Related Experiment Videos
Short photoperiods evoke testicular apoptosis in white-footed mice (Peromyscus leucopus)
K A Young1, B R Zirkin, R J Nelson
1Department of Biochemistry, School of Public Health, The Johns Hopkins University, Baltimore, Maryland 21218, USA. kyoung@ren.psy.jhu.edu
Abstract:
Many small, nontropical mammals stop breeding during winter. Chronic exposure of males to short days (<12.5 h light/day) causes the testes to atrophy and both steroidogenesis and gametogenesis to decrease. Male white-footed mice (Peromyscus leucopus) exposed to inhibitory short day lengths provide a natural animal model to study the cellular mechanisms regulating testicular regression. In the present study, the possible role of apoptosis was assessed during naturally occurring, short day-induced gonadal regression in white-footed mice by in situ terminal transferase-mediated end labeling (TUNEL), quantitative DNA 3'-end-labeling autoradiography (laddering) of DNA fragments, and quantification of Fas protein expression, an early initiator of apoptosis. Sexually mature male mice were exposed to short (8 h of light, 16 h of darkness) or long (16 h of light, 8 h of darkness) day lengths for 2, 4, 6, 8, or 10 weeks; gonads were then removed and processed for detection of apoptotic activity. In common with previous studies, the first significant reduction in relative testis mass was observed at week 10 of short day exposure. A 2- to 3-fold increase in apoptotic (TUNEL-positive) germ cells per seminiferous tubule was observed in the testes of mice exposed to short days for 4, 6, 8, or 10 weeks compared with the testes of long day animals. The extent of 3'-end labeling of low mol wt DNA increased with 4-8 weeks of short day exposure. Western blot analysis revealed an up-regulation of the Fas protein in the testes of short day males at 4, 8, and 10 weeks. Fas staining was primarily localized to spermatocytes and spermatids. Plasma testosterone concentrations decreased in short compared with long day animals after 6, 8, or 10 weeks. The increase in TUNEL positive-labeled germ cells, testicular DNA fragmentation, and up-regulation of the Fas protein before short day reductions of testis mass and function suggest that apoptosis is important for the mediation of photoperiod-induced testicular regression in white-footed mice.
Insights
Short day lengths induce testicular regression in male white-footed mice by increasing germ cell apoptosis. This process involves DNA fragmentation and Fas protein up-regulation, preceding reductions in testis mass and testosterone levels.
Area of Science:
- Reproductive biology
- Mammalian physiology
- Cellular mechanisms
Background:
- Seasonal breeding is common in small mammals, with short winter days inhibiting reproductive function.
- Photoperiodic testicular regression in males involves decreased steroidogenesis and gametogenesis.
- White-footed mice (Peromyscus leucopus) serve as a model for studying short day-induced testicular regression.
Purpose of the Study:
- To investigate the role of apoptosis in short day-induced testicular regression in male white-footed mice.
- To assess changes in germ cell apoptosis, DNA fragmentation, and Fas protein expression during seasonal testicular atrophy.
Main Methods:
- Male white-footed mice were exposed to short (8L:16D) or long (16L:8D) day lengths for up to 10 weeks.
- Apoptosis was detected using in situ terminal transferase-mediated end labeling (TUNEL) and DNA fragmentation assays.
- Fas protein expression was quantified via Western blot analysis and immunohistochemistry.
- Testis mass and plasma testosterone concentrations were measured.
Main Results:
- Short day exposure led to a significant increase in apoptotic germ cells (TUNEL-positive) starting at 4 weeks.
- Testicular DNA fragmentation increased with 4-8 weeks of short day exposure.
- Fas protein expression was upregulated in testes of short day males, localized to spermatocytes and spermatids.
- Testis mass and plasma testosterone levels decreased after 6-10 weeks of short day exposure.
Conclusions:
- Apoptosis plays a crucial role in mediating photoperiod-induced testicular regression in white-footed mice.
- Increased germ cell apoptosis and Fas protein upregulation precede the functional decline of the testes.
- These findings elucidate cellular mechanisms underlying seasonal reproductive changes in mammals.