Derivation and maintenance of murine trophoblast stem cells under defined conditions

Abstract

Trophoblast stem cells (TSCs) are in vitro equivalents to the precursor cells of the placenta. TSCs are cultured in serum-rich medium with fibroblast growth factor 4, heparin, and embryonic-fibroblast-conditioned medium. Here, we developed a simple medium consisting of ten chemically defined ingredients for culture of TSCs on Matrigel or synthetic substrates, named TX medium. Gene expression and DNA methylation profiling demonstrated the faithful propagation of expression profiles and epigenomic characteristics of TSCs cultured in TX. Further, TX medium supported the de novo derivation of TSC lines. Finally, TSCs cultured in TX differentiate into all derivatives of the trophectodermal lineage in vitro, give rise to hemorrhagic lesions in nude mice, and chimerize the placenta, indicating that they retained all hallmarks of TSCs. TX media formulation no longer requires fetal bovine serum and conditioned medium, which facilitates and standardizes the culture of this extraembryonic lineage.

Figure 1

Maintenance of TSC Characteristics in TX Medium (A) Photomicrographs of TS_6.5 cells in TS and TX medium at passage 11+10. The scale bar indicates 100 μm. (B) Cell-cycle analysis using propidium iodide for TS cells grown in TX medium (gray bars) and TS medium (black bars) for 20 passages. Data are presented as mean of three TSC lines with SD. (C and D) Quantitative RT-PCR analysis of indicated marker genes of undifferentiated (C) and differentiated (D) trophoblast in TSCs cultured in TS (black bars) and TX media (gray bars) for ten passages. Bars represent mean values with SD of three different TSC lines (TS-EGFP, TS_6.5, and TS_3.5). (E) Immunofluorescent staining against EOMES, CDX2, and TFAP2C of TSCs cultured for ten passages in TX medium. Smaller pictures display Hoechst staining. The scale bar represents 50 μm. (F) Immunoblot against CDX2, EOMES, TFAP2C, and ELF5 of whole-cell lysates from TSCs cultured for ten passages in TS and TX medium. β-ACTIN serves as a loading control. (G) Metaphase spreads of TS_6.5 cells at early (p11+12) and late (p11+40) passage in TX medium. See also Figures S1–S3 and Table 2.

Figure 2

In Vitro and In Vivo Differentiation Potential of TSCs Cultured in TX Medium Compared to TS Medium (A) Schematic of experimental approach. TS_6.5 cultured for ten passages in TS and TX media were switched to differentiation media. (B) Photomicrographs of TSCs differentiated for 7 days, previously cultured in TS and TX media in the indicated differentiation conditions. The scale bar represents 100 μm. (C) Quantitative RT-PCR analyses of indicated marker genes in TS diff media (black bars), TX→ TS diff (dark gray bars), and TX diff (light gray bars) conditions. Bars represent mean values (n = 3) and SD of individual RNA preparations. (D) Stained paraffin sections of hemorrhagic lesions 7 days after subcutaneous injection of TS_3.5 cells cultured in TS and TX media (p30+12). H&E, hematoxylin and eosin; immunohistochemical staining against TFAP2C and CD31. The scale bars represent 200 μm. (E) Photographs of a chimeric placenta (view of the embryo-facing side) following blastocyst injection of TS-EGFP cells cultured in TX medium and the corresponding embryo. TS-EGFP cells contributed to the placenta, but not to the embryo proper. EGFP, green channel; bf, bright field. The scale bar represents 1 mm.

Figure 3

Characterization of De-Novo-Derived TSC Lines in TX Medium (A) Schematic representation of culture conditions of newly derived TSC lines. (B) Photomicrographs of TSC line 1 at p1 and p10 derived in TX media displaying typical TSC morphology. The scale bar represents 100 μm. (C) Quantitative RT-PCR analysis of indicated TS marker genes of TSC lines derived in TX medium compared to TSC lines derived in standard conditions and thereafter cultured for ten passages in TX medium. Each bar represents mean values and SD of two individual TSC lines. See also Table S1.

Figure 4

Global Gene Expression Analyses of TSCs Grown in TX Compared to Standard TS Medium (A) Hierarchical clustering of TS lines (TS-EGFP, TS_6.5, and TS_3.5) in TS and TX media. (B) Pairwise scatterplot of global gene expression of TS-EGFP line in TS medium versus TX medium. Black lines indicate boundaries of 2-fold change in Log₂ scale. Genes downregulated in TX medium are represented as green dots; genes upregulated are represented as red dots. Color bar displays the scattering density: the darker the color, the higher the density. R, Fisher’s correlation coefficient. (C) Venn diagram comparing 2-fold downregulated (in Log₂) transcripts in TX medium between three TSC lines (TS-EGFP, TS_6.5, and TS_3.5). (D) Venn diagram comparing 2-fold upregulated (in Log₂) transcripts in TX medium between three TSC lines (TS-EGFP, TS_6.5, and TS_3.5). See also Figure S4 and Tables S2 and S3.

Figure 5

Global DNA Methylation Profiles of TSCs Grown in TX Compared to Standard TS Medium (A and B) DNA methylation patterns determined by meDIP-Seq at the Elf5 locus, which is hypomethylated in TSCs but methylated in ESCs, and Nanog, which exhibits the opposite methylation profile. The distribution and enrichment of methylation at these key transcription factors remains unchanged in TX medium. (C and D) Scatter plots displaying Pearson’s correlation of global methylation between cells grown in TS versus TX medium. Each point corresponds to a 5 kb in silico probe spaced 20 kb apart. Values were normalized for total read count and converted to a Log₂ scale. R values very close to one indicate that the methylation profiles of TSCs grown in TX and TS media are extremely similar to each other on a global scale. (E) CpG islands (CGIs) displayed the most striking methylation differences between the two culture conditions with less reads mapping to CGIs in TX medium. See also Figure S5.