Membrane-bottomed microwell array added to Transwell insert to facilitate non-contact co-culture of spermatogonial stem cell and STO feeder cell

Abstract

In vivo cells express their characteristics in three-dimensional (3D) microenvironments via cell-cell interactions through autocrine, contact-dependent, paracrine, and synaptic signaling, often between heterologous cell types. Various in vitro 3D microwell-based culture methods have been proposed to further identify cellular characteristics by recreating cellular environments, typically in the form of spheroids and organoids, thereby realizing contact-based cell-cell interactions. However, in vivo cells generally exhibit multiple cellular interaction modes that have not been completely evaluated using existing microwell-based methods. This has led to a demand for more advanced and comprehensive methods. This study introduces a novel apparatus, the membrane-bottomed microwell (MBM) for non-contact co-cultures and 3D cell cultures. The MBM is a combination of a Transwell and a microwell array; these have previously been utilized to facilitate heterologous cell co-culturing and spheroid 3D cell culturing, respectively. In the Transwell insert, the lower part of the MBM is immersed in the culture media in which the cells are being two-dimensionally (2D) cultured, and the spheroids of the MBM are affected by the 2D cultured cells via the membrane at the bottom of the microwell. Here, we describe the methods for manufacturing the MBM in detail and elucidate the results of simulations of diffusion through the bottom of the membrane. We validate the proposed MBM for the spheroid culture of spermatogonial stem cells (SSCs), which had previously been 2D co-cultured with Sandos inbred mouse (SIM)-derived 6-thioguanine- and ouabain-resistant (STO; a mouse embryonic feeder cell line) feeder cells. The proposed system is shown to facilitate successful SSC spheroid culturing with paracrine signaling of STOs through an apparatus that simplifies both the loading and the evaluation processes; therefore, we believe that our findings will enable a more comprehensive understanding of SSCs and associated phenomena and that our system can be applied to various in vitro cell and tissue experiments.