Simple and efficient derivation of mouse embryonic stem cell lines using differentiation inhibitors or proliferation stimulators

FOXO1-mediated lipid metabolism maintains mammalian embryos in dormancy

Mammalian developmental timing is adjustable in vivo by preserving pre-implantation embryos in a dormant state called diapause. Inhibition of the growth regulator mTOR (mTORi) pauses mouse development in vitro, yet how embryonic dormancy is maintained is not known. Here we show that mouse embryos in diapause are sustained by using lipids as primary energy source. In vitro, supplementation of embryos with the metabolite L-carnitine balances lipid consumption, puts the embryos in deeper dormancy and boosts embryo longevity. We identify FOXO1 as an essential regulator of the energy balance in dormant embryos and propose, through meta-analyses of dormant cell signatures, that it may be a common regulator of dormancy across adult tissues. Our results lift a constraint on in vitro embryo survival and suggest that lipid metabolism may be a critical metabolic transition relevant for longevity and stem cell function across tissues.

Dual role of lipids for genome stability and pluripotency facilitates full potency of mouse embryonic stem cells

While Mek1/2 and Gsk3β inhibition ("2i") supports the maintenance of murine embryonic stem cells (ESCs) in a homogenous naïve state, prolonged culture in 2i results in aneuploidy and DNA hypomethylation that impairs developmental potential. Additionally, 2i fails to support derivation and culture of fully potent female ESCs. Here we find that mouse ESCs cultured in 2i/LIF supplemented with lipid-rich albumin (AlbuMAX) undergo pluripotency transition yet maintain genomic stability and full potency over long-term culture. Mechanistically, lipids in AlbuMAX impact intracellular metabolism including nucleotide biosynthesis, lipid biogenesis, and TCA cycle intermediates, with enhanced expression of DNMT3s that prevent DNA hypomethylation. Lipids induce a formative-like pluripotent state through direct stimulation of Erk2 phosphorylation, which also alleviates X chromosome loss in female ESCs. Importantly, both male and female "all-ESC" mice can be generated from de novo derived ESCs using AlbuMAX-based media. Our findings underscore the importance of lipids to pluripotency and link nutrient cues to genome integrity in early development.

Regulation of Embryonic Stem Cell Self-Renewal

Embryonic stem cells (ESCs) are a type of cells capable of self-renewal and multi-directional differentiation. The self-renewal of ESCs is regulated by factors including signaling pathway proteins, transcription factors, epigenetic regulators, cytokines, and small molecular compounds. Similarly, non-coding RNAs, small RNAs, and microRNAs (miRNAs) also play an important role in the process. Functionally, the core transcription factors interact with helper transcription factors to activate the expression of genes that contribute to maintaining pluripotency, while suppressing the expression of differentiation-related genes. Additionally, cytokines such as leukemia suppressor factor (LIF) stimulate downstream signaling pathways and promote self-renewal of ESCs. Particularly, LIF binds to its receptor (LIFR/gp130) to trigger the downstream Jak-Stat3 signaling pathway. BMP4 activates the downstream pathway and acts in combination with Jak-Stat3 to promote pluripotency of ESCs in the absence of serum. In addition, activation of the Wnt-FDZ signaling pathway has been observed to facilitate the self-renewal of ESCs. Small molecule modulator proteins of the pathway mentioned above are widely used in in vitro culture of stem cells. Multiple epigenetic regulators are involved in the maintenance of ESCs self-renewal, making the epigenetic status of ESCs a crucial factor in this process. Similarly, non-coding RNAs and cellular energetics have been described to promote the maintenance of the ESC's self-renewal. These factors regulate the self-renewal and differentiation of ESCs by forming signaling networks. This review focused on the role of major transcription factors, signaling pathways, small molecular compounds, epigenetic regulators, non-coding RNAs, and cellular energetics in ESC's self-renewal.

Efficient generation of embryonic stem cells from single blastomeres of cryopreserved mouse embryos in the presence of signalling modulators

CONTEXT

Derivation of embryonic stem cells (ESC) from single blastomeres is an interesting alternative to the use of whole blastocysts, but derivation rates are lower and the requirements for successful ESC obtention are still poorly defined.

AIMS

To investigate the effects of embryo cryopreservation and of signalling modulators present during embryo culture and/or ESC establishment on ESC derivation efficiency from single 8-cell mouse blastomeres.

METHOD

Fresh and cryopreserved 2-cell embryos were cultured and biopsied at the 8-cell stage. Single blastomeres were cultured in the presence of 2i or R2i cocktails, with or without adrenocorticotropic hormone (ACTH). We analysed ESC derivation efficiencies and characterised pluripotency genes expression and karyotype integrity of the resulting lines. We also evaluated the impact of embryo preculture with R2i on epiblast cell numbers and derivation rates.

KEY RESULTS

The ESC generation was not compromised by embryo cryopreservation and ACTH was dispensable under most of the conditions tested. While 2i and R2i were similarly effective for ESC derivation, R2i provided higher karyotype integrity. Embryo preculture with R2i yielded increased numbers of epiblast cells but did not lead to increased ESC generation.

CONCLUSIONS

Our findings help to define a simplified and efficient procedure for the establishment of mouse ESC from single 8-cell blastomeres.

IMPLICATIONS

This study will contribute to improving the potential of this experimental procedure, providing a tool to investigate the developmental potential of blastomeres isolated from different embryonic stages and to reduce the number of embryos needed for ESC derivation.

WNT signalling supported by MEK/ERK inhibition is essential to maintain pluripotency in bovine preimplantation embryo

Capturing stable embryonic stem cell (ESC) lines from domesticated animals still remains one of the challenges of non-rodent embryology. The stake is high, as stable ESCs derived from species such as cattle present high economic and scientific value. Understanding of the processes leading to the embryonic lineage segregation is crucial to provide species-orientated molecular environment capable of supporting self-renewal and pluripotency. Therefore, the aim of this study was to validate the action of the two core regulatory pathways (WNT and MEK/ERK) during bovine embryo development. In vitro produced bovine embryos were obtained in the presence of inhibitors (i), which enable activation of the WNT pathway (via GSK3i, CHIR99021) and suppression of MEK signalling by PD0325901 in the 2i system and PD184325 and SU5402 in the 3i system. We have followed the changes in the distribution of the key lineage specific markers both at the transcript and protein level. Our results showed that WNT signalling promotes the expression of key inner cell mass (ICM) specific markers in bovine embryos, regardless of the MEK/ERK inhibitor cocktail used. MEK/ERK downregulation is crucial to maintain OCT4 and NANOG expression within the ICM and to prevent their exclusion from the trophectoderm (TE). At the same time, the classical TE marker (CDX2) was downregulated at the mRNA and protein level. As a follow up for the observed pluripotency stimulating effect of the inhibitors, we have tested the potential of the 2i and the 3i culture conditions (supported by LIF) to derive primary bovine ESC lines. As a result, we propose a model in which all of the primary signalling pathways determining embryonic cell fate are active in bovine embryos, yet the requirement for pluripotency maintenance in cattle may differ from the described standards. WNT activation leads to the formation (and stabilisation of the ICM) and MEK/ERK signalling is maintained at low levels. Unlike in the mouse, GATA6 is expressed in both ICM and TE. MEK/ERK signalling affects HP formation in cattle, but this process is activated at the post-blastocyst stage. With regard to self-renewal, 2i is preferable, as 3i also blocks the FGF receptor, what may prevent PI3K signalling, important for pluripotency and self-renewal.

Generation of embryonic stem cells derived from the inner cell mass of blastocysts of outbred ICR mice

Embryonic stem cells (ESCs) derived from outbred mice which share several genetic characteristics similar to humans have been requested for developing stem cell-based bioengineering techniques directly applicable to humans. Here, we report the generation of ESCs derived from the inner cell mass of blastocysts retrieved from 9-week-old female outbred ICR mice mated with 9-week-old male outbred ICR mice (_ICRESCs). Similar to those from 129/Ola mouse blastocysts (_E14ESCs), the established _ICRESCs showed inherent characteristics of ESCs except for partial and weak protein expression and activity of alkaline phosphatase. Moreover, _ICRESCs were not originated from embryonic germ cells or pluripotent cells that may co-exist in outbred ICR strain-derived mouse embryonic fibroblasts (_ICRMEFs) used for deriving colonies from inner cell mass of outbred ICR mouse blastocysts. Furthermore, instead of outbred _ICRMEFs, hybrid _B6CBAF1MEFs as feeder cells could sufficiently support in vitro maintenance of _ICRESC self-renewal. Additionally, _ICRESC-specific characteristics (self-renewal, pluripotency, and chromosomal normality) were observed in _ICRESCs cultured for 40th subpassages (164 days) on _B6CBAF1MEFs without any alterations. These results confirmed the successful establishment of ESCs derived from outbred ICR mice, and indicated that self-renewal and pluripotency of the established _ICRESCs could be maintained on _B6CBAF1MEFs in culture.

Single blastomeres as a source of mouse embryonic stem cells: effect of genetic background, medium supplements, and signaling modulators on derivation efficiency

PURPOSE

To assess the role of the genetic background, the culture medium supplements, and the presence of modulators of signaling pathways on mouse embryonic stem cell derivation from single blastomeres from 8-cell embryos.

METHODS

Mice from permissive and non-permissive genetic backgrounds, different culture media supplements, knockout serum replacement (KSR) and N2B27, and the presence or absence of 2i treatment were used to derive mouse embryonic stem cells (mESC) from single blastomeres isolated from 8-cell embryos and from control embryos at the blastocyst stage. After the sixth passage, the putative mESC were analyzed by immunofluorescence to assess their pluripotency and, after in vitro differentiation induction, their ability to differentiate into derivatives of the three primary germ layers. Selected mESC lines derived from single blastomeres in the most efficient culture conditions were further characterized to validate their stemness.

RESULTS

In control embryos, high mESC derivation efficiencies (70-96.9%) were obtained from permissive backgrounds or when embryos were cultured in medium complemented with 2i regardless of their genetic background. By contrast, only blastomeres isolated from embryos from permissive background cultured in KSR-containing medium complemented with 2i were moderately successful in the derivation of mESC lines (22.9-24.5%). Moreover, we report for the first time that B6CBAF2 embryos behave as permissive in terms of mESC derivation.

CONCLUSIONS

Single blastomeres have higher requirements than whole blastocysts for pluripotency maintenance and mESC derivation. The need for 2i suggests that modulation of signaling pathways to recreate a commitment towards inner cell mass could be essential to efficiently derive mESC from single blastomeres.

Preferable in vitro condition for maintaining faithful DNA methylation imprinting in mouse embryonic stem cells

Epigenetic properties of cultured embryonic stem cells (ESCs), including DNA methylation imprinting, are important because they affect the developmental potential. Here, we tested a variety of culture media, including knockout serum replacement (KSR) and fetal bovine serum (FBS) with or without inhibitors of Gsk3β and Mek1/2 (2i) at various time points. In addition to the previously known passage-dependent global changes, unexpected dynamic DNA methylation changes occurred in both maternal and paternal differentially methylated regions: under the widely used condition of KSR with 2i, a highly hypomethylated state occurred at early passages (P1-7) as well as P10, but DNA methylation increased over further passages in most conditions, except under KSR with 2i at P25. Dramatic DNA demethylation under KSR+2i until P25 was associated with upregulated Tet1 and Parp1, and their related genes, whereas 2i regulated the expressions of DNA methyltransferase-related genes for the change in DNA methylation during the cumulative number of passages. Although DNA methylation imprinting is more labile under KSR with and without 2i, it can be more faithfully maintained under condition of cooperative FBS and 2i. Thus, our study will provide the useful information for improved epigenetic control of ESCs and iPSCs in applications in regenerative medicine.

Loss of heme oxygenase-1 accelerates mesodermal gene expressions during embryoid body development from mouse embryonic stem cells

Heme oxygenase (HO)-1 is an inducible stress response protein and well known to protect cells and tissues against injury. Despite its important function in cytoprotection against physiological stress, the role of HO-1 in embryonic stem cell (ESC) differentiation remains largely unknown. We showed previously that induced pluripotent stem (iPS) cells that lack HO-1 are more sensitive to oxidant stress-induced cell death and more prone to lose pluripotent markers upon LIF withdrawal. To elucidate the role of HO-1 in ESC differentiation and to rule out the controversy of potential gene flaws in iPS cells, we derived and established mouse HO-1 knockout ESC lines from HO-1 knockout blastocysts. Using wild type D3 and HO-1 knockout ESCs in the 3-dimensional embryoid body (EB) differentiation model, we showed that at an early time point during EB development, an absence of HO-1 led to enhanced ROS level, concomitant with increased expressions of master mesodermal regulator brachyury and endodermal marker GATA6. In addition, critical smooth muscle cell (SMC) transcription factor serum response factor and its coactivator myocardin were enhanced. Furthermore, HO-1 deficiency increased Smad2 in ESCs and EBs, revealing a role of HO-1 in controlling Smad2 level. Smad2 not only mediates mesendoderm differentiation of mouse ESCs but also SMC development. Collectively, loss of HO-1 resulted in higher level of mesodermal and SMC regulators, leading to accelerated and enhanced SMC marker SM α-actin expression. Our results reveal a previously unrecognized function of HO-1 in regulating SMC gene expressions during ESC-EB development. More importantly, our findings may provide a novel strategy in enhancing ESC differentiation toward SMC lineage.

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Loss of HO-1 in ESCs promotes adipogenesis but reduces osteogenesis.

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During early EB development, loss of HO-1 results in robust induction of brachyury.

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During early EB development, lack of HO-1 leads to enhanced ROS level.

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Loss of HO-1 increases SMC transcription factor SRF and cofactor myocardin.

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HO-1 deficiency promotes mesodermal SMC differentiation during EB development.

An Eye Organoid Approach Identifies Six3 Suppression of R-spondin 2 as a Critical Step in Mouse Neuroretina Differentiation

Recent advances in self-organizing, 3-dimensional tissue cultures of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) provided an in vitro model that recapitulates many aspects of the in vivo developmental steps. Using Rax-GFP-expressing ESCs, newly generated Six3-/- iPSCs, and conditional null Six3delta/f;Rax-Cre ESCs, we identified Six3 repression of R-spondin 2 (Rspo2) as a required step during optic vesicle morphogenesis and neuroretina differentiation. We validated these results in vivo by showing that transient ectopic expression of Rspo2 in the anterior neural plate of transgenic mouse embryos was sufficient to inhibit neuroretina differentiation. Additionally, using a chimeric eye organoid assay, we determined that Six3 null cells exert a non-cell-autonomous repressive effect during optic vesicle formation and neuroretina differentiation. Our results further validate the organoid culture system as a reliable and fast alternative to identify and evaluate genes involved in eye morphogenesis and neuroretina differentiation in vivo.

Inhibition of mTOR induces a paused pluripotent state

Cultured pluripotent stem cells are a cornerstone of regenerative medicine owing to their ability to give rise to all cell types of the body. Although pluripotent stem cells can be propagated indefinitely in vitro, pluripotency is paradoxically a transient state in vivo, lasting 2-3 days around the time of blastocyst implantation. The exception to this rule is embryonic diapause, a reversible state of suspended development triggered by unfavourable conditions. Diapause is a physiological reproductive strategy widely employed across the animal kingdom, including in mammals, but its regulation remains poorly understood. Here we report that the partial inhibition of mechanistic target of rapamycin (mTOR), a major nutrient sensor and promoter of growth, induces reversible pausing of mouse blastocyst development and allows their prolonged culture ex vivo. Paused blastocysts remain pluripotent and competent-able to give rise to embryonic stem (ES) cells and live, fertile mice. We show that both naturally diapaused blastocysts in vivo and paused blastocysts ex vivo display pronounced reductions in mTOR activity, translation, histone modifications associated with gene activity and transcription. Pausing can be induced directly in cultured ES cells and sustained for weeks without appreciable cell death or deviations from cell cycle distributions. We show that paused ES cells display a remarkable global suppression of transcription, maintain a gene expression signature of diapaused blastocysts and remain pluripotent. These results uncover a new pluripotent stem cell state corresponding to the epiblast of the diapaused blastocyst and indicate that mTOR regulates developmental timing at the peri-implantation stage. Our findings have implications in the fields of assisted reproduction, regenerative medicine, cancer, metabolic disorders and ageing.

Choice of Feeders Is Important When First Establishing iPSCs Derived From Primarily Cultured Human Deciduous Tooth Dental Pulp Cells

Feeder cells are generally required to maintain embryonic stem cells (ESCs)/induced pluripotent stem cells (iPSCs). Mouse embryonic fibroblasts (MEFs) isolated from fetuses and STO mouse stromal cell line are the most widely used feeder cells. The aim of this study was to determine which cells are suitable for establishing iPSCs from human deciduous tooth dental pulp cells (HDDPCs). Primary cultures of HDDPCs were cotransfected with three plasmids containing human OCT3/4, SOX2/KLF4, or LMYC/LIN28 and pmaxGFP by using a novel electroporation method, and then cultured in an ESC qualified medium for 15 days. Emerging colonies were reseeded onto mitomycin C-treated MEFs or STO cells. The colonies were serially passaged for up to 26 passages. During this period, colony morphology was assessed to determine whether cells exhibited ESC-like morphology and alkaline phosphatase activity to evaluate the state of cellular reprogramming. HDDPCs maintained on MEFs were successfully reprogrammed into iPSCs, whereas those maintained on STO cells were not. Once established, the iPSCs were maintained on STO cells without loss of pluripotency. Our results indicate that MEFs are better feeder cells than STO cells for establishing iPSCs. Feeder choice is a key factor enabling efficient generation of iPSCs.

Suppression of transforming growth factor β signaling promotes ground state pluripotency from single blastomeres

STUDY QUESTION

Can transforming growth factor β (TGFβ) inhibition promote ground state pluripotency of embryonic stem cells (ESCs) from single blastomeres (SBs) of cleavage embryos in different mouse stains?

SUMMARY ANSWER

Small molecule suppression of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) and TGFβ signaling (designated as R2i) can enhance the generation of mouse ESCs from SBs of different cleavage stage embryos compared with the dual suppression of ERK1/2 and glycogen synthase kinase 3 (GSK3), designated as 2i, regardless of the strain of mouce.

WHAT IS KNOWN ALREADY

It is known that chemical inhibition of TGFβ promotes ground state pluripotency in the generation and sustenance of naïve ES cells from mouse blastocysts compared with the well-known 2i condition. However, the positive effect of this inhibition on mouse ESCs from early embryonic SBs remains obscure.

STUDY DESIGN, SIZE, DURATION

We used 155 cleavage-stage mouse embryos to optimize the culture conditions for blastocyst development. Then, to assess the effects of R2i and 2i on ESC generation from SBs, we cultured isolated SBs in 2i and R2i for 10 days. SBs were replated under the same conditions to produce ESCs. In total, 46 embryos and 321 SBs from two- to eight-cell stages were recovered from NMRI and BALB/c mouse strains and used in this study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blastomeres from 2- to 8-cell stage mouse embryos were dispersed and individually seeded into a 96-well plates that included mitotically inactivated feeder cells. ESCs were generated in B27N2 defined medium supplemented with R2i or 2i. Randomly selected ESC lines, generated from SBs of each stage, were assessed for pluripotency and germ-line transmission.

MAIN RESULTS AND THE ROLE OF CHANCE

We demonstrated that dual inhibition of ERK1/2 and TGFβ (R2i) enhanced efficient blastocyst development and efficient establishment of ESCs from SB of 2- to 8-cell stage mouse embryos compared with the dual inhibition of ERK1/2 and GSK3 (2i) regardless of the embryonic stage and strain of mice. The proportions of SBs that produced ESC were 50-60 versus 20-30%.

LIMITATIONS, REASONS FOR CAUTION

This study was done with mouse embryos, it is not known whether these findings are transferable to humans.

WIDER IMPLICATIONS OF THE FINDINGS

These findings resulted in an increased efficiency of ESC generation from one biopsied blastomere for autogeneic or allogeneic matched pluripotent cells without the need to destroy viable embryos. The results also provided information about the developmental capacity of early embryonic blastomeres.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by grants provided from Royan Institute, the Iranian Council of Stem Cell Research and Technology and the Iran National Science Foundation. The authors have no conflict of interest to declare.

Generating chimeric mice from embryonic stem cells via vial coculturing or hypertonic microinjection

The generation of a fertile embryonic stem cell (ESC)-derived or F0 (100 % coat color chimerism) mice is the final criterion in proving that the ESC is truly pluripotent. Many methods have been developed to produce chimeric mice. To date, the most popular methods for generating chimeric embryos is well sandwich aggregation between zona pellucida (ZP) removed (denuded) 2.5-day post-coitum (dpc) embryos and ESC clumps, or direct microinjection of ESCs into the cavity (blastocoel) of 3.5-dpc blastocysts. However, due to systemic limitations and the disadvantages of conventional microinjection, aggregation, and coculturing, two novel methods (vial coculturing and hypertonic microinjection) were developed in recent years at my laboratory.Coculturing 2.5-dpc denuded embryos with ESCs in 1.7-mL vials for ~3 h generates chimeras that have significantly high levels of chimerism (including 100 % coat color chimerism) and germline transmission. This method has significantly fewer instrumental and technological limitations than existing methods, and is an efficient, simple, inexpensive, and reproducible method for "mass production" of chimeric embryos. For laboratories without a microinjection system, this is the method of choice for generating chimeric embryos. Microinjecting ESCs into a subzonal space of 2.5-dpc embryos can generate germline-transmitted chimeras including 100 % coat color chimerism. However, this method is adopted rarely due to the very small and tight space between ZP and blastomeres. Using a laser pulse or Piezo-driven instrument/device to help introduce ESCs into the subzonal space of 2.5-dpc embryos demonstrates the superior efficiency in generating ESC-derived (F0) chimeras. Unfortunately, due to the need for an expensive instrument/device and extra fine skill, not many studies have used either method. Recently, ESCs injected into the large subzonal space of 2.5-dpc embryos in an injection medium containing 0.2-0.3 M sucrose very efficiently generated viable, healthy, and fertile chimeric mice with 100 % coat color chimerism.Both vial coculture and hypertonic microinjection methods are useful and effective alternatives for producing germline chimeric or F0 mice efficiently and reliably. Furthermore, both novel methods are also good for induced pluripotent stem cells (iPSCs) to generate chimeric embryos.

Identifying nuclear protein-protein interactions using GFP affinity purification and SILAC-based quantitative mass spectrometry

Many cellular proteins assemble into macromolecular protein complexes. Therefore, identifying protein-protein interactions (PPIs) is essential to gain insight into the function of proteins. Recently established quantitative mass spectrometry-based techniques have significantly improved the unbiased search for PPIs. In this chapter, we describe a single-step GFP affinity purification method combined with SILAC-based quantitative mass spectrometry that can be used to identify nuclear PPIs in mammalian cells.

Human foreskin fibroblast produces interleukin-6 to support derivation and self-renewal of mouse embryonic stem cells

Introduction

Embryonic stem cells (ESCs) provide an attractive cell source for basic research and disease treatment. Currently, the common culture system for mouse ESC requires mouse embryonic fibroblast (MEF) as a feeder layer supplemented with leukemia inhibitory factor (LIF). The drawbacks associated with MEF and the cost of LIF have motivated exploration of new feeder cell types to maintain self-renewal of mouse ESCs without the need of exogenous LIF. However, why these feeder cells could maintain ESCs at the undifferentiated state independent of exogenous LIF is unclear.

Methods

We derived mouse ESC lines using human foreskin fibroblast (HFF) in the absence of exogenous LIF. We also examined the dependence of HFF on the JAK-Stat3 pathway to maintain ESC identities and explored the potential molecular basis for HFF to support self-renewal of ESCs.

Results

HFF supported mouse ESC self-renewal superiorly to MEFs. Using the HFF system, multiple lines of mouse ESCs were successfully derived without addition of exogenous LIF and any small molecular inhibitors. These ESCs had capacities to self-renew for a long period of time and to differentiate into various cell types of the three germ layers both in vitro and in vivo. Moreover, the ESCs participated in embryonic development and contributed to germ cell lineages in the chimeric mouse. At a molecular level, HFF was dependent on the JAK-Stat3 pathway to maintain ESC self-renewal. The high level of interleukin-6 (IL-6) produced by HFF might be responsible for the exogenous LIF-independent effect.

Conclusion

This study describes an efficient, convenient and economic system to establish and maintain mouse ESC lines, and provides insights into the functional difference in the support of ESC culture between MEF and HFF.

Quantitative and semiquantitative immunoassay of growth factors and cytokines in the conditioned medium of STO and CF-1 mouse feeder cells

Feeder cells of irradiated mouse fibroblasts are commonly used for, and are generally necessary for, the in vitro maintenance and growth of many fastidious cell types, particularly embryonic stem cells or induced pluripotent stem cells. Quantitative and semiquantitative immunoassays of conditioned media were performed to identify some of the soluble cytokines, chemokines, protein hormones, and cell matrix/adhesion molecules that are elaborated from two commonly used feeder cells, STO and CF-1. Among those quantitatively assayed, the most abundant cytokine proteins expressed by the feeder cells were activin A, hepatocyte growth factor (HGF), insulin-like growth factor 1, insulin-like growth factor 2, insulin-like growth factor binding protein (IGFBP)-6, macrophage colony-stimulating factor (a.k.a. CSF-1), and pigment epithelium-derived factor (a.k.a. serine protease inhibitor, clade F, member 1). CF-1 cells expressed ten times more activin A than STO cells and also produced larger amounts of interleukin-6 and IGFBP-2, IGFBP-3, IGFBP-4, and IGFBP-5. Conversely, STO cell produced almost ten times more HGF and five times more stem cell factor (a.k.a. c-kit ligand) than CF-1 cells. Assayed semiquantitatively, relatively large amounts of chemokines were produced by both feeder cells including fractalkine (CX3CL1), interferon-inducible protein 10 (a.k.a. CXCL10 and cytokine-responsive gene-2, CRG-2), monocyte chemotactic protein (MCP)-1 (a.k.a. CCL2 and junctional epithelium chemokine (JE), MCP-5/CCL12), keratinocyte-derived chemokine (a.k.a. CXCL1 and growth-related oncogene alpha, GROα), nephroblastoma overexpressed gene (CCN3, IGFBP-9), stromal cell-derived factor 1 (CXCL12), and serpin E1 (PAI-1). In contrast to one another, STO produced more CXCL16 than CF-1 cells, and CF-1 cell produced more MCP-5 (CCL12), macrophage inflammatory protein (MIP)-1α (CCL3), MIP-1β (CCL4), pentraxin-3 (TSG-14), and platelet factor-4 (CXCL4) than STO cells. Soluble adhesion molecule, sICAM (ICAM-1, CD54), was expressed by CF-1 cells, but not STO cells, and similarly, the cell matrix-associated molecules endocan (endothelial cell-specific molecule 1), endostatin (collagen XVIII), and matrix metalloproteinase 3 were expressed more by CF-1 cells. Tissue inhibitor of metalloproteinases 1 was robustly expressed by both feeder cells. Other proteins primarily detected from CF-1 cells included retinol-binding protein 4 and FGF21, while STO cells secreted more interferon gamma. Both feeder cells produced no or low amounts of LIF, tumor necrosis factor alpha, vascular endothelial growth factor (VEGF), VEGF-B, prolactin, various interleukins, fibroblast growth factor (FGF)-1, FGF-2, FGF-7, EGF, HB-EGF, and amphiregulin. The results may explain some of the cell growth and maintenance responses by various types of cells co-cultured on STO or CF-1 feeder cells.