Genotype and the cryopreservation process affect the levels of aneuploidy and chromosome breakage in cultured human fibroblasts

Preserving Porcine Genetics: A Simple and Effective Method for On-Site Cryopreservation of Ear Tissue Using Direct Cover Vitrification

Cell cryopreservation is widely used for porcine genetic conservation; however, isolating and freezing primary cells in farms without adequate experimental equipment and environment poses a significant challenge. Therefore, it is necessary to establish a quick and simple method to freeze tissues on-site, which can be used for deriving primary fibroblasts when needed to achieve porcine genetic conservation. In this study, we explored a suitable approach for porcine ear tissue cryopreservation. The porcine ear tissues were cut into strips and frozen by direct cover vitrification (DCV) in the cryoprotectant solution with 15% EG, 15% DMSO and 0.1 M trehalose. Histological analysis and ultrastructural evaluation revealed that thawed tissues had normal tissue structure. More importantly, viable fibroblasts could be derived from these tissues frozen in liquid nitrogen for up to 6 months. Cells derived from thawed tissues did not show any cell apoptosis, had normal karyotypes and could be used for nuclear transfer. These results suggest that this quick and simple ear tissue cryopreservation method can be applied for porcine genetic conservation, especially in the face of a deadly emerging disease in pigs.

Satellite DNA at the Centromere is Dispensable for Segregation Fidelity

The typical vertebrate centromeres contain long stretches of highly repeated DNA sequences (satellite DNA). We previously demonstrated that the karyotypes of the species belonging to the genus Equus are characterized by the presence of satellite-free and satellite-based centromeres and represent a unique biological model for the study of centromere organization and behavior. Using horse primary fibroblasts cultured in vitro, we compared the segregation fidelity of chromosome 11, whose centromere is satellite-free, with that of chromosome 13, which has similar size and a centromere containing long stretches of satellite DNA. The mitotic stability of the two chromosomes was compared under normal conditions and under mitotic stress induced by the spindle inhibitor, nocodazole. Two independent molecular-cytogenetic approaches were used—the interphase aneuploidy analysis and the cytokinesis-block micronucleus assay. Both assays were coupled to fluorescence in situ hybridization with chromosome specific probes in order to identify chromosome 11 and chromosome 13, respectively. In addition, we tested if the lack of centromeric satellite DNA affected chromatid cohesion under normal and stress conditions. We demonstrated that, in our system, the segregation fidelity of a chromosome is not influenced by the presence of long stretches of tandem repeats at its centromere. To our knowledge, the present study is the first analysis of the mitotic behavior of a natural satellite-free centromere.

Vitrification of goat, sheep, and cattle skin samples from whole ear extirpated after death and maintained at different storage times and temperatures

Proper tissue preservation from a wide range of animals of different species is of paramount importance, as these tissue samples could be used to reintroduce lost genes back into the breeding pool by somatic cloning. We aim to study the temporal and thermal post-mortem limits, tested in rabbits and pigs, within which there will be guarantees of obtaining living skin cells in goat, sheep, and cattle. We also intend to study the effect of vitrification on the ability of ear skin cells, stored at different times and temperatures, to attach to the substratum and grow in vitro after warming. Ears were stored either at 4 degrees C for 12, 252, and 348 h post-mortem (hpm), or at room temperature (22-25 degrees C) for 60 and 96 hpm. In all cases, skin samples from these ears were sorted into two groups: one group was in vitro cultured immediately after storage, and the other group was vitrified after storage and further in vitro cultured. In goat and sheep, no differences in attachment (100%: goat; 90-100%: sheep) or subconfluence (75-100%: goat; 70-100%: sheep) rates were observed between experimental groups. However, in days of culture to reach subconfluence, significant differences between non-vitrified and vitrified groups were observed when ears were stored at 4 degrees C for 12 and 252 hpm. In cattle, with respect to attachment rate, vitrified samples from ears stored at 22-25 degrees C for 60 hpm were different from non-vitrified control group (60 vs. 100%, respectively; P < 0.05). Also, days of culture to reach subconfluence were analysed by a non-parametric Cox Survival Analysis. In general, results from ANOVA and Survival Analysis were similar, because the proportion of censored data was quite low (9%), so the bias when using ANOVA is not too high. In spite of all the above, the lowest survival rates (75%: goat; 70%: sheep; and 40%: cattle) were sufficiently high to enable collection of skin samples from the majority of dead animals and their cryopreservation.

Rabbit and pig ear skin sample cryobanking: effects of storage time and temperature of the whole ear extirpated immediately after death

The post-mortem temporal and thermal limits within which there will be ample guarantees of rescuing living skin cells from dead specimens of two species, rabbit and pig, were studied. Post-mortem extirpated whole ears were stored (in non-aseptic conditions) either at 4 degrees C or at room temperature (from 22 to 25 degrees C) or at 35 degrees C for different time lapses after animal death. In both species, the post-mortem maximum time lapses where cell viability was not significantly reduced were 240, 72, and 24 h post-mortem (hpm) for 4, 22-25 and 35 degrees C, respectively. Once the post-mortem temporal limits for each tested thermal level at which cells from skin samples are able to grow in culture were defined, the survival ability of skin samples submitted to these temporal limits and cryopreserved were tested. In the pig, skin samples stored at the three tested thermal levels survived after vitrification-warming, reaching confluence in culture. In rabbit, only tissue samples from ears stored at 35 degrees C for 24 hpm did not survive after vitrification-warming. In conclusion, we should remark that cell survival rates obtained according to the assayed post-mortem time lapses and thermal levels are sufficient to collect and to cryopreserve skin samples from the majority of dead specimens.

Vitrification and rapid freezing of rabbit fetal tissues and skin samples from rabbits and pigs

Vitrification (3.58 M EG and 2.82 M DMSO in PBS with 20% FCS) and rapid-freezing (0.25 M sucrose, 2.25 M EG, and 2.25 M DMSO in PBS with 20% FCS) procedures were assayed to cryopreserve rabbit tissue samples from 12-day fetuses, and skin samples from live born pups and adult rabbits. These methods were also assayed to cryopreserve pig skin samples obtained from abattoir animals. The ability of rabbit tissue samples to attach and colonize the substratum by cell proliferation was not affected by the assayed cryopreservation procedures, regardless of specimen age. In porcines, sample attachment and cell proliferation capability of primary cultures were not affected by applied cryopreservation procedures. Almost all primary cultures from cryopreserved skin samples reached confluency (from 92 to 100%). Results reported here allow us to establish in both species, rabbit and pig, a cryobank of skin samples from adult specimens classified as outliers for longevity (in rabbits) and prolificacy (in pigs).

Induction of telomere shortening and replicative senescence by cryopreservation

Cryopreservation can alter cellular function under certain conditions. In this report, we demonstrate the induction of cellular senescence after cells have been cryopreserved using a standard protocol. A retinal pigment epithelial cell line frozen at a specific freezing rate and subsequently thawed showed severely impaired proliferation compared to cells that were not cryopreserved. The induction of senescence was suggested by senescent associated beta-galactosidase activity and diminished bromo-deoxyuridine incorporation. A remarkable increase of single-strand DNA breaks in terminal restriction fragment (TRF) were found in cryopreserved cells immediately after thawing. The rate of mean TRF length shortening was accelerated after cryopreservation. Given this evidence, we hypothesize that cryopreservation may cause telomere shortening and cellular senescence under certain freezing conditions.

Long-term effects of embryo freezing in mice

Embryo cryopreservation does not induce clear-cut anomalies at detectable rates, but several mechanisms exist for nonlethal damage during the freeze-thaw process, and the risk of moderate or delayed consequences has not been extensively investigated. In a long-term study including senescence, we compared cryopreserved and control mice for several quantitative traits. Significant differences were seen in morphophysiological and behavioral features, some of them appearing in elderly subjects. Thus, apart from its immediate toxicity, embryo cryopreservation, without being severely detrimental, may have delayed effects. These results, consistent with other findings, question the neutrality of artificial reproductive technologies and draw attention to the preimplantation stages in developmental toxicology.

Different rate of chromosome breakage in human fibroblast strains after storage in liquid nitrogen

Cytogenetic investigation was carried out on fibroblasts stored in liquid nitrogen during a period of 7-99 months. Cell strains were from 9 individuals, 2 of whom were affected by xeroderma pigmentosum group C (XPC), and 2 XPC heterozygotes. In cell samples from 3 normal subjects and from 1 patient, high frequencies of abnormal mitoses were observed at the first passage after thawing, which returned to normal values after a few subcultures. The most frequent lesions were chromosome gaps and breaks. The cells damaged the most were those from one XP patient. These findings indicate that cells from some individuals are hypersensitive to clastogenic factors acting during freezing and thawing procedures. This sensitivity could be related to the genetic constitution, although the XP homozygous condition is not an essential or sufficient factor.