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.

Previously, the wheat non-specific lipid transfer proteins (TaLTP), members of a small multigene family, appear to show a complex pattern of expression regulation. For further assessment of expression diversity of the TaLTP genes, we have attempted to evaluate their expression profiles of responses to abiotic stresses via the semi-quantitative RT-PCR method. The expression profiles revealed that the TaLTP genes in group A evidenced highly similar (but not identical) responses against abiotic stresses, whereas much differential expression pattern among genes in each group. The four promoters of TaLTP1, TaLTP7, and TaLTP10 of group A and TaLTP3 of group B were fused to a GUS reporter gene and the recombinant genes were introduced into Arabidopsis. The promoters of TaLTP1, TaLTP7 and TaLTP10 of group A, drove strong but various GUS expression in cotyledons, hypocotyls, epidemic and sub-epidemic cells of young shoots and leaves, floral organs as well as siliques. By contrast, the promoter of TaLTP3 just directed trace expression in cotyledons, young emerged leaves and epidemic cells of flower ovaries. The promoter of TaLTP1 directed the expression in root system whereas the promoters of TaLTP1 and TaLTP10 showed some degree of expression during seed development. The expression diversity of TaLTP genes suggests their multiple physiological functions, evidencing subfunctionalization over evolutionary time.