State Key Laboratory of Agrobiotechnology and School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, Peoples Republic of China.|State Key Laboratory of Agrobiotechnology and School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, Peoples Republic of China.|Department of Cell Biology and Genetics, School of Basic Medical Sciences, Shenzhen University Health Science Center, Nanhai Ave 3688, Shenzhen, 518060, Peoples Republic of China.|Centre of Reproduction, Development and Aging, Faculty of Health Sciences, University of Macau, Taipa, Macau, Peoples Republic of China.|State Key Laboratory of Agrobiotechnology and School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, Peoples Republic of China. djguo@cuhk.edu.hk.