regulated in wild-type and temperature-sensitive SV40 large T antigen-expressing cells, 60% of the remaining genes were shared between cells arrested by inactivation of SV40 T antigen and by confluence. We identified 125 up-regulated and 39 down-regulated candidate genes/expressed sequence tags that are regulated upon SV40 T antigen inactivation and not during heat shock or confluence and classified these based on their kinetic profiles. Our study identified genes that fall into different functional clusters, such as transforming growth factor-beta-related genes and transcription factors, and included genes not identified previously as senescence associated. The genes are candidates as early regulators of the senescence checkpoint and may be potential molecular targets for novel anticancer drugs.

The 5T4 oncofoetal antigen is an early differentiation marker of mouse ES cells and its absence is a useful means to assess pluripotency

5T4 oncotrophoblast antigen is a transmembrane glycoprotein expressed by trophoblast and many carcinomas but not most normal adult tissues. Results from overexpression of human and mouse 5T4 cDNA in cell lines are consistent with it having an influence on adhesion, shape and motility. We show that murine embryonic stem cell lines are 5T4 negative but that there is rapid up regulation of protein and transcripts upon differentiation, including derivatives of each primary germ layer, as evidenced by cell surface FACS, western and RT-PCR analyses. The kinetics of differentiation and 5T4 expression are closely correlated, with early events linking 5T4 expression to changes in motility and morphology. Comparison of 5T4 expression with other ES cell transcript (Oct 3/4; Rex-1) and antigen markers (Forsmann, SSEA-1) establishes 5T4 as a useful marker for the non-destructive detection of early differentiation of ES cells. For example, `undifferentiated' ES phenotype defined as SSEA-1 positive and 5T4 negative is seven times more efficient at chimera formation than SSEA-1-positive/5T4-positive cells. Thus, 5T4 glycoprotein expression is associated with early differentiative events of ES cells involving altered motility, and it has useful practical consequences for assessing ES potency and studying similar processes in development and metastasis.

The homeoprotein Nanog is required for maintenance of pluripotency in mouse epiblast and ES cells

Embryonic stem (ES) cells derived from the inner cell mass (ICM) of blastocysts grow infinitely while maintaining pluripotency. Leukemia inhibitory factor (LIF) can maintain self-renewal of mouse ES cells through activation of Stat3. However, LIF/Stat3 is dispensable for maintenance of ICM and human ES cells, suggesting that the pathway is not fundamental for pluripotency. In search of a critical factor(s) that underlies pluripotency in both ICM and ES cells, we performed in silico differential display and identified several genes specifically expressed in mouse ES cells and preimplantation embryos. We found that one of them, encoding the homeoprotein Nanog, was capable of maintaining ES cell self-renewal independently of LIF/Stat3. nanog-deficient ICM failed to generate epiblast and only produced parietal endoderm-like cells. nanog-deficient ES cells lost pluripotency and differentiated into extraembryonic endoderm lineage. These data demonstrate that Nanog is a critical factor underlying pluripotency in both ICM and ES cells.

In vivo stabilization of the Dnmt1 (cytosine-5)- methyltransferase protein

The Dnmt1o form of the Dnmt1 (cytosine-5)-methyltransferase enzyme is synthesized and stored in the cytoplasm of the oocyte and is used after fertilization to maintain methylation patterns on imprinted genes. After implantation of the blastocyst, Dnmt1o is replaced by the Dnmt1 form, which has an additional 118 aa at its amino terminus. To investigate functional differences between Dnmt1o and Dnmt1, mice were generated with a mutant allele, Dnmt1(V), which synthesized Dnmt1o instead of Dnmt1 in all somatic cells. Homozygous Dnmt1(V) mice were phenotypically normal, and had normal levels of genomic methylation, indicating that Dnmt1o adopts the maintenance methyltransferase function of Dnmt1. Despite the apparent equivalence of Dnmt1o and Dnmt1 maintenance methyltransferase function in somatic cells, the Dnmt1o protein was found at high levels (with a corresponding high enzymatic activity) in Dnmt1(V) mice. In heterozygous Dnmt1(V)/+ embryonic stem cells and early embryos, equal steady-state levels of Dnmt1o and Dnmt1 proteins were produced from the Dnmt1(V) and the WT Dnmt1 alleles, respectively. However, in older embryos and adults, the Dnmt1(V) allele produced five times the steady-state level of protein of the WT Dnmt1 allele. The difference in Dnmt1o and Dnmt1 levels is due to a developmentally regulated mechanism that degrades the Dnmt1 protein. The intrinsic stability of the Dnmt1o protein is the most likely reason for its use as a maternal-effect protein; stable ooplasmic stores of Dnmt1o would be available to traffick into the nuclei of the eight-cell stage embryo and maintain methylation patterns on alleles of imprinted genes during the fourth embryonic S phase.

A molecular view on pluripotent stem cells

Pluripotent stem cells are undifferentiated cells that are capable of differentiating to all three embryonic germ layers and their differentiated derivatives. They are transiently found during embryogenesis, in preimplantation embryos and fetal gonads, or as established cell lines. These unique cell types are distinguished by their wide developmental potential and by their ability to be propagated in culture indefinitely, without loosing their undifferentiated phenotype. This short review intends to give a general overview on the pluripotent nature of embryo-derived stem cells with a focus on human embryonic stem cells.

A highly active homeobox gene promoter regulated by Ets and Sp1 family members in normal granulosa cells and diverse tumor cell types

One mechanism by which normal cells become converted to tumor cells involves the aberrant transcriptional activation of genes that are normally silent. We characterize a promoter that normally exhibits highly tissue- and stage-specific expression but displays ubiquitous expression when cells become immortalized or malignant, regardless of their lineage or tissue origin. This promoter normally drives the expression of the Pem homeobox gene in specific cell types in ovary and placenta but is aberrantly expressed in lymphomas, neuroblastomas, retinoblastomas, carcinomas, and sarcomas. By deletion analysis we identified a region between nucleotides -80 and -104 that was absolutely critical for the expression from this distal Pem promoter (Pem Pd). Site-specific mutagenesis and transfection studies revealed that this region contains two consensus Ets sites and a single Sp1 site that were necessary for Pem Pd expression. Gel shift analysis showed that Ets and Sp1 family members bound to these sites. Transfection studies demonstrated that the Ets family members Elf1 and Gabp and the Sp1 family members Sp1 and Sp3 transactivated the Pem Pd. Surprisingly, we found that Sp3 was a more potent activator of the Pem Pd than was Sp1; this is unusual, because Sp3 is either a weak activator or a repressor of most other promoters. Activation by either Elf1 or Gabp required an intact Sp1 family member binding site, suggesting that Ets and Sp1 family members cooperate to activate Pem Pd transcription. Expression from the Pem Pd (either transiently transfected or endogenous) depended on the Ras pathway, which could explain both its Ets- and Sp1-dependent expression in normal cells and its aberrant expression in tumor cells, in which ras protooncogenes are frequently mutated. We suggest that the Pem Pd may be a useful model system to understand the molecular mechanism by which a tissue-specific promoter can be corrupted in tumor cells.

Normal gonadal development in mice lacking GPBOX, a homeobox protein expressed in germ cells at the onset of sexual dimorphism

Gpbox is a paired-like homeobox gene that colocalizes with two other members of the family, PsxI and Pem, on the proximal portion of the mouse X chromosome. Gpbox is expressed in the extraembryonic placenta and within the germ cells of the embryonic gonad. Beginning with the onset of sexual dimorphism (embryonic day [E]11.5 to 12.5), GPBOX transcripts accumulate faster in female than in male germ cells but disappear later in embryogenesis (E16) and have not been reported in adult tissues. To investigate the function of Gpbox, mouse cell lines lacking GPBOX were established using targeted mutagenesis in embryonic stem cells. Both homozygous Gpbox null female and hemizygous Gpbox null male mice were fertile and reproduced normally. Additionally, the development of male and female gonads in the null background was indistinguishable from that observed in normal littermates. The lack of an obvious phenotype raises the possibility that another member of this homeobox gene family provides the absent Gpbox function.

Directed differentiation of embryonic stem cells: genetic and epigenetic methods

Embryonic stem cells are derived from the inner cell mass of the pre-implantation blastocyst, and can both self-renew and differentiate into all the cells and tissues of the body. The embryonic stem cell is an unsurpassed starting material to begin to understand a critical, largely inaccessible, period of development, as well as an important source of cells for transplantation and gene therapy. Despite their potential, attempts to obtain specific cell types from embryonic stem cells have been only partially successful because many of the growth factor combinations and developmental control genes involved in cell type restricted differentiation are unknown. This article summarizes some of the recent advances in promoting lineage restricted differentiation of embryonic stem cells, focusing on growth factor manipulation, or genetically altering embryonic stem cells to produce a desired phenotype. The two approaches epitomize current scientific concerns regarding the therapeutic use of these cells; genetic alterations will produce more pure cells with the risk of increasing the likelihood of malignant transformation; epigenetic methods for the manipulation of stem cell phenotype are often incomplete and remaining pluripotent cells are likely to form teratomas. As more is known about lineage specification during development, it will be possible to more precisely control cell type specification.

Menin interacts directly with the homeobox-containing protein Pem

The tumour suppressor gene causing multiple endocrine neoplasia type 1 (MEN1) encodes a 610 amino acid protein, menin. In order to identify menin-interacting proteins we used a yeast two-hybrid assay to screen a 12.5-dpc mouse embryo library with partial menin encompassing amino acids 278 to 476. This identified a homeobox containing protein encoded by a placenta and embryonic expression gene, referred to as Pem. GST-pull-down and coimmunoprecipitation experiments confirmed the interaction. Both proteins colocalised predominantly in the nucleus but were occasionally also found in the cytoplasm. Furthermore, in situ hybridisation studies revealed similarities in their expression patterns in mouse embryos and adult tissues. In adult mice both Men1 and Pem yielded strong signals in testis, Sertoli cells and particularly in seminiferous tubules. Thus, our study has identified that menin interacts with Pem, and the high expression of these proteins in the testis suggests a role in spermatogenesis.

Cell lineage determination in the mouse

During the peri-implantation development of the mouse embryo from the blastocyst through gastrulation, Pou5f1 (OCT-4) down-regulation is closely linked to the initial step of lineage allocation to extraembryonic and embryonic somatic tissues. Subsequently, differentiation of the lineage precursors is subject to inductive tissue interactions and intercellular signalling that regulate cell proliferation and the acquisition of lineage-specific morphological and molecular characteristics. A notable variation of this process of lineage specification is the persistence of Pou5f1 activity throughout the differentiation of the primordial germ cells, which may underpin their ability to produce pluripotent progeny either as stem cells (embryonic germ cells) in vitro or as gametes in vivo. Nevertheless, intercellular signalling still plays a critical role in the specification of the primordial germ cells. The findings that primordial germ cells can be induced from any epiblast cells and that they share common progenitors with other somatic cells provide compelling evidence for the absence of a pre-determined germ line in the mouse embryo.

Irradiation selectively inhibits expression from the androgen-dependent Pem homeobox gene promoter in sertoli cells

How radiation blocks spermatogenesis in certain strains of rats, such as LBNF(1), is not known. Because the block depends on androgen, we propose that androgen affects Sertoli cell function in irradiated LBNF(1) rats, resulting in the failure of spermatogonial differentiation. To begin to identify genes that may participate in this irradiation-induced blockade of spermatogenesis, we investigated the expression of several Sertoli genes in response to irradiation. The expression of the PEM: homeobox gene from its androgen-dependent Sertoli-specific proximal promoter (Pp) was dramatically reduced more than 100-fold in response to irradiation. In contrast, most other genes and gene products reported to be localized to the Sertoli cell, including FSH receptor (FSHR), androgen receptor (AR), SGP1, and the transcription factor CREB, did not exhibit significant changes in expression, whereas transferrin messenger RNA (mRNA) expression dramatically increased in response to irradiation. Irradiation also decreased Pp-driven PEM: mRNA levels in mouse testes (approximately 10-fold), although higher doses of irradiation than in rats were required to inhibit PEM: gene expression in testes of mice, consistent with their greater radioresistance. The decrease in Pem gene expression in mouse testis was also selective, as the expression of CREB, GATA-1, and SGP1 were little affected by irradiation. We conclude that the dramatic irradiation-triggered reduction of Pem expression in Sertoli cells is a conserved response that may be a marker for functional changes in response to irradiation.

The initial phase of embryonic patterning in mammals

Although specification of the antero-posterior axis is a critical intial step in development of the fetus, it is not known either how, or at what stage in development, this process begins. Such information is vital for understanding not only normal development in mammals but also monozygotic twinning, which, at least in man, is associated with a significantly increased incidence of birth defects. According to recent studies in the mouse, specification of the fetal anteroposterior axis begins well before gastrulation, and probably even before the conceptus implants. Moreover, evidence is accruing that the origin of relevant asymmetries depends on information that is already present in the zygote before it embarks on cleavage. Hence, early development in mammals does not differ as markedly from that in other animals as has generally been assumed. Consequently, at present, the possibility of adverse effects of techniques used to assist human reproduction cannot be disregarded.

Serological analysis of BALB/C methylcholanthrene sarcoma Meth A by SEREX: identification of a cancer/testis antigen

Antigens of BALB/c methylcholanthrene-induced fibrosarcoma Meth A recognized by the host humoral immune response were investigated by serological analysis of antigens by recombinant expression cloning (SEREX). Immunoscreening a cDNA library from Meth A (Kgamma) cells (Meth A retrovirally transfected with murine IFN-gamma cDNA) with sera from BALB/c mice growing parental Meth A transplants identified 10 antigens. One of them, OY-MS-4, showed characteristics of a cancer/testis (CT) antigen. Nucleotide sequence analysis revealed that OY-MS-4 was identical to a mouse placenta and embryonic expression gene (pem) known to be selectively expressed during embryogenesis and in transformed cell lines. In adult mice, expression of OY-MS-4 was restricted to testis and placenta. Four of 6 methylcholanthrene-induced fibrosarcomas in BALB/c mice showed strong expression of OY-MS-4. In 6 T-cell leukemias, only a dimethylbenzanthracene-induced leukemia, EL4 (C57BL), showed strong expression. Two other tumors, A20.2J and P815, induced by ethylnitrosourea and methylcholanthrene, respectively, also strongly expressed OY-MS-4. The other 9 gene products identified in Meth A by SEREX were expressed in all 15 tumors tested and in a range of normal tissues. Sequence analysis of cDNA inserts coding for the SEREX-defined antigens showed no evidence of mutation. Despite the expression of OY-MS-1-10 antigens in methylcholanthrene sarcomas other than Meth A, no antibody was detected in the sera of mice bearing these other sarcomas. The basis for the unique immunogenicity of OY-MS-1-10 presented by Meth A, but not by other syngeneic tumors expressing these gene products, is unknown.

Serological analysis of BALB/C methylcholanthrene sarcoma Meth A by SEREX: identification of a cancer/testis antigen

Antigens of BALB/c methylcholanthrene-induced fibrosarcoma Meth A recognized by the host humoral immune response were investigated by serological analysis of antigens by recombinant expression cloning (SEREX). Immunoscreening a cDNA library from Meth A (Kgamma) cells (Meth A retrovirally transfected with murine IFN-gamma cDNA) with sera from BALB/c mice growing parental Meth A transplants identified 10 antigens. One of them, OY-MS-4, showed characteristics of a cancer/testis (CT) antigen. Nucleotide sequence analysis revealed that OY-MS-4 was identical to a mouse placenta and embryonic expression gene (pem) known to be selectively expressed during embryogenesis and in transformed cell lines. In adult mice, expression of OY-MS-4 was restricted to testis and placenta. Four of 6 methylcholanthrene-induced fibrosarcomas in BALB/c mice showed strong expression of OY-MS-4. In 6 T-cell leukemias, only a dimethylbenzanthracene-induced leukemia, EL4 (C57BL), showed strong expression. Two other tumors, A20.2J and P815, induced by ethylnitrosourea and methylcholanthrene, respectively, also strongly expressed OY-MS-4. The other 9 gene products identified in Meth A by SEREX were expressed in all 15 tumors tested and in a range of normal tissues. Sequence analysis of cDNA inserts coding for the SEREX-defined antigens showed no evidence of mutation. Despite the expression of OY-MS-1-10 antigens in methylcholanthrene sarcomas other than Meth A, no antibody was detected in the sera of mice bearing these other sarcomas. The basis for the unique immunogenicity of OY-MS-1-10 presented by Meth A, but not by other syngeneic tumors expressing these gene products, is unknown.

Gpbox (Psx2), a homeobox gene preferentially expressed in female germ cells at the onset of sexual dimorphism in mice

XX gonads differentiate into ovaries, a morphologic event evident by embryonic day 13.5 (E13.5) in mice. To identify early markers of oogenesis, sex-specific urogenital ridge cDNA libraries were constructed from E12-13 embryos. After mass excision and isolation of plasmid DNA, approximately 4800 expressed sequence tags were determined and compared to existing databases. Few cDNAs were specifically expressed in the urogenital ridge, but one, designated GPBOX, encodes a 227-amino-acid homeobox protein that is first expressed at E10.5 in the embryo as well as in the extraembryonic tissues. The Gpbox gene is single copy in the mouse genome and is located on the X chromosome in close proximity to two other homeobox genes, Pem and Psx1. Within the embryo, its expression is limited to the gonad, and transcripts are not detected in adult tissues. Although comparable levels are initially present in both sexes, GPBOX transcripts accumulate faster in female germ cells and peak at E12.5 when they are present in fivefold greater abundance than in males. The persistence of GPBOX transcripts in female germ cells until E15.5 and their virtual disappearance in males by E13.5 suggest that Gpbox may play a role in mammalian oogenesis.