Homeodomain protein HLX is expressed primarily in cytotrophoblast cell types in the early pregnancy human placenta
Gayathri Rajaraman A , Padma Murthi A C , Leonie Quinn B , Shaun P. Brennecke A and Bill Kalionis AA Pregnancy Research Centre, Department of Perinatal Medicine, Royal Women’s Hospital and Department of Obstetrics and Gynaecology, RWH Campus, Carlton, Vic. 3053, Australia.
B Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Vic. 3052, Australia.
C Corresponding author. Email: padma@unimelb.edu.au
Reproduction, Fertility and Development 20(3) 357-367 https://doi.org/10.1071/RD07159
Submitted: 14 September 2007 Accepted: 16 December 2007 Published: 5 February 2008
Abstract
Homeobox genes are a large family of transcription factors. Of these, the HLX homeobox gene (previously known as HLX1 and HB24) is important for normal placentation. We have previously shown that HLX mRNA expression is significantly reduced in fetal growth-restricted human placentae compared with control placentae. In this study, a rabbit polyclonal antibody to the homeodomain protein HLX was raised and characterised. Western analysis revealed a protein of 50 kDa. HLX protein was detected in cellular nuclei in the cytotrophoblast-derived cell lines HTR8/SVneo, SGHPL-4, JEG-3, JAR and BeWo. Dual labelling with cytokeratin 7 was used to determine the spatial distribution of HLX in the early placenta and fetal membranes, showing both a perinuclear and punctate nuclear distribution for HLX. In the early pregnancy placenta HLX was localised to villous cytotrophoblast, and extravillous cytotrophoblast nuclei in the proximal regions of the cytotrophoblast cell columns, but was not detected at significant levels in the syncytiotrophoblast. In first trimester placental bed biopsies, HLX expression was not localised to the nucleus but instead was found in the cytoplasm. We conclude that HLX is primarily expressed in cytotrophoblast cell types in the human placenta and propose that HLX is involved in cytotrophoblast proliferation and downregulation of cell differentiation.
Acknowledgements
The authors wish to gratefully acknowledge the patients and the clinical and nursing staff of the hospitals participating in this study for the supply of samples. We thank Dr Miriam Hanssens for supplying placental bed biopsy samples for this study. The Early Career Researcher Scheme, University of Melbourne, supported P. Murthi. A grant from Equity Trustees on behalf of the Lynne Quayle Charitable Trust supported the work. The University of Melbourne, Felix Myer postgraduate scholarship award, supported G. Rajaraman.
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