# African pygmy mouse iPSCs as a model for in vitro embryogenesis, interspecies chimerism, and blastocyst complementation

## TL;DR

Researchers created stem cells from African pygmy mice that can form chimeras with house mice, offering new insights into development and regenerative medicine.

## Contribution

The study introduces chimera-competent iPSCs from African pygmy mice, enabling interspecies chimerism and blastocyst complementation.

## Key findings

- APM-iPSCs differentiate into multiple cell types and form gastruloids in vitro.
- Interspecies chimeras showed APM contributions to various tissues, including germ cells.
- Blastocyst complementation produced APM muscle stem cells in mice.

## Abstract

Somatic cell reprogramming into induced pluripotent stem cells (iPSCs) has been achieved in various mammals; however, assessing iPSC contribution to full-term chimeras beyond laboratory rodents remains challenging. Here, we demonstrate induction of pluripotency in male and female fibroblasts from the African pygmy mouse (APM), one of the smallest mammals. Using transcription factors and small molecules, we derived expandable APM-iPSCs that express pluripotency markers, differentiate into various cell types in vitro, and form gastruloids. Injection of APM-iPSCs into house mouse blastocysts generated full-term interspecies chimeras demonstrating extensive contribution to various tissues, including testicular germ cells. Notably, high APM contribution in organs such as heart and testes correlated with reduced organ size compared with mouse organs. Lastly, injection of APM-iPSCs into mouse blastocysts carrying a Pax7 ablation system enabled substantial production of APM muscle stem cells in chimeras. Collectively, this study establishes APM-iPSCs as a developmental model for pluripotency, differentiation, and interspecies chimerism.

•Enhanced conditions for generating African pygmy mouse (APM) iPSCs•APM-iPSCs differentiate into multiple cell types in vitro and form gastruloids•Characterization of full-term interspecies chimerism between APM and the house mouse•Blastocyst complementation enhances the production of APM muscle stem cells in mice

Enhanced conditions for generating African pygmy mouse (APM) iPSCs

APM-iPSCs differentiate into multiple cell types in vitro and form gastruloids

Characterization of full-term interspecies chimerism between APM and the house mouse

Blastocyst complementation enhances the production of APM muscle stem cells in mice

Understanding the mechanisms governing pluripotency and interspecies chimerism is central to developmental biology and regenerative medicine. However, generating full-term chimeras, especially across species boundaries, remains challenging. The African pygmy mouse (Mus minutoides, APM), one of the smallest rodents, presents a unique model to study these and related developmental questions due to its exceptionally small body size, unique karyotypic evolution, and an unusual sex-determination system. By deriving chimera-competent APM-iPSCs, we uncovered principles related to reprogramming in non-laboratory rodents, interspecies chimerism with the house mouse, and blastocyst complementation, thereby expanding the repertoire of mammalian iPSC models available for stem cell research.

Gjonlleshaj et al. report chimera-competent induced pluripotent stem cells from the African pygmy mouse, a rodent with distinctive genetics and exceptionally small size. These iPSCs reveal principles of differentiation in non-laboratory rodents and enable interspecies chimerism and blastocyst complementation with the house mouse, thereby expanding models for developmental and regenerative research.