Foxd4l1.1 negatively regulates transcription of neural repressor ventx1.1 during neuroectoderm formation in Xenopus embryos

Shiv Kumar,Zobia Umair,Jaebong Kim,Vijay Kumar,Santosh Kumar,Unjoo Lee

doi:10.1038/s41598-020-73662-4

Abstract

Neuroectoderm formation is the first step in development of a proper nervous system for vertebrates. The developmental decision to form a non-neural ectoderm versus a neural one involves the regulation of BMP signaling, first reported many decades ago. However, the precise regulatory mechanism by which this is accomplished has not been fully elucidated, particularly for transcriptional regulation of certain key transcription factors. BMP4 inhibition is a required step in eliciting neuroectoderm from ectoderm and Foxd4l1.1 is one of the earliest neural genes highly expressed in the neuroectoderm and conserved across vertebrates, including humans. In this work, we focused on how Foxd4l1.1 downregulates the neural repressive pathway. Foxd4l1.1 inhibited BMP4/Smad1 signaling and triggered neuroectoderm formation in animal cap explants of Xenopus embryos. Foxd4l1.1 directly bound within the promoter of endogenous neural repressor ventx1.1 and inhibited ventx1.1 transcription. Foxd4l1.1 also physically interacted with Xbra in the nucleus and inhibited Xbra-induced ventx1.1 transcription. In addition, Foxd4l1.1 also reduced nuclear localization of Smad1 to inhibit Smad1-mediated ventx1.1 transcription. Foxd4l1.1 reduced the direct binding of Xbra and Smad1 on ventx1.1 promoter regions to block Xbra/Smad1-induced synergistic activation of ventx1.1 transcription. Collectively, Foxd4l1.1 negatively regulates transcription of a neural repressor ventx1.1 by multiple mechanisms in its exclusively occupied territory of neuroectoderm, and thus leading to primary neurogenesis. In conjunction with the results of our previous findings that ventx1.1 directly represses foxd4l1.1, the reciprocal repression of ventx1.1 and foxd4l1.1 is significant in at least in part specifying the mechanism for the non-neural versus neural ectoderm fate determination in Xenopus embryos.

Highlights

Central to vertebrate embryogenesis, during the gastrula stage of embryogenesis, neuroectoderm develops from the naive ectoderm, giving rise to the neural plate, neural tube, and the neural crest
Ventx1.1 suppressed foxd4l1.1 and EnRfoxd4l1.1-induced expression of neural genes, including ncam, ngnr, otx[20], krox[20] and hoxB9 in animal cap explants (Fig. 1b, lane[1] vs. lane[2] and lane[3] vs. lane[4]). These results collectively suggested that foxd4l1.1 inhibits BMP4 signaling and expression of its downstream target genes, leading to neuroectoderm formation
We focused on elaborating the repressive activity of the neural specific transcription factor (TF), foxd4l1.1

Summary

Introduction

Central to vertebrate embryogenesis, during the gastrula stage of embryogenesis, neuroectoderm develops from the naive ectoderm, giving rise to the neural plate, neural tube, and the neural crest. It is known that the vertebrate neuroectoderm develops in response to the dorsal mesoderm (the Spemann organizer)[1,2,3,4] with BMP signaling becoming inhibited[5,6,7] In this regard, inhibition of BMP4 signaling by various BMP4-antagonists such as the dominant-negative BMP receptor (DNBR), noggin and chordin cause dorso-anteriorization and neuroectoderm formation of embryos[5,6,7,8]. Both BMP/ Smad[1] and FGF/Xbra synergistically upregulate transcription of neural repressor ventx1.1 and inhibit neuroectoderm formation in Xenopus embryos[15,18]. This study suggests that neuroectoderm specific repressor Foxd4l1.1 inhibits expression of the neural repressive transcription factor ventx1.1 to commit and maintain the neuroectoderm fate, obviating mesoderm commitment during germ-layer specification of Xenopus embryos

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Results

Conclusion