Identification of Prdm genes in human corneal endothelium

Prdm (Positive regulatory domain) family of transcriptional regulators and chromatin modifiers are important for driving differentiation of a variety of cellular types. Many Prdm proteins are expressed in specific precursor cell populations and are necessary for their progression to a fully differentiated phenotype. In the present work, we sought to identify members of the Prdm gene family which are specifically expressed in human (h) CECs with a view to begin addressing their potential roles in CEC biology, focussing especially on Prdm 4 and 5 genes. By performing semi-quantitative reverse transcription coupled to PCR amplification we found that in addition to Prdm4 and Prdm5, Prdm2 and Prdm10 genes are expressed in hCECs. We further found that cultured primary hCECs or immortalised HCEC-12 cells express all of the Prdm genes found in CECs, but also express additional Prdm transcripts. This difference is most pronounced between Prdm gene expression patterns of CECs isolated from healthy human corneas and immortalised HCEC-12 cells. We further investigated Prdm 4 and Prdm 5 protein expression in cultured primary hCECs and HCEC-12 cells as well as in a human cadaveric whole cornea. Both Prdm 4 and Prdm 5 are expressed in human corneal endothelium, primary hCECs and in HCECs-12 cells, characterised by expression of the Na+/K+-ATPase. We observed that both proteins exhibit cytosolic (intracellular, but non-nuclear and distinct from extracellular fluid) as well as nuclear localisation within the endothelial layer, with Prdm 5 being more concentrated in the nuclei of the endothelial cells than Prdm 4. Thus, our work identifies novel Prdm genes specifically expressed in corneal endothelial cells which may be important in the control of CEC differentiation and proliferation.