AUTHOR=Vanni Virginia , Salonna Marika , Gasparini Fabio , Martini Margherita , Anselmi Chiara , Gissi Carmela , Manni Lucia 

TITLE=Yamanaka Factors in the Budding Tunicate Botryllus schlosseri Show a Shared Spatio-Temporal Expression Pattern in Chordates

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2022.782722

DOI=10.3389/fcell.2022.782722

ISSN=2296-634X

ABSTRACT=<p>In vertebrates, the four transcription factors <italic>Sox2</italic>, <italic>c-Myc</italic>, <italic>Pou5f1</italic> and <italic>Klf4</italic> are involved in the differentiation of several tissues during vertebrate embryogenesis; moreover, they are normally co-expressed in embryonic stem cells and play roles in pluripotency, self-renewal, and maintenance of the undifferentiated state in adult cells. The <italic>in vitro</italic> forced co-expression of these factors, named Yamanaka factors (YFs), induces pluripotency in human or mouse fibroblasts. <italic>Botryllus schlosseri</italic> is a colonial tunicate undergoing continuous stem cell-mediated asexual development, providing a valuable model system for the study of pluripotency in the closest living relatives of vertebrates. In this study, we identified <italic>B. schlosseri</italic> orthologs of human <italic>Sox2</italic> and <italic>c-Myc</italic> genes<italic>,</italic> as well as the closest homologs of the vertebrate-specific <italic>Pou5f1</italic> gene, through an in-depth evolutionary analysis of the YF gene families in tunicates and other deuterostomes. Then, we studied the expression of these genes during the asexual cycle of <italic>B. schlosseri</italic> using <italic>in situ</italic> hybridization in order to investigate their possible involvement in tissue differentiation and in pluripotency maintenance. Our results show a shared spatio-temporal expression pattern consistent with the reported functions of these genes in invertebrate and vertebrate embryogenesis. Moreover, <italic>Myc</italic>, <italic>SoxB1</italic> and <italic>Pou3</italic> were expressed in candidate stem cells residing in their niches, while <italic>Pou2</italic> was found expressed exclusively in the immature previtellogenic oocytes, both in gonads and circulating in the colonial vascular system. Our data suggest that <italic>Myc</italic>, <italic>SoxB1</italic> and <italic>Pou3</italic> may be individually involved in the differentiation of the same territories seen in other chordates, and that, together, they may play a role in stemness even in this colonial ascidian.</p>