engleski

Expression of the intermediate filaments cytokeratin 8 and vimentin in the early human gonad development

The development of human gonads starts in the 3rd week of development and is a result of epithelial-mesenchymal (EMT) and mesenchymal- epithelial (MET) transitions, which differentiates gonads into ovaries or testes (1). The morphological and functional tissue maturation is accompanied by appearance and disappearance of certain intermediate filaments, especially cytokeratin 8 (CK8), the marker of the epithelial differentiation, and vimentine the marker of mesenchymal differentiation (2). However, the epithelial or mesenchymal origin of follicular epithelial cells in gonads is still not fully understood. Proper EMT and MET in gonad differentiation is of special interest because of their involvement in metastatic cancer spreading (3). The distribution of the CK8 and vimentin markers was investigated in the cells of developing human gonads. Paraffin sections of 12 human conceptuses between 5th and 9th developmental weeks were analysed by immunohistochemical and immunofluorescence methods. Quantification of reacting cells was performed by counting the ratio of positive cells stained to specific antibodies in different gonad parts. Data were expressed as mean±SD, while the difference between different gonad parts were analysed by the t- test or Kruskal-Wallis test. In the 5th-6th developmental week, CK8 was positive in both the gonad surface epithelium (56%) and gonad stroma 42% (t-test, p<0.001). During 7th-8th developmental week, the number of CK8 positive cells decreased to 42% in the gonad surface epithelium and increased in the gonad stroma 50%, while in the gonad medulla there were 23% of CK8 positive cells (Kruskal- Wallis, p<0.001 and p<0.0001 respectively). In the early fetal period the number of CK8 positive cells increased to 92% in gonad surface epithelium, 60% in the gonad stroma, while in the medulla increased to 42% (Kruskal- Wallis, p<0.0001 and p<0.001 respectively). Primordial germ cells (PGCs) remained CK8 negative during all investigated period. In the 5th-6th developmental week, vimentin positive cells dominated in the gonad stroma (73%) in comparison to the gonad surface epithelium (18%) (t-test, p<0.001). The expression of vimentin in the gonad surface epithelium significantly increased during the investigated period (18% - 97%). The number of vimentin positive cells in the gonad stroma increased to 88% in the 9th developmental week, while the medulla had the highest vimentin expression in the 7th-8th developmental week (93%). There were statistically significant differences in the number of vimentin positive cells between the gonad surface epithelium and stroma and between the gonad stroma and the medulla in the 7th-8th week (Kruskal-Wallis, p<0.001). During investigated period vimentin and CK8 co- localized in the somatic cells, while some PGCs showed a vimentin expression only. Our results indicate that follicular cells originate from both sources (the epithelium and mesenchyme of coelomic mesonephros), which is in agreement with the presence of two different types of early follicular cell light (mesenchymal origin) and dark (the origin of coelomic epithelium). Additionally our results indicate possible EMT and MET of somatic cells within gonad, while role of vimentin diminish in further PGCs differentiation and contribute to PGCs apoptosis. Both intermediate filaments seem to operate during early human gonad development, while their intensity varies depending on the cell type and developmental period analysed.

human gonad development; intermediate filaments; cytokeratin 8; vimentin

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