SAT-176 - To What Extent is Testis Specific Action of Follistatin Like 3 (FSTL3) Linked to the Inhibition of Activin-Induced Gene Expression?

Activin, a TGFb ligand, and one of its endogenous inhibitors follistatin-like 3 (FSTL3) are crucial for testicular development and function. In addition to activin, FSTL3 inhibits GDF11 and myostatin. As well as being secreted FSTL3 is nuclear. FSTL3 function is, therefore, likely not limited to activin inhibition. To dissociate FSTL3 action from that of activin we identified testis-specific effects of FSTL3 deletion by comparing our RNA expression data in the testis versus the liver in FSTL3 deleted (FSTL3-KO) mice. Sets of upregulated/downregulated transcripts differed between testis and liver but there were 7 genes (e.g. Akap9 and Enpp2) upregulated and 10 genes (e.g. Cd44 and Col1A1) downregulated in both testis and liver. These most likely reflect core pathway/s, including cellular proliferation, that are activated or inhibited in the absence of FSTL3. The remainder of differences in gene expression in FSTL3 KO testis are therefore most likely testis-specific. This gene set was compared with published activin-stimulated Sertoli cell gene expression data to find activin-induced gene expression in FSTL3 KO mouse testis. There was a large excess of genes (1143) induced in the absence of FSTL3 in the testis compared to those induced in Sertoli cells in response to activin (176), 7 of which, including Myh6 and En1, were induced in both. To holistically identify gene transcription in FSTL3 KO and WT testis that is modulated directly downstream of TGFb ligands in a SMAD4-dependent manner we performed SMAD4 ChIP Seq analysis. This identified 904 genes that are therefore directly TGFb ligand responsive in the testis. Interestingly, not all genes identified by ChIP Seq are induced in the FSTL3 KO testis or activin treated mouse Sertoli cells and vice versa. Continuing this analysis we have identified 5 genes that are most likely directly induced most proximally to activin/ SMAD signalling, e.g. Prkd3 and Lphn3. A comparison of FSTL3 KO testis gene expression and SMAD4 ChIP data allows identification of TGFb and SMAD regulated genes. Exclusion of activin induced SMAD4 dependent transcription then allows identification of gene expression (19 upregulated and 7 downregulated) in the testis that is regulated by FSTL3 but not involving activin. Our WordMiner program linked these genes with meiosis, oncogenesis and cell-migration. Identifying their roles in the testis will be instrumental in elucidating FSTL3 and SMAD dependent regulation of testis form and function.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*