We determined that the level of the Glass bottom boat (Gbb) 55-kDa precursor, the signaling molecule of the main GSC self-renewal regulator bone morphogenetic protein (BMP) (transforming growth factor β (TGF-β)) pathway [63,64], was significantly increased in the testes of males with belKD in cyst cells (Figure S10). This evidence concerns the gene TGFB1 and cyst.