Glioblastoma (GB) is the most frequent and aggressive type of glioma. The lack of reliable GB models, together with its considerable clinical heterogeneity, has impaired a comprehensive investigation of the mechanisms that lead to tumorigenesis, cancer progression, and response to treatments. Recently, 3D cultures have opened the possibility to overcome these challenges and cerebral organoids are emerging as a leading-edge tool in GB research. The opportunity to easily engineer brain organoids via gene editing and to perform co-cultures with patient-derived tumor spheroids has enabled the analysis of cancer development in a context that better mimics brain tissue architecture. Moreover, the establishment of biobanks from GB patient-derived organoids represents a crucial starting point to improve precision medicine therapies. This review exemplifies relevant aspects of 3D models of glioblastoma, with a specific focus on organoids and their involvement in basic and translational research.

Human embryo implantation involves attachment of the blastocyst to the endometrial epithelium to subsequently gain access to the underlying stromal compartment. The blastocyst is believed to cross the epithelium either by migration through, or upon apoptosis of, the endometrial epithelial cell layer. Yet, how the blastocyst exactly traverses the endometrial epithelium remains unknown. Here, we describe an in vitro implantation model of human blastoids and hormonally matured endometrial organoids amenable to high-resolution live imaging. We demonstrate that the initial step of implantation is mediated by the direct fusion of blastoid cells with endometrial epithelial cells. Blastoids express the fusion proteins Syncytin-1 and -2, while the endometrial epithelium mainly expresses the fusion co-receptor for Syncytin-2, called MFSD2A. CRISPR-induced loss of MFSD2A in the endometrial epithelium prevents blastoids from attaching and abolishes fusion. Together, these findings support a model in which fetal-maternal cell fusion constitutes the critical initiating mechanism of human embryo implantation, with endometrial MFSD2A playing an indispensable role in this process.