OC6 Scrotal Heat Stress in Mice Affects Viability and DNA Integrity of Sperm, and Sex Ratio of the Offspring

Luminal fluid of epididymis and vas deferens contributes to sperm chromatin fragmentation

STUDY QUESTION

Do the luminal fluids of the epididymis and the vas deferens contribute to sperm chromatin fragmentation (SCF) in mice?

SUMMARY ANSWER

The luminal fluids of both organs are required for activating SCF in mice, but the vas deferens luminal fluid does this more efficiently than that of the epididymis.

WHAT IS KNOWN ALREADY

Mice sperm have the ability to degrade their DNA in an apoptotic-like fashion when treated with divalent cations in a process termed SCF. SCF has two steps: the induction of reversible double-strand DNA breaks at the nuclear matrix attachment sites, followed by the irreversible degradation of DNA by nuclease. Single stranded DNA breaks accompany SCF.

STUDY DESIGN, SIZE, DURATION

Luminal fluids from two reproductive organs of the mouse (B6D2F1 strain), the epididymis and vas deferens, were extracted and tested for SCF activation with divalent cations using four different combinations of the sperm and the surrounding luminal fluids: (i) in situ--sperm were kept in their luminal fluid and activated directly; (ii) reconstituted--sperm were centrifuged and resuspended in their luminal fluid before SCF activation; (iii) mixed--sperm were centrifuged and resuspended in the luminal fluid of the other organ; (iv) no luminal fluid--sperm were centrifuged and reconstituted in buffer. All four experiments were performed without (controls) and with divalent cations (resulting in SCF). For each experimental condition, two different mice were used and the analyses averaged.

PARTICIPANTS/MATERIALS, SETTING, METHODS

DNA damage by SCF was analyzed by three different methods, the sperm chromatin structure assay (SCSA), terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) analysis and field inversion gel electrophoresis.

MAIN RESULTS AND THE ROLE OF CHANCE

In all three assays that we used, the vas deferens luminal fluid was much more efficient in stimulating SCF in the sperm from either source than that of the epididymis (P < 0.0001). Vas deferens sperm were capable of initiating lower levels of SCF in the absence of luminal fluid (P < 0.0001).

LIMITATIONS, REASONS FOR CAUTION

Analyses were performed in only one species, the mouse, but we used three separate assays in our analysis.

WIDER IMPLICATIONS OF THE FINDINGS

The data suggest that the luminal fluid of the male reproductive tract interacts with sperm during their transit providing a mechanism to degrade the DNA. We hypothesize that this is part of an apoptotic-like mechanism that allows the reproductive tract to eliminate defective sperm. The SCF model also allowed us to identify differences in the types of DNA lesions that the three tests can identify, providing important background information for the use of these tests clinically.

Heat stress induces Cdc2 protein decrease prior to mouse spermatogenic cell apoptosis

Both mitosis and meiosis are driven by M-phase promoting factor (MPF), a complex with Cdc2 and Cyclin B. The concentration of Cdc2 remains relatively constant during the cell cycle, while the concentration of Cyclin B fluctuates periodically. Many studies have demonstrated high expression levels of Cdc2 and Cyclin B in the testis. In some gene knock-out mice insufficient amounts of MPF blocked the spermatocytes at the G2/M transition and this was followed by spermatocyte apoptosis. In this study, we examined the expression and the alteration of Cdc2 in testis during the spermatocyte apoptosis process induced by transient heat stress. The results showed that the spermatogenic cell apoptosis was detectable by the TUNEL assay at 4h post-treatment. At 10h, almost all spermatocytes began apoptosis. In situ hybridization and immunohistochemistry indicated that cdc2 was primarily expressed in spermatocytes. Neither the distribution nor the amount of cdc2 mRNA was significantly influenced by the heat stress. In contrast, the amount of Cdc2 protein decreased significantly at 3h post-treatment, which was detectable before apoptosis. This indicated that Cdc2 was susceptible to heat stress in the testis. Cdc2 levels remained low until 8h post-treatment. It was possible that the swift decline in Cdc2 and the resulting lack of MPF blocked the spermatocytes at G2/M transition. Meiosis in the spermatocytes was disrupted leading to the initiation of apoptosis. The results provide evidence that the lack of Cdc2 might induce spermatocyte apoptosis after transient heat stress.

Potential factors affecting semen quality in the Asian elephant (Elephas maximus)

BACKGROUND

One of the major obstacles in using artificial insemination to manage genetics of elephant population in captivity is the large variations in semen quality among ejaculates within the same and among individuals. The objectives of this study were to determine the influences of (1) age (2) seasonality (3) and circulating testosterone (SrTest), triiodothyronine (SrT3) and tetraiodothyronine (SrT4), as well as seminal (4) testosterone (SpTest), zinc (SpZn) and protein (SpTP) on semen quality in the Asian elephant

METHODS

Analyses, including motility, viability and morphology were performed in semen samples collected twice monthly from 13 elephant bulls (age range, 10-to 72-years) by manual stimulation between July 2004 and June 2005. Serum samples obtained monthly were assessed for SrTest, SrT3, SrT4, and seminal plasma samples were evaluated for, SpTest, SpZn and SpTP.

RESULTS

The highest semen quality was observed at age 23 to 43 years. Percentages of progressive motility and viable sperm were lowest at age 51 to 70 years (P < 0.05); on the other hand, sperm concentration was lowest at age 10 to 19 years (P < 0.05). Percentage of sperm with normal morphology was highest at age 23 to 43 years. The levels of SrT3, SrTest, SpTest and SpZn were lowest at age 51 to 70 years, whereas SrT4 was lowest at age 23 to 43 years. Seasonality significantly affected semen characteristics in which percentage of viable sperm and cell concentration were highest during rainy season and lowest during summer months (P < 0.05). However, percentage of sperm with normal morphology was highest in summer and lowest in rainy season (P < 0.05). Seasonality significantly influenced SrTest with elevated concentrations observed in rainy season and winter (P < 0.05).

CONCLUSION

This study indicates that age and seasonality had influence on semen characteristics in the Asian elephant. The knowledge obtained in this study will improve our understanding of the reproductive biology of this species.

Scrotal heat stress effects on sperm viability, sperm DNA integrity, and the offspring sex ratio in mice

Evidence exists to suggest detrimental effects of heat stress on male fertility. This study was designed to assess the effects of scrotal heat stress on mature and developing sperm in a mouse model. After receiving shock heat treatment (42 degrees C for 30 min), mature spermatozoa were recovered from the epididymis hours (6) or Days (7, 14, 21, 28, 60) later, to determine the variables: number of spermatozoa, sperm viability, motility and progressive motility, sperm DNA integrity as established by the TUNEL method, embryo implantation rate, and sex ratio of the fetuses conceived using the heat-exposed spermatozoa. Our results indicate that transient mild heat treatment does not affect in the same way the different types of male germ cells. Spermatocytes present within the testis at the time of heat stress resulted into a lower concentration of spermatozoa with reduced viability and low motility. Even though, DNA integrity of spermatozoa resulting from spermatocytes was also compromised by heat stress, the higher degree of DNA damage was found among spermatozoa resulting from spermatids present within the testis at the time of heat stress. At last, heat shock effect on spermatozoa present in the epididymis at the time of thermal stress resulted into a sex ratio distortion. These findings point to a higher sensitivity of spermatocytes to heat exposure and also suggest a different response of X and Y chromosome-bearing spermatozoa to heat stress that warrants further investigation.