학술논문
Transcriptional regulation mechanism study of PV.1 during neuro-ectoderm and mesoderm formation in early embryos of xenopus laevis / 아프리카 발톱 개구리의 초기 신경외배엽과 중배엽 발생 과정에서 PV.1의 전사조절 기전에 대한 연구
Document Type
Dissertation/ Thesis
Author
Source
Subject
Language
English
Abstract
Crosstalk of cell signaling plays crucial roles in cell fate determination, cell differentiation and proliferation. Signaling crosstalk regulates the fine tuning control of various biological events. Both BMP-4-Smad-1 and FGF-Xbra signaling induce the expression of PV.1 that inhibits the early neurogenesis. However, BMP-4-Smad-1 and FGF-Xbra signaling crosstalk in the regulation of PV.1 transcription is still largely unknown. Our study showed that Smad-1 and Xbra synergistically cooperated in transcriptional regulation of PV.1 through physical binding of these proteins, and direct binding of Xbra and Smad-1 on the respective consensus binding site within proximal region of PV.1 promoter. In addition, Smad-1 and Xbra enhanced the binding of their respective interacting partner to PV.1 promoter region. Maximum cooperation was achieved in the presence of intact binding sites of both smad1 and Xbra, but either mutation of one DNA binding site did not completely abolish the synergistic activation of PV.1 transcription. Taken together, the results indicated that BMP-4-Smad-1 and FGF-Xbra signal crosstalk was required to activate the PV.1 transcription in a synergistic manner. We suggest that crosstalk of BMP-4 and FGF signaling is necessary for fine tuning regulation of PV.1 to modulate the early neurogenesis in the ectoderm and mesoderm during the early development of Xenopus.
The inhibition of BMP signaling is an initial step, which is critically required for triggering the neurogenesis in ectoderm. FoxD5b is an earliest neural gene that is induced in ectodermal animal cap explants after inhibition of BMP signaling. Our previous study demonstrated that PV.1 is a direct target of BMP signaling and negatively regulates the early neurogenesis through inhibiting the FoxD5b. Studies demonstrated that FoxD5b inhibits the BMP-4 signaling. However, the detailed mechanism of FoxD5b-mediated BMP-4 inhibition is still largely unknown. In this study, we found that FoxD5b directly bound and inhibited the PV.1 promoter activity. We identified the cis-acting FoxD5b response element (FRE, ATAAAAA, -39bp~-33bp), which regulated the BMP-4 signaling via inhibiting both promoter activity of PV.1 and activation of Smad-1. In addition, FoxD5b physically interacted with Xbra and inhibited Xbra and Smad-1-mediated PV.1 promoter activation. Ectopic expression of FoxD5b also strongly abolished Xbra and Smad-1 binding with endogenous PV.1 promoter in directly and indirectly manner. Taken together, this study suggests that reciprocal repression of PV.1 and FoxD5b is a crucial regulatory process to maintain the balance between ectoderm-neuroectoderm transitions during early development of Xenopus leavis.
The inhibition of BMP signaling is an initial step, which is critically required for triggering the neurogenesis in ectoderm. FoxD5b is an earliest neural gene that is induced in ectodermal animal cap explants after inhibition of BMP signaling. Our previous study demonstrated that PV.1 is a direct target of BMP signaling and negatively regulates the early neurogenesis through inhibiting the FoxD5b. Studies demonstrated that FoxD5b inhibits the BMP-4 signaling. However, the detailed mechanism of FoxD5b-mediated BMP-4 inhibition is still largely unknown. In this study, we found that FoxD5b directly bound and inhibited the PV.1 promoter activity. We identified the cis-acting FoxD5b response element (FRE, ATAAAAA, -39bp~-33bp), which regulated the BMP-4 signaling via inhibiting both promoter activity of PV.1 and activation of Smad-1. In addition, FoxD5b physically interacted with Xbra and inhibited Xbra and Smad-1-mediated PV.1 promoter activation. Ectopic expression of FoxD5b also strongly abolished Xbra and Smad-1 binding with endogenous PV.1 promoter in directly and indirectly manner. Taken together, this study suggests that reciprocal repression of PV.1 and FoxD5b is a crucial regulatory process to maintain the balance between ectoderm-neuroectoderm transitions during early development of Xenopus leavis.