# Non-Canonical Maternal WNT4 Activates Canonical Zygotic WNT8C for Early Embryonic Development in Chicken

## TL;DR

This study shows how maternal WNT4 activates embryonic WNT8C in chickens, helping to establish body patterns during early development.

## Contribution

The study reveals a novel maternal-to-zygotic WNT signaling relay in chickens involving WNT4 and WNT8C.

## Key findings

- Maternal WNT4 activates zygotic WNT8C via the JNK pathway in chicken embryos.
- WNT8C then activates the canonical WNT/β-catenin pathway necessary for normal development.
- Blocking maternal WNT signaling disrupts proper WNT8C activation and embryonic polarity.

## Abstract

Early embryonic development requires precise coordination between maternal factors stored in the egg and genes that activate in the developing embryo. WNT signaling proteins play a particularly important role during the maternal-to-zygotic transition; however, the process in birds has remained unclear. This study examined WNT signaling in chicken embryos, revealing that two distinct maternal WNT proteins, WNT4 and WNT6, are predominantly expressed during the early stages of chicken development. By blocking maternal WNT signaling in eggs before laying, the researchers found that a key embryonic WNT protein, WNT8C, failed to activate properly. Further experiments revealed that maternal WNT4 triggers WNT8C expression via the JNK signaling pathway. WNT8C then activates the WNT/β-catenin pathway, which is necessary for normal development. These findings reveal how maternal signals are converted into embryonic gene activity in birds and suggest that this maternal WNT4-to-zygotic WNT8C relay helps establish the embryonic body pattern in chicken.

The proper regulation of signaling pathways, including WNT signaling, during early embryonic development is critical for whole-organism development. In particular, maternally enriched WNTs play critical roles in cell cleavage and axis formation through non-canonical and canonical pathways during early embryogenesis. However, early developmental processes related to maternal WNTs and their underlying mechanisms have remained unstudied in avian species. In this study, we investigated WNT signaling-mediated early development in the chicken embryo. We found that WNT4 and WNT6, different ligands from other species, exhibited expression patterns consistent with maternal enrichment in chicken. The chemical inhibition of maternal WNT signaling in intrauterine embryos led to aberrant zygotic expression of WNT8C, which is important for primitive streak formation. Combined with in vitro functional studies, we demonstrated that WNT4 increased WNT8C expression through the non-canonical JNK pathway and that WNT8C subsequently promoted the canonical β-catenin pathway. Our results indicate that maternal WNT4 activates zygotic WNT8C and potentially regulates embryonic polarity in chicken.