Int. J. Dev. Biol. 52: 43 - 53 (2008)

https://doi.org/10.1387/ijdb.072274yl

Vol 52, Issue 1

Spa-1 regulates the maintenance and differentiation of human embryonic stem cells

Original Article | Published: 1 November 2007

Young-Jin Lee^1,2, Hee-Young Nah¹, Seok-Ho Hong¹, Ji-Won Lee¹, Ilkyung Jeon¹, Jhang Ho Pak³, Joo-Ryung Huh⁴, Sung-Hoon Kim¹, Hee-Dong Chae¹, Byung-Moon Kang¹, Chul Geun Kim² and Chung-Hoon Kim^1,*

¹Dept. of Obstetrics & Gynecology, College of Medicine, University of Ulsan, Asan Medical Center, ²Dept. of Life Science, College of Natural Sciences and Stem Cell Research Center, Hanyang University, ³Dept. of Obstetrics & Gynecology, College of Medicine, Asan Institute for Life Science, Asan Medical Center and ⁴Dept. of Pathology, College of Medicine, University of Ulsan, Asan Medical Center, Seoul, Republic of Korea

Abstract

Human embryonic stem cells (hESCs) are pluripotent, whereby they can proliferate endlessly and differentiate into many different cell types. At the molecular level, little is known of the mechanisms underlying their capability for self-renewal and differentiation. In the present study, we established two new hESC lines (AMC-hES1 and AMC-hES2) and demonstrated the existence of a regulator that may be a key molecule in hESC dynamics. Spa-1 is a principal Ras-proximate 1 (Rap1) GTPase-activating protein in hematopoietic progenitor cells that regulates Rap1-related signal transduction and is expressed restrictively in human adult tissues (bone marrow, thymus, and spleen). To investigate its functions in hESCs, we examined spa-1 expression profiles during hESC differentiation and used RNA interference (RNAi) to downregulate spa-1 in these cells. Our results show that Spa-1 is expressed in undifferentiated hESCs and is downregulated during hESC differentiation. In addition, the process of passing from the mode of self-renewal to that of differentiation in hESCs was regulated by spa-1 via Rap1/Raf/mitogen-activated protein kinase kinase/extracellular signal-related kinase signaling. An RNAi expression vector against spa-1 (pSUPER.retro.puro) was transfected into hESCs, which were seen to differentiate into three germ layers in spite of being in the undifferentiated condition. Based on our findings, therefore, it appears that spa-1 may be involved in hESC dynamics, and our results provide fundamental information regarding the self-renewal and differentiation of hESCs.

Keywords

signal transduction, fate decision, gene regulation, differentiation