Foxn1 overexpression promotes thymic epithelial progenitor cell proliferation and mTEC maintenance, but does not prevent thymic involution

The transcription factor FOXN1 is essential for fetal thymic epithelial cell (TEC) differentiation and proliferation. Postnatally, Foxn1 levels vary widely between TEC subsets, from low/undetectable in putative TEC progenitors to highest in differentiated TEC subsets. Correct Foxn1 expression is required to maintain the postnatal microenvironment; premature downregulation of Foxn1 causes a rapid involution-like phenotype, and transgenic overexpression can cause thymic hyperplasia and/or delayed involution. We investigated a K5.Foxn1 transgene that drives overexpression in mouse TECs, but causes neither hyperplasia nor delay or prevention of aging-related involution. Similarly, this transgene cannot rescue thymus size in Foxn1lacZ/lacZ mice, which undergo premature involution as a result of reduced Foxn1 levels. However, TEC differentiation and cortico-medullary organization are maintained with aging in both K5.Foxn1 and Foxn1lacZ/lacZ mice. Analysis of candidate TEC markers showed co-expression of progenitor and differentiation markers as well as increased proliferation in Plet1+ TECs associated with Foxn1 expression. These results demonstrate that the functions of FOXN1 in promoting TEC proliferation and differentiation are separable and context dependent, and suggest that modulating Foxn1 levels can regulate the balance of proliferation and differentiation in TEC progenitors.

Embryology of the Parathyroid Glands

The parathyroid glands are essential for regulating calcium homeostasis in the body. The genetic programs that control parathyroid fate specification, morphogenesis, differentiation, and survival are only beginning to be delineated, but are all centered around a key transcription factor, GCM2. Mutations in the Gcm2 gene as well as in several other genes involved in parathyroid organogenesis have been found to cause parathyroid disorders in humans. Therefore, understanding the normal development of the parathyroid will provide insight into the origins of parathyroid disorders.

The untapped potential of the GENSAT mice-A valuable resource for developmental biology

Gene Expression Nervous System Atlas (GENSAT) transgenic mice express EGFP, tdTomato, or Cre recombinase in a wide range of cell types. The mice and the bacterial artificial chromosome transgenes are available from repositories (MMRRC or CHORI), thereby making these resources readily available to the research community. This resource of 1,386 transgenic lines was developed and validated for neuroscience research. However, GENSAT mice have many potential applications in other contexts including studies of development outside of the CNS. The cell type-specific expression of fluorescent proteins in these mice has been used to identify cells in living embryos, in living embryo explants, and in stem or progenitor cell populations in postnatal tissues. The large number of fluorescent protein driver lines generated by GENSAT greatly expands the range of cell type markers that can be used for live cell sorting. In addition, the GENSAT project has generated 278 new Cre driver lines. This review provides an overview of the GENSAT lines and information for identifying lines that may be useful for a particular application. I also provide a review of the few published cases in which GENSAT mice have been used for studies of embryonic development or analysis of stem/progenitor cells in nonneural tissues. genesis 54:245-256, 2016. © 2016 Wiley Periodicals, Inc.

SDF and GABA interact to regulate axophilic migration of GnRH neurons

Stromal derived growth factor (SDF-1) and gamma-aminobutyric acid (GABA) are two extracellular cues that regulate the rate of neuronal migration during development and may act synergistically. The molecular mechanisms of this interaction are still unclear. Gonadotropin releasing hormone-1 (GnRH) neurons are essential for vertebrate reproduction. During development, these neurons emerge from the nasal placode and migrate through the cribriform plate into the brain. Both SDF-1 and GABA have been shown to regulate the rate of GnRH neuronal migration by accelerating and slowing migration, respectively. As such, this system was used to explore the mechanism by which these molecules act to produce coordinated cell movement during development. In the present study, GABA and SDF-1 are shown to exert opposite effects on the speed of cell movement by activating depolarizing or hyperpolarizing signaling pathways, GABA via changes in chloride and SDF-1 via changes in potassium. GABA and SDF-1 were also found to act synergistically to promote linear rather than random movement. The simultaneous activation of these signaling pathways, therefore, results in tight control of cellular speed and improved directionality along the migratory pathway of GnRH neurons.

A focused in situ hybridization screen identifies candidate transcriptional regulators of thymic epithelial cell development and function

Background

Thymic epithelial cells (TECs) are necessary for normal T cell development. Currently, one transcription factor, Foxn1 is known to be necessary for the progression of fetal TEC differentiation. However, some aspects of fetal TEC differentiation occur in Foxn1 mutants, suggesting the existence of additional transcriptional regulators of TEC differentiation. The goal of this study was to identify some of the additional candidate transcription factors that may be involved in the specification and/or differentiation of TECs during fetal development.

Methodology/Principal Findings

We identified candidate fetal TEC transcriptional regulators via data and text mining. From our data mining we selected the transcription factors Foxg1, Isl1, Gata3, Nkx2-5, Nkx2-6 and Sox2 for further studies. Whole mount in situ hybridizations confirmed the expression of these transcription factors within subdomains of the third pharyngeal pouch from E9.5–E10.5. By E11.5 days Foxg1 and Isl1 transcripts were the only mRNAs from this group of genes detected exclusively within the thymus domain of the third pouch. Based on this initial in situ hybridization analysis, we focused on defining the expression of Foxg1 and Isl1 during multiple stages of thymus development and TEC differentiation. We found that Foxg1 and Isl1 are specifically expressed in differentiating TECs during fetal and postnatal stages of thymus development. In addition, we found differential expression of Islet1 and Foxn1 within the fetal and postnatal TEC population.

Conclusions/Significance

Our studies have identified two developmental transcription factors that are excellent candidate regulators of thymic epithelial cell specification and differentiation during fetal development. Our results suggest that Foxg1 and Isl1 may play a role in the regulation of TEC differentiation during fetal and postnatal stages. Our results also demonstrate heterogeneity of TECs marked by the differential expression of transcription factors, potentially providing new insights into the regulation of TEC differentiation.

Whole mount in situ hybridization of E8.5 to E11.5 mouse embryos

Whole mount in situ hybridization is a very informative approach for defining gene expression patterns in embryos. The in situ hybridization procedures are lengthy and technically demanding with multiple important steps that collectively contribute to the quality of the final result. This protocol describes in detail several key quality control steps for optimizing probe labeling and performance. Overall, our protocol provides a detailed description of the critical steps necessary to reproducibly obtain high quality results. First, we describe the generation of digoxygenin (DIG) labeled RNA probes via in vitro transcription of DNA templates generated by PCR. We describe three critical quality control assays to determine the amount, integrity and specific activity of the DIG-labeled probes. These steps are important for generating a probe of sufficient sensitivity to detect endogenous mRNAs in a whole mouse embryo. In addition, we describe methods for the fixation and storage of E8.5-E11.5 day old mouse embryos for in situ hybridization. Then, we describe detailed methods for limited proteinase K digestion of the rehydrated embryos followed by the details of the hybridization conditions, post-hybridization washes and RNase treatment to remove non-specific probe hybridization. An AP-conjugated antibody is used to visualize the labeled probe and reveal the expression pattern of the endogenous transcript. Representative results are shown from successful experiments and typical suboptimal experiments.

An evolving NGF-Hoxd1 signaling pathway mediates development of divergent neural circuits in vertebrates

Species are endowed with unique sensory capabilities encoded by divergent neural circuits. One potential explanation for how divergent circuits have evolved is that conserved extrinsic signals are differentially interpreted by developing neurons of different species to yield unique patterns of axonal connections. Although NGF controls survival, maturation and axonal projections of nociceptors of different vertebrates, whether the NGF signal is differentially transduced in different species to yield unique features of nociceptor circuits is unclear. We identified a species-specific signaling module induced by NGF and mediated by a rapidly evolving Hox transcription factor, Hoxd1. Mice lacking Hoxd1 display altered nociceptor circuitry which resembles that normally found in chicks. Conversely, ectopic expression of Hoxd1 in developing chick nociceptors promotes a pattern of axonal projections reminiscent of the mouse. We propose that conserved growth factors control divergent neuronal transcriptional events which mediate interspecies differences in neural circuits and the behaviors they control.

Gata3-deficient mice develop parathyroid abnormalities due to dysregulation of the parathyroid-specific transcription factor Gcm2

Heterozygous mutations of GATA3, which encodes a dual zinc-finger transcription factor, cause hypoparathyroidism with sensorineural deafness and renal dysplasia. Here, we have investigated the role of GATA3 in parathyroid function by challenging Gata3+/- mice with a diet low in calcium and vitamin D so as to expose any defects in parathyroid function. This led to a higher mortality among Gata3+/- mice compared with Gata3+/+ mice. Compared with their wild-type littermates, Gata3+/- mice had lower plasma concentrations of calcium and parathyroid hormone (PTH) and smaller parathyroid glands with a reduced Ki-67 proliferation rate. At E11.5, Gata3+/- embryos had smaller parathyroid-thymus primordia with fewer cells expressing the parathyroid-specific gene glial cells missing 2 (Gcm2), the homolog of human GCMB. In contrast, E11.5 Gata3-/- embryos had no Gcm2 expression and by E12.5 had gross defects in the third and fourth pharyngeal pouches, including absent parathyroid-thymus primordia. Electrophoretic mobility shift, luciferase reporter, and chromatin immunoprecipitation assays showed that GATA3 binds specifically to a functional double-GATA motif within the GCMB promoter. Thus, GATA3 is critical for the differentiation and survival of parathyroid progenitor cells and, with GCM2/B, forms part of a transcriptional cascade in parathyroid development and function.

Textpresso site-specific recombinases: A text-mining server for the recombinase literature including Cre mice and conditional alleles

Textpresso Site Specific Recombinases (http://ssrc.genetics.uga.edu/) is a text-mining web server for searching a database of more than 9,000 full-text publications. The papers and abstracts in this database represent a wide range of topics related to site-specific recombinase (SSR) research tools. Included in the database are most of the papers that report the characterization or use of mouse strains that express Cre recombinase as well as papers that describe or analyze mouse lines that carry conditional (floxed) alleles or SSR-activated transgenes/knockins. The database also includes reports describing SSR-based cloning methods such as the Gateway or the Creator systems, papers reporting the development or use of SSR-based tools in systems such as Drosophila, bacteria, parasites, stem cells, yeast, plants, zebrafish, and Xenopus as well as publications that describe the biochemistry, genetics, or molecular structure of the SSRs themselves. Textpresso Site Specific Recombinases is the only comprehensive text-mining resource available for the literature describing the biology and technical applications of SSRs.

Cleft palate is caused by CNS dysfunction in Gad1 and Viaat knockout mice

Background

Previous studies have shown that disruption of GABA signaling in mice via mutations in the Gad1, Gabrb3 or Viaat genes leads to the development of non-neural developmental defects such as cleft palate. Studies of the Gabrb3 and Gad1 mutant mice have suggested that GABA function could be required either in the central nervous system or in the palate itself for normal palatogenesis.

Methodology/Principal Findings

To further examine the role of GABA signaling in palatogenesis we used three independent experimental approaches to test whether Gad1 or Viaat function is required in the fetal CNS for normal palate development. We used oral explant cultures to demonstrate that the Gad1 and Viaat mutant palates were able to undergo palatogenesis in culture, suggesting that there is no defect in the palate tissue itself in these mice. In a second series of experiments we found that the GABA_A receptor agonist muscimol could rescue the cleft palate phenotype in Gad1 and Viaat mutant embryos. This suggested that normal multimeric GABA_A receptors in the CNS were necessary for normal palatogenesis. In addition, we showed that CNS-specific inactivation of Gad1 was sufficient to disrupt palate development.

Conclusions/Significance

Our results are consistent with a role for Gad1 and Viaat in the central nervous system for normal development of the palate. We suggest that the alterations in GABA signaling lead to non-neural defects such as cleft palate as a secondary effect due to alterations in or elimination of fetal movements.

Textpresso Site Specific Recombinases: a text mining tool to aid in identifying Cre expressing mice and conditional alleles (42.23)

The use of site-specific recombinases such as Cre and Flp in mouse genetics has risen dramatically. The number of mouse strains designed to express Cre recombinase activity in specific tissues and the number of mouse strains carrying conditional "floxed" alleles has increased explosively. As a result, the scientific literature describing these valuable research resources has burgeoned to more than 6000 peer reviewed publications. The large size and rapid growth of this literature makes it very easy to miss key papers that contain critical information relevant to your research. To assist investigators in identifying appropriate Cre recombinase expressing mice, conditional floxed alleles and other research resources based on site specific recombinase technology we have generated a new online resource based on the widely used Textpresso text mining software (http://www.textpresso.org). Our text mining tool, Textpresso Site Specific Recombinases (Textpresso SSR) allows researchers to search a database containing the full text of over 6000 peer-reviewed publications. This database contains most of the publications that describe or use Cre expressing mice as well as papers describing mouse strains carrying conditional mutant alleles. The database can be searched using keywords or combinations of keywords and categories. For each publication that matches the search terms Textpresso SSR displays the abstract as well as the individual sentences that match the query. Textpresso SSR also provides a unique tool for the in depth text mining of publications that describe the results of tissue specific or temporal specific mouse gene knockouts. Textpresso SSR can be accessed at http://ssrc.genetics.uga.edu.

This work was supported by the University of Georgia.

An in situ hybridization screen reveals new transcriptional regulators of third pharyngeal pouch and thymic epithelial cell differentiation. (86.12)

Thymic epithelial cells (TECs) are the major component of the non-lymphoid framework of the thymus and are essential for normal T cell development. In mice, TECs develop from a domain of the embryonic third pharyngeal pouch endoderm marked by Foxn1 expression. Although Foxn1 is necessary for proliferation and differentiation of TECs, it is not required for specification of TECs from the pouch endoderm. Also, some aspects of TEC differentiation are Foxn1-independent. This suggests that there are additional transcription factors expressed within the third pouch endoderm that are responsible for early specification and differentiation of TECs. To identify additional transcriptional regulators of third pouch and TEC differentiation, we performed an in situ hybridization screen on a set of candidate transcription factors identified through a systematic analysis of gene expression databases. We found that most of the genes selected for detailed characterization were expressed in the third pharyngeal pouch endoderm and many of them were specifically expressed in the thymus domain of the pouch. These transcription factors are highly likely to be involved in the earliest steps of TEC development. Our work also shows that data mining of gene expression databases is an efficient way to identify genes involved in the development of a specific tissue or organ.

Temporal migration of gonadotrophin-releasing hormone-1 neurones is modified in GAD67 knockout mice

Gonadotrophin-releasing hormone (GnRH-1) neurones reside in the forebrain and regulate gonadal function via the hypothalamic-pituitary-gonadal axis. Disruption of this axis results in reproductive dysfunction. During embryonic development, GnRH-1 neurones migrate from the nasal pit through the nasal/forebrain junction (NFJ) into the developing brain. Prenatally gamma-aminobutyric acid (GABA) is excitatory and has been shown to play a role in nervous system development. Both in vivo and in vitro experiments suggest that GABA inhibits migration of GnRH-1 neurones. The present study examines the migration of GnRH-1 neurones in GAD67 knockout (KO) mice to further elucidate the role of GABA on GnRH-1 neuronal development. Three stages were examined, embryonic day (E)12.5, E14.5 and E17.5. GnRH-1 cell number and location were analysed by immunocytochemistry and in situ hybridisation histochemistry. The total number of GnRH-1 immunopositive cells was similar between wild-type (WT) and KO mice. However, significant differences were found in the overall distribution of GnRH-1 immunopositive cells in GAD67 KO compared to WT mice at all stages. Subsequent analysis by area revealed differences occurred at the NFJ with an increase in GnRH-1 cells in GAD67 KO at E14.5 and a decrease in GnRH-1 cells in GAD67 KO at E17.5. Comparable counts for cells expressing GnRH-1 transcript and protein were obtained. These data indicate that attenuated levels of GABA accelerate GnRH-1 cell migration in nasal areas as well as movement of GnRH-1 cells into the central nervous system at the NFJ.

Ceramide regulates atypical PKCzeta/lambda-mediated cell polarity in primitive ectoderm cells. A novel function of sphingolipids in morphogenesis

In mammals, the primitive ectoderm is an epithelium of polarized cells that differentiates into all embryonic tissues. Our study shows that in primitive ectoderm cells, the sphingolipid ceramide was elevated and co-distributed with the small GTPase Cdc42 and cortical F-actin at the apicolateral cell membrane. Pharmacological or RNA interference-mediated inhibition of ceramide biosynthesis enhanced apoptosis and impaired primitive ectoderm formation in embryoid bodies differentiated from mouse embryonic stem cells. Primitive ectoderm formation was restored by incubation with ceramide or a ceramide analog. Ceramide depletion prevented plasma membrane translocation of PKCzeta/lambda, its interaction with Cdc42, and phosphorylation of GSK-3beta, a substrate of PKCzeta/lambda. Recombinant PKCzeta formed a complex with the polarity protein Par6 and Cdc42 when bound to ceramide containing lipid vesicles. Our data suggest a novel mechanism by which a ceramide-induced, apicolateral polarity complex with PKCzeta/lambda regulates primitive ectoderm cell polarity and morphogenesis.

Notch signaling is inactive but inducible in human embryonic stem cells

The NOTCH signaling pathway performs a wide range of critical functions in a number of different cell types during development and differentiation. The role of NOTCH signals in human embryonic stem cells (hESCs) has not been tested. We measured the activity of canonical NOTCH signaling in undifferentiated embryonic stem (ES) cells and tested the requirement for NOTCH activity in hESC self-renewal or differentiation by growing hESCs in the presence of gamma-secretase inhibitors. Our results suggest that NOTCH signaling is not required for the propagation of undifferentiated human ES cells but instead is required for the maintenance of the differentiating cell types that accumulate in human ES cell cultures. Our studies suggest that NOTCH signaling is not required in human embryonic differentiation until the formation of extraembryonic, germ layer, or tissue-specific stem cells and progenitors.

Direct Binding to Ceramide Activates Protein Kinase Cζ before the Formation of a Pro-apoptotic Complex with PAR-4 in Differentiating Stem Cells

We have reported that ceramide mediates binding of atypical protein kinase C (PKC) zeta to its inhibitor protein, PAR-4 (prostate apoptosis response-4), thereby inducing apoptosis in differentiating embryonic stem cells. Using a novel method of lipid vesicle-mediated affinity chromatography, we showed here that endogenous ceramide binds directly to the PKCzeta.PAR-4 complex. Ceramide and its analogs activated PKCzeta prior to binding to PAR-4, as determined by increased levels of phosphorylated PKCzeta and glycogen synthase kinase-3beta and emergence of a PAR-4-to-phosphorylated PKCzeta fluorescence resonance energy transfer signal that co-localizes with ceramide. Elevated expression and activation of PKCzeta increased cell survival, whereas expression of PAR-4 promoted apoptosis. This suggests that PKCzeta counteracts apoptosis, unless its ceramide-induced activation is compromised by binding to PAR-4. A luciferase reporter assay showed that ceramide analogs activate nuclear factor (NF)-kappaB unless PAR-4-dependent inhibition of PKCzeta suppresses NF-kappaB activation. Taken together, our results show that direct physical association with ceramide and PAR-4 regulates the activity of PKCzeta. They also indicate that this interaction regulates the activity of glycogen synthase kinase-3beta and NF-kappaB.

The mouse vesicular inhibitory amino acid transporter gene: Expression during embryogenesis, analysis of its core promoter in neural stem cells and a reconsideration of its alternate splicing

The vesicular inhibitory amino acid transporter, VIAAT (also known as vesicular GABA transporter VGAT) transports GABA or glycine into synaptic vesicles. To initiate an analysis of the expression and regulation of VIAAT during neurogenesis we have cloned and characterized the mouse Viaat gene. We find that the mouse Viaat coding sequence is encoded by two exons spanning 5.3 kb. A survey of expression by whole mount in situ hybridization of mouse embryos indicates that Viaat is activated early in neuron differentiation and is expressed widely within the developing CNS; however, we did not detect expression in the superficial non-neural structures that express the GABA synthase Gad1. Analysis of the Viaat promoter indicates that a minimal promoter region containing a CG rich sequence is sufficient for efficient expression in neural stem and precursor cells. Our analysis of the Viaat sequence and splicing does not support the existence of two Viaat isoforms as previously proposed [Ebihara et al., Brain Res. Mol Brain Res. 110 (2003), 126-139]. Instead, the alternative isoform Viaat-a appears to be due to PCR artifacts that have occurred independently in multiple labs.

Differentiation of Human Embryonic Stem Cells to Dopaminergic Neurons in Serum-Free Suspension Culture

The use of human embryonic stem cells (hESCs) as a source of dopaminergic neurons for Parkinson's disease cell therapy will require the development of simple and reliable cell differentiation protocols. The use of cell cocultures, added extracellular signaling factors, or transgenic approaches to drive hESC differentiation could lead to additional regulatory as well as cell production delays for these therapies. Because the neuronal cell lineage seems to require limited or no signaling for its formation, we tested the ability of hESCs to differentiate to form dopamine-producing neurons in a simple serum-free suspension culture system. BG01 and BG03 hESCs were differentiated as suspension aggregates, and neural progenitors and neurons were detectable after 2-4 weeks. Plated neurons responded appropriately to electrophysiological cues. This differentiation was inhibited by early exposure to bone morphogenic protein (BMP)-4, but a pulse of BMP-4 from days 5 to 9 caused induction of peripheral neuronal differentiation. Real-time polymerase chain reaction and whole-mount immunocytochemistry demonstrated the expression of multiple markers of the midbrain dopaminergic phenotype in serum-free differentiations. Neurons expressing tyrosine hydroxylase (TH) were killed by 6-hydroxydopamine (6-OHDA), a neurotoxic catecholamine. Upon plating, these cells released dopamine and other catecholamines in response to K+ depolarization. Surviving TH+ neurons, derived from the cells differentiated in serum-free suspension cultures, were detected 8 weeks after transplantation into 6-OHDA-lesioned rat brains. This work suggests that hESCs can differentiate in simple serum-free suspension cultures to produce the large number of cells required for transplantation studies.

Selective apoptosis of pluripotent mouse and human stem cells by novel ceramide analogues prevents teratoma formation and enriches for neural precursors in ES cell-derived neural transplants

The formation of stem cell-derived tumors (teratomas) is observed when engrafting undifferentiated embryonic stem (ES) cells, embryoid body-derived cells (EBCs), or mammalian embryos and is a significant obstacle to stem cell therapy. We show that in tumors formed after engraftment of EBCs into mouse brain, expression of the pluripotency marker Oct-4 colocalized with that of prostate apoptosis response-4 (PAR-4), a protein mediating ceramide-induced apoptosis during neural differentiation of ES cells. We tested the ability of the novel ceramide analogue N-oleoyl serinol (S18) to eliminate mouse and human Oct-4(+)/PAR-4(+) cells and to increase the proportion of nestin(+) neuroprogenitors in EBC-derived cell cultures and grafts. S18-treated EBCs persisted in the hippocampal area and showed neuronal lineage differentiation as indicated by the expression of beta-tubulin III. However, untreated cells formed numerous teratomas that contained derivatives of endoderm, mesoderm, and ectoderm. Our results show for the first time that ceramide-induced apoptosis eliminates residual, pluripotent EBCs, prevents teratoma formation, and enriches the EBCs for cells that undergo neural differentiation after transplantation.

PITX2 is required for normal development of neurons in the mouse subthalamic nucleus and midbrain

Pitx2, a homeodomain transcription factor, is essential for normal development of the pituitary gland, craniofacial region, eyes, heart, abdominal viscera, and limbs. Complete loss of Pitx2 in mice (Pitx2(-/-)) results in embryonic lethality by approximately e15 due to cardiac defects, whereas embryos with partial loss of function (Pitx2(neo/-) or Pitx2(neo/neo)) survive until later in development (e17-e19). Pitx2 is expressed in discrete populations of postmitotic neurons in the mouse brain, but its role in mammalian central nervous system (CNS) development is not known. We undertook an analysis of Pitx2-deficient embryos to determine whether loss of Pitx2 affects CNS development. The CNS is normal in hypomorphic e16.5 Pitx2(neo/-) and e18.5 Pitx2(neo/neo) embryos, with no evidence of midline or other defects. Midgestation (e10.5) Pitx2(-/-) embryos have normally formed neural tube structures and cerebral vesicles, whereas older (e14.5) Pitx2(-/-) embryos exhibit loss of gene expression and axonal projections in the subthalamic nucleus (a group of cells in the ventrolateral thalamus) and in the developing superior colliculus of dorsal midbrain. Our results suggest a role for Pitx2 in regulating regionally specific terminal neuronal differentiation in the developing ventrolateral thalamus and midbrain.

Gene expression in human embryonic stem cell lines: unique molecular signature

Human embryonic stem (huES) cells have the ability to differentiate into a variety of cell lineages and potentially provide a source of differentiated cells for many therapeutic uses. However, little is known about the mechanism of differentiation of huES cells and factors regulating cell development. We have used high-quality microarrays containing 16 659 seventy-base pair oligonucleotides to examine gene expression in 6 of the 11 available huES cell lines. Expression was compared against pooled RNA from multiple tissues (universal RNA) and genes enriched in huES cells were identified. All 6 cell lines expressed multiple markers of the undifferentiated state and shared significant homology in gene expression (overall similarity coefficient > 0.85).A common subset of 92 genes was identified that included Nanog, GTCM-1, connexin 43 (GJA1), oct-4, and TDGF1 (cripto). Gene expression was confirmed by a variety of techniques including comparison with databases, reverse transcriptase-polymerase chain reaction, focused cDNA microarrays, and immunocytochemistry. Comparison with published "stemness" genes revealed a limited overlap, suggesting little similarity with other stem cell populations. Several novel ES cell-specific expressed sequence tags were identified and mapped to the human genome. These results represent the first detailed characterization of undifferentiated huES cells and provide a unique set of markers to profile and better understand the biology of huES cells.

Directed neuronal differentiation of human embryonic stem cells

Background

We have developed a culture system for the efficient and directed differentiation of human embryonic stem cells (HESCs) to neural precursors and neurons.

HESC were maintained by manual passaging and were differentiated to a morphologically distinct OCT-4⁺/SSEA-4^- monolayer cell type prior to the derivation of embryoid bodies. Embryoid bodies were grown in suspension in serum free conditions, in the presence of 50% conditioned medium from the human hepatocarcinoma cell line HepG2 (MedII).

Results

A neural precursor population was observed within HESC derived serum free embryoid bodies cultured in MedII conditioned medium, around 7–10 days after derivation. The neural precursors were organized into rosettes comprised of a central cavity surrounded by ring of cells, 4 to 8 cells in width. The central cells within rosettes were proliferating, as indicated by the presence of condensed mitotic chromosomes and by phosphoHistone H3 immunostaining. When plated and maintained in adherent culture, the rosettes of neural precursors were surrounded by large interwoven networks of neurites. Immunostaining demonstrated the expression of nestin in rosettes and associated non-neuronal cell types, and a radial expression of Map-2 in rosettes. Differentiated neurons expressed the markers Map-2 and Neurofilament H, and a subpopulation of the neurons expressed tyrosine hydroxylase, a marker for dopaminergic neurons.

Conclusion

This novel directed differentiation approach led to the efficient derivation of neuronal cultures from HESCs, including the differentiation of tyrosine hydroxylase expressing neurons. HESC were morphologically differentiated to a monolayer OCT-4⁺ cell type, which was used to derive embryoid bodies directly into serum free conditions. Exposure to the MedII conditioned medium enhanced the derivation of neural precursors, the first example of the effect of this conditioned medium on HESC.

A domain of Foxn1 required for crosstalk-dependent thymic epithelial cell differentiation

Thymic epithelial cells (TECs) are required for T cell maturation within the thymus. In the nude (Foxn1(nu/nu)) mouse, TECs fail to differentiate. We have generated a hypomorphic allele called Foxn1(Delta), from which an N-terminal domain was deleted. The phenotype was thymus specific, identifying a tissue-specific activity for this domain. Foxn1(Delta/Delta) mice showed abnormal thymic architecture, lacking cortical and medullary domains. In contrast to thymi in mice with the null allele, the Foxn1(Delta/Delta) thymus promoted T cell development, but with specific defects at both the double-negative and double-positive stages. Thus, initiation and progression of TEC differentiation are genetically separable functions of Foxn1, and the N-terminal domain is required for crosstalk-dependent TEC differentiation.

Regulation of cell death in mitotic neural progenitor cells by asymmetric distribution of prostate apoptosis response 4 (PAR-4) and simultaneous elevation of endogenous ceramide

Cell death and survival of neural progenitor (NP) cells are determined by signals that are largely unknown. We have analyzed pro-apoptotic signaling in individual NP cells that have been derived from mouse embryonic stem cells. NP formation was concomitant with elevated apoptosis and increased expression of ceramide and prostate apoptosis response 4 (PAR-4). Morpholino oligonucleotide-mediated antisense knockdown of PAR-4 or inhibition of ceramide biosynthesis reduced stem cell apoptosis, whereas PAR-4 overexpression and treatment with ceramide analogs elevated apoptosis. Apoptotic cells also stained for proliferating cell nuclear antigen (a nuclear mitosis marker protein), but not for nestin (a marker for NP cells). In mitotic cells, asymmetric distribution of PAR-4 and nestin resulted in one nestin(-)/PAR-4(+) daughter cell, in which ceramide elevation induced apoptosis. The other cell was nestin(+), but PAR-4(-), and was not apoptotic. Asymmetric distribution of PAR-4 and simultaneous elevation of endogenous ceramide provides a possible mechanism underlying asymmetric differentiation and apoptosis of neuronal stem cells in the developing brain.

Differentiation of rhesus embryonic stem cells to neural progenitors and neurons

Embryonic stem (ES) cells are pluripotent cells capable of differentiating into cell lineages derived from all primary germ layers including neural cells. In this study we describe an efficient method for differentiating rhesus monkey ES cells to neural lineages and the subsequent isolation of an enriched population of Nestin and Musashi positive neural progenitor (NP) cells. Upon differentiation, these cells exhibit electrophysiological characteristics resembling cultured primary neurons. Embryoid bodies (EBs) were formed in ES growth medium supplemented with 50% MEDII. After 7 days in suspension culture, EBs were transferred to adherent culture and either differentiated in serum containing medium or expanded in serum free medium. Immunocytochemistry on differentiating cells derived from EBs revealed large networks of MAP-2 and NF200 positive neurons. DAPI staining showed that the center of the MEDII-treated EBs was filled with rosettes. NPs isolated from adherent EB cultures expanded in serum free medium were passaged and maintained in an undifferentiated state by culture in serum free N2 with 50% MEDII and bFGF. Differentiating neurons derived from NPs fired action potentials in response to depolarizing current injection and expressed functional ionotropic receptors for the neurotransmitters glutamate and gamma-aminobutyric acid (GABA). NPs derived in this way could serve as models for cellular replacement therapy in primate models of neurodegenerative disease, a source of neural cells for toxicity and drug testing, and as a model of the developing primate nervous system.

New serum-free in vitro culture technique for midgestation mouse embryos

Current in vitro culture methods for mouse embryos are critically dependent on specially prepared rodent serum. Rodent serum requires careful preparation and stringent assessment of serum quality, while commercially available whole embryo culture serum is expensive and shows considerable lot variability. Thus, preparation and testing of suitable serum represents a considerable investment of time and resources, particularly for laboratories with only short-term embryo culture requirements. In addition, serum supplementation of culture medium may introduce unknown serum components that could interfere with interpretation of experimental results, especially where the study is geared towards analysis of a specific growth factor. Here we describe the composition of a standardized serum free culture medium comprised of commercially available stem cell media supplements. With this method, we have successfully cultured midgestation stage mouse embryos and demonstrated, using both morphological and gene expression criteria, that these embryos exhibited proper developmental progression. We believe this method to be a significant advance in whole embryo culture technology that will be of particular use to laboratories needing to utilize whole embryo culture to study midgestation organogenesis.

Experience-dependent plasticity of mouse visual cortex in the absence of the neuronal activity-dependent marker egr1/zif268

Neuronal activity elicits a rapid increase in the expression of several immediate early genes (IEGs). To clarify a role for IEG response in activity-dependent development, we examined the contribution of the egr1/zif268 gene during visual cortical processing and plasticity in mice. We first analyzed the expression of egr1 mRNA in wild-type (WT) mice using Northern blot hybridization. In the visual cortex, expression of egr1 mRNA increased dramatically after eye opening, systemic injection of kainate, or 30 min of photostimulation after a brief (5 d) period of dark adaptation. Thus, the expression of egr1 is regulated by synaptic activity in the mouse visual cortex, as it is in other species (e.g., monkeys, cats, and rats). To evaluate whether this transcription factor is directly involved in activity-dependent plasticity, mice lacking Egr1 were deprived of the use of one eye during the developmental critical period [postnatal day 24 (P24)-P34]. Extracellular in vivo single-unit recordings from the binocular zone of the visual cortex revealed that visual responses developed normally in egr1 knock-out (KO) mice. Moreover, a similarly significant shift of responsiveness in favor of the open eye was produced in both KO and WT mice by either brief (4 d) or long-term (>2 weeks) occlusion of one eye. There was no apparent compensation among egr2, egr3, or c-fos mRNA and protein expression in the visual cortex of egr1 KO mice. Taken together, these results indicate that egr1 is a useful marker of sensory input in mice but is not intrinsically necessary for the experience-dependent plasticity of the visual cortex. Our findings underscore a mechanistic distinction between sensory plasticity and long-lasting forms of synaptic potentiation in the hippocampus, for which egr1/zif268 was recently found to be essential.

Conserved function of Caenorhabditis elegans UNC-30 and mouse Pitx2 in controlling GABAergic neuron differentiation

We are taking a cross-species approach to identify genes that are required for mammalian GABAergic neuron differentiation. On the basis of homeodomain similarity, the vertebrate Pitx genes appear to be orthologs of unc-30, a Caenorhabditis elegans gene necessary for differentiation of the GABAergic phenotype of type D neurons. One of the Pitx genes, Pitx2, is expressed in regions of GABAergic neurogenesis in the mammalian brain. These observations led us to test the functional conservation of the mouse Pitx2 and worm unc-30 genes using a rescue assay. Pitx2 rescues the GABAergic differentiation defect and partially rescues the axon guidance and behavioral phenotypes of unc-30 mutants, indicating a high degree of functional conservation between these evolutionarily related genes. Previous studies show that UNC-30 directly regulates the unc-25/glutamate decarboxylase gene that encodes the enzyme for GABA synthesis. We find that the promoter regions of the mouse and human genes coding for the 67 kDa glutamate decarboxylase (Gad1) also contain binding sites matching the UNC-30/Pitx2 consensus binding site sequence. We show that these sites specifically bind to Pitx2 protein in vitro and that in transfected neuroblastoma cells, the Pitx2 binding sites contribute to the basal activity of the Gad1 promoter. Furthermore, in cotransfection experiments, we find that Pitx2 strongly activates the Gad1 promoter. These results indicate that Pitx2 may regulate Gad1 expression in mammals, suggesting a new role for this key developmental transcription factor as a regulator of GABAergic differentiation during mammalian neural development. Our results suggest that some of the mechanisms regulating GABAergic differentiation are evolutionarily conserved.

Neuronal development of embryonic stem cells: a model of GABAergic neuron differentiation

Neural cultures derived from differentiating embryonic stem (ES) cells are a potentially powerful in vitro model of neural development. We show that neural cells derived from mouse ES cells express mRNAs characteristic of GABAergic neurons. The glutamate decarboxylase genes (Gad1 and Gad2), required for GABA synthesis and the vesicular inhibitory amino acid transporter (Viaat) gene, required for GABA vesicular packaging are activated in the ES-derived cultures. Nearly half of the ES-derived neurons express the GAD67 protein, the product of the Gad1 gene. Building on these results we show that Gad1-lacZ "knockin" reporter ES cell lines can be used to easily monitor Gad1 expression patterns and expression levels during ES differentiation. We also demonstrate that the ES-derived neural progenitors can be infected with retroviruses or transfected with plasmids via lipofection. These experiments outline the basic strategies and methods required for studies of GABAergic gene expression and regulation in ES-derived neuronal cultures.

Down-regulation of dendritic spine and glutamic acid decarboxylase 67 expressions in the reelin haploinsufficient heterozygous reeler mouse

Heterozygous reeler mice (HRM) haploinsufficient for reelin express approximately 50% of the brain reelin content of wild-type mice, but are phenotypically different from both wild-type mice and homozygous reeler mice. They exhibit, (i) a down-regulation of glutamic acid decarboxylase 67 (GAD(67))-positive neurons in some but not every cortical layer of frontoparietal cortex (FPC), (ii) an increase of neuronal packing density and a decrease of cortical thickness because of neuropil hypoplasia, (iii) a decrease of dendritic spine expression density on basal and apical dendritic branches of motor FPC layer III pyramidal neurons, and (iv) a similar decrease in dendritic spines expressed on the basal dendrite branches of CA1 pyramidal neurons of the hippocampus. To establish whether the defect of GAD(67) down-regulation observed in HRM is responsible for neuropil hypoplasia and decreased dendritic spine density, we studied heterozygous GAD(67) knockout mice (HG(67)M). These mice exhibited a down-regulation of GAD(67) mRNA expression in FPC (about 50%), but they expressed normal amounts of reelin and had no neuropil hypoplasia or down-regulation of dendritic spine expression. These findings, coupled with electron-microscopic observations that reelin colocalizes with integrin receptors on dendritic spines, suggest that reelin may be a factor in the dynamic expression of cortical dendritic spines perhaps by promoting integrin receptor clustering. These findings are interesting because the brain neurochemical and neuroanatomical phenotypic traits exhibited by the HRM are in several ways similar to those found in postmortem brains of psychotic patients.

Dynamic expression of a glutamate decarboxylase gene in multiple non-neural tissues during mouse development

BACKGROUND

Glutamate decarboxylase (GAD) is the biosynthetic enzyme for the neurotransmitter gamma-aminobutyric acid (GABA). Mouse embryos lacking the 67-kDa isoform of GAD (encoded by the Gad1 gene) develop a complete cleft of the secondary palate. This phenotype suggests that this gene may be involved in the normal development of tissues outside of the CNS. Although Gad1 expression in adult non-CNS tissues has been noted previously, no systematic analysis of its embryonic expression outside of the nervous system has been performed. The objective of this study was to define additional structures outside of the central nervous system that express Gad1, indicating those structures that may require its function for normal development.

RESULTS

Our analysis detected the localized expression of Gad1 transcripts in several developing tissues in the mouse embryo from E9.0-E14.5. Tissues expressing Gad1 included the tail bud mesenchyme, the pharyngeal pouches and arches, the ectodermal placodes of the developing vibrissae, and the apical ectodermal ridge (AER), mesenchyme and ectoderm of the limb buds.

CONCLUSIONS

Some of the sites of Gad1 expression are tissues that emit signals required for patterning and differentiation (AER, vibrissal placodes). Other sites correspond to proliferating stem cell populations that give rise to multiple differentiated tissues (tail bud mesenchyme, pharyngeal endoderm and mesenchyme). The dynamic expression of Gad1 in such tissues suggests a wider role for GABA signaling in development than was previously appreciated.

Neuronal differentiation of cryopreserved neural progenitor cells derived from mouse embryonic stem cells

Embryonic stem cells (ES cells) are developmentally pluripotent cells isolated from pre-implantation mammalian embryos. In cell culture ES cells can be easily differentiated to generate cultures of neural progenitors. We present a simple method for the cryopreservation of these ES-derived neural progenitors. Cryopreserved neural progenitor stocks can be thawed, expanded with FGF2, and differentiated into functional neurons. This method will facilitate studies using ES-derived neural progenitor cells as a cell culture model system for neural development and differentiation. It will also aid studies designed to test the ability of these progenitor cells to functionally engraft and repair damaged neural tissue.

Glutamate decarboxylase and GABA in pancreatic islets: lessons from knock-out mice

The GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) is expressed in pancreatic beta-cells and GABA has been suggested to play a role in islet cell development and function. Mouse beta-cells predominantly express the larger isoform of the enzyme, GAD67, and very low levels of the second isoform, GAD65. Yet GAD65 has been shown to be a target of very early autoimmune T-cell responses associated with beta-cell destruction in the non-obese diabetic (NOD) mouse model of Type 1 diabetes. Mice deficient in GAD67, GAD65 or both were used to assess whether GABA is important for islet cell development, and whether GAD65 is required for initiation of insulitis and progression to Type 1 diabetes in the mouse. Lack of either GAD65 or GAD67 did not effect the development of islet cells and the general morphology of islets. When GAD65-/-(129/Sv) mice were backcrossed into the NOD strain for four generations, GAD65-deficient mice developed insulitis similar to GAD65+/+ mice. Furthermore, at the low penetrance of diabetes in this backcross, GAD65-deficient mice developed disease at the same rate and incidence as wildtype mice. The results suggest that GABA generated by either GAD65 or GAD67 is not critically involved in islet formation and that GAD65 expression is not an absolute requirement for development of autoimmune diabetes in the NOD mouse.

Cleft palate in mice with a targeted mutation in the gamma-aminobutyric acid-producing enzyme glutamic acid decarboxylase 67

The functions of neurotransmitters in fetal development are poorly understood. Genetic observations have suggested a role for the inhibitory amino acid neurotransmitter gamma-aminobutyric acid (GABA) in the normal development of the mouse palate. Mice homozygous for mutations in the beta-3 GABAA receptor subunit develop a cleft secondary palate. GABA, the ligand for this receptor, is synthesized by the enzyme glutamic acid decarboxylase. We have disrupted one of the two mouse Gad genes by gene targeting and also find defects in the formation of the palate. The striking similarity in phenotype between the receptor and ligand mutations clearly demonstrates a role for GABA signaling in normal palate development.

Mice with targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 reveal synergistic interactions

The Hox genes encode transcription factors which mediate the formation of the mammalian body plan along the anteroposterior and appendicular axes. Paralogous Hox genes within the separate linkage groups are closely related with respect to DNA sequence and expression, suggesting that they could have at least partially redundant functions. We showed previously that mice homozygous for independent targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 had no defects in common. But our current analysis of double mutants has revealed strong, dosage-dependent interactions between these genes. We report here that in hoxd-3- homozygotes the first cervical vertebra, the atlas, is homeotically transformed to the adjacent anterior structure. Unexpectedly, in double mutants, rather than observing a more extensive homeotic transformation, the entire atlas is deleted. These observations are interpreted in terms of a model in which these Hox genes differentially regulate the proliferation rates of the appropriate sets of precursor cells.

Mice homozygous for a targeted disruption of Hoxd-3 (Hox-4.1) exhibit anterior transformations of the first and second cervical vertebrae, the atlas and the axis

Gene targeting in embryo-derived stem (ES) cells was used to generate mice with a disruption in the homeobox-containing gene Hoxd-3 (Hox-4.1). Mice homozygous for this mutation show a radically remodeled craniocervical joint. The anterior arch of the atlas is transformed to an extension of the basioccipital bone of the skull. The lateral masses of the atlas also assume a morphology more closely resembling the exoccipitals and, to a variable extent, fuse with the exoccipitals. Formation of the second cervical vertebra, the axis, is also affected. The dens and the superior facets are deleted, and the axis shows ‘atlas-like’ characteristics. An unexpected observation is that different parts of the same vertebra are differentially affected by the loss of Hoxd-3 function. Some parts are deleted, others are homeotically transformed to more anterior structures. These observations suggest that one role of Hox genes may be to differentially control the proliferation rates of the mesenchymal condensations that give rise to the vertebral cartilages. Within the mouse Hox complex, paralogous genes not only encode very similar proteins but also often exhibit very similar expression patterns. Therefore, it has been postulated that paralogous Hox genes would perform similar roles. Surprisingly, however, no tissues or structures are affected in common by mutations in the two paralogous genes, Hoxa-3 and Hoxd-3.

Most of the homeobox-containing Xhox 36 transcripts in early Xenopus embryos cannot encode a homeodomain protein

Multiple Xhox 36 transcripts accumulate in Xenopus embryos from gastrula to early tadpole stages. The transcripts were characterized by sequencing cDNA clones and by S1 protection and Northern (RNA) blotting of embryonic RNA with probes derived from the cDNAs. The Xhox 36 RNAs included unspliced precursor transcripts that accumulated in the embryonic nuclei, spliced transcripts that contained multiple stop codons in frame with the homeobox, and less abundant coding mRNAs. These transcripts were generated either by alternative splicing or multiple initiations from a single Xhox 36 gene. The sequence of a cDNA clone of the unspliced transcript showed that the intron contained a noncanonical 3' splice site. However, the intron was spliced efficiently when expressed from a plasmid injected into Xenopus embryos, suggesting that the inefficient splicing of the endogenous RNA is not due to the unusual 3' splice site. The accumulation of noncoding and unspliced transcripts suggests multiple levels of regulation in the embryonic expression of the Xhox 36 gene.

Posterior expression of a homeobox gene in early Xenopus embryos

The homeobox containing transcript Xhox-36 is expressed exclusively in the posterior mesoderm and ectoderm of early Xenopus embryos. Therefore, the transcript shows region-specific rather than tissue-specific expression in the gastrula and neurula, a time when cells are becoming committed to defined fates. Exposure of early embryos to LiCl, which shifts posterior cells to more anterior fates, reduces the abundance of this posterior-specific transcript. In contrast, embryos ventralized by u.v. treatment express normal levels of the transcript, implying that expression of the gene is not absolutely linked to dorsal cell identity. The sequence of a full-length cDNA corresponding to this transcript predicts a homeodomain-containing protein of 209 amino acids.