Geographical patterns of social cohesion drive disparities in early COVID infection hazard.

The uneven spread of COVID-19 has resulted in disparate experiences for marginalized populations in urban centers. Using computational models, we examine the effects of local cohesion on COVID-19 spread in social contact networks for the city of San Francisco, finding that more early COVID-19 infections occur in areas with strong local cohesion. This spatially correlated process tends to affect Black and Hispanic communities more than their non-Hispanic White counterparts. Local social cohesion thus acts as a potential source of hidden risk for COVID-19 infection.

Spatial heterogeneity can lead to substantial local variations in COVID-19 timing and severity.

Standard epidemiological models for COVID-19 employ variants of compartment (SIR or susceptible-infectious-recovered) models at local scales, implicitly assuming spatially uniform local mixing. Here, we examine the effect of employing more geographically detailed diffusion models based on known spatial features of interpersonal networks, most particularly the presence of a long-tailed but monotone decline in the probability of interaction with distance, on disease diffusion. Based on simulations of unrestricted COVID-19 diffusion in 19 US cities, we conclude that heterogeneity in population distribution can have large impacts on local pandemic timing and severity, even when aggregate behavior at larger scales mirrors a classic SIR-like pattern. Impacts observed include severe local outbreaks with long lag time relative to the aggregate infection curve, and the presence of numerous areas whose disease trajectories correlate poorly with those of neighboring areas. A simple catchment model for hospital demand illustrates potential implications for health care utilization, with substantial disparities in the timing and extremity of impacts even without distancing interventions. Likewise, analysis of social exposure to others who are morbid or deceased shows considerable variation in how the epidemic can appear to individuals on the ground, potentially affecting risk assessment and compliance with mitigation measures. These results demonstrate the potential for spatial network structure to generate highly nonuniform diffusion behavior even at the scale of cities, and suggest the importance of incorporating such structure when designing models to inform health care planning, predict community outcomes, or identify potential disparities.

Whole-body radiofrequency coil for (31) P MRSI at 7 T.

Widespread use of ultrahigh-field (31) P MRSI in clinical studies is hindered by the limited field of view and non-uniform radiofrequency (RF) field obtained from surface transceivers. The non-uniform RF field necessitates the use of high specific absorption rate (SAR)-demanding adiabatic RF pulses, limiting the signal-to-noise ratio (SNR) per unit of time. Here, we demonstrate the feasibility of using a body-sized volume RF coil at 7 T, which enables uniform excitation and ultrafast power calibration by pick-up probes. The performance of the body coil is examined by bench tests, and phantom and in vivo measurements in a 7-T MRI scanner. The accuracy of power calibration with pick-up probes is analyzed at a clinical 3-T MR system with a close to identical (1) H body coil integrated at the MR system. Finally, we demonstrate high-quality three-dimensional (31) P MRSI of the human body at 7 T within 5 min of data acquisition that includes RF power calibration. Copyright © 2016 John Wiley & Sons, Ltd.

Lethal alpha-thalassaemia created by gene targeting in mice and its genetic rescue.

Mutations at the alpha-globin locus are the most common class of mutations in humans, with deletion of all four adult alpha-globin genes resulting in the perinatal lethal condition haemoglobin Barts hydrops fetalis. Using gene targeting in mice, we have deleted a 16 kilobase region encompassing both adult alpha-globin genes. Animals homozygous for this deletion become hydropic and die late in gestation mimicking humans with hydrops fetalis. Introduction of a human alpha-globin transgene rescued these animals from perinatal death thus demonstrating the utility of this murine model in the development of cellular and gene based approaches for treating this human genetic disease.

Transgenic mice containing a human heavy chain immunoglobulin gene fragment cloned in a yeast artificial chromosome.

We have developed a method for the introduction of yeast artificial chromosomes (YACs) into transgenic mice. An 85 kilobase (kb) fragment of the human heavy chain immunoglobulin gene was cloned as a YAC, and embryonic stem cell lines carrying intact, integrated YACs were derived by co-lipofection of the YAC with an unlinked selectable marker. Chimaeric founder animals were produced by blastocyst injection, and offspring transgenic for the YAC were obtained. Analysis of serum from these offspring for human heavy chain antibody subunits demonstrated expression of the YAC-borne immunoglobulin gene fragment. Co-lipofection may prove to be a highly-successful means of producing transgenic mice containing large gene fragments in YACs.

Skin graft rejection by beta 2-microglobulin-deficient mice.

Mice homozygous for a beta 2-microglobulin (beta 2-m) gene disruption lack beta 2-m protein and are deficient for functional major histocompatibility complex class I (MHC-I) molecules. The mutant mice have normal numbers of CD4+8- T helper cells, but lack MHC-I-directed CD4-8+ cytotoxic T lymphocytes (CTLs). In this study we used the beta 2-m mutant mice to study the importance of MHC-I-directed immunity in skin graft rejection. Our results indicate that MHC-I-directed CD8+ CTLs are not essential in the rejection of allografts with whole MHC or multiple minor H differences. However, the absence of MHC-I-guided immunity profoundly reduces the ability of mutant mice to reject H-Y disparate grafts. In addition, we show that natural killer cells which vigorously reject MHC-I-deficient bone marrow grafts, are not effective in the destruction of MHC-I-deficient skin grafts.

Complementary roles of BDNF and NT-3 in vestibular and auditory development.

The physiological role of BDNF and NT-3 in the development of the vestibular and auditory systems was investigated in mice that carry a deleted BDNF and/or NT-3 gene. BDNF was the major survival factor for vestibular ganglion neurons, and NT-3, for spiral ganglion neurons. Lack of BDNF and NT-3 did not affect ingrowth of nerve fibers into the vestibular epithelium, but BDNF mutants failed to maintain afferent and efferent innervation. In the cochlea, BDNF mutants lost type 2 spiral neurons, causing an absence of outer hair cell innervation. NT-3 mutants showed a paucity of afferents and lost 87% of spiral neurons, presumably corresponding to type 1 neurons, which innervate inner hair cells. Double mutants had an additive loss, lacking all vestibular and spiral neurons. These results show that BDNF and NT-3 are crucial for inner ear development and, although largely coexpressed, have distinct and nonoverlapping roles in the vestibular and auditory systems.

Anchoring of CREB binding protein to the human T-cell leukemia virus type 1 promoter: a molecular mechanism of Tax transactivation.

The human T-cell leukemia virus type 1 (HTLV-1)-encoded Tax protein activates viral transcription through interaction with the cellular transcription factor CREB (cyclic AMP response element [CRE] binding protein). Although Tax stabilizes the binding of CREB to the Tax-responsive viral CREs in the HTLV-1 promoter, the precise molecular mechanism by which Tax mediates strong transcriptional activation through CREB remains unclear. In this report, we show that Tax promotes high-affinity binding of the KIX domain of CREB binding protein (CBP) to CREB-viral CRE complexes, increasing the stability of KIX in these nucleoprotein complexes by up to 4.4 kcal/mol. Comparable KIX binding affinities were measured for both phosphorylated and unphosphorylated forms of CREB, and in all cases high-affinity binding was dependent upon both Tax and the viral CRE. Tax also promoted association of KIX to a truncated form of CREB containing only the 73-amino-acid basic leucine zipper (bZIP) domain, indicating that the entire amino-terminal CBP-interacting domain of CREB is nonessential in the presence of Tax. Functional studies upheld the binding studies, as expression of the bZIP domain of CREB was sufficient to support Tax transactivation of HTLV-1 transcription in vivo. Finally, we show that transfection of a KIX expression plasmid, which lacks activation properties, inhibited Tax transactivation in vivo. This suggests that KIX occupies the CBP binding site on Tax, and therefore CBP is likely a cofactor in mediating Tax stimulation of HTLV-1 transcription. Together, these data support a model in which Tax anchors CBP to the HTLV-1 promoter, with strong transcriptional activation resulting from the CBP-associated activities of nucleosome remodeling and recruitment of the general transcription machinery.

High-throughput quantitative histological analysis of Alzheimer's disease pathology using a confocal digital microscanner.

To develop a rapid method of quantifying immunohistochemical information in tissue sections, we tested a confocal laser fluorescence microscanner initially designed for DNA microarray analysis. This instrument collects digital images at multiple wavelengths, scans entire sections at a resolution of 5 or 10 microm in less than 10 min, and quantifies structures labeled with fluorescent or nonfluorescent probes. We assessed the microscanner by studying immunostained amyloid plaques in the Alzheimer's disease (AD) brain and in the brain of a transgenic mouse model of AD amyloidosis, as efforts to correlate measures of amyloid plaques in brain sections with behavioral impairments are impeded by limitations in current morphometric methods. Microscanner analysis was used to determine amyloid burden in the occipital and entorhinal cortices of the mouse (3.7%) and human AD brain (1.6%). We also quantified the colocalization of plaque beta-amyloid (Abeta) with glial fibrillary acidic protein, a marker of gliosis (mouse 0.9%, human AD 3.7%). The microscanner may be generally applicable to a wide variety of human histopathologies and their animal models, wherever rapid unbiased quantitative analysis is needed.

Messenger RNAs encoding mouse histone macroH2A1 isoforms are expressed at similar levels in male and female cells and result from alternative splicing.

Two protein isoforms of histone macroH2A1 (mH2A1) are found in mammalian cells. One isoform, mH2A1.2 is highly concentrated on the heterochromatinized inactive X chromosome (Xi) of female cells. mH2A1.2 protein is also present in male cells, but fails to form dense concentrations. Another protein isoform, mH2A1.1, differs from mH2A1.2 by a single short segment of amino acids. In this study, we cloned and characterized the genomic locus of the mouse mH2A1 gene and mapped it to chromosome 13. Two alternatively spliced transcripts derived from the mH2A1 locus are responsible for the generation of the two mH2A1 protein isoforms with mH2A1.2 mRNA being the most abundant spliced form in all tissues examined. The absolute amount of mH2A1 mRNA is similar in male and female cells for most tissues with the exception of testes where it is par-ticularly abundant. Both spliced forms are present in all adult tissues analyzed as well as in female embryonic stem cells. In contrast, male embryonic stem cells expressed mH2A1.1 at low levels if at all. The relatively abundant expression of mH2A1 in both sexes suggests that mH2A1 has functions in addition to a possible involvement in X chromosome inactivation.

Permissive role of the pituitary in the induction and growth of estrogen-dependent renal tumors.

Prolonged administration of estrogen to hamsters by implanted pellets induces not only renal adenocarcinomas but also enlarges pituitaries with hyperplastic and neoplastic changes, especially in the pars intermedia. The pituitaries of the diethylstilbestrol-implanted animals weigh 90 to 150 mg; those of control animals without diethylstilbestrol pellets weigh 7 to 12 mg. The enlarged pituitaries have 9.7 x 10(-10) M progesterone receptors compared to 0.75 x 10(-10) M in the controls. Castrated male hamsters were hypophysectomized, implanted with diethylstilbestrol pellets, fed laboratory chow ad libitum, and given 5% glucose in water to drink. New pellets were implanted every 3 months, and the animals survived for 12 to 15 months. At autopsy, none of the animals had a tumor. Sixty-two of 65 control castrated males with the same schedule of pellet implantation developed tumors. Hypophysectomized castrated males implanted with diethylstilbestrol pellets were given daily injections of 1 microgram each of follicle-stimulating hormone, luteinizing hormone, and prolactin; or with 0.9% NaCl solution. These animals survived for 12 to 15 months, but none developed kidney tumors. Other castrated males were hypophysectomized and implanted with diethylstilbestrol pellets, and 2 months later tumor tissues were transplanted under the kidney capsule. Eighty days later, no tumors were evident in the kidneys of these animals. Control castrated males were implanted with diethylstilbestrol pellets, and 2 months later tumor tissue was transplanted under the kidney capsule. Between 60 and 85 days later, 13 of the 15 controls had developed renal tumors. The concentrations of follicle-stimulating hormone, luteinizing hormone, and prolactin were measured by radioimmunoassays. The concentrations of circulating follicle-stimulating hormone and luteinizing hormone in animals with diethylstilbestrol implants decreased with time and, by 7 months, were similar to those in hypophysectomized animals. The concentration of prolactin in animals with diethylstilbestrol pellets increased with time and reached twice the value in the control animals without diethylstilbestrol pellets. These studies suggest that some factor secreted by the pituitary may be involved as a promoter or a cocarcinogen in the estrogen induction of kidney tumors.

Effects of adrenocorticotropic hormone, human chorionic gonadotropin, and insulin on steroid production by human adrenocortical carcinoma cells in culture.

Adrenocortical carcinoma tissue removed from a mildly hirsute 16-year-old girl was cultured in order to assess steroidogenesis and responsiveness of the cells to adrenocorticotropic hormone (ACTH), human chorionic gonadotropin (HCG), and insulin. The cells in culture produced large amounts of androstenedione and testosterone; however, production of cortisol, which was initially high, decreased with time. No aldosterone, estrone, or estradiol was produced in vitro. Both monolayer cells maintained for 6 weeks and organ culture explants maintained for over 3 days responded to ACTH (10(-7) M) with increased production of androgens (testosterone, androstenedione, dehydroepiandrosterone) but decreased production of cortisol as measured by radioimmunoassay of steroids in the culture media. Concomitant with decreased cortisol production was the enhanced formation of 11-deoxycortisol in cells exposed to ACTH, suggesting impaired 11 beta-hydroxylation. Tissue exposed to HCG (10(-7) M) in organ culture showed an increase in androgen production over control levels, but no significant effect of HCG on glucocorticoid production was found. Tumor cells differed in their androgen response to ACTH and HCG, with enhanced adrenal androgens in the presence of ACTH and more gonadal-type androgens after exposure to HCG. Insulin exposure had no effect on production of either androgen or glucocorticoid by tumor tissue in organ culture. Thus, this adrenocortical carcinoma showed marked androgen production in culture which was enhanced in different ways by ACTH and HCG. 11 beta-Hydroxylation was impaired with time in culture. No specific effect of insulin on steroidogenesis was noted.

At the interface of the immune system and the nervous system: how neuroinflammation modulates the fate of neural progenitors in vivo.

Neural stem and progenitor cells express a variety of receptors that enable them to sense and react to signals emanating from physiological and pathophysiological conditions in the brain as well as elsewhere in the body. Many of these receptors and were first described in investigations of the immune system, particularly with respect to hematopoietic stem cells. This emerging view of neurobiology has two major implications. First, many phenomena known from the hematopoietic system may actually be generalizable to stem cells from many organ systems, reflecting the cells' progenitor-mediated regenerative potential. Second, regenerative interfaces may exist between diverse organ systems; populations of cells of neuroectodermal and hematopoietic origin may interact to play a crucial role in normal brain physiology, pathology, and repair. An understanding of the origins of signals and the neural progenitors' responses might lead to the development of effective therapeutic strategies to counterbalance acute and chronic neurodegenerative processes. Such strategies may include modifying and modulating cells with regenerative potential in subtle ways. For example, stem cells might be able to detect pathology-associated signals and be used as "interpreters" to mediate drug and other therapeutic interventions. This review has focused on the role of inflammation in brain repair. We propose that resident astroglia and blood-born cells both contribute to an inflammatory signature that is unique to each kind of neuronal degeneration or injury. These cells play a key role in coordinating the neural progenitor cell response to brain injury by exerting direct and indirect environmentally mediated influence on neural progenitor cells. We suggest that investigations of the neural progenitor-immunologic interface will provide valuable data related to the mechanisms by which endogenous and exogenous neural progenitor cells react to brain pathology, ultimately aiding in the design of more effective therapeutic applications of stem cell biology. Such improvements will include: (1) ascertaining the proper timing for implanting exogenous neural progenitor cells in relation to the administration of anti-inflammatory agents; (2) identifying what types of molecules might be administered during injury to enhance the mobilization and differentiation of endogenous and exogenous neural progenitor cells while also inhibiting the detrimental aspects of the inflammatory reaction; (3) divining clues as to which molecules may be required to change the lesioned environment in order to invite the homing of reparative neural progenitor cells.

Studies on the physiological role of brain-derived neurotrophic factor and neurotrophin-3 in knockout mice.

Brain-derived neurotrophic factor and neurotrophin-3 deficient mice were generated by gene targeting. The analysis of these mice has led to the characterization of their role in the survival of neurons in the peripheral nervous system. NT-3 deficient mice displayed severe movement defects and most died shortly after birth. The mutation causes loss of substantial portions of cranial and spinal peripheral sensory and sympathetic neurons. Significantly, spinal proprioceptive afferents and their peripheral sense organs (muscle spindles and Golgi tendon organs) were completely absent in homozygous mutant mice. BDNF deficient mice displayed deficiencies in coordination and balance. Excessive loss of neurons was detected in most of the peripheral sensory ganglia examined, but the survival of sympathetic neurons was not affected. The most marked reduction of neurons was observed in the vestibular ganglion, leading to a loss of innervation of the sensory epithelia of the vestibular compartments of the inner ear.

Spatiotemporal expression pattern of keratins in skin of AP-2alpha-deficient mice.

Transcription factor AP-2alpha has been implicated as being a cell-type-specific regulator of gene expression during vertebrate embryogenesis based on its expression pattern in neural crest cells, ectoderm, and the nervous system in mouse and frog embryos. In mice, AP-2alpha is expressed in surface ectoderm beginning at the single cell layer state around E8.75. AP-2alpha-deficient mice, derived by targeted mutagenesis, display a severe ventral closure defect resulting in cranio-abdominoschisis and a hypoplasia of the cranial ganglia. This study analyzed the effect of a targeted disruption of the AP-2alpha gene on the architecture and the expression of intermediate filaments in skin. We analyzed skin samples from newborn mice and found no difference in either the morphology of the skin or the amount of intermediate filaments expressed. This suggests that despite the results from other analyses, loss of transcription factor AP-2alpha does not affect the expression of intermediate filaments in the skin of newborn animals. We found an altered spatial distribution of intermediate filament expression in the single layered cranial ectoderm during days 9-12 of gestation leading to an evenly distributed expression of keratin 5 and 15 in the mutants. Furthermore, the mutants lack a ring of ectodermal cells highly positive for keratin 15 in the area where lens induction occurs, indicating a defect in the inductive interactions underlying eye formation.

Rational design of an animal model for Alzheimer's disease: introduction of multiple human genomic transgenes to reproduce AD pathology in a rodent.

A major obstacle to understanding the pathogenesis of Alzheimer's disease is the lack of easily studied animal models. Our approach is to apply transgenic methods to humanize mice and rats, employing methods that introduce large genomic transgenes, because this improves the level of transgene protein expression and the tissue specificity of expression. Our plan is to reproduce AD pathology in rodents by making them transgenic for several human proteins involved in AD. This report describes transgenic animal lines that we have produced, and summarizes our current approach and future plans. Two human genes known to be involved in AD pathology are the amyloid precursor protein (APP) and the E4 isoform of apolipoprotein E (apoE4). So far, we have produced and analyzed a transgenic line carrying the entire human APP gene cloned in a yeast artificial chromosome. We have also produced but not yet analyzed a mouse carrying the human apoE4 gene. Work is in progress to produce a transgenic line carrying a disease-causing mutation in the human APP gene. As we produce these animals, we are breeding them together, and also breeding them with a mouse line that lacks endogenous apoE, to produce an animal model carrying several human proteins whose interaction is believed to be instrumental in development of AD pathology. These transgenic animals will be useful for dissecting the biochemical and physiological steps leading to AD, and for development of therapies for disease intervention.

Parental schizophrenia spectrum disorders in childhood-onset and adult-onset schizophrenia.

OBJECTIVE: Childhood onset of "adult" psychiatric disorders may be caused, in part, by more salient genetic risk. In this study, the rates of schizophrenia spectrum disorders among parents of patients with childhood-onset and adult-onset schizophrenia and parents of community comparison subjects were compared. METHOD: To assess the presence of axis I and axis II disorders associated with schizophrenia, parents of patients with childhood-onset schizophrenia (95 parents), patients with adult-onset schizophrenia (86 parents), and community comparison subjects (123 parents) were interviewed directly by using semistructured instruments. Information on 19 additional parents (parents of childhood-onset patients, N=2; parents of adult-onset patients, N=11; parents of community comparison subjects, N=6) was obtained by using a family history interview with the same instruments. Transcribed interviews were scored by a rater blind to group membership, and the morbid risks for schizophrenia spectrum disorders in the three groups were compared. RESULTS: Parents of patients with childhood-onset schizophrenia had a significantly higher morbid risk of schizophrenia spectrum disorders (24.74%) than parents of patients with adult-onset schizophrenia (11.35%), and parents of both patient groups had a greater risk of schizophrenia spectrum disorders than did parents of comparison subjects (1.55%). CONCLUSIONS: Parents of patients with childhood-onset schizophrenia have a higher rate of schizophrenia spectrum disorders than parents of patients with adult-onset illness. This is consistent with the hypothesis that a childhood onset of schizophrenia is due, at least in part, to a greater familial diathesis for the disorder.

Twofold overexpression of human beta-amyloid precursor proteins in transgenic mice does not affect the neuromotor, cognitive, or neurodegenerative sequelae following experimental brain injury.

By using transgenic mice that overexpress human beta-amyloid precursor proteins (APPs) at levels twofold higher than endogenous APPs, following introduction of the human APP gene in a yeast artificial chromosome (YAC), we examined the effects of controlled cortical impact (CCI) brain injury on neuromotor/cognitive dysfunction and the development of Alzheimer's disease (AD)-like neuropathology. Neuropathological analyses included Nissl-staining and immunohistochemistry to detect APPs, beta-amyloid (Abeta), neurofilament proteins, and glial fibrillary acidic protein, whereas Abeta levels were measured in brain homogenates from mice subjected to CCI and control mice by using a sensitive sandwich enzyme-linked immunosorbent assay. Twenty APP-YAC transgenic mice and 17 wild type (WT) littermate controls were anesthetized and subjected to CCI (velocity, 5 m/second; deformation depth, 1 mm). Sham (anesthetized but uninjured) controls (n = 10 APP-YAC; n = 8 WT) also were studied. Motor function was evaluated by using rotarod, inclined-plane, and forelimb/hindlimb flexion tests. The Morris water maze was used to assess memory. Although CCI induced significant motor dysfunction and cognitive deficits, no differences were observed between brain-injured APP-YAC mice and WT mice at 24 hours and 1 week postinjury. By 1 week postinjury, both cortical and hippocampal CA3 neuron loss as well as extensive astrogliosis were observed in all injured animals, suggesting that overexpression of human APPs exhibited no neuroprotective effects. Although AD-like pathology (including amyloid plaques) was not observed in either sham or brain-inj ured animals, a significant decrease in brain concentrations of only Abeta terminating at amino acid 40 (Abeta x-40) was observed following brain injury in APP-YAC mice (P < 0.05 compared with sham control levels). Our data show that the APP-YAC mice do not develop AD-like neuropathology following traumatic brain injury. This may be because this injury does not induce elevated levels of the more amyloidogenic forms of human Abeta (i.e., Abeta x-42/43) in these mice.

Ornithine decarboxylase activity and polyamine content of the placenta and decidual tissue in the rat.

Measurements of ornithine decarboxylase (ODC) activity and of the amounts of putrescine, spermidine and spermine in the placenta and uterus of the pregnant rat and in decidual tissue of the pseudo-pregnant rat showed that these wax and wane with the growth rate of the tissues. Human term placenta has essentially no ODC activity, but placentae from 15-week human gestations have substantial amounts of enzyme. The ODC activity of the rat placenta increases 40-fold from day 10 to day 17 of pregnancy, then gradually decreases. The content of the polyamines in the placenta also reaches a peak on day 17. The ODC activity of the endometrium between implantation sites remains low until the end of pregnancy and then increases eight-fold on days 21 and 22. This may represent increased uterine activity in preparation for parturition. The ODC activity and the polyamine content of decidual tissue responds to administered oestradiol with increases that reach a peak within four hours. The ODC activity and polyamine content of decidual tissue decrease after the fifth day of decidualization. Nuclei isolated from decidual tissue respond to the addition of spermine or spermidine with an increase in the rate of RNA synthesis. Spermidine increases the elongation of RNA chains, but does not initiate the synthesis of new RNA chains in decidual nuclei.

A gene expression profile of embryonic stem cells and embryonic stem cell-derived neurons.

Embryonic stem (ES) cells have the ability to differentiate into a variety of cell lineages. We are examining ES cell differentiation in vitro by using cDNA microarrays to generate a molecular phenotype for each cell type. El4 ES cells induced by retinoic acid after forming embryoid bodies differentiate almost exclusively to neurons. We obtained expression patterns for about 8500 gene sequences by comparing mRNAs from undifferentiated ES cells and their differentiated derivatives in a competitive hybridization. Our results indicate that the genes expressed by ES cells change dramatically as they differentiate (58 gene sequences up-regulated, 34 down-regulated). Most notably, totipotent ES cells expressed high levels of a repressor of Hox expression (the polycomb homolog Mphl) and a co-repressor (CTBP2). Expression of these genes was undetectable in differentiated cells; the ES cell-derived neurons expressed a different set of transcriptional regulators, as weil as markers of neurogenesis. The gene expression profiles indicate that ES cells actively suppress differentiation by transcriptional repression; cell-cell contact in embryoid bodies and retinoic acid treatment may overcome this suppression, allowing expression of Hox genes and inducing a suite of neuronal genes. Gene expression profiles will be a useful outcome measure for comparing in vitro treatments of differentiating ES cells and other stem cells. Also, knowing the molecule phenotype of transplantable cells will allow correlation of phenotype with the success of the transplant.