| Functional |
"First, in the skin of terrestrial mammals, KLK8 activates antimicrobial proteolytic cascades in sweat (Eissa et al. 2011). As neither cetaceans nor manatees have sweat glands (Berta et al. 2015; Mouton and Botha 2012; Rodrigues et al. 2014), in contrast to the semi-aquatic pinnipeds and terrestrial mammals that have an intact KLK8 gene, the antimicrobial of functions of KLK8 are likely no longer useful for aquatic mammals. Furthermore, the epidermis of KLK8 knockout mouse
exhibits delayed recovery from the UVB-induced inflammation (Kirihara et al. 2003). UVB-induced inflammation might be less important for fully-aquatic mammals that live in an environment where
UVB light penetration substantially decreases after a few meters of depths (Tedetti and Sempere
2006).Finally, KLK8 also plays a role in keratinocyte proliferation and desquamation (Kishibe et al. 2007). In dolphins, it is known that the desquamation rate of the outer most epidermal cell layers is 8.5 times faster than in humans, which is likely an adaptation that maintains a smooth surface and limits microbe colonization in the aquatic environment (Hicks et al. 1985), and may have further
contributed to KLK8 loss in dolphin." |
10.1093/gbe/evx239 |
| Mutation Description |
"Our inspection revealed 12 mutations that would inactivate KLK8 in the bottlenose dolphin, killer whale, minke whale, and the manatee (fig. 1). These mutations include frameshifting deletions, mutations that disrupt the conserved splice site dinucleotides, mutations that terminate translation by creating in-frame stop codons, and the entire deletion of the coding exon 5." |
10.1093/gbe/evx239 |
| Timing of Loss |
"Our inspection of the genome alignments also revealed that the exon 5 deletion in dolphin and killer whale has the same breakpoint (fig. 2B). This suggests that the exon 5 deletion occurred in the common ancestor of both species, and rules out the possibility of an assembly error in two inde
pendently assembled genomes. In addition, the presence of a shared in-frame stop codon in the third KLK8 exon further corroborates that KLK8 was lost in the common ancestor of dolphin and killer whale." |
10.1093/gbe/evx239 |
| Other |
"It should be noted that whereas kallikreins comprise a gene family, the protein and nucleotide sequence of the different members are sufficiently diverged from each other. In particular, KLK8 has at
most 51% nucleotide identity to other KLK genes (Prassas et al. 2015)." |
10.1093/gbe/evx239 |