Current knowledge of stem cell biology, as well as various cell culture technologies that have been established in recent years, supports the field of developmental biology and regenerative medicine (Ikeya et al., 2021a, b). Stem cells include embryonic stem cells (Martin, 1981;Thomson et al., 1998) with pluripotent differentiation ability retained by fertilized eggs, and induced Pluripotent Stem (iPS) cells (Takahashi et al., 2007;Takahashi and Yamanaka, 2006), which have been developed by cell culture and molecular biological technologies. In addition, mesenchymal stem cells (MSCs) derived from bone marrow are known as multipotent adult stem cells (Gao et al., 2021), capable of differentiating into various mesenchymal cells and have contributed to regenerative medicine as have biological microdevices. Tissue-specific stem/progenitor cells that can be isolated from various adult tissues can contribute to the specific tissue types for physiological tissue maintenance and repair after damage (Prentice, 2019). The use of these stem/progenitor cells has been further enhanced by genetic engineering and embryological strategies (Wang et al., 2021). For example, the use of signal transduction mimicking the developmental stages of tissues to induce specific cell differentiation, the construction of target tissues by organoid culture, a three-dimensional culture method, and the use of exosomes, which play an important role in cell-cell communication, have recently attracted attention. Stem cell biology and regenerative medicine can be systematized by combining these fundamental technologies related to developmental biology and stem cells.This Editors' pick research topic aims to highlight a few of the most noteworthy manuscripts published in the Stem Cell section of Frontier in Cell and Development al Biology over 2020 and 2021. The 12 selected manuscripts, highlighted in this topic, were not part of a research topic but have caught our attention and that of the readers by their scope, novelty and quality.Four primary research manuscripts were chosen to be part of this Editors' pick. In the first one, Tagliaferri et al. uncovered the molecular mechanism by which retinoic acid induces the transition of embryonic stem cell to a 2-cell like state, implicating DUX and DUXbl1 in this process (Tagliaferri et al.). The second manuscript, by Gao et al. describes the use of patient specific retinal organoids to recapitulate feature of retinitis pigmentosa, establishing the first in vitro model system to study the mechanism implicated in the development of this disease (Gao et al.). In the third highlighted manuscript, Chen et al. investigated the role of the Mediator subunit Med23 in adult mouse hippocampal neurogenesis through loss-of-function approach, demonstrating a critical role for Med23 in the regulation of adult brain neurogenesis and function (Chen et al.). In the last primary research manuscript selected for this topic, Chen et al. explored the role of the thyroid hormone T3 on BMP9-induced osteogenesis, demonstrated t...
