Ribosomal protein L21 (RPL21) plays an important role in ribosome assembly. It is considered to be a major cause for the occurrence of the hypotrichosis simplex (HTS), a type of sustained hair loss from early childhood to adulthood. In this study, the full-length sequence of pig RPL21 gene (GenBank accession number: KU891824) was cloned and identified for the first time. We found it contains a 483-bp open reading frame (ORF) encoding 160 amino acids. It is located in the plus strand of chromosome 11, which spans 2,167 bp from 4,199,792 to 4,201,958. We found RPL21 expression level is closely related to cell proliferation and cell cycle arrest. In the knockdown group, the cell proliferation activity was significantly decreased (P<0.01) and an obvious accumulation of cells at the G2/M phase with a simultaneous up-regulation of p53 and p21 was observed. This likely due to knockdown of RPL21 triggered ribosomal stress, which affected the normal ribosome assembly and caused defective ribosome biogenesis. The unassembled RPs were released consequently from the nucleolus to the nucleoplasm where they can activate p53-dependent cell-cycle responsive factors and led to a G2/M arrest. We expect these results may provide valid information for further study on the pig RPL21 gene and the cause of hypo trichosis simplex.

To improve the efficiency of production of cloned embryos and animals by nuclear transplantation in the rabbit, the effect of cell cycle of donor nuclei and type of recipient cytoplasm on the in vitro developmental potential and production efficiency of offspring was determined. The embryos of 16-cell stage were collected from the mated does at 48h post-hCG injection and they were synchronized to G phase of 32-cell stage. The oocytes collected at 14h post-hCG injection were freed from cumulus cells and then enucleated. One group of the enucleated cytoplasms was activated by electrical stimulation prior to injection of donor nucleus, and the other group was not pre-activated. The separated Gphase blastomeres of 32-cell stage embryos were injected into the perivitelline space of recipient cytoplasms. After culture for 20h post-hCG injection, the nuclear transplant oocytes were electrofused and activated by electrical stimulation and the fused nuclear transplant embryos were co-cultured for 120h and the nuclear transplant embryos developed to blastocyst stage were stained with Hoechst 33342 dye and their blastomeres were counted. Some of the nuclear transplant embryos developed in vitro to 2- to 4-cell stage were transferred into the oviducts of synchronized recipient does. The electrofusion rate was similar between the types of donor nuclei and recipient cytoplasms used. However, the nuclear transplant embryos using G phase donor nuclei were developed to blastocyst at higher rate(60.3%) than those using S phase ones(24.7%). Also, when non-preactivated oocytes were used as recipient cytplasms, the develop-mental rates of nuclear transplant embryos to blastocysts were significantly(P< 0.05) higher(57.1%) than those using preactivated ones(20.8%). The cell counts of nuclear transplant embryos developed to blastosyst stage were increased signficantly(P<0.05) more in the non-preactivated recipient cytoplasm(163.7 cells), as compared whit the preactivated recipient cytoplasm(85.4 cells), A total of 49 nuclear transplant embryos were tranferrid into 5 recipient does, of which two offsprings were produced from a foster mother 31 days after embryo transfer. these results showed that the blastomeres of G1 phase and non-preactivated oocytes might be utillzed efficiently as donor nuclei and recipient cytoplasms in the nuclear transplant procedure, thought the offspring production remained still low.