Conclusions
.
After comparing the genome of Danionella dracula with that of Danio rerio using bioinformatics tools, we have come up with the following results:
A total of 42 proteins have been characterised in Danionella dracula: DIO1, DIO2, DIO3a, eEFsec, GPX1a, GPx1b, Gpx2, GPx3a, GPx3b, GPx4a, GPx4b, GPx8, MsrA,Msra_2, MsrB1a, MsrB1, MsrB1b,MsrB1b_2, MSRB2, MSRB3, PSTK, SECp43, SecS, Sel15, SELENOE, SELENOI, SELENOJ1, SELENOK, SELENON, SELENOO1, SELENOP, SELENOS, SELENOT1b, SELENOU1a, SELENOU2, SELENOU3, SELENOW, SEPHS2, SEPHS, TXNRD2, and TXNRD3 . They can be classified as following:
Selenoproteins: DIO1, DIO2, DIO3a, GPx1a, GPx1b, Gpx2, GPx3a, GPx3b,GPx4a, GPx4b, Sel15, SELENOE, SELENOI, SELENOJ1, SELENON, SELENOO1, SELENOP, SELENOS, SELENOT1b, SELENOU1a, SELENOW, SEPHS2, TXNRD3, MrsB1b, MrsB1B_2
Cysteine-containing homologues: GPx8, MsrA,MsrA_2, MsrB2, MsrB3, SELENOK, SELENOU2, SELENOU3, SEPHS.
Selenoprotein machinery: eEFSec, PSTK, Secp43, Secs.
To put it shortly, we found several proteins that are found in Danio rerio but not in Danionella dracula, and the number of proteins duplications we noticed was relatively low compared to what we would expect from a fish from the cypriniformes class, since, as we said in the introduction, they underwent a whole genome duplication millions of years ago. We also found several proteins that were present but in a truncated form or showing a poor alignment.
One possible explanation for these results is the fact that Danionella dracula is a characteristically underdeveloped fish, and even though it is a close relative to Danio Rerio, it misses several structures, specially bones, apart from having a particularly simple layout, with a small size, no scales or very developed limbs. In addition, its transparency could be an indicator of structural simplicity. We speculate that these morphological qualities could be reflected at the proteic level by a distinct lack of proteins, which would be consistent with ours observed results.
A critique to this theory would be that selenoproteins, including those that were not identified in Danionella dracula, mainly have enzymatic functions and very few of them are structural, so a simple structure would not necessarily mean a smaller selenoproteome.
All in all, the results of this project show us that Danionella dracula is an outlier in the world of fishes, and very few aspects of its nature are known, with only a few papers published on the subject that mainly address morphological and developmental issues. This convinces us that further research is needed on this fish, not only a more in-depth characterization of its selenoproteome but a deeper look into its genome and proteome.
