Senior Researcher Leibniz Institute for Zoo and Wildlife Research Berlin, Germany
Abstract Authors: Beate C. Braun1, Michał M. Hryciuk1 & Dorina Meneghini2
1Department of Reproduction Biology, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
2Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
Abstract Text: Corpora lutea (CLs) are usually transient endocrine glands that pass through different life cycles. In the domestic cat, formation, development/maintenance, early and late involution have been described; at the end of the cycle, they transform into corpora albicantia, which disappear completely. To characterize the CL life cycle, its regulation and functionality in more detail, we performed a transcriptome analysis using RNA sequencing (RNA-Seq). In the present sub-study, we have analyzed the data set with regard to the expression of tight junction (TJ) proteins, as these are important for paracellular structure and transport. We hypothesized that they change during the life cycle of CL, especially between the active development/maintenance stage and the subsequent regression phase.
The group of TJ proteins consist of transmembrane proteins like occludin (OCLN) and claudins (CLDN), and cytoplasmic scaffolding proteins like cingulin (CGN) and the tight junction proteins 1, 2 and 3 (TJP1/ZO-1, TPJ2/ZO-2, TPJ3/ZO-3). They regulate the paracellular pathway for the movement of ions and solutes in-between cells. Claudins are responsible for the paracellular barrier function of TJs, and in some cases confer paracellular channel functions to the paracellular barriers of TJs. But components of tight junctions are also expressed in cell types not forming tight junctions.
For RNA-Seq-analysis, we have used CLs from domestic cat of development/maintenance (dm, n = 8) and regression stages (re, n = 12). As one of the highest upregulated genes in dm compared to re (log2FoldChange = -9.24), the gene coding for claudin 4 (CLDN4) was identified. Looking at the expression of other claudins in the data set, we detected transcripts for 15 different CLDNs. Nine of them were very low expressed in both stages; of the other six, five genes were differently expressed between the stages. In addition to CLDN4, also CLDN1 and CLDN18 (log2FoldChanges: -3.49, -4.01) were upregulated in dm, whereas CLDN5 and CLDN11 (log2FoldChanges: 0.85, 3.39) were upregulated in re. Of the other TJs, OCLN, CGN, TPJ1 and TPJ3 were higher expressed in regression stage (log2FoldChanges: 1.37, 1.10, 0.72, 1.63), TPJ2 was not differentially expressed. The protein expression of CLDN1 was analyzed by immunohistochemistry, but the staining did not reflect the gene expression. Thus, clear staining was only visible in a few, but not in all dm samples examined, as well as in some of the regression samples. We have observed staining of large and small luteal cells. Further studies would be required to characterize the protein staining of the other TJs.
Interestingly, with regard to the expression of claudins in corpora lutea, only the expression of CLDN1 and CLDN5 was described before. It has been discussed that they play a role as junctional proteins and act as regulators of vascular permeability. The cytoplasm staining of steroidogenic cells for CLDN1 in our study hints at further functions.
Based on our gene expression data we hypothesize that the composition of the tight junctions changes during the transition from the dm to the re stage, which may influence the type of exchange of substances and/or the para- and intracellular structures at the different stages.
