Soojung Hahn a, 1, Mi Sun Kim b, 1, Seon Young Choi a, 1, Sukin Jeong a, JooHyun Jee a, Han Kyung Kim a, Sang Yun Jeong a, Hyunsoo Shin b, Hyoung Sun Kim c,Joon Seong Park c, d, Jongman Yoo a, *

ABSTRACT
An organoid is a complex, multi-cell three-dimensional (3D) structure that contains tissue-speciic cells. Epithelial stem cells, which are marked by leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5), have the potential for self-renewal and expansion as organoids. However, in the case of intestinal organoids from Lgr5-EGFP-IRES-CreERT2 transgenic mice, in vitro expansion of the Lgr5 expression is limited in a culture condition supplemented with essential proteins, such as epidermal growth factor (E), noggin (N), and R-spondin 1 (R). In this study, we hypothesized that self-renewal of Lgr5+ stem cells in a 3D culture system can be stimulated by deined compounds (CHIR99021, Valproic acid, Y-27632, and A83-01). Our results demonstrated that dissociated single cells from organoids were organized into a 3D structure in the four compounds containing the ENR culture medium in a 3D and two-dimensional (2D) culture system. Moreover, the Lgr5 expression level of organoids from the ENR- and compound- containing media increased. Furthermore, the conversion of cultured Lgr5+ stem cells from 2D to 3D was conirmed. Therefore, deined compounds promote the expansion of Lgr5+ stem cells in organoids. © 2018 Elsevier Inc. All rights reserved.

Keywords:Lgr5+ stem cell;Stemness;3D culture;Organoid

1.Introduction
Adult stem cells (ASCs) can be formed as organoids in the absence of feeder cells by supplementing the culture medium with well-deined stem cell niche factors. ASCs-based organoids that preserve their tissue identity provide basic insight into the devel- opmental processes and clinical approaches used in regenerative medicine [1]. Among tissue-speciic multipotent ASCs, the leucine- rich repeat-containing G-protein coupled receptor 5 (Lgr5) expressing stem cells (a receptor for the secreted Wnt-amplifying R-spondin) are organized as organ-like structures in different areas of the body, including the small intestine and colon [2]. However, the current versions of organoids are not perfectly matched in vivo, and they are partially recapitulated without other surrounding cells such as blood vessels and immune cells [3].Small intestinal organoids were formed and cultured using a previously reported method [4]. Moreover, the isolated Lgr5+ stem cells from crypts of Lgr5-EGFP-IRES-CreERT2 mice were grown under Matrigel-based 3-dimensional (3D) in vitro growth condi- tions supplied with epidermal growth factor (E), noggin (N), and R- spondin 1 (R) as a Wnt agonist. In this growth condition, Lgr5+ stem cells have self-organizing properties that enable them to form small intestinal organoids containing crypt-villus structures that recapitulate the native carbonate porous-media intestinal epithelium [5,6]. Although Lgr5+ stem cells can be expanded for multiple passages in the regenera- tion of organoids, a typical growth condition yields a low number of self-renewal cells due to the heterogeneous nature of cell popula- tion, which includes stem cells and differentiated cells [4,7].Lgr5+ stem cells retain their capacity to self-renew and regen- erate the intestinal epithelium due to their position in the stem cell niche [8]. In the intestinal niche, several signaling pathways are related to self-renewal and proliferation of Lgr5+ stem cells [4,8].

Moreover, the self-renewal and proliferation of Lgr5+ stem cells are dependent on cell communications between Lgr5+ stem cells and Paneth cells, which regulate the fate of stem cells by providing Wnt, Notch, and EGF signals within intestinal crypts [9e11]. Based on knowledge of the signaling pathway in the intestinal stem cell niche, Dr. Hans Clevers’ group published a technique for culturing intestinal crypts from the intestines of adult mice using Matrigel and growth medium supplemented with E,N, and R (ENR),thereby mimicking the stem cell niche to maintain stemness in a culture system without Paneth cells [4].To improve the growth condition for maintenance of homoge- nous Lgr5+ stem cells, several researchers have proposed that some compounds facilitate the survival and self-renewal of Lgr5+ stem cells. Xiaolei et al., suggested that CHIR99021, as a glycogen synthase kinase 3β, and valproic acid, as a histone deacetylase in- hibitor, promote the maintenance of self-renewal of mouse Lgr5+ intestinal stem cells (ISCs) in the absence of Paneth cells with a typical growth medium containing ENR [12]. Furthermore, Lgr5+ stem cells in an adult mouse liver model were expanded as liver organoids in a culture condition with A83-01 as a small molecule [13]. Y-27632 has been reported to increase the survival rate of human and mouse embryonic stem cells [14]. However, there is no evidence that A83-01 and Y-27632 have an impact on the expan- sion of Lgr5+ stem cell-derived organoids from adult mouse in- testinal crypts.Thus, in the present study, we investigated whether combina- tions of CHIR99021, valproic acid, Y-27632 (Rho-associated coiled- coil protein kinase [ROCK] inhibitor), and A83-01 in typical ENR- containing growth conditions promoted the maintenance of self- renewal of Lgr5+ ISCs in mouse and human small intestinal orga- noids and facilitated the regeneration of small intestinal organoids. We also suggested that Lgr5+ stem cells had stemness properties in a two-dimensional (2D) culture condition with a four compound- containing medium as well as in a three-dimensional (3D) culture condition.

2.Materials and methods
2.1.Animals
This study was approved by and followed the guidelines of the CHA University Institutional Animal Care and Use Committee (IACUC). The IACUC number for our study is 170092. All the ex- periments were done to minimize animal suffering and to reduce the number of animals. Lgr5-EGFP-IRES-CreERT2 mice were ob- tained from the Jackson laboratory (Bar Harbor, ME, USA), and the male C57Bl/6 mice were obtained from Orient Bio, Inc. (Seongnam, Korea). The animals were maintained in the animal facility at CHA University under 12-h light/dark cycle with food and water ad libitum.

2.2.Preparation of organoids from mouse small intestine
Preparation of the mouse small intestinal organoids was done with 7-9-week-old mice, and using procedures from our previous method [15]. Briefly, the small intestine tissue was washed until the supernatant was clear. Small intestine crypts were isolated from the tissues cut longitudinally into 5 mm pieces using a gentle cell dissociation reagent (STEMCELL Technologies, CANADA). The iso- lated crypts were iltered through a 70 μm cellstrainer before being mixed with Matrigel (BD Biosciences, NJ, USA) at a ratio of 1:1 and seeded in 48-well plates. The small intestinal organoids were cultured in Advanced DMEM/F-12 (Thermo Fisher Scientiic, MA, USA), HEPES buffer (Thermo Fisher Scientiic), Glutamax-I supple- ment (Thermo Fisher Scientiic), penicillin-streptomycin solutions(WELGENE, Korea), N-acetyl-L-cysteine (Sigma-Aldrich, MO, USA),B-27 serum-free supplement (Thermo Fisher Scientiic), N-2 sup- plement (Thermo Fisher Scientiic), animal-free recombinant mu- rine epidermal growth factor (EGF) (PeproTech, Inc., NJ, USA), recombinant murine Noggin (PeproTech) and Cultrex® R-spondin- 1 conditioned medium(Trevigen,MD, USA) containing 3 μM CHIR99021 (C), 2 mM valproic acid (V), 10 μM Y-27632 (Y), and 5 μM A83-01 (A).

2.3.Preparation of human small intestinal organoids
Human small intestinal tissue was obtained from the CHA Bundang hospital. This study was approved by and followed the guidelines of the CHA University Institutional Review Board (IRB). The IRB number for our study is CHAMC201805024-HE014. The tissues were washed with DPBS containing 1% penicillin/strepto- mycin. The tissues were cut into pieces that were as small as possible and washed until supernatant became clear. 10 mL Gentle Cell Dissociation Reagent (STEMCELL Technologies, CANADA) was added in tissues and the tissues were incubated in a shaker at a speed of 40 rpm for 30 min, under 10 。C. Ice-cold DMEM containing 1% BSA was added in tissues and detach the crypts from the tissue. The detached crypts were iltered through a 70 μm cellstrainer and centrifuged at 200 g for 10 min. The collected crypts were embedded in Matrigel at a ratio of 1:1 covered with growth me- dium containing 3 μM CHIR99021 (C), 2 mM valproic acid (V), 10 μM Y-27632 (Y), and 5 μM A83-01 (A) same as growth medium for mouse small intestinal organoid.

2.4.Preparation of the 2D platform culture system
Organoids from the 3D system were dissociated until single cells were obtained using TrypLE™ (STEMCELL Technologies, CANADA) for 5e10 min at 37。C and 5% CO2. The dissociated single cells were seeded ontoMatrigel-coated plates, and the plates were incubated for 2 h at 37。C in a CO2 incubator to semi-solidify the wells. The single cells were seeded onto a coated surface with growth medium containing 3 μM CHIR99021 (C), 2 mM valproic acid (V), 10 μM Y- 27632 (Y), and 5 μMA83-01 (A). C,V,Y, and A were purchased from Sigma-Aldrich.

2.5. Real-time RT-PCR analysis
The small intestinal organoids were treated with a cell recovery solution (Corning) to remove the Matrigel, and total RNA was extracted using the MagListo™ 5M cell total RNA extraction kit (Bioneer, Daejeon, Korea). The manufacturer’s total RNA extraction procedure was followed. RNA was synthesized to cDNA using the PrimeScript™ RT Master Mix (TAKARA, JAPAN). Quantitative po- lymerase chain reaction (qPCR) was performed to measure the mRNA expression level by mixing cDNA with SYBR® Premix Ex Taq™ II (TAKARA). Data was exported from MRQ system (TAKARA). Table 1 represents primers for quantitative real-time PCR. Experi- ments were performed in triplicate wells.

2.6.Immunofluorescence
The organoids were ixed with 4% paraformaldehyde to disin- tegrate the Matrigel. The permeabilization was performed with 0.1% Tween-20 and 0.2% Triton-X100 in PBS, and then, 5% bovine serum albumin (BSA) in DPBS was used to reduce non-speciic binding. After the ixed organoids were treated with primary an- tibodies at 4。C overnight, the samples were bound with secondary antibodies at room temperature for 2 h. The following antibodies used for the staining: Mucin-2 (Santa Cruz, CA, USA), Ki67 antibody (Abcam, MA, USA), Lgr5 (Abcam), E-cadherin (Santa Cruz), Chro- mogranin A (Santa Cruz), Lysozyme (Diagnostic Biosystems, Fre- mont, CA, USA), Sox 9, HNF4, Alb (Santa Cruz, CA, USA), β-catenin (BD Biosciences), and Villin (Santa Cruz, CA, USA). The following secondary antibodies were used: Alexa Flour 488 conjugated anti- rabbit IgG and Alexa Flour 594 conjugated anti-mouse IgG (Thermo Fisher Scientiic).

2.7.Statistical analysis
Students’ t-test was used to analyze the differences between two groups. Three or more experimental groups were compared using one-way ANOVA followed by the Student-Bonferroni post hoc test. Differences between the groups were considered statis- tically signiicant at p < 0.05.

3.Results
3.1. Effect of combinations of four compounds on the establishment
of mouse and human small intestinal organoids based on a typical 3D culture system
To observe the biopolymeric membrane growth of mouse and human small intestinal organoids in a 3D culture system using combination of four com- pounds (denoted as CVYA), the mouse and human small intestinal crypts were cultured in typical ENR-containing growth medium supplemented with the four compounds, and the morphologies were measured using daily microscopic tracking. The result showed that the mouse (Fig.1A) and human (Fig.1B) small intestinal crypts in the CV-containing growth medium and the CVYA-containing growth medium were grown as organoids. Additionally, morpho- logically, the mouse small intestinal organoids in the CVe and CVYA-containing growth media were longer than those in the typical ENR-containing growth medium (Fig. 1A). The Lgr5-GFP intensity of the mouse small intestinal organoids was compared to investigate the effect of the four compounds on Lgr5 expression. The result showed that the Lgr5-GFP intensity was stronger in the CVYA-containing growth medium than in the typical ENR- containing growth medium (Fig. 1C). The Lgr5 marker for stem cells and Lyz marker for Paneth cells mRNA expression levels of the mouse small intestinal organoids in the CVe and CVYA-containing growth media were signiicantly increased in comparison to the organoids in the typical ENR-containing growth medium at day 4 and day 8 (Fig. 1D). The Lgr5 mRNA expression level was higher in the human small intestinal organoids grown in the CVYA- containing growth medium in comparison to the organoids grown in the ENR-containing growth medium at day 4 and day 8 (Fig.1E). Moreover, the Muc2,Vill, Lyz,and ChrgA mRNA expression levels were lower in the organoids grown in the CVYA-containing growth medium in comparison to the organoids grown in the typical ENR-containing growth medium at day 4 and day 8. How- ever, the Muc2 marker for goblet cells, Vill marker for enterocytes, and ChrgA marker for enteroendocrine cells mRNA expression levels of the organoids decreased in the CVe and CVYA-containing growth media in comparison to the organoids in the typical ENR- containing growth medium. Additionally, immunocytochemistry staining showed that several markers for mouse (Fig. 1F) and hu- man (Fig.1G) small intestinal cells were expressed in the organoids

Fig. 1. Establishment of the 3D mouse and human small intestinal organoids (A) Growth of the mouse small intestinal organoids (B) Growth of the human small instestinal organoids in the 3D culture with different compounds Binimetinib mw (the upper images from each group X4 magniication, lower images X10, scale bar 50 mm); (C) The Lgr5+ GFP and GFP intensity measurement of Lgr5-GFP of mouse small intestinal organoids (X4 magniication, scale bar 50 mm); (D, E) Relative mRNA expression using quantitative PCR to analyze the gene expression pattern from each compound combination; (F, G) Immunocytochemistry results using markers for Ki67, Lyz, Vill, and Muc2 (X40 magniication, scale bar 50 mm). Results are mean ± SD of the triplicate experiment. *P < 0.05, **P < 0.005, ***P < 0.0005.

Fig. 2.Establishment of the 2D platform based on the use of four compounds to culture the Lgr5+ ISCs. (A) Growth of the mouse small intestinal organoids in the 3D culture with different combinations of compounds (the upper images from each group X4 magniication, lower images X10, scale bar 50 mm); (B) The number of colonies was counted in each compound group; (C) the Lgr5-GFP + colonies in each compound group (X4 magniication, scale bar 50 mm); (D) Relative mRNA expression using quantitative PCR to analyze the gene expression pattern. While chromogranin A decreased,Lgr5, a marker for ISCs increased; (E) Immunocytochemistry results of Ki67, Lyz,Vill, and Muc2 (X20 magniication, scale bar 50 mm). Results are mean ± SD of the triplicate experiment. *P < 0.05, **P < 0.005, ***P < 0.0005 from the crypts. The expression level of Lgr5-GFP, Ki67, and Lyz was greater in the organoids cultured in the CVYA-containing growth medium than in the organoids cultured in the ENR-containing medium.

3.2.Expansion of Lgr5+ ISCs in a 2D culture system with the combined four compounds
The effect of the four compounds on the expansion of Lgr5+ ISCs was evaluated in a 2D culture system using the typical ENR me- dium. The result showed that the Lgr5+ ISCs isolated from adult tissue-derived organoids expanded in the CVYA-containing growth medium and but not in the 2D culture system with the ENR- containing growth medium (Fig. 2A). Additionally, the number of cells in the colonies was greater in the 2D culture system with the CVYA-containing growth medium than in the 2D culture system with the ENR-containing growth medium (Fig. 2B). Moreover, the Lgr5-GFP intensity in the small intestinal colonies was greater in the 2D culture system with the CVYA-containing growth medium in comparison to in the 2D culture system that only contained ENR (Fig. 2C). The Lgr5 mRNA expression level increased in the colonies grown in the 2D culture system with CVYA-containing growth medium (Fig. 2D). In contrast, the ChrgA mRNA expression level of the colonies grown in 2D culture system with CVYA-containing growth medium decreased. Furthermore, the Vill and Muc2 mRNA expressions levels of the colonies grown in the 2D culture system with the CVYA-containing growth medium decreased. Additionally, the intestinal cell-speciic markers of the Lgr5+ col- onies in the 2D culture systems were detected in the CVYA- containing culture medium (Fig. 2E).

3.3.Identification of an additional compound to promote expansion of Lgr5+ ISCs in a 2D culture system
To identify another compound to expand Lgr5+ ISCs, several signaling modulators were tested in a 2D culture system using the four compound-containing medium. The result showed that the Lgr5-GFP intensity increased in the colonies grown in the Wnt3a, PD98059 (P), Bay11-7082, and SB202190-containing culture me- diums (Fig. 3A). Moreover, the Lgr5-GFP expression level w10 μM PD98059 as greater in the colonies grown in the ive compound- containing growth medium(CVYA and) than in the colonies grown in the CVYA-containing growth medium (Fig. 3B). The Lgr5 mRNA expression level increased in the colonies grown in the growth medium containing ive compounds in comparison to the colonies grown in the CVYA-containing growth medium. The EphB3 and CD44 mRNA expression levels decreased in the colonies grown in the growth medium containing ive compounds (Fig. 3C). Furthermore, Lgr5-GFP and several small intestinal markers were found in the colonies grown in the growth medium containing ive compounds(Fig.3D).Additionally, the number of colonies increased in a time-dependent manner in the growth medium containing ive compounds in comparison to the growth medium that only contained CVYA (Fig. 3E).

3.4.Expansion of Lgr5+ ISCs in conversed small intestinal
organoids transferred from a 2D culture system to a 3D culture system with five compounds
To evaluate the eficacy of the ive compounds to expand 2D cultured Lgr5+ ISCs as organoids, the cultured colonies in the 2D culture system were transferred to a 3D culture system. Moreover, the effect of the ive compounds on expanding Lgr5+ ISCs in a 3D culture system was tested by transferring cells from the 2D culture system to the 3D culture system using three different media as follows: a 3D culture system with an ENR-containing medium, a 3D culture system with a ive compound-containing medium from a 2D culture system with a ive compound-containing medium, and a 3D culture system with an ENR-containing medium from a 2D culture system with ive compound-containing medium. The result showed that the colonies from the 2D culture system were grown as small intestinal organoids in each of the three culture conditions (Fig. 4A). Moreover, the Lgr5-GFP intensity increased in the orga- noids grown in the 3D culture system with ENR-containing growth medium and the ive compound-containing growth medium (Fig. 4B). Notably, the Lgr5-GFP intensity of the organoids that were transferred to the 3D culture system with the ENR-containing medium from the 2D culture system with the ive compound- containing medium was greater than those in the other groups (Fig. 4B).

To evaluate the lineage markers, the mRNA expression levels of epithelial lineage markers were measured in three groups (Fig. 4C). The Lgr5 mRNA expression level of the organoids trans- ferred from the 2D cultured system to the 3D culture system increased in comparison to the organoids that were only grown in the 3D culture system. The Muc2,Vill, and ChrgA mRNA expression levels of the colonies transferred from the 2D cultured system with the ive compound-containing medium to the 3D culture system with ive compounds-containing medium decreased in comparison to the other groups (Fig. 4C). To compare the effect of the CVYA and the ive compounds on the expansion of Lgr5+ ISCs, the colonies in the 2D culture system with the CVYA-containing medium and the ive compound-containing medium were transferred to the 3D culture system with the CVYA-containing medium and the ive compound-containing media. The result showed that the Lgr5-GFP intensity was greater in the organoids in the 3D culture system with the ive compound-containing medium than the organoids in the 3D culture system with the CVYA-containing medium (Fig. 4D). Moreover, the mRNA expression levels of Wnt targets, CD44,Axin2, Sox9, and EphB3, were greater in the mouse small intestinal organoids in the 3D culture system with the ive compound- containing medium than the organoids in the 3D culture system with the ENR- and CVYA-containing media (Fig. 4E). To test the intestinal function of the organoids transferred from the 2D culture system to the 3D culture system, the organoids transferred from the 2D culture system with the ive compound-containing medium to the 3D culture system with the ENR-containing medium were treated with Forskolin, such as a cystic ibrosis transmembrane conductance regulator (CFTR) agonist. The result showed that there was no difference in the organoids’ response to Forskolin between the groups (Fig. 4F). Likewise, there was no difference in the per- centage of swollen organoids between the groups (Fig. 4G).

4.Discussion
Recent advances in 3D culture methodology and knowledge about the niche factors for Lgr5+ stem cells isolated from the gastrointestinal tract have enabled the generation of epithelial organoids [4,8,16]. Although these studies have shown the poten- tials ofLgr5+ stem cells for regenerative organoids, there are still several limitations to generating a high yield of a pure population of Lgr5+ stem cells.To overcome these limitations, the modulation of signaling pathways has been used to control the expansion of Lgr5+ stem cells. Yin et al. reported a chemical modulation of the Wnt and Notch signaling pathways to enable ex vivo expansion of Lgr5+ stem cells [12]. Moreover, Xiaolei et al. reported the effect of CHIR99021 and valproic acid on the expansion of Lgr5+ stem cells in mouse small intestinal organoids with a typical culture medium [12].That study reported that CHIR99021 (GSK-3β inhibitor) increased the percentage and green fluorescent protein (GFP)

Fig. 3.Identiication of another compound to expand the Lgr5+ ISCs on the 2D matrix. (A) The expression of Lgr5-GFP in the small intestinal organoids in the 2D culture condition with four factors (X4 magniication, scale bar 100 mm); (B) Expression of GFP in the four- and ive-compound-containing conditions in the 2D culture system (the left images from each group X4 magniication, right images X10, scale bar 50 mm); (C) Relative mRNA expressions in the small intestinal organoids treated with 4 and 5 compounds-containing conditions in the 2D culture system; (D) Immunocytochemistry of Ki67, Lyz, Vill, and Muc2 of the organoids in ive compound-containing condition in the 2D culture system (X20 magniication, scale bar 50 mm); (E) Comparison of the growth of organoids between the four and ive compound-containing conditions using daily microscope tracking (X4 magniication, scale bar 50 mm). Results are mean ± SD of the triplicate experiment. *P < 0.05, ***P < 0.0005.

Fig. 4. Differentiation of the enriched Lgr5+ ISCs grown in the ive compound containing condition to generate organoids. (A) The organoids in three conversion groups (the upper/ middle images from each group X4 magniication, lower images X10, scale bar 50 mm); (B) The expression of Lgr5-GFP of the organoids in three conversion groups (X20 magniication, scale bar 50 mm); (C) Relative mRNA expression of LGR5, Ecad, Muc2, Lyz, and ChrgA; (D) Lgr5-GFP expression of the organoids in the four and ive compound-intensity of Lgr5+ stem cells which indicates increased self- renewal of Lgr5+ stem cells. Moreover, valproic acid (histone deacetylase inhibitor) plays a role in Notch activation in organoids which also increases the self-renewal of stem cells.To enhance the eficacy of the ex vivo expansion of Lgr5+ stem cells, we modiied the growth conditions containing signaling modulators, such as Y-27632 and A83-01, which were added to a typical culture medium and a CV combination-containing culture medium. ROCK regulates caspase signaling cascades and apoptosis [17], and ROCK proteins can be activated by removing the inhibitory carboxyl terminal of ROCK1 and ROCK2 by caspase 3 mediated cleavage [18]. Several studies have suggested that the ROCK in- hibitor, Y-27632, reduced caspase-dependent cell apoptosis [19e21], and treating with Y-27632 increased the cloning eficacy and survival rate of stem cells [14]. Moreover, the TGF-β signaling pathway affects stem cell clonal expansion and differentiation of the secretary cell lineage [22].

Additionally, A83-01, as a TGF-β in- hibitor, maintains stem cells in an undifferentiated state and in- creases their plating eficacy and long-term survival [23]. In the present study, the results showed that the combination of the four compounds (CVYA) promoted the expansion of the Lgr5+ orga- noids in a 3D culture system. The culture medium containing combinations of Y-27632 and A83-01 with CV maintained self- renewal of Lgr5+ organoids from adult intestinal tissues and affected the regeneration of small intestinal organoids in the CV- containing culture medium. Moreover, the self-renewal of Lgr5+ organoids from other tissues such as liver and pancreas was maintained (Supplemental Figs. 1 and 2). Furthermore, markers for several types of cells were expressed in organoids. Results mean Lgr5+ stem cells were expanded in CVYA-containing medium, also organoids consisted of several type of cells similar with tissues. PD98059 is a mitogen-activated protein kinase (MAPK) inhibitor that prevents differentiation of embryonic stem cells and mesen- chymal stem cells [24]. In particular, PD98059 maintains Lgr5 expression while enhancing the expression of intestinal markers- and pharmacokinetic-genes in intestinal organoids [25]. In the present study, we demonstrated that PD98059 enhanced the Lgr5+-GPF intensity of organoids in the CVYA-containing growth condition. Thus, we demonstrated the expansion of Lgr5+ stem cells using CVYA and PD98059 containing growth media in a 3D culture system.

Although a 3D culture system based on Matrigel has many ad- vantages for regeneration of mouse small intestinal organoids, these structures are rarely microscopic mini-structure versions of the originating epithelial tissue, and the technique is dificult to implement [6]. To develop easy, fast, and cost-eficient methods to generate units of intestinal organoids, studies were conducted to establish a 2D culture system [6,16]. Fetal human intestinal stem cells were cultured in 2D culture systems with a feeder layer to generate homogenous Lgr5+ stem cells [26]. Moreover, a 2D cul- ture system was reported to support self-sustaining Lgr5+ stem cells of intestinal organoids from Lgr5-EGFP-IRES-CreERT2 trans- genic mice [27]. However, it is unclear if these 2D culture systems are suitable for self-renewal of Lgr5+ stem cells [28e30]. In the present study, the results showed that Lgr5+ colonies in a 2D culture system with four and ive compounds can be formed as organoids that had normal function when transferred to a 3D cul- ture system. These small intestinal organoids also showed an increased Lgr5 expression level, which indicates maintenance of self-renewal. However, in the 2D culture system, the Lgr5+ colonies did not reconstruct to organoids. Thus, further study is needed to reconstruct organoids in a 2D culture system Grants This work was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & future Planning, Republic of Korea [NRF- 2017R1C1B2008808] and by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Republic of Korea [HI16C1634, HI17C2094].