Until today, success in germline cells and tissue cryopreservation is limited mainly due to the poor understanding of the complex physiological processes can lead to cell damage during cryopreservation. Germline cells, from both male and female, have unique ability to differentiate into one or more cell lines and thus it becomes a crucial point to store them in subzero temperature with the minimal damage of their functional properties and maximum recovery of unchanged and viable cells when thawed. In the past three decades, a vast research has been performed using various different animal models which in fact have led to development of new methodologies and optimization of older one. However, successful use of animal model has provided the opportunity in research with human germline cells and tissues preservation, but not in all the cases. Therefore, the use of new cryo-protective chemicals and modified protocols have been often found in different groups of researchers based on the types, physical structures, utility and animal species of the specimens to be cryopreserved. This review discusses about the basics of different types of cryopreservation methodologies and commonly used optimized protocols and cryoprotectants for germline cells and tissues preservation.

Recently, we published a microinjection method for generating transgenic cattle using the DNA transposon system and their analysis by next-generation sequencing (Yum et al. Sci Rep. 2016 Jun 21;6:27185). In that study, we generated transgenic cattle using two different types of DNA transposon system, sleeping beauty (SB) and piggybac (PB), carrying Yellow fluorescent protein with SB (SB-YFP, female) and green fluorescent protein with PB (PB-GFP, male) under the control of the ubiquitous CAG promoter, respectively. The female and male founder cattle have been grown up to date (the female age: 40 months old, the male age: 33 months old) without any health issues. In genomic instability and blood analysis, there was no significant differences between wild type and founder cattle. In the present study, we confirmed germ-line transmission of the transposon-mediated transgene integrations and ubiquitous and persistent expression of transgene in second generation of offspring (F1). The F1 was born without any assistance and expressed GFP in the eyes without UV light. The ubiquitous expression of GFP was detected in skin fibroblast from the ear tissue and confirmed by genomic DNA PCR, which suggest that the transgene from the PB-GFP was successfully transmitted. Unfortunately, no transgene from SB-YFP were identified. To confirm the transgene integration site, the genomic DNA from blood was extracted and performed next-generation sequencing (NGS). The GFP gene was integrated in chromosome 4 (two copies), and 6. As results, a total of two copies of paternal transgene transmitted into the F1. All the integrated position was not related with coding region and there was no significant difference in genomic variants between transgenic and non-transgenic cattle. To our knowledge, this is the first report of germ-line transmission through non-viral transgenic founder cattle. Those transgenic cattle will be valuable resource to many fields of biomedical research and agricultural science.

In the present study, using a MoMLV-based retrovirus vector, we successfully generated a new transgenic chicken line expressing high levels of hEPO. A replication-defective Moloney murine leukemia virus (MoMLV)-based vectors packaged with vesicular stomatitis virus G glycoprotein (VSV-G) was injected beneath the blastoderm of non-incubated chicken embryos (stage X). One rooster was mated to wild-type hens to produce 748 G1 progeny. PCR analysis of blood samples from these progeny revealed that there were seven G1 transgenic offspring, corresponding to a 0.9% germline transmission rate. Subsequently, Southern blot analysis of the genomic DNA from three G1 transgenic chickens was carried out to verify the stable genomic integration and copy number of the transgene in the genome. Quantitative analyses of the blood samples taken from G1 transgenic chickens resulted in 4,150 ～ 10,823 IU/㎖ (34.6 ～ 90.2 ㎍/㎖) of hEPO in the blood. The biological activity of the recombinant hEPO in transgenic chicken serum was comparable to its commercially available counterpart. Red blood cell numbers were more than three-fold higher in the transgenic chickens compared to the non-transgenic chickens. Successful germline transmission of the transgene was also confirmed in G2 transgenic chicks produced from crossing G1 transgenic roosters with non-transgenic hens. We confirmed that 13 transgenic chicks of 45 G2 progeny, corresponding to a 28.9% germline transmission rate. These results will help establish a useful transgenic chicken model system for studies of embryonic development and for efficient production of transgenic chickens as bioreactors. This work was supported by the Bio-industry Technology Development Program, Ministry of Agriculture, Food and Rural Affairs, Republic of Korea, and by a grant from the Next-Generation BioGreen 21 Program (No. PJ011178), Rural Development Administration, Republic of Korea.

The Oct-4 (octamer-4), a member of the POU family transcription factor, is expressed in early mouse embryogenesis and in pluripotent embryonic stem (ES) lines. Oct-4 expression is thought to remain confined to the germline after gastrulation in the embryo. Therefore, the study was designed to, study the location of Oct-4 protein in the ovaries, placenta and testis of Korean native cattle (Hanwoo). Expression of Oct-4 mRNA in the ovaries and placenta of bovine was confirmed by RT-PCR and immunohistochemical analysis. Oct-4 was expressed in granulosa, thecal cells irrespective of the shape and size of follicles and endometerium of Korean native cattle (Hanwoo). Expression of Oct-4 was profound in all the tissues of Korean native cattle (Hanwoo) suggestung their role in them. Oct-4 localization and expression could contribute to further developmental studies in Korean native cattle (Hanwoo).

Spermatogonial stem cells(SSCs) only are responsible for the generation of progeny and for the transmission of genetic information to the next generation in male. Other in vitro studies have cultured SSCs for proliferation, differentiation, and genetic modification in mouse and rat. Currently, information regarding in vitro culture of porcine Germline Stem Cell(GSC) such as gonocyte or SSC is limited and is in need of further studies. Therefore, in this study, we report development of a successful culture system for gonocytes of neonatal porcine testes. Testis cells were extracted from 10～14-day-old pigs. These cells were harvested using enzymatic digestion, and the harvested cells were purified with combination of percoll, laminin, and gelatin selection techniques. The most effective culture system of porcine gonocytes was established through trial experiments which made a comparison between different feeder cells, medium, serum concentrations, temperatures, and O2 tensions. Taken together, the optimal condition was established using C166 or Mouse Embryonic Fibroblast(MEF) feeder cell, Rat Serum Free Medium(RSFM), 0% serum concentration, 37℃ temperature, and O2 20% tension. Although we discovered the optimal culture condition for proliferation of porcine gonocytes, the gonocyte colonies ceased to expand after one month. These results suggest inadequate acquirement of ingredients essential for long term culture of porcine GSCs. Consequently, further study should be conducted to establish a successful long-term culture system for porcine GSCs by introducing various growth factors or nutrients.