From pluripotency to differentiation: laying foundations for the body pattern in the mouse embryo

Disease modelling in human organoids

The past decade has seen an explosion in the field of in vitro disease modelling, in particular the development of organoids. These self-organizing tissues derived from stem cells provide a unique system to examine mechanisms ranging from organ development to homeostasis and disease. Because organoids develop according to intrinsic developmental programmes, the resultant tissue morphology recapitulates organ architecture with remarkable fidelity. Furthermore, the fact that these tissues can be derived from human progenitors allows for the study of uniquely human processes and disorders. This article and accompanying poster highlight the currently available methods, particularly those aimed at modelling human biology, and provide an overview of their capabilities and limitations. We also speculate on possible future technological advances that have the potential for great strides in both disease modelling and future regenerative strategies.

Summary: Human organoids are important tools for modelling disease. This At a Glance article summarises the current organoid models of several human diseases, and discusses future prospects for these technologies.

LGR4 and LGR5 Function Redundantly During Human Endoderm Differentiation

BACKGROUND & AIMS

The Lgr family of transmembrane proteins (Lgr4, 5, 6) act as functional receptors for R-spondin proteins (Rspo 1, 2, 3, 4), and potentiate Wnt signaling in different contexts. Lgr5 is arguably the best characterized of the Lgr family members in a number of adult and embryonic contexts in mice. However, the function of LGR family members in early embryonic development is unclear, and has not been explored during human development or tissue differentiation in detail.

METHODS

We interrogated the function and expression of LGR family members using human pluripotent stem cell-derived tissues including definitive endoderm, mid/hindgut, and intestinal organoids. We performed embryonic lineage tracing in Lgr5-GFP-IRES-CreERT2 mice.

RESULTS

We show that LGR5 is part of the human definitive endoderm (DE) gene signature, and LGR5 transcripts are induced robustly when human pluripotent stem cells are differentiated into DE. Our results show that LGR4 and 5 are functionally required for efficient human endoderm induction. Consistent with data in human DE, we observe Lgr5 reporter (eGFP) activity in the embryonic day 8.5 mouse endoderm, and show the ability to lineage trace these cells into the adult intestine. However, gene expression data also suggest that there are human-mouse species-specific differences at later time points of embryonic development.

CONCLUSIONS

Our results show that LGR5 is induced during DE differentiation, LGR receptors are functionally required for DE induction, and that they function to potentiate WNT signaling during this process.

Determinant molecular markers for peri-gastrulating bovine embryo development

Peri-gastrulation defines the time frame between blastocyst formation and implantation that also corresponds in cattle to elongation, pregnancy recognition and uterine secretion. Optimally, this developmental window prepares the conceptus for implantation, placenta formation and fetal development. However, this is a highly sensitive period, as evidenced by the incidence of embryo loss or early post-implantation mortality after AI, embryo transfer or somatic cell nuclear transfer. Elongation markers have often been used within this time frame to assess developmental defects or delays, originating either from the embryo, the uterus or the dam. Comparatively, gastrulation markers have not received great attention, although elongation and gastrulation are linked by reciprocal interactions at the molecular and cellular levels. To make this clearer, this peri-gastrulating period is described herein with a focus on its main developmental landmarks, and the resilience of the landmarks in the face of biotechnologies is questioned.