Quantification of apoptosis (programmed cell death) in mammalian testis by DNA-fragmentation ELISA

Birchen and Blue Leonesa sperm cryopreservation: a new technique for evaluating the integrity of cockerel sperm membranes

1. Birchen and Blue Leonesa are two endangered chicken breeds mainly raised in Curueño Valley in North Spain. The establishment of a germplasm bank to guarantee the preservation of these breeds is needed. However, cockerels from different breeder flocks can show variance in semen cryoresistance.2. The following work focused on the sperm characterisation and cryopreservation of Birchen and Blue Leonesa cockerels from four different breeders. A total of 30 semen pools were analysed. Besides conventional sperm analysis, including motility by computer-aided sperm analysis (CASA) and DNA fragmentation by TUNEL, the present study tested a double staining method (MitoTracker^TM Green FM/propidium iodide). This gave simultaneous assessment of plasma and acrosomal and mitochondrial membranes, which were previously validated by SYBR-14/PI, CASA, aniline blue and TUNEL.3. No significant differences were found among fresh semen variables between breeds and breeders. For post-thawed variables, significant differences (P < 0.05) were found between breeders in sperm viability (58.0 ± 1.90 breeder D vs. 35.2 ± 7.41 breeder A, 37.2 ± 4.09 breeder B and 22.3 ± 5.92 breeder C) and DNA fragmentation (62.4 ± 9.91 breeder C vs. 31.8 ± 7.08 breeder B and 24.5 ± 5.49 breeder D). The lowest DNA fragmentation values for semen from breeder D birds were coincident with higher integrity of the mitochondrial membrane.4. The results revealed higher sperm cryoresistance in the cockerels from one of the breeders, possibly due to differences in management system (e.g. diet, housing, control of stress elements and pathogens, reproduction practices or maintenance of genetic diversity). These differences may determine the sperm freezability, and thus the effectiveness of developing a germplasm bank.

Tissue-specific epigenetic inheritance after paternal heat exposure in male wild guinea pigs

External temperature change has been shown to modify epigenetic patterns, such as DNA methylation, which regulates gene expression. DNA methylation is heritable, and as such provides a mechanism to convey environmental information to subsequent generations. Studies on epigenetic response to temperature increase are still scarce in wild mammals, even more so studies that compare tissue-specific epigenetic responses. Here, we aim to address differential epigenetic responses on a gene and gene pathway level in two organs, liver and testis. We chose these organs, because the liver is the main metabolic and thermoregulation organ, and epigenetic modifications in testis are potentially transmitted to the F2 generation. We focused on the transmission of DNA methylation changes to naive male offspring after paternal exposure to an ambient temperature increase of 10 °C, and investigated differential methylated regions of sons sired before and after the paternal exposure using Reduced Representation Bisulfite Sequencing. We detected both a highly tissue-specific epigenetic response, reflected in genes involved in organ-specific metabolic pathways, and a more general regulation of single genes epigenetically modified in both organs. We conclude that genomes are context-specifically differentially epigenetically regulated in response to temperature increase. These findings emphasize the epigenetic relevance in cell differentiation, which is essential for the specific function(s) of complex organs, and is represented in a diverse molecular regulation of genes and gene pathways. The results also emphasize the paternal contribution to adaptive processes.

Environmental Change-Dependent Inherited Epigenetic Response

Epigenetic modifications are a mechanism conveying environmental information to subsequent generations via parental germ lines. Research on epigenetic responses to environmental changes in wild mammals has been widely neglected, as well as studies that compare responses to changes in different environmental factors. Here, we focused on the transmission of DNA methylation changes to naive male offspring after paternal exposure to either diet (~40% less protein) or temperature increase (10 °C increased temperature). Because both experiments focused on the liver as the main metabolic and thermoregulation organ, we were able to decipher if epigenetic changes differed in response to different environmental changes. Reduced representation bisulfite sequencing (RRBS) revealed differentially methylated regions (DMRs) in annotated genomic regions in sons sired before (control) and after the fathers’ treatments. We detected both a highly specific epigenetic response dependent on the environmental factor that had changed that was reflected in genes involved in specific metabolic pathways, and a more general response to changes in outer stimuli reflected by epigenetic modifications in a small subset of genes shared between both responses. Our results indicated that fathers prepared their offspring for specific environmental changes by paternally inherited epigenetic modifications, suggesting a strong paternal contribution to adaptive processes.

Semen cryopreservation in black-footed (Spheniscus demersus) and gentoo (Pygoscelis papua) penguins: Effects of thawing temperature on semen characteristics

In this study, there was an examination of the effect on the characteristics of cryopreserved black-footed (Spheniscus demersus) and gentoo (Pygoscelis papua) penguin semen, of thawing at 37 and 5 °C. For two consecutive years, semen was collected and frozen during the April-June period from six gentoo penguins, and during the October-November period from 13 black-footed penguins. After thawing, sperm motility variables were examined by computer-assisted sperm analysis. Propidium iodide and SYBR-14 were used as fluorochromes for the examination of membrane integrity. For the gentoo penguins, no differences were detected in the values of frozen-thawed semen characteristics after thawing at 37 or 5 °C. For the black-footed penguins, however, thawing at 5 °C resulted in greater values (P < 0.05) for straight-line velocity (VSL), average path velocity (VAP), linearity (LIN), straightness (STR), and wobble (WOB) as compared with thawing at 37 °C. After thawing at 37 ºC, there were greater values with gentoo penguin sperm for percentage motile sperm, progressive motility, curvilinear velocity (VCL), VSL VAP, LIN, STR, WOB and beat-cross frequency (BCF; P < 0.05) than that for black-footed penguin sperm. After thawing at 5 ºC, there were no differences in values for any variables between the two species. In conclusion, thawing temperature affects semen characteristics in a species-specific manner. The present data strongly suggest that cryopreservation procedures should be adapted for use with each penguin species. Cryopreserved black-footed penguin semen should be thawed after cryopreservation at 5 ºC, while that of gentoo penguins can be thawed at either 5 or 37 ºC.

Diet changes alter paternally inherited epigenetic pattern in male Wild guinea pigs

Epigenetic modifications, of which DNA methylation is the most stable, are a mechanism conveying environmental information to subsequent generations via parental germ lines. The paternal contribution to adaptive processes in the offspring might be crucial, but has been widely neglected in comparison to the maternal one. To address the paternal impact on the offspring's adaptability to changes in diet composition, we investigated if low protein diet (LPD) in F0 males caused epigenetic alterations in their subsequently sired sons. We therefore fed F0 male Wild guinea pigs with a diet lowered in protein content (LPD) and investigated DNA methylation in sons sired before and after their father's LPD treatment in both, liver and testis tissues. Our results point to a 'heritable epigenetic response' of the sons to the fathers' dietary change. Because we detected methylation changes also in the testis tissue, they are likely to be transmitted to the F2 generation. Gene-network analyses of differentially methylated genes in liver identified main metabolic pathways indicating a metabolic reprogramming ('metabolic shift'). Epigenetic mechanisms, allowing an immediate and inherited adaptation may thus be important for the survival of species in the context of a persistently changing environment, such as climate change.

Circannual Testis Changes in Seasonally Breeding Mammals

In the non-equatorial zones of the Earth, species concentrate their reproductive effort in the more favorable season. A consequence of seasonal breeding is seasonal testis regression, which implies the depletion of the germinative epithelium, permeation of the blood-testis barrier, and reduced androgenic function. This process has been studied in a number of vertebrates, but the mechanisms controlling it are not yet well understood. Apoptosis was assumed for years to be an important effector of seasonal germ cell depletion in all vertebrates, including mammals, but an alternative mechanism has recently been reported in the Iberian mole as well as in the large hairy armadillo. It is based on the desquamation of meiotic and post-meiotic germ cells as a consequence of altered Sertoli-germ cell adhesion molecule expression and distribution. Desquamated cells are either discarded alive through the epididymis, as in the mole, or subsequently die by apoptosis, as in the armadillo. Also, recent findings on the reproductive cycle of the greater white-toothed shrew at the meridional limits of its distribution area have revealed that the mechanisms controlling seasonal breeding are in fact far more plastic and versatile than initially suspected. Perhaps these higher adaptive capacities place mammals in a better position to face the ongoing climate change.

Thioredoxin rod-derived cone viability factor protects against photooxidative retinal damage

Rod-derived cone viability factor (RdCVF) is a trophic factor of the thioredoxins family that promotes the survival of cone photoreceptors. It is encoded by the nucleoredoxin-like gene 1 Nxnl1 which also encodes by alternative splicing a long form of RdCVF (RdCVFL), a thioredoxin enzyme that interacts with TAU. The known role of thioredoxins in the defense mechanism against oxidative damage led us to examine the retinal phenotype of the Nxnl1(-/-) mice exposed to photooxidative stress. Here we found that, in contrast to wild-type mice, the rod photoreceptors of Nxnl1(-/-) mice are more sensitive to light after exposure to 1700 or 2500 lx. The delivery of RdCVF by AAV to mice deficient of Nxnl1(-/-) protects rod photoreceptors from light damage. Interestingly, the RdCVF2L protein, encoded by the paralog gene Nxnl2, is able to reduce TAU phosphorylation, as does RdCVFL, but does not protect the rod from light damage. Our result shows that the Nxnl1 gene, through the thioredoxin RdCVFL, is part of an endogenous defense mechanism against photooxidative stress that is likely of great importance for human vision.

Identification of live germ-cell desquamation as a major mechanism of seasonal testis regression in mammals: a study in the Iberian mole (Talpa occidentalis)

In males of seasonally breeding species, testes undergo a severe involution at the end of the breeding season, with a major volume decrease due to massive germ-cell depletion associated with photoperiod-dependent reduced levels of testosterone and gonadotropins. Although it has been repeatedly suggested that apoptosis is the principal effector of testicular regression in vertebrates, recent studies do not support this hypothesis in some mammals. The purpose of our work is to discover alternative mechanisms of testis regression in these species. In this paper, we have performed a morphological, hormonal, ultrastructural, molecular, and functional study of the mechanism of testicular regression and the role that cell junctions play in the cell-content dynamics of the testis of the Iberian mole, Talpa occidentalis, throughout the seasonal breeding cycle. Desquamation of live, nonapoptotic germ cells has been identified here as a new mechanism for seasonal testis involution in mammals, indicating that testis regression is regulated by modulating the expression and distribution of the cell-adhesion molecules in the seminiferous epithelium. During this process, which is mediated by low intratesticular testosterone levels, Sertoli cells lose their nursing and supporting function, as well as the impermeability of the blood-testis barrier. Our results contradict the current paradigm that apoptosis is the major testis regression effector in vertebrates, as it is clearly not true in all mammals. The new testis regression mechanism described here for the mole could then be generalized to other mammalian species. Available data from some previously studied mammals should be reevaluated.

Distinct cellular responses induced by saporin and a transferrin-saporin conjugate in two different human glioblastoma cell lines

Glioblastoma multiforme (GBM) is the most common primary brain tumour in adults, with a median survival of ~12-18 months post-diagnosis. GBM usually recurs within 12 months post-resection, with poor prognosis. Thus, novel therapeutic strategies to target and kill GBM cells are urgently needed. The marked difference of tumour cells with respect to normal brain cells renders glioblastoma a good candidate for selective targeted therapies. Recent experimental strategies focus on over expressed cell surface receptors. Targeted toxins represent a new class of selective molecules composed by a potent protein toxin and a carrier ligand. Targeted toxins approaches against glioblastoma were under investigation in phase I and II clinical trials with several immunotoxins (IT)/ligand toxins such as IL4-Pseudomonas aeruginosa exotoxin A (IL4-PE, NBI-3001), tumour growth factor fused to PE38, a shorter PE variant, (TGF)alpha-TP-38, IL13-PE38, and a transferrin-C diphtheriae toxin mutant (Tf-CRM107). In this work, we studied the effects of the plant ribosome-inactivating saporin and of its chimera transferrin-saporin against two different GBM cell lines. The data obtained here indicate that cell proliferation is affected by the toxin treatments but that different mechanisms are used, directly linked to the presence of an active or inactive p53. A model is proposed for these alternative intracellular pathways.

Apoptotic changes in the epithelium germinativum of the cat (Felis catus s. domestica, L. 1758) at different ages and breeding seasons

Apoptosis (programmed cell death) could be considered as a physiological process that takes part in a healthy organism, which helps to maintain organism homeostasis. The visible deterioration of semen quality and the number of germ cells is accompanied by a seasonal decrease of the reproductive activity in some species. This post-effect cascade is caused by apoptosis, which is the primary mechanism responsible for the elimination of germ cells during spermatogenesis. The aim of our study was to assess apoptotic changes in the epithelium germinativum in cat testes at different ages. One hundred and two pairs of testes were obtained from domestic cats aged between 4 months and 10 years. The paraffin-embedded tissue sections were labelled using the Oncogene and Calbiochem Research Products DNA Fragmentation Detection Kit (Cat# QIA21; Darmstadt, Germany), which allows the recognition of apoptotic nuclei in tissue sections with Fragment End Labelling (FragEL) of DNA. The activity of apoptotic processes in cat testes collected from the spring-summer period compared with the autumn-winter season revealed that, 59.42% and 51.51%, respectively, males testes were characterized by insignificant changes. The obtained data revealed a distinctive apoptotic changes in the young animal testes before spermatogenesis onset. An intensification of programmed death cells in the epithelium germinativum in the elder cats (between 3-6 and 6-10 years) was not observed. Apoptotic changes slightly intensified in cats aged between 12 and 36 months.

Inverse relationship between testicular proliferation and apoptosis in mammalian seasonal breeders

Seasonal cycles of testicular activity occur in many mammals and can include transitions between total arrest and recrudescence of spermatogenesis. We hypothesize that involution and reactivation of testis result from two antagonistic processes, proliferation and programmed cell death (apoptosis), which are activated at different times. To test this hypothesis, quantitative measurements of both proliferation-specific marker and apoptotic produced nucleosomes have been compared with sperm and testosterone production in testes from adult roe deer during breeding and non-breeding seasons (May to September). Testes of brown hare were included from periods of testes regression (June to August) and recrudescence (November to December). The highest testicular weights in roe deer were found in the rutting period from late July to early August (27.25 +/- 8.56 g), corresponding with the highest number of testicular sperm/g parenchyma. The peak of sperm production coincided with a peak in testosterone concentration (1.19 +/- 0.53 microg/g testis). The maximum level of proliferation-specific marker was also found during the breeding season (98.6 +/- 58.2 U/g testis in comparison to 20.1 +/- 22.0 U/g in the prerutting period). In contrast, the most significant apoptosis was observed in the nonbreeding season than the breeding period (71.11 +/- 5.79 U/mg testis and 18.88 +/- 6.79 U/mg, respectively). Testicular proliferation was low in the brown hare (0.061 +/- 0.062 U/g) during involution of the testes. It was newly activated in November and December (0.85 +/- 0.33 U/g), preceding the increase in testicular volume. Testosterone production increased in conjunction with testicular proliferation. At this time, testicular apoptosis was significantly lower (14.16 +/- 2.12 U/mg testis) than during the period of pronounced testicular regression (30.16 +/- 19.95 U/g). These results suggest that regulation of seasonal testicular activity is characterized by an inverse relationship of proliferation and apoptosis.

Apoptosis is not the cause of seasonal testicular involution in roe deer

Apoptosis is involved in the regulation of spermatogenesis. The involution of testes in seasonal breeders might be expected to involve enhanced apoptotic cell elimination. We have compared seasonally changing testicular apoptosis in roe deer with that in non-seasonally breeding cattle. Apoptotic cells were detected as TUNEL-positive cells by both flow-cytometric analysis and in situ localisation of fragmented DNA in tissue sections. Apoptosis-induced DNA fragments were also assessed by enzyme-linked immunosorbent assay (ELISA) in homogenised testicular parenchyma. As expected, the testis mass and the percentage of haploid cells in roe deer showed a seasonal pattern with a significant maximum during the rut (August), whereas no annual variation of these parameters was found in bulls. All three methods for determining apoptosis showed similar findings. Roe deer exhibited significant seasonal fluctuation of total apoptotic activity (ELISA, apoptotic cells per tubule cross section) with a maximum during the breeding season. However, the seasonal differences in the number of apoptotic cells corresponded to the variable total numbers of spermatogonia and spermatocytes per tubule cross section. Thus, the percentages of TUNEL-positive cells related to the combined number of both germ cell types showed no seasonal variance, as confirmed by percentages of apoptotic cells analysed flow-cytometrically. The maximum level of apoptosis during the rut in roe deer was similar to the values obtained during the invariably high spermatogenic activity in cattle. These results suggest that, in roe deer, apoptosis is not the cause of the seasonal involution of testes.

Testicular mitosis, meiosis and apoptosis in mink (Mustela vison) during breeding and non-breeding seasons

Testes of mink were compared between the breeding (March) and non-breeding seasons with the start (November) and cessation (May) of spermatogenic activity. Testicular mass and spermatozoa per gram testis were assessed. Percentages of haploid (1C), diploid (2C) and tetraploid (4C) cells were monitored using DNA flow cytometry and the proportions of somatic and spermatogenetic cells were determined after selective labelling of somatic cells with a vimentin antibody. Apoptosis was examined by cell death detection ELISA, and testosterone concentrations were measured with an enzyme-immunoassay. The significantly higher testis mass during the breeding period coincided with higher numbers of testicular spermatozoa per gram testis and peak of testicular testosterone concentration in comparison with non-breeding periods. The proportions of 1C, 2C and 4C cells showed corresponding strong differences between these periods with the maximum of 1C cells during breeding. The proportions of testicular cells in G2-M phase of mitosis were very low during the period of peak spermatogenesis; they were markedly increased in the time of autumnal resumption in November but were even higher during testis involution in May. However. the meiotic transformation (1C:4C ratio) is maximal in March. The total as well as the relative proportions of spermatogenic and somatic cells differed significantly not only between breeding and non-breeding periods but also between the periods at the start and at the end of active spermatogenesis. The intensity of apoptosis was also seasonally dependent. The highest level in March indicates a stimulated apoptosis even during the breeding period. In conclusion, the production of spermatozoa in mink is intensified by enlargement of gonads as well as enhanced efficiency of spermatogenesis during breeding. In this time, the testosterone concentration and the meiotic transformation show high levels, but the mitotic activity of spermatogenic cells is already significantly diminished and an intensified apoptosis seems to precede the forthcoming testis involution after breeding. The results suggest that the regulation of seasonal testicular activity is characterised by co-ordinated shifts in the relationships between mitosis, meiosis, apoptosis and testosterone production.

Influence of environmental cadmium on testicular proliferation in roe deer

The influence of cadmium on spermatogenesis in roe deer was studied, comparing animals from areas with high (n = 37) and low (n = 23) cadmium exposure. Testes were evaluated during pre-rut (May) and rut (July/August). During these periods the cadmium accumulation (mg/kg kidney) in polluted regions averaged 3.41 and 3.52 in comparison with 1.61 and 1.81 in controls. Cadmium accumulation was positively correlated with testis weight during both seasons. In May the proliferation (units of tissue polypeptid specific antigen/g parenchyma) was lower in animals with higher cadmium (24.02 compared with 78.20; P < 0.01). During the rut, testicular proliferation and spermatozoa/g testis as well as apoptosis showed no significant changes with increased cadmium contamination. The results suggest delayed proliferation during the pre-rutting period in animals with high cadmium exposure, but other indications of effects on the testis were not significant.

Effect of growth hormone and induced IGF-I release on germ cell population and apoptosis in the bovine testis

Bovine growth hormone has been used in dairy cattle to increase milk production,but it also increases the twin parturition rate. This effect is mediated by insulin-like growth factor-I (IGF-I), which prevents follicular atresia by hindering apoptosis of granulosa cells. The action of GH and IGF-I on testicular function remains unclear. The goal of this study, therefore, was to verify the effects of short-term administration of GH and induced IGF-I release on the number of testicular germ cells, testicular morphology, and apoptosis in the bovine testis. Twenty Zebu bulls were split into 2 groups. The bulls in Group 1 (n = 10) were treated with 2 subcutaneous injections of bovine GH (500 mg/bull) 7 d apart. Group 2 bulls (n = 10) received placebos under the same protocol. All of the bulls were slaughtered 14 d after the start of treatment. Fragments of the testis were collected, fixed in Bouin's solution, embedded in paraffin, and the sections stained with hematoxilin and eosin. The paraffin-embedded sections were also used for in situ detection of apoptotic cells. Blood samples were collected at slaughter to measure serum levels of IGF-I, FSH and LH. Neither the number of Stage I seminiferous epithelium germ cells and the morphometric parameters (tubular diameter, seminiferous epithelium height, and volumetric proportions of structural components) nor the blood levels of FSH and LH showed a significant difference between the 2 groups. However, the treated animals showed an increase in serum IGF-I (P<0.01). Apoptotic germ cells were detected in the testis of both groups, showing the same pattern and a stage-specific apoptosis pattern. Most of the labeled cells were spermatocytes. The localization of apoptotic germ cells did not differ between groups. These results suggest that short-term administration of GH does not affect bovine spermatogenesis in adult bulls.

DNA degradation in mural granulosa cells of non- and slightly atretic follicles of fresh and cold-stored domestic cat ovaries

Apoptosis of granulosa cells is associated with follicular atresia and may occur before atresia becomes morphologically evident. Detection of DNA fragmentation by in situ end-labeling (ISEL) with terminal transferase allows the histological assessment of apoptotic cells on conventional histological sections. Degradation of DNA also may occur after prolonged cold storage of ovaries caused by the release of lysosomal enzymes. The objectives of this study were to assess follicle atresia and the impact of cold storage for 8, 12, 24, and 48 hr after ovarian excision by assessing DNA degradation in mural granulosa cells of cat ovaries. Follicles were distinguished by morphological criteria as nonatretic (NA), slightly atretic (SA), or atretic, and the mean number (+/-SEM) of granulosa cells labeled by ISEL was determined. About 50% of follicles showed some sign of atresia independent from the stage of the reproductive cycle of the ovarian donor. Number of ISEL-stained granulosa cells for NA and SA, freshly collected follicles was 7.5 +/- 0.6 and 9.3 +/- 0.8 cells/field, respectively, compared to 16.2 +/- 0.8 cells/field in the wall of atretic follicles (P < 0.001). Fresh NA follicles from luteal phase ovaries had more (P < 0.05) labeled granulosa cells (9.2 +/- 0.7 cells/field) than measured in follicles of cats in a follicular phase (5.7 +/- 0.7). During cold storage, DNA degradation began within 12 hr (NA, 12.2 +/- 0.7 cells/field; SA, 13.3 +/- 0.5), both values being different (P < 0.05) from fresh controls. By 24 hr, DNA degradation was at the level of a positive control subjected to DNAse treatment. In summary, results reveal that granulosa cell DNA degeneration precedes the loss of developmental capacity of cat oocytes during atresia and postexcision storage. Finding irreversible changes in granulosa cell DNA after storage of cat ovaries for > 12 hr may be important for developing oocyte rescue protocols for rare felids in cases where prolonged storage and transport may be required.