Does the apoptosis pathway play a critical role in gonocyte transformation?

Undescended Testes (UDT) are prevalent in 2%-5% of male infants and cause malignancy and infertility. During germ cell development, abnormal gonocytes usually undergo apoptosis. This process is believed to involve BAX (Bcl-2 Associated X) protein in clearing abnormal gonocytes which may fail in UDT, resulting in persisting gonocytes causing seminomas later in life. We aim to investigate the role of BAX in gonocyte apoptosis.

BAXKO (BAX-knockout) mice were back-crossed to OG2 mice (Oct4-promoter driving enhanced green fluorescent protein-eGFP) to produce BAXOG2 mice. Testes (wildtype-BAX^+/+, heterozygous-BAX^+/- and homozygous-BAX^-/- mice, n = 6/group) on postnatal days 1, 3, 6, 9 were fixed and embedded in OCT for frozen sectioning. Sections were labeled with Anti-Müllerian Hormone (Sertoli cell marker), Mouse Vasa Homolog (germ cell marker) and DAPI (nucleus marker) and imaged using confocal microscopy. Oct4-GFP+ve germ cells, germ cells on/off the basement membrane and Sertoli cells were counted using ImageJ followed by data analysis with GraphPad.

BAX^-/-OG2 mice had significantly higher number of germ cells/tubule comparing to BAX^+/+OG2 on day 9. There were Oct4-GFP+ve gonocyte-like germ cells that persisted in the center of the tubules in BAX^-/-OG2 even after the completion of gonocyte transformation. This suggests that abnormal gonocytes in BAX^-/-OG2 mice failed to undergo apoptosis and are allowed to persist.

This study demonstrated that apoptosis is important in regulating germ cell migration and differentiation during gonocyte transformation in neonatal mice. In addition, inhibition of apoptosis results in persisting neonatal gonocytes which might become seminomas in patients with UDT.