A small exon is easily skipped and a large exon usually contains internal cryptic splice sites. The amelogenin gene follows that golden rule perfectly, as exon 4 is usually skipped. The exon 2b revealed in this study consists of just 39 nucleotides encoding 13 amino acid residues. As far as we know, it is the smallest exon among amelogenin exons detected so far. Although analysis of amelogenin gene sequence spanning intron 2 in several species did not identify a typical exon/intron boundary, there is indeed a region with a moderate sequence identity to exon 2b nucleotide sequence. Exon 6 is the largest exon of the amelogenin gene containing several internal cryptic splice sites that could lead to its further sub-division into four domains named exon 6A, exon 6B, exon 6C, and exon 6D. During the processing of amelogenin premRNA, one well-defined amelogenin splicing form contains the majority of N-terminal of exon 6 spliced out and played a role in enamel biomineralization and enamel organ epithelial cell differentiation. The splicing form of P.cinereus-50 discovered in present study only contains exons 2, 3, 5 and 7 with exon 6 completely spliced out. As far as we know, this is the first amelogenin splicing transcript in which the entire exon 6 sequence is spliced out. Structure comparison of the putative P.cinereus-50 with the LRAP splicing form revealed a similar secondary structure in which two potential helix regions existed: one on the C-terminus, the other on the N-terminus, implying the putative P.cinereus-50 is likely to function in a similar way as LRAP. Although different approaches have been used to explore the effect of exon 2b on the secondary and tertiary structure of putative P.cinereus-195, our results did not show a significant effect of exon 2b on P.cinereus-195 secondary structure; however HHpred prediction identified a few homologs/domains that are different from those of P.cinereus-182, indicating that exon 2b has an effect on the tertiary structure of putative P.cinereus-195, thus likely its functions. 
The novel amelogenin transcripts and the unique exon 2b detected in the salamander will contribute to the understanding of tooth enamel evolution by revealing the conservation and divergence of significant exons of the amelogenin gene throughout vertebrate evolution. Discovery of additional amelogenin sequences will result in enhanced understanding of the origin and evolution of vertebrate teeth. Hepatocellular carcinoma is a common malignancy worldwide, but especially in China and other East Asian countries. Although survival of patients with HCC has improved due to advances in surgical techniques and perioperative management, long-term survival after surgical resection remains low due to the high rate of recurrence and metastasis. Although some clinicopathological features of HCC, such as tumor multifocality, vascular invasion and tumor size, are useful to evaluate the prognosis of HCC patients.