Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1 alpha

Hypoxia is an essential developmental and physiological stimulus that plays a key role in the pathophysiology of cancer, heart attack, stroke, and other major causes of mortality. Hypoxia-inducible factor 1 (HIF-1) is the only known mammalian transcription factor expressed uniquely in response to physiologically relevant levels of hypoxia. We now report that in Hif1a-/- embryonic stem cells that did not express the O2-regulated HIF-1alpha subunit, levels of mRNAs encoding glucose transporters and glycolytic enzymes were reduced, and cellular proliferation was impaired. Vascular endothelial growth factor mRNA expression was also markedly decreased in hypoxic Hif1a-/- embryonic stem cells and cystic embryoid bodies. Complete deficiency of HIF-1alpha resulted in developmental arrest and lethality by E11 of Hif1a-/- embryos that manifested neural tube defects, cardiovascular malformations, and marked cell death within the cephalic mesenchyme. In Hif1a+/+ embryos, HIF-1alpha expression increased between E8.5 and E9.5, coincident with the onset of developmental defects and cell death in Hif1a-/- embryos. These results demonstrate that HIF-1alpha is a master regulator of cellular and developmental O2 homeostasis.

Derivation of pluripotent stem cells from cultured human primordial germ cells

Human pluripotent stem cells would be invaluable for in vitro studies of aspects of human embryogenesis. With the goal of establishing pluripotent stem cell lines, gonadal ridges and mesenteries containing primordial germ cells (PGCs, 5-9 weeks postfertilization) were cultured on mouse STO fibroblast feeder layers in the presence of human recombinant leukemia inhibitory factor, human recombinant basic fibroblast growth factor, and forskolin. Initially, single PGCs in culture were visualized by alkaline phosphatase activity staining. Over a period of 7-21 days, PGCs gave rise to large multicellular colonies resembling those of mouse pluripotent stem cells termed embryonic stem and embryonic germ (EG) cells. Throughout the culture period most cells within the colonies continued to be alkaline phosphatase-positive and tested positive against a panel of five immunological markers (SSEA-1, SSEA-3, SSEA-4, TRA-1-60, and TRA-1-81) that have been used routinely to characterize embryonic stem and EG cells. The cultured cells have been continuously passaged and found to be karyotypically normal and stable. Both XX and XY cell cultures have been obtained. Immunohistochemical analysis of embryoid bodies collected from these cultures revealed a wide variety of differentiated cell types, including derivatives of all three embryonic germ layers. Based on their origin and demonstrated properties, these human PGC-derived cultures meet the criteria for pluripotent stem cells and most closely resemble EG cells.

Targeted disruption of the mouse factor VIII gene produces a model of haemophilia A

Haemophilia A is a classic X-linked disease which affects 1 in 5-10,000 males in all populations and is caused by defects in coagulation factor VIII. Roughly 60% of patients have severe disease with factor VIII activity < 1% of normal; they have frequent spontaneous bleeding into joints, soft tissues, muscles and internal organs. These patients usually require regular injections of plasma-derived or recombinant human factor VIII. Because this is expensive and can potentially lead to life-threatening complications, other forms of therapy, including gene therapy, have been proposed. Natural canine models of factor VIII and factor IX deficiency have been available for many years, and gene therapy attempts on these dogs have met with partial success. However, a small animal model of the disease is desirable for studies of factor VIII function and gene therapy. Using gene targeting, we have made a mouse with severe factor VIII deficiency.

A locus control region adjacent to the human red and green visual pigment genes

Deletion of sequences 5' of the human red and green pigment gene array results in blue cone monochromacy, a disorder in which both red and green cone function are absent. To test whether these sequences are required for transcription of the adjacent visual pigment genes in cone photoreceptors, we produced transgenic mice carrying sequences upstream of the red and green pigment genes fused to a beta-galactosidase reporter. The patterns of transgene expression indicate that the human sequences direct expression to both long and short wave-sensitive cones in the mouse retina and that a region between 3.1 kb and 3.7 kb 5' of the red pigment gene transcription initiation site is essential for expression. Sequences within this region are highly conserved among humans, mice, and cattle, even though the latter two species have only a single visual pigment gene at this locus. These experiments suggest a model in which an interaction between the conserved 5' region and either the red or the green pigment gene promoter determines which of the two genes a given cone expresses.

Introduction and expression of the 400 kilobase amyloid precursor protein gene in transgenic mice [corrected]

Overexpression of the gene encoding the beta-amyloid precursor protein (APP) may have a key role in the pathogenesis of both Alzheimer's disease (AD) and Down Syndrome (DS). We have therefore introduced a 650 kilobase (kb) yeast artificial chromosome (YAC) that contains the entire, unrearranged 400 kb human APP gene into mouse embryonic stem (ES) cells by lipid-mediated transfection. ES lines were generated that contain a stably integrated, unrearranged human APP gene. Moreover, we demonstrate germ line transmission of the APP YAC in transgenic mice and expression of human APP mRNA and protein at levels comparable to endogenous APP. This transgenic strategy may prove invaluable for the development of mouse models for AD and DS.

The end of the beginning for pluripotent stem cells

Pluripotent stem cells can be expanded seemingly indefinitely in culture, maintain a normal karyotype and have the potential to generate any cell type in the body. As such they represent an incredible resource for the repair of diseased or damaged tissues in our bodies. These cells also promise to open a new window into the embryonic development of our species.

The neurobiologic consequences of Down syndrome

Trisomy of the whole or distal part of human chromosome 21 (HSA 21) (Ts21) results in Down Syndrome (DS), which is characterized in part by mental retardation and associated neurological abnormalities. Structural abnormalities observed frequently include reduced brain weight, decreased number and depth of sulci in the cerebral cortices, neuronal heterotopias, and reduced numbers of specific populations of neurons, such as granule cells, in the cerebral cortices. Abnormalities in the structure of cells, primarily of the dendrites, are observed in portions of the neuraxis, such as the hippocampus, cerebellum, and cerebral cortices. Functional abnormalities in membrane properties in peripheral structures and in neurotransmitter enzyme systems in both peripheral and central structures are observed also. Brains of DS individuals over the age of 40 exhibit the characteristic neuropathologic and neurochemical stigmata of Alzheimer's disease (AD). The cholinergic and noradrenergic systems appear to be particularly vulnerable. To elucidate the mechanisms responsible for these abnormalities, identification of the genes located in the distal part of HSA 21 and the systematic study of animal model systems with close genetic homology are essential.

Optimization of direct fibroblast reprogramming to cardiomyocytes using calcium activity as a functional measure of success

Direct conversion of fibroblasts to induced cardiomyocytes (iCMs) has great potential for regenerative medicine. Recent publications have reported significant progress, but the evaluation of reprogramming has relied upon non-functional measures such as flow cytometry for cardiomyocyte markers or GFP expression driven by a cardiomyocyte-specific promoter. The issue is one of practicality: the most stringent measures - electrophysiology to detect cell excitation and the presence of spontaneously contracting myocytes - are not readily quantifiable in the large numbers of cells screened in reprogramming experiments. However, excitation and contraction are linked by a third functional characteristic of cardiomyocytes: the rhythmic oscillation of intracellular calcium levels. We set out to optimize direct conversion of fibroblasts to iCMs with a quantifiable calcium reporter to rapidly assess functional transdifferentiation. We constructed a reporter system in which the calcium indicator GCaMP is driven by the cardiomyocyte-specific Troponin T promoter. Using calcium activity as our primary outcome measure, we compared several published combinations of transcription factors along with novel combinations in mouse embryonic fibroblasts. The most effective combination consisted of Hand2, Nkx2.5, Gata4, Mef2c, and Tbx5 (HNGMT). This combination is >50-fold more efficient than GMT alone and produces iCMs with cardiomyocyte marker expression, robust calcium oscillation, and spontaneous beating that persist for weeks following inactivation of reprogramming factors. HNGMT is also significantly more effective than previously published factor combinations for the transdifferentiation of adult mouse cardiac fibroblasts to iCMs. Quantification of calcium function is a convenient and effective means for the identification and evaluation of cardiomyocytes generated by direct reprogramming. Using this stringent outcome measure, we conclude that HNGMT produces iCMs more efficiently than previously published methods.

Cell-type-specific and hypoxia-inducible expression of the human erythropoietin gene in transgenic mice

Synthesis of erythropoietin, the primary humoral regulator of erythropoiesis, in liver and kidney is inducible by anemia or hypoxia. Analysis of human erythropoietin gene expression in transgenic mice revealed that sequences located 6-14 kilobases 5' to the gene direct expression to the kidney, whereas sequences within the immediate 3'-flanking region control hepatocyte-specific expression. Human erythropoietin transcription initiation sites were differentially utilized in liver and kidney. Inducible transgene expression was precisely targeted to peritubular interstitial cells in the renal cortex that synthesize endogenous mouse erythropoietin. These studies demonstrate that multiple erythropoietin gene regulatory elements control cell-type-specific expression and inducibility by a fundamental physiologic stimulus, hypoxia.

Human embryonic germ cell derivatives express a broad range of developmentally distinct markers and proliferate extensively in vitro

Human pluripotent stem cells (hPSCs) have been derived from the inner cell mass cells of blastocysts (embryonic stem cells) and primordial germ cells of the developing gonadal ridge (embryonic germ cells). Like their mouse counterparts, hPSCs can be maintained in culture in an undifferentiated state and, upon differentiation, generate a wide variety of cell types. Embryoid body (EB) formation is a requisite step in the process of in vitro differentiation of these stem cells and has been used to derive neurons and glia, vascular endothelium, hematopoietic cells, cardiomyocytes, and glucose-responsive insulin-producing cells from mouse PSCs. EBs generated from human embryonic germ cell cultures have also been found to contain a wide variety of cell types, including neural cells, vascular endothelium, muscle cells, and endodermal derivatives. Here, we report the isolation and culture of cells from human EBs as well as a characterization of their gene expression during growth in several different culture environments. These heterogeneous cell cultures are capable of robust and long-term [>70 population doublings (PD)] proliferation in culture, have normal karyotypes, and can be cryopreserved, clonally isolated, and stably transfected. Cell cultures and clonal lines retain a broad pattern of gene expression including simultaneous expression of markers normally associated with cells of neural, vascular/hematopoietic, muscle, and endoderm lineages. The growth and expression characteristics of these EB-derived cells suggest that they are relatively uncommitted precursor or progenitor cells. EB-derived cells may be suited to studies of human cell differentiation and may play a role in future transplantation therapies.

Unusual topography of bovine rhodopsin promoter-lacZ fusion gene expression in transgenic mouse retinas

To define the cis-acting DNA elements required for rhodopsin expression, we generated lines of transgenic mice carrying sequences upstream of the bovine rhodopsin gene fused to the E. coli beta-galactosidase gene (lacZ). Upstream sequences extending from -2174 to +70 bp, from -734 to +70 bp, and from -222 to +70 bp direct photoreceptor-specific expression. All three -2174 lines demonstrate a superior-temporal to inferior-nasal gradient of expression across the retina, whereas lines carrying the shorter constructs demonstrate either spatially continuous expression across the retina, discrete clusters of expression, or both. As a complementary approach to defining regulatory elements, we compared DNA sequences 5' of the murine, bovine, and human rhodopsin genes. Significant homology between all three species was found just upstream of the transcription start site and at approximately 1.5 kb upstream.

Expression of NF-L in both neuronal and nonneuronal cells of transgenic mice: increased neurofilament density in axons without affecting caliber

We have generated transgenic mice containing additional copies of the murine NF-L gene in order to examine the consequences of neurofilament-L overexpression on axonal morphology. Founder mice were constructed to carry a transgene in which the presumptive 5' promoter sequences of NF-L were replaced with the strong murine sarcoma virus long terminal repeat promoter. The transgenes were expressed prominently in several tissues, including skeletal muscle and kidney where NF-L accumulated to approximately 2% of cell protein. This was not accompanied by an overt phenotype, except that expression in lens led to cataract formation. In the brains of these animals, transgene RNA levels exceeded the endogenous NF-L RNAs by up to 20-fold, although no additional protein accumulated, indicating posttranscriptional regulation of NF-L expression. However, in peripheral neurons transgene RNA was approximately fourfold higher than endogenous NF-L mRNAs, and a corresponding increase in NF-L subunits was found in axons arising from these neurons. Myelinated nerve fibers of transgenic animals contained increased numbers of NFs, assembled predominantly of NF-L. This was reflected in an increase in the density of axonal NFs; axonal caliber was not affected.

Inhibition of TGFβ signaling increases direct conversion of fibroblasts to induced cardiomyocytes

Recent studies have been successful at utilizing ectopic expression of transcription factors to generate induced cardiomyocytes (iCMs) from fibroblasts, albeit at a low frequency in vitro. This work investigates the influence of small molecules that have been previously reported to improve differentiation to cardiomyocytes as well as reprogramming to iPSCs in conjunction with ectopic expression of the transcription factors Hand2, Nkx2.5, Gata4, Mef2C, and Tbx5 on the conversion to functional iCMs. We utilized a reporter system in which the calcium indicator GCaMP is driven by the cardiac Troponin T promoter to quantify iCM yield. The TGFβ inhibitor, SB431542 (SB), was identified as a small molecule capable of increasing the conversion of both mouse embryonic fibroblasts and adult cardiac fibroblasts to iCMs up to ∼5 fold. Further characterization revealed that inhibition of TGFβ by SB early in the reprogramming process led to the greatest increase in conversion of fibroblasts to iCMs in a dose-responsive manner. Global transcriptional analysis at Day 3 post-induction of the transcription factors revealed an increased expression of genes associated with the development of cardiac muscle in the presence of SB compared to the vehicle control. Incorporation of SB in the reprogramming process increases the efficiency of iCM generation, one of the major goals necessary to enable the use of iCMs for discovery-based applications and for the clinic.

Astrocytosis and axonal proliferation in the hippocampus of S100b transgenic mice

S100 beta is a calcium-binding protein that is expressed at high levels in brain primarily by astrocytes. Addition of the disulfide-bonded dimeric form of S100 beta to primary neuronal and glial cultures and established cell lines induces axonal extension and alterations in astrocyte proliferation and phenotype, but evidence that S100 beta exerts the same effects in vivo has not been presented. An 8.9-kb murine S100b genomic clone was used to produce two lines of transgenic mice in which S100 beta RNA is increased in a dose-related manner to 2-fold and 7-fold above normal. These lines show concomitant increased S100 beta protein throughout the brain. Expression in both lines is cell type- and tissue-appropriate, and expression levels are correlated with the transgene copy number, demonstrating that sequences necessary for normal regulation of the gene are included within the cloned segment. In the hippocampus of adult transgenic mice, Western blotting detects elevated levels of glial fibrillary acidic protein and several markers of axonal sprouting, including neurofilament L, phosphorylated epitopes of neurofilament H and M, and beta-tubulin. Immunocytochemistry demonstrates alterations in astrocyte morphology and axonal sprouting, especially in the dentate gyrus. Thus, both astrocytosis and neurite proliferation occur in transgenic mice expressing elevated levels of S100 beta. These transgenic mice provide a useful model for studies of the role of S100 beta in glial-neuronal interactions in normal development and function of the brain and for analyzing the significance of elevated levels of S100 beta in Down syndrome and Alzheimer disease.

Efficient conversion of astrocytes to functional midbrain dopaminergic neurons using a single polycistronic vector

Direct cellular reprogramming is a powerful new tool for regenerative medicine. In efforts to understand and treat Parkinson's Disease (PD), which is marked by the degeneration of dopaminergic neurons in the midbrain, direct reprogramming provides a valuable new source of these cells. Astrocytes, the most plentiful cells in the central nervous system, are an ideal starting population for the direct generation of dopaminergic neurons. In addition to their potential utility in cell replacement therapies for PD or in modeling the disease in vitro, astrocyte-derived dopaminergic neurons offer the prospect of direct in vivo reprogramming within the brain. As a first step toward this goal, we report the reprogramming of astrocytes to dopaminergic neurons using three transcription factors - ASCL1, LMX1B, and NURR1 - delivered in a single polycistronic lentiviral vector. The process is efficient, with 18.2±1.5% of cells expressing markers of dopaminergic neurons after two weeks. The neurons exhibit expression profiles and electrophysiological characteristics consistent with midbrain dopaminergic neurons, notably including spontaneous pacemaking activity, stimulated release of dopamine, and calcium oscillations. The present study is the first demonstration that a single vector can mediate reprogramming to dopaminergic neurons, and indicates that astrocytes are an ideal starting population for the direct generation of dopaminergic neurons.

Functional antigen-presenting leucocytes derived from human embryonic stem cells in vitro

BACKGROUND

Differentiated cells derived from pluripotent human embryonic stem (hES) cells offer the opportunity for new transplantation therapies. However, hES cells and their differentiated progeny express highly polymorphic MHC molecules that serve as major graft rejection antigens to the immune system of allogeneic hosts. To achieve sustained engraftment of donor cells, strategies must be developed to overcome graft rejection without broadly suppressing host immunity. One approach entails induction of donor-specific immune tolerance by establishing chimeric engraftment in hosts with haemopoietic cells derived from an existing hES cell line. We aimed to develop methods to efficiently differentiate hES cells to haemopoietic cells, including immune-modulating leucocytes, a prerequisite of the tolerance induction strategies applying to hES cell-mediated transplantation.

METHODS

We developed a method to generate a broad range of haemopoietic cells from hES-generated embryonic bodies in the absence of murine stromal feeder cells. Embryonic bodies were further cultured in the presence of haemopoietic cytokines. In addition to flow cytometric analyses of haemopoietic cell markers, we analysed the hES cell-derived haemopoietic cells by colony-forming assays (for erythroid and myeloid progenitor cells), cytochemical staining, and mixed leucocyte reactions to determine the functional capacity of the generated antigen-presenting cells.

FINDINGS

12 independent experiments were done. When selected growth factors were added, leucocytes expressing CD45 were generated and released into culture media for 6-7 weeks. Under the condition used, both erythroid and myeloid progenitor cells were generated. About 25% of the generated leucocytes acquired MHC class II and costimulatory molecule expression. These hES-derived, MHC class II+ leucocytes resembled dendritic cells and macrophages, and they functioned as antigen-presenting cells capable of eliciting allogeneic CD4 and CD8 T-cell responses in culture.

INTERPRETATION

The hES cell-derived antigen-presenting cells could be used to regulate alloreactive T cells and induce immune tolerance for improvement of the transplant acceptance of hES-cell derivatives.

MicroRNA expression profiling of oligodendrocyte differentiation from human embryonic stem cells

BACKGROUND

Cells of the oligodendrocyte (OL) lineage play a vital role in the production and maintenance of myelin, a multilamellar membrane which allows for saltatory conduction along axons. These cells may provide immense therapeutic potential for lost sensory and motor function in demyelinating conditions, such as spinal cord injury, multiple sclerosis, and transverse myelitis. However, the molecular mechanisms controlling OL differentiation are largely unknown. MicroRNAs (miRNAs) are considered the "micromanagers" of gene expression with suggestive roles in cellular differentiation and maintenance. Although unique patterns of miRNA expression in various cell lineages have been characterized, this is the first report documenting their expression during oligodendrocyte maturation from human embryonic stem (hES) cells. Here, we performed a global miRNA analysis to reveal and identify characteristic patterns in the multiple stages leading to OL maturation from hES cells including those targeting factors involved in myelin production.

METHODOLOGY/PRINCIPAL FINDINGS

We isolated cells from 8 stages of OL differentiation. Total RNA was subjected to miRNA profiling and validations preformed using real-time qRT-PCR. A comparison of miRNAs from our cultured OLs and OL progenitors showed significant similarities with published results from equivalent cells found in the rat and mouse central nervous system. Principal component analysis revealed four main clusters of miRNA expression corresponding to early, mid, and late progenitors, and mature OLs. These results were supported by correlation analyses between adjacent stages. Interestingly, the highest differentially-expressed miRNAs demonstrated a similar pattern of expression throughout all stages of differentiation, suggesting that they potentially regulate a common target or set of targets in this process. The predicted targets of these miRNAs include those with known or suspected roles in oligodendrocyte development and myelination including C11Orf9, CLDN11, MYTL1, MBOP, MPZL2, and DDR1.

CONCLUSIONS/SIGNIFICANCE

We demonstrate miRNA profiles during distinct stages in oligodendroglial differentiation that may provide key markers of OL maturation. Our results reveal pronounced trends in miRNA expression and their potential mRNA target interactions that could provide valuable insight into the molecular mechanisms of differentiation.

Polycythemia in transgenic mice expressing the human erythropoietin gene

Erythropoietin is a glycoprotein hormone that regulates mammalian erythropoiesis. To study the expression of the human erythropoietin gene, EPO, 4 kilobases of DNA encompassing the gene with 0.4 kilobase of 5' flanking sequence and 0.7 kilobase of 3' flanking sequence was microinjected into fertilized mouse eggs. Transgenic mice were generated that are polycythemic, with increased erythrocytic indices in peripheral blood, increased numbers of erythroid precursors in hematopoietic tissue, and increased serum erythropoietin levels. Transgenic homozygotes show a greater degree of polycythemia than do heterozygotes as well as striking extramedullary erythropoiesis. Human erythropoietin RNA was found not only in fetal liver, adult liver, and kidney but also in all other transgenic tissues analyzed. Anemia induced increased human erythropoietin RNA levels in liver but not kidney. These transgenic mice represent a unique model of polycythemia due to increased erythropoietin levels.

Conserved chromosomal positions of dual domains of the ets protooncogene in cats, mice, and humans

The mammalian protooncogene homologue of the avian v-ets sequence from the E26 retrovirus consists of two sequentially distinct domains located on different chromosomes. Using somatic cell hybrid panels, we have mapped the mammalian homologue of the 5' v-ets-domain to chromosome 11 (ETS1) in man, to chromosome 9 (Ets-1) in mouse, and to chromosome D1 (ETS1) in the domestic cat. The mammalian homologue of the 3' v-ets domain was similarly mapped to human chromosome 21 (ETS2), to mouse chromosome 16 (Ets-2), and to feline chromosome C2 (ETS2). Both protooncogenes fell in syntenic groups of homologous linked loci that were conserved among the three species. The occurrence of two distinct functional protooncogenes and their conservation of linkage positions in the three mammalian orders indicate that these two genes have been separate since before the evolutionary divergence of mammals.

Altered metabolism of familial Alzheimer's disease-linked amyloid precursor protein variants in yeast artificial chromosome transgenic mice

Missense mutations in the beta-amyloid precursor protein gene (APP) co-segregate with a small subset of autosomal dominant familial Alzheimer's disease (FAD) cases wherein deposition of the 39-43 amino acid beta-amyloid (A beta) peptide and neurodegeneration are principal neuropathological hallmarks. To accurately examine the effect of missense mutations on APP metabolism and A beta production in vivo, we have introduced yeast artificial chromosomes (YACs) containing the entire approximately 400 kbp human APP gene encoding APP harboring either the asparagine for lysine and leucine for methionine FAD substitution at codons 670 and 671 (APP(K670N/M671L)), the isoleucine for valine FAD substitution at codon 717 (APP(V7171)) or a combination of both substitutions into transgenic mice. We demonstrate that, relative to YAC transgenic mice expressing wild-type APP, high levels of A beta peptides are detected in the brains of YAC transgenic mice expressing human APP(K670N/M671L) that is associated with a concomitant diminution in the levels of apha-secretase-generated soluble APP derivatives. Moreover, the levels of longer A beta peptides (species terminating at amino acids 42/43) are elevated in YAC transgenic mice expressing human APP(V7171). These mice should prove valuable for detailed analysis of the in vivo effects of the APP FAD mutations in a variety of tissues and throughout aging and for testing therapeutic agents that specifically alter APP metabolism and A beta production.

Expression of pluripotent stem cell markers in the human fetal ovary

BACKGROUND

Human primordial germ cells (PGCs) can give rise to pluripotent stem cells such as embryonal carcinoma cells (ECCs) and embryonic germ cells (EGCs).

METHODS

In order to determine whether PGCs express markers associated with pluripotency in EGCs and ECCs, the following study cross examines the expression patterns of multiple pluripotent markers in the human fetal ovary, 5.5-15 weeks post-fertilizaton (pF) and relates this expression with the ability to derive pluripotent EGCs in vitro.

RESULTS

Specific subpopulations were identified which included OCT4(+)/Nanog(+)/cKIT(+)/VASA(+) PGCs and oogonia. Interestingly, these cells also expressed SSEA1 and alkaline phosphatase (AP) and SSEA4 expression occurred throughout the entire gonad. Isolation of SSEA1(+) cells from the gonad resulted in AP(+) EGC colony formation. The number of OCT4(+) or Nanog(+) expressing cells peaked by week 8 and then diminished after week 9 pF, as oogonia enter meiosis. In addition, the efficiency of EGC derivation was associated with the number of OCT4(+) cells. TRA-1-60 and TRA-1-81 were only detected in the lining of the mesonephric ducts and occasionally in the gonad.

CONCLUSIONS

These results demonstrate that PGCs, a unipotent cell, express most, but not all, of the markers associated with pluripotent cells in the human fetal ovary.

Genetic basis for a mouse model of Down syndrome

The Trisomy 16 (Ts16) mouse has been proposed as a model for Down Syndrome (DS) in humans, based on genetic homology between mouse chromosome 16 (MMU 16) and human chromosome 21 (HSA 21). Translocations of HSA 21 resulting in trisomy for only a portion of the genetic information contained on this chromosome can result in a DS phenotype. Thus, these translocations help to define a "DS region" of the chromosome. A number of genes from this DS region of HSA 21 have been mapped to MMU 16. Techniques for localizing genes on chromosomes have been used to identify the portion of MMU 16 which corresponds to the DS region of HSA 21. This region appears to be highly conserved between mouse and human, providing further support for a mouse model of DS.