Foxd4l1.1 Negatively Regulates Chordin Transcription in Neuroectoderm of Xenopus Gastrula.

Soochul Park,Ravi Shankar Goutam,Vijay Kumar,Jaebong Kim,Zobia Umair,Unjoo Lee

doi:10.3390/cells10102779

Soochul Park, Ravi Shankar Goutam + Show 4 more

Open Access

https://doi.org/10.3390/cells10102779

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Journal: Cells	Publication Date: Oct 17, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: Sookmyung Women's University, Hallym University

Abstract

Inhibition of the bone morphogenetic proteins (BMPs) is the primary step toward neuroectoderm formation in vertebrates. In this process, the Spemann organizer of the dorsal mesoderm plays a decisive role by secreting several extracellular BMP inhibitors such as Chordin (Chrd). Chrd physically interacts with BMP proteins and inhibits BMP signaling, which triggers the expression of neural-specific transcription factors (TFs), including Foxd4l1.1. Thus, Chrd induces in a BMP-inhibited manner and promotes neuroectoderm formation. However, the regulatory feedback mechanism of Foxd4l1.1 on mesodermal genes expression during germ-layer specification has not been fully elucidated. In this study, we investigated the regulatory mechanism of Foxd4l1.1 on chrd (a mesodermal gene). We demonstrate that Foxd4l1.1 inhibits chrd expression during neuroectoderm formation in two ways: First, Foxd4l1.1 directly binds to FRE (Foxd4l1.1 response elements) within the chrd promoter region to inhibit transcription. Second, Foxd4l1.1 physically interacts with Smad2 and Smad3, and this interaction blocks Smad2 and Smad3 binding to activin response elements (AREs) within the chrd promoter. Site-directed mutagenesis of FRE within the chrd(-2250) promoter completely abolished repressor activity of the Foxd4l1.1. RT-PCR and reporter gene assay results indicate that Foxd4l1.1 strongly inhibits mesoderm- and ectoderm-specific marker genes to maintain neural fate. Altogether, these results suggest that Foxd4l1.1 negatively regulates chrd transcription by dual mechanism. Thus, our study demonstrates the existence of precise reciprocal regulation of chrd transcription during neuroectoderm and mesoderm germ-layer specification in Xenopus embryos.

Highlights

Gastrulation is the central event of vertebrate embryonic development, allowing the formation of three germ layers
We examined the ectopic expression of Foxd4l1.1-inhibiting epidermal target genes bmp4 and ventx1.1 (Figure 1A, lane 1 vs. 2), as previously reported [13]
Several studies have demonstrated that Smad2 induces mesoderm genes chrd, gsc, and nog, as well as neural foxd4l1.1, zic3, ncam expression in Xenopus embryos [13,19,23]

Summary

Introduction

Gastrulation is the central event of vertebrate embryonic development, allowing the formation of three germ layers. In this process, the Spemann organizer of the dorsal mesoderm plays a crucial role by influencing the neighboring ectodermal (epidermal) cells to achieve neural fate [1,2]. The organizer releases potent BMP inhibitors (such as Chrd and Noggin (Nog)) to block BMP signaling in the surrounding embryonic region. The reciprocal repression between the ectoderm (BMP signaling) and the dorsal mesoderm (BMP antagonism) is integrated for controlling neuroectoderm formation and overall embryonic patterning. Several reports have demonstrated that BMP antagonists secrete from the dorsal mesoderm, physically interact with BMP proteins, and block cognate signaling in the adjacent region [5,6]. BMP downstream repressor Ventx1.1 maintains and reinforces the gradient by suppressing the targeted neural and dorsal genes in the ventral region of Xenopus embryos [7,8,9,10]

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