Significant heparin effect on bovine embryo development during sexed in vitro fertilization.

The aim of this study was to investigate the effect of different heparin concentrations in the course of sexed in vitro fertilization (IVF), on bovine embryonic development and development to term following embryo transfer (ET). With a total of 9156 oocytes for IVF, sorted as well as unsorted sperm from four bulls had different heparin requirements for achieving the highest rate of development in vitro. However, when optimal heparin concentrations were used (40 to 80 µg/ml), the performance of X-sorted sperm (0.3 × 106/ml/IVF droplet) from all four bulls, as judged by blastocyst development (Bulls A, B, C, and D: 25.2, 19.7, 25.1, and 9.8%, respectively), was significantly increased, and the blastocyst rate was comparable to that observed with unsorted sperm at certain heparin concentrations within the four bulls. We determined that near-optimal blastocyst development was possible with sorted sperm from all four bulls, when a heparin concentration of 40 µg/ml was used. Pregnancy rates at d 70 post ET ranged from 39.1 to 40.3% (P > 0.05), and the calving rates ranged from 34.4 to 35.1% (P > 0.05), when heparin was used at a concentration of 10 µg/ml (n = 236), 20 µg/ml (n = 189), and 40 µg/ml (n = 305), respectively. Our study demonstrates that, although the sorted sperm of different bulls performed optimally over a range of heparin concentrations, a generally accepted heparin concentration of 40 µg/ml can be set for sexed IVF. This improvement is beneficial when sexed embryo production by ovum pickup and IVF is an essential component of genetic breeding programs.

Derivation of Rabbit Embryonic Stem Cells from Vitrified-Thawed Embryos.

The rabbit is a useful animal model for regenerative medicine. We previously developed pluripotent rabbit embryonic stem cell (rbESC) lines using fresh embryos. We also successfully cryopreserved rabbit embryos by vitrification. In the present work, we combined these two technologies to derive rbESCs using vitrified-thawed (V/T) embryos. We demonstrate that V/T blastocysts (BLs) can be used to derive pluripotent rbESCs with efficiencies comparable to those using fresh BLs. These ESCs are undistinguishable from the ones derived from fresh embryos. We tested the developmental capacity of rbESCs derived from V/T embryos by BL injection experiments and produced chimeric kits. Our work adds cryopreservation to the toolbox of rabbit stem cell research and applications and will greatly expand the available research materials for regenerative medicine in a clinically relevant animal model.

Generation of human lactoferrin transgenic cloned goats using donor cells with dual markers and a modified selection procedure.

The objective was to use dual markers to accurately select genetically modified donor cells and ensure that the resulting somatic cell nuclear transfer kids born were transgenic. Fetal fibroblast cells were transfected with dual marking gene vector (pCNLF-ng) that contained the red-shifted variant of the jellyfish green fluorescent protein (LGFP) and neomycin resistance (Neo) markers. Cell clones that were G418-resistant and polymerase chain reaction-positive were subcultured for several passages; individual cells of the clones were examined with fluorescence microscopy to confirm transgenic integration. Clones in which every cell had bright green fluorescence were used as donor cells for nuclear transfer. In total, 86.7% (26/30) cell clones were confirmed to have transgenic integration of the markers by polymerase chain reaction, 76.7% (23/30) exhibited fluorescence, but only 40% (12/30) of these fluorescent cell clones had fluorescence in all cell populations. Moreover, through several cell passages, only 20% (6/30) of the cell clones exhibited stable LGFP expression. Seven transgenic cloned offspring were produced from these cells by nuclear transfer. Overall, the reconstructed embryo fusion rate was 76.6%, pregnancy rates at 35 and 60 days were 39.1% and 21.7%, respectively, and the offspring birth rate was 1.4%. There were no significant differences between nuclear transfer with dual versus a single (Neo) marker (overall, 73.8% embryo fusion rate, 53.8% and 26.9% pregnancy rates, and 1.9% birth rate with five offspring). In conclusion, the use of LGFP/Neo dual markers and an optimized selection procedure reliably screened genetically modified donor cells, excluded pseudotransgenic cells, and led to production of human lactoferrin transgenic goats. Furthermore, the LGFP/Neo markers had no adverse effects on the efficiency of somatic cell nuclear transfer.

Hybrid expression cassettes consisting of a milk protein promoter and a cytomegalovirus enhancer significantly increase mammary-specific expression of human lactoferrin in transgenic mice.

It is very important to develop an effective, specific, and robust expression cassette that ensures a high level of expression in the mammary glands. In this study, we designed and constructed a series of mammary gland-specific vectors containing a complex hybrid promoter/enhancer by utilizing promoter sequences from milk proteins (i.e., goat ß-casein, bovine αs1-casein, or goat ß-lactoglobulin) and cytomegalovirus enhancer sequences; vectors containing a single milk protein promoter served as controls. Chicken ß-globin insulator sequences were also included in some of these vectors. The expression of constructs was analyzed through the generation of transgenic mice. Enzyme-linked immunosorbent assay (ELISA) analysis revealed that the hybrid promoter/enhancer could drive the expression of recombinant human lactoferrin (rhLF) cDNA at high levels (1.17-8.10 mg/ml) in the milk of transgenic mice, whereas control promoters achieved a very low rhLF expression (7-40 ng/ml). Moreover, the expression of rhLF was not detected in the serum or saliva of any transgenic animal. This result shows that all constructs, driven by the hybrid promoter/enhancer, had high mammary gland-specific expression pattern. Together, our results suggest that the use of a hybrid promoter/enhancer is a valuable alternative approach for increasing mammary-specific expression of recombinant hLF in a transgenic mouse model.