The transcription factor Zic4 promotes tentacle formation and prevents epithelial transdifferentiation in Hydra

Abstract

The molecular mechanisms that maintain cellular identities and prevent dedifferentiation or transdifferentiation remain mysterious. However, both processes are transiently used during animal regeneration. Therefore, organisms that regenerate their organs, appendages, or even their whole body offer a fruitful paradigm to investigate the regulation of cell fate stability. Here, we used Hydra as a model system and show that Zic4, whose expression is controlled by Wnt3/β-catenin signaling and the Sp5 transcription factor, plays a key role in tentacle formation and tentacle maintenance. Reducing Zic4 expression suffices to induce transdifferentiation of tentacle epithelial cells into foot epithelial cells. This switch requires the reentry of tentacle battery cells into the cell cycle without cell division and is accompanied by degeneration of nematocytes embedded in these cells. These results indicate that maintenance of cell fate by a Wnt-controlled mechanism is a key process both during homeostasis and during regeneration.

TheWnt/β-catenin/TCF/Sp5/Zic4gene network that regulates head organizer activity inHydrais differentially regulated in epidermis and gastrodermis

“…We recently showed that the Hydra transcription factor Zic4 ( Hy Zic4), which is involved in the differentiation of tentacles and the maintenance of their identity, is a downstream target gene of HySp5 [34]. We considered the possibility that Zic4 also regulates Sp5 expression in a feedback loop.…”

“…epithelial epidermal, epithelial gastrodermal and interstitial, which constantly self-renew in the body column to maintain Hydra homeostasis. In intact animals, Wnt3 , Sp5 and Zic4 are predominantly expressed in epithelial cells of both gastrodermis and the epidermis [25,33,34], a finding confirmed by single-cell sequencing [35] ( Figure S1 ). However, while Wnt3 , Sp5 and Zic4 are expressed at highest levels apically, their respective profiles in the apical region are very different: Wnt3 is detected at a maximum level at the tip of the head, around the mouth opening, where the organizing activity is located [25,27].…”

“…As anticipated, after mid-gastric bisection, Sp5 and Wnt3 are up-regulated in the apical-regenerating tips, within two to three hours for Wnt3 , after eight hours for Sp5 , and both of them remain expressed at high levels throughout the entire head regenerative process but not the foot one [33]. Also, the transcription factor Zic4, whose gene expression is positively-regulated by Sp5, is responsible for the maintenance of tentacle differentiation and for their formation during apical development [34].…”

Differentiation trajectories of theHydranervous system reveal transcriptional regulators of neuronal fate

“…In addition to exhibiting continual, widespread neuronal regeneration, Hydra are amenable to genetic manipulations, such as gene knock-down through the expression of RNA hairpins (Juliano, Reich, et al, 2014;Lohmann et al, 1999) or the electroporation of siRNAs (Lohmann et al, 1999;Vogg et al, 2022). Additionally, it is straightforward to create stable transgenic Hydra lines using cell-type-specific promoters (Dupre & Yuste, 2017;Klimovich et al, 2019;Siebert et al, 2019;Wittlieb et al, 2006).…”

“… ABSTRACT The small freshwater cnidarian polyp Hydra vulgaris uses adult stem cells (interstitial stem cells) to continually replace neurons throughout its life. This feature, combined with the ability to image the entire nervous system (Badhiwala et al, 2021; Dupre & Yuste, 2017) and availability of gene knockdown techniques (Juliano, Reich, et al, 2014; Lohmann et al, 1999; Vogg et al, 2022), makes Hydra a tractable model for studying nervous system development and regeneration at the whole-organism level. In this study, we use single-cell RNA sequencing and trajectory inference to provide a comprehensive molecular description of the adult nervous system.…”