Scientific Resources

Environmental influences and insults by reproductive toxicant exposure can lead to impaired spermatogenesis or infertility. Understanding how toxicants disrupt spermatogenesis is critical for determining how environmental factors contribute to impaired fertility. While current animal models are available,understanding of the reproductive toxic effects on human fertility requires a more robust model system. We recently demonstrated that human pluripotent stem cells can differentiate into spermatogonial stem cells/spermatogonia,primary and secondary spermatocytes,and haploid spermatids; a model that mimics many aspects of human spermatogenesis. Here,using this model system,we examine the effects of 2-bromopropane (2-BP) and 1,2,dibromo-3-chloropropane (DBCP) on in vitro human spermatogenesis. 2-BP and DBCP are non-endocrine disrupting toxicants that are known to impact male fertility. We show that acute treatment with either 2-BP or DBCP induces a reduction in germ cell viability through apoptosis. 2-BP and DBCP affect viability of different cell populations as 2-BP primarily reduces spermatocyte viability,whereas DBCP exerts a much greater effect on spermatogonia. Acute treatment with 2-BP or DBCP also reduces the percentage of haploid spermatids. Both 2-BP and DBCP induce reactive oxygen species (ROS) formation leading to an oxidized cellular environment. Taken together,these results suggest that acute exposure with 2-BP or DBCP causes human germ cell death in vitro by inducing ROS formation. This system represents a unique platform for assessing human reproductive toxicity potential of various environmental toxicants in a rapid,efficient,and unbiased format. View Publication

Traditionally,human embryonic stem cells (hESCs) are cultured on inactivated live feeder cells. For clinical application using hESCs,there is a requirement to minimize the risk of contamination with animal components. Extracellular matrix (ECM) derived from feeder cells is the most natural way to provide xeno-free substrates for hESC growth. In this study,we optimized the step-by-step procedure for ECM processing to develop a xeno-free ECM that supports the growth of undifferentiated hESCs. In addition,this newly developed xeno-free substrate can be stored at 4°C and is ready to use upon request,which serves as an easier way to amplify hESCs for clinical applications. View Publication

While enucleation is a critical step in the terminal differentiationbackslashnof human red blood cells,the molecular mechanisms underlying thisbackslashnunique process remain unclear. To investigate erythroblast enucleationbackslashnwe studied the erythroid differentiation of human embryonic stembackslashncells (hESCs),which provide a unique model for deeper understandingbackslashnof the development and differentiation of multiple cell types. Firstly,backslashnusing a two-step protocol,we demonstrated that terminal erythroidbackslashndifferentiation from hESCs is directly dependent on the age of thebackslashnembryoid bodies. Secondly,by choosing hESCs in two extreme conditionsbackslashnof erythroid culture,we obtained an original differentiation modelbackslashnwhich allows one to study the mechanisms underlying the enucleationbackslashnof erythroid cells by analyzing the gene and miRNA (miR) expressionbackslashnprofiles of cells from these two culture conditions. Thirdly,usingbackslashnan integrated analysis of mRNA and miR expression profiles,we identifiedbackslashn5 miRs potentially involved in erythroblast enucleation. Finally,backslashnby selective knockdown of these 5 miRs we found miR-30a to be a regulatorbackslashnof erythroblast enucleation in hESCs. This article is protected bybackslashncopyright. All rights reserved. View Publication

Fibroblast growth factors (FGFs) are essential for maintaining self-renewal in human embryonic stem cells and induced pluripotent stem cells. Recombinant basic FGF (bFGF or FGF2) is conventionally used to culture pluripotent stem cells; however,because of the instability of bFGF,repeated addition of fresh bFGF into the culture medium is required in order to maintain its concentration. In this study,we demonstrate that a heat-stable chimeric variant of FGF,termed FGFC,can be successfully used for maintaining human pluripotent stem cells. FGFC is a chimeric protein composed of human FGF1 and FGF2 domains that exhibits higher thermal stability and protease resistance than do both FGF1 and FGF2. Both human embryonic stem cells and induced pluripotent stem cells were maintained in ordinary culture medium containing FGFC instead of FGF2. Comparison of cells grown in FGFC with those grown in conventional FGF2 media showed no significant differences in terms of the expression of pluripotency markers,global gene expression,karyotype,or differentiation potential in the three germ lineages. We therefore propose that FGFC may be an effective alternative to FGF2,for maintenance of human pluripotent stem cells. View Publication

In recent years,several studies have shed light into the processes that regulate epidermal specification and homeostasis. We previously showed that a broad-spectrum γ-secretase inhibitor DAPT promoted early keratinocyte specification in human embryonic stem cells triggered to undergo ectoderm specification. Here,we show that DAPT accelerates human embryonic stem cell differentiation and induces expression of the ectoderm protein AP2. Furthermore,we utilize RNA sequencing to identify several candidate regulators of ectoderm specification including those involved in epithelial and epidermal development in human embryonic stem cells. Genes associated with transcriptional regulation and growth factor activity are significantly enriched upon DAPT treatment during specification of human embryonic stem cells to the ectoderm lineage. The human ectoderm cell signature identified in this study contains several genes expressed in ectodermal and epithelial tissues. Importantly,these genes are also associated with skin disorders and ectodermal defects,providing a platform for understanding the biology of human epidermal keratinocyte development under diseased and homeostatic conditions. View Publication

Pediatric-onset ataxias often present clinically as developmental delay and intellectual disability,with prominent cerebellar atrophy as a key neuroradiographic finding. Here we describe a new clinically distinguishable recessive syndrome in 12 families with cerebellar atrophy together with ataxia,coarsened facial features and intellectual disability,due to truncating mutations in the sorting nexin gene SNX14,encoding a ubiquitously expressed modular PX domain-containing sorting factor. We found SNX14 localized to lysosomes and associated with phosphatidylinositol (3,5)-bisphosphate,a key component of late endosomes/lysosomes. Patient-derived cells showed engorged lysosomes and a slower autophagosome clearance rate upon autophagy induction by starvation. Zebrafish morphants for snx14 showed dramatic loss of cerebellar parenchyma,accumulation of autophagosomes and activation of apoptosis. Our results characterize a unique ataxia syndrome due to biallelic SNX14 mutations leading to lysosome-autophagosome dysfunction. View Publication

Inactivation of the Pancreatic and Duodenal Homeobox 1 (PDX1) gene causes pancreatic agenesis,which places PDX1 high atop the regulatory network controlling development of this indispensable organ. However,little is known about the identity of PDX1 transcriptional targets. We simulated pancreatic development by differentiating human embryonic stem cells (hESCs) into early pancreatic progenitors and subjected this cell population to PDX1 chromatin immunoprecipitation sequencing (ChIP-seq). We identified more than 350 genes bound by PDX1,whose expression was upregulated on day 17 of differentiation. This group included known PDX1 targets and many genes not previously linked to pancreatic development. ChIP-seq also revealed PDX1 occupancy at hepatic genes. We hypothesized that simultaneous PDX1-driven activation of pancreatic and repression of hepatic programs underlie early divergence between pancreas and liver. In HepG2 cells and differentiating hESCs,we found that PDX1 binds and suppresses expression of endogenous liver genes. These findings rebrand PDX1 as a context-dependent transcriptional repressor and activator within the same cell type. View Publication

The incidence of cardiovascular disease represents a significant and growing health-care challenge to the developed and developing world. The ability of native heart muscle to regenerate in response to myocardial infarct is minimal. Tissue engineering and regenerative medicine approaches represent one promising response to this difficulty. Here,we present methods for the construction of a cell-seeded cardiac patch with the potential to promote regenerative outcomes in heart muscle with damage secondary to myocardial infarct. This method leverages iPS cells and a fibrin-based scaffold to create a simple and commercially viable tissue-engineered cardiac patch. Human-induced pluripotent stem cells (hiPSCs) can,in principle,be differentiated into cells of any lineage. However,most of the protocols used to generate hiPSC-derived endothelial cells (ECs) and cardiomyocytes (CMs) are unsatisfactory because the yield and phenotypic stability of the hiPSC-ECs are low,and the hiPSC-CMs are often purified via selection for expression of a promoter-reporter construct. In this chapter,we describe an hiPSC-EC differentiation protocol that generates large numbers of stable ECs and an hiPSC-CM differentiation protocol that does not require genetic manipulation,single-cell selection,or sorting with fluorescent dyes or other reagents. We also provide a simple but effective method that can be used to combine hiPSC-ECs and hiPSC-CMs with hiPSC-derived smooth muscle cells to engineer a contracting patch of cardiac cells. View Publication

There is ample evidence that the ubiquitin-proteasome system is an important regulator of transcription and its activity is necessary for maintaining pluripotency and promoting cellular reprogramming. Moreover,proteasome activity contributes to maintaining the open chromatin structure found in pluripotent stem cells,acting as a transcriptional inhibitor at specific gene loci generally associated with differentiation. The current study was designed to understand further the role of proteasome inhibition in reprogramming and its ability to modulate endogenous expression of pluripotency-related genes and induced pluripotent stem cells (iPSCs) colony formation. Herein,we demonstrate that acute combinatorial treatment with the proteasome inhibitors MG101 or MG132 and the histone deacetylase (HDAC) inhibitor valproic acid (VPA) increases gene expression of the pluripotency marker Oct3/4,and that MG101 alone is as effective as VPA in the induction of Oct3/4 mRNA expression in fibroblasts. Prolonged proteasome inhibition cyclically upregulates gene expression of Oct3/4 and Nanog,but reduces colony formation in the presence of the iPSC induction cocktail. In conclusion,our results demonstrate that the 26S proteasome is an essential modulator in the reprogramming process. Its inhibition enhances expression of pluripotency-related genes; however,efficient colony formation requires proteasome activity. Therefore,discovery of small molecules that increase proteasome activity might lead to more efficient cell reprogramming and generation of pluripotent cells. View Publication

Cardiac malformations and disease are the leading causes of death in the United States in live-born infants and adults,respectively. In both of these cases,a decrease in the number of functional cardiomyocytes often results in improper growth of heart tissue,wound healing complications,and poor tissue repair. The field of cardiac tissue engineering seeks to address these concerns by developing cardiac patches created from a variety of biomaterial scaffolds to be used in surgical repair of the heart. These scaffolds should be fully degradable biomaterial systems with tunable properties such that the materials can be altered to meet the needs of both in vitro culture (e.g. disease modeling) and in vivo application (e.g. cardiac patch). Current platforms do not utilize both structural anisotropy and proper cell-matrix contacts to promote functional cardiac phenotypes and thus there is still a need for critically sized scaffolds that mimic both the structural and adhesive properties of native tissue. To address this need,we have developed a silk-based scaffold platform containing cardiac tissue-derived extracellular matrix (cECM). These silk-cECM composite scaffolds have tunable architectures,degradation rates,and mechanical properties. Subcutaneous implantation in rats demonstrated that addition of the cECM to aligned silk scaffold led to 99% endogenous cell infiltration and promoted vascularization of a critically sized scaffold (10 × 5 × 2.5 mm) after 4 weeks in vivo. In vitro,silk-cECM scaffolds maintained the HL-1 atrial cardiomyocytes and human embryonic stem cell-derived cardiomyocytes and promoted a more functional phenotype in both cell types. This class of hybrid silk-cECM anisotropic scaffolds offers new opportunities for developing more physiologically relevant tissues for cardiac repair and disease modeling. View Publication

For diseases of the brain,the pig (Sus scrofa) is increasingly being used as a model organism that shares many anatomical and biological similarities with humans. We report that pig induced pluripotent stem cells (iPSC) can recapitulate events in early mammalian neural development. Pig iPSC line (POU5F1(high)/SSEA4(low)) had a higher potential to form neural rosettes (NR) containing neuroepithelial cells than either POU5F1(low)/SSEA4(low) or POU5F1(low)/SSEA4(high) lines. Thus,POU5F1 and SSEA4 pluripotency marker profiles in starting porcine iPSC populations can predict their propensity to form more robust NR populations in culture. The NR were isolated and expanded in vitro,retaining their NR morphology and neuroepithelial molecular properties. These cells expressed anterior central nervous system fate markers OTX2 and GBX2 through at least seven passages,and responded to retinoic acid,promoting a more posterior fate (HOXB4+,OTX2-,and GBX2-). These findings offer insight into pig iPSC development,which parallels the human iPSC in both anterior and posterior neural cell fates. These in vitro similarities in early neural differentiation processes support the use of pig iPSC and differentiated neural cells as a cell therapy in allogeneic porcine neural injury and degeneration models,providing relevant translational data for eventual human neural cell therapies. View Publication

Morpholino oligonucleotides (MO) are an innovative tool that provides a means for examining and modifying gene expression outcomes by antisense interaction with targeted RNA transcripts. The site-specific nature of their binding facilitates focused modulation to alter splice variant expression patterns. Here we describe the steric-blocking of human telomerase reverse transcriptase (hTERT) $$$$ and $$$$ splice variants using MO to examine cellular outcomes related to pluripotency and differentiation in human embryonic stem cells. View Publication