Abstract
Here, we studied the impact of exposure to short daylight conditions on the expression of senescence marker (p16), membrane androgen receptor (ZIP9) and extracellular signal-regulated kinase (ERK 1/2), as well as cyclic AMP (cAMP) and testosterone levels in the testes of mature bank voles. Animals were assigned to groups based on an analysis of testis diameter, weight, seminiferous tubule diameter and the interstitial tissue area: group 1, not fully regressed (the highest parameters); group 2 (medium parameters); or group 3, regressed (the lowest parameters). Cells positive for p16 were observed only in the seminiferous tubule epithelium. However, in groups 1 and 2, these were mostly cells sloughed into the tubule lumen. In group 3, senescent cells resided in between cells of the seminiferous epithelium. Staining for ZIP9 was found in Sertoli cells. Western blot analysis showed a trend towards a decreased expression of p16 and ZIP9 in the testes of the voles in groups 2 and 3, compared to group 1. In addition, a trend towards an increased expression of ERK, as well as an increase of cAMP and testosterone levels, was revealed in group 2. In the regressed testes, a functional link exists between senescence and androgen levels with implication of ZIP9 and cAMP/ERK signaling pathways.
Highlights
Seasonal breeding describes a lack of continual reproduction throughout the year due to circannual fluctuations in environmental conditions resulting from climatic seasons in particular species or populations inhabiting nonequatorial areas
Bank voles were divided into three groups according to diameter and weight of their testes, as well as the seminiferous tubule diameter and interstitial tissue area measurements (Figure 1)
This study shows, for the first time, that senescent cells are present in the spermatogenic epithelium in various stages of bank vole testes regression
Summary
Seasonal breeding describes a lack of continual reproduction throughout the year due to circannual fluctuations in environmental conditions resulting from climatic seasons in particular species or populations inhabiting nonequatorial areas. In the mole, a new mechanism of testes regression has been reported based on massive desquamation (sloughing, exfoliation) of live, nonapoptotic meiotic and postmeiotic germ cells [18] In this species, there is an indication that testes regression is regulated by modulation of the expression and/or distribution of the cell adhesion (junctional) molecules connecting Sertoli and germ cells in the seminiferous epithelium with constant involvement of low intratesticular androgen levels. The potency of the negative feedback actions of testosterone is one of the principal mechanisms driving seasonal changes in reproductive system function [19,20] Findings, both in vitro and in vivo, in prostate cancer cells revealed that androgen deprivation induces senescence, a stress response that stops the proliferation of dysfunctional cells [21]. In light of the above facts, the role of ZIP9 in relation to senescence in the responses of regressed bank vole testicular tissue is fascinating
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