Abstract

The corpus luteum (CL) is a transient gland formed in the ovary after ovulation and is the major source of progesterone. In the Iberian and Eurasian lynx, CL physiologically persist after parturition and retain their capacity to produce progesterone, thus suppressing the ovarian activity. This unique reproductive characteristic has a big impact on the success of assisted reproduction techniques in the endangered Iberian lynx. The mechanisms behind CL persistence are not yet understood and require extensive studies on potential luteotropic and luteolytic factors in felids. Because the apoptosis system has been shown to be involved in structural regression of CL in many species, we aimed to investigate the capacity of perCL to undergo apoptosis. In addition, we performed initial studies on the apoptosis system in the luteal phase of the domestic cat. No previous research on this system has been made in this species. Our factors of interest included agents of the intrinsic apoptosis pathway, i.e., pro-survival B-cell CLL/lymphoma 2 (BCL2) and pro-apoptotic BCL2-associated X protein (BAX), the executioner caspase-3 (CASP3), as well as of the extrinsic pathway, i.e., pro-apoptotic receptor FAS, and tumor necrosis factor (TNF) and its receptors (pro-apoptotic TNFRSF1A and pro-survival TNFRSF1B). We analyzed the relative mRNA levels of these factors, as well as protein localization of CASP3 and TNF during stages of pregnancy and the non-pregnant luteal phase in CL of domestic cats. The same factors were investigated in freshly ovulated CL (frCL) and perCL of Iberian and Eurasian lynx, which were histologically analyzed. All factors were present in the CL tissue of both domestic cat and lynx throughout all analyzed stages. The presence of pro-apoptotic factors BAX, CASP3, FAS and TNFRSF1A in perCL of the Eurasian and Iberian lynx might indicate the potential sensitivity of perCL to apoptotic signals. The expression of pro-survival factors BCL2 and TNFRSF1B was significantly higher in perCL compared to frCL of studied Iberian lynx, suggesting the potential involvement of these factors in the structural integrity of perCL. In both Iberian lynx and pregnant and non-pregnant domestic cats, the expression of TNFRSF1A was significantly higher in forming CL compared to other stages, suggesting the conserved involvement of this factor in the tissue reorganization during formation of the feline CL. The mRNA levels of CASP3 and TNFRSF1B were highest during regression stages of domestic cat CL. The current study provides initial results on the possible involvement of the apoptosis system in the structure and function of the feline CL and in its physiological persistence.

Highlights

  • The Lynx genus includes four species that inhabit different parts of the world: the Eurasian lynx (Lynx lynx) in the broad range of Europe and Asia, the Canada lynx (Lynx canadensis) and the bobcat (Lynx rufus) in North America, and the Iberian lynx (Lynx pardinus) in the Iberian Peninsula

  • Gene expression of tumor necrosis factor (TNF) receptors changed significantly during pregnancy: TNFRSF1A (Fig 1E) relative mRNA levels were higher during the pre-implantation period compared to post-implantation (P = 0.0019) and corpus luteum (CL) regression (P = 0.013); TNFRSF1B (Fig 1F) relative mRNA levels were higher during CL regression compared to post-implantation (P = 0.055)

  • Throughout the non-pregnant luteal phase, relative mRNA levels of B-cell CLL/lymphoma 2 (BCL2), CASP3, TNFRSF1A and TNFRSF1B changed significantly, while no significant changes were observed for BCL2-associated X protein (BAX), Fas cell surface death receptor (FAS) and TNF (Fig 1)

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Summary

Introduction

The Lynx genus includes four species that inhabit different parts of the world: the Eurasian lynx (Lynx lynx) in the broad range of Europe and Asia, the Canada lynx (Lynx canadensis) and the bobcat (Lynx rufus) in North America, and the Iberian lynx (Lynx pardinus) in the Iberian Peninsula. All three monoestrous lynx species exhibit a unique reproductive characteristic associated with the corpus luteum (CL), a transient gland that forms in the ovary after ovulation and supports pregnancy via its production of progesterone [6]. It has been widely shown among different species that, in the event of a non-pregnant cycle or at the end of pregnancy, the CL regresses from the ovarian tissue and a new cycle is initiated [7, 8]. CL persist morphologically and functionally after parturition and weaning in all three monoestrous lynx species: Iberian, Eurasian and Canada lynx

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