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. 2021 Jun 18;9:661243. doi: 10.3389/fcell.2021.661243

FIGURE 6.

FIGURE 6

Analysis of WNT signaling effectors and downstream targets in fetal gonads by immunostaining. (A) Immunofluorescence of CTNNB1, SFRP2, or TCF7L2, with DDX4 and POU5F1 or SOX17 in the first trimester (10 WD, top) or second trimester (20 WD bottom) fetal testis. No nuclear CTNNB1 is observed in germ cells, suggesting that canonical WNT signaling is not active. SFRP2 expression is age dependent, being expressed in 10-WD PGCs, but not 20-WD PGCs. In 20 WD germ cells, TCF7L2 is upregulated in GONs (POU5F1−). Yellow boxes indicate zoom-in of a PGC (POU5F1+), and cyan boxes indicate zoom-in of a GON (POU5F1−). Se, St, and Gr annotate Sertoli, stromal, and granulosa cells, respectively. Scale bar indicates 10 μm. (B) Immunofluorescence of CTNNB1, SFRP2, or TCF7L2, with DDX4 and POU5F1 or SOX17 in the first trimester (9 or 10 WD, top) or second trimester (18 WD, bottom) fetal ovary. Faint staining of CTNNB1 is observed in some 18-WD GONs, suggesting (modest) activation of canonical WNT signaling. SFRP2 expression is highly upregulated in PGCs compared to GONs, especially in 18-WD ovary. TCF7L2 is expressed in both PGC and OGONs. (C) A schematic model of active signaling WNT axes in germ cells representing a combination of results from CellphoneDB analysis and differentially expressed gene analysis. Genes upregulated in GONs are depicted in green, while those upregulated in PGCs are depicted in red.