Effects of nanostructures and mouse embryonic stem cells on in vitro morphogenesis of rat testicular cords.

Morphogenesis of tubular structures is a common event during embryonic development. The signals providing cells with topographical cues to define a cord axis and to form new compartments surrounded by a basement membrane are poorly understood. Male gonadal differentiation is a late event during organogenesis and continues into postnatal life. The cellular changes resemble the mechanisms during embryonic life leading to tubular structures in other organs. Testicular cord formation is dependent on and first recognized by SRY-dependent aggregation of Sertoli cells leading to the appearance of testis-specific cord-like structures. Here we explored whether testicular cells use topographical cues in the form of nanostructures to direct or stimulate cord formation and whether embryonic stem cells (ES) or soluble factors released from those cells have an impact on this process. Using primary cell cultures of immature rats we first revealed that variable nanogratings exerted effects on peritubular cells and on Sertoli cells (at less than <1000 cells/mm(2)) by aligning the cell bodies towards the direction of the nanogratings. After two weeks of culture testicular cells assembled into a network of cord-like structures. We revealed that Sertoli cells actively migrate towards existing clusters. Contractions of peritubular cells lead to the transformation of isolated clusters into cord-like structures. The addition of mouse ES cells or conditioned medium from ES cells accelerated this process. Our studies show that epithelial (Sertoli cell) and mesenchymal (peritubular cells) cells crosstalk and orchestrate the formation of cords in response to physical features of the underlying matrix as well as secretory factors from ES cells. We consider these data on testicular morphogenesis relevant for the better understanding of mechanisms in cord formation also in other organs which may help to create optimized in vitro tools for artificial organogenesis.