Fig. S5.

Working model for the regulation of the Lhb gene by TET1 during gonadotrope differentiation (Discussion). (Left) In immature, poorly differentiated gonadotropes (as in αT3-1 gonadotrope-precursor cells and proliferating gonadotropes in immature or gonadectomized mice), Tet1 and Tet2 are readily expressed, but Lhb expression is at low or very low levels (minor differences between the cell models noted in brackets). In these cells, the upstream CpG-rich region of Lhb is methylated (5mC) and associated with the truncated TET1 isoform, which represses Lhb expression, possibly involving recruitment of the methyl transferase-containing PRC2 complex, which catalyzes the repressive H3K27me3. With differentiation (Right), the levels of TET1 decrease, facilitated by exposure to GnRH, which inhibits Tet1 expression, leading to a decrease in the ratio of TET1:TET2, which allows TET2 to bind the Lhb promoter. TET2 catalyzes the hydroxymethylation (5hmC) of the CpG-rich region, whereas the region closest to the TSS is hydroxymethylated and/or demethylated to allow transcription, further facilitated by independent effects of GnRH via the activation of various gene-specific transcription factors (TFs). This state is further strengthened by the repressive effect of the steroids produced in the active gonads, which maintain repression on Tet1 in the sexually mature animal.