Nanostructure and β1-integrin distribution analysis of pig's spermatogonial stem cell by atomic force microscopy

Spermatogonial stem cells (SSCs) provide the foundation for spermatogenesis and male fertility. However, spermatogenesis has direct links with some adhesion molecules on SSCs membrane. Β1-integrin (CD29) is such a kind of adhesion molecule and a biomarker of pig's SSCs. Therefore, quantitative characteristics of β1-integrin expression level in a single cell could help us to capture the signal switch and understand the mechanism of spermatogenesis. In this study, atomic force microscopy (AFM) was used to obtain the morphology and ultrastructure of SSCs at nanometer level, and the CD29 Ab-functionalized AFM tip was used to examine β1-integrin distribution on the cell membrane. There were many force-binding spots on about 50% of cell membrane binding to the CD29 Ab-functionalized AFM tip, and the mean bind rupture force was 283.63±12.56PN which was much larger than the non-specific average force 70.75±10.95PN. Meanwhile, β1-integrin on SSCs membrane was distributed non-uniformly, and there were some β1-integrins appeared to be expressed as 150-350 nm nanoclusters on the membrane. Our results discovered the structure of SSCs at nanometer level by AFM. The force between β1-integrin antigen-antibody interactions and the distribution of β1-integrin protein on SSCs membrane were also firstly demonstrated.