Dynamic changes in gene expression patterns and cell behaviour are evident throughout embryonic and neonatal germ cell development in the mouse. In the testes, the postnatal period represents a time when the male germline stem cells (GSCs) or, gonocytes migrate to the basement membrane of the seminiferous tubules preparing for a lifetime of spermatogenesis and is an important area of study. Here we use the transgenic mouse that expresses green fluorescent protein under the Oct 4 promoter (Oct4::GFP transgenic mouse). A novel ex vivo model was developed to image cell migration, proliferation and apoptotic events during GSCs development in the seminiferous tubules of the late mouse embryo and neonate. In the male neonatal testes, the germ cells demonstrated motile behaviour as they translocate from the centre to the basement membrane of the seminiferous tubules.
We identified live germ cell movements, proliferation and apoptotic events within the seminiferous tubules during the late fetal and early neonatal period in the mouse. Timelapse microscopy captured 2 peaks of apoptosis in the Oct4::GFP germ cells- during late embryonic stages and most notably at postnatal day 4 (P4), which was correlated with high levels of cleaved caspase-3 expression. At postnatal P4 there was terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. Correspondingly, the number of Oct 4::GFP cells per seminiferous tubule (mean±S.D.) decreased from 9.1±3.67 cells/tubule at E17.5 to 2.7±2.72 cells at P0, and 2.2±1.89 cells by P5 thus correlating with apoptosis captured during live imaging. Concomitant germ cell proliferation was noted during apoptotic waves. Confocal videomicroscopy has allowed us to visualize living peri- and neonatal events during mouse testicular development. Male germ cells change their characteristics dramatically during perinatal development and the paracrine factors involved in this process is an exciting area of future work.