Abstract:
The evolution of the ability of planarians such as Schmidtea mediterranea to
regenerate organs and tissues through neoblasts has interested biologists for a long
time. This study determined if there were genes that had been lost in the
molecular evolution of pluripotency genes from planarians to humans. Utilizing
miRBase and a study by Palakodeti, et al. (2006) as reference, 9 miRNAs were
found to be conserved in humans. Two of these miRNAs have potential targets
related to pluripotency: sme-let-7a and sme-mir-190b. Comparative miRnomics of
the 2 miRNAs with miRNAs found in human embryonic stem cells was
conducted and the results were compared to microarray data from Cao, et al.
(2008). Two planarian miRNAs, let-7a and mir-190b that were conserved in
humans v/ere (bund partially homologous to 8 hESC miRNAs that target
pluripotency genes: hsa-mir-299, hsa-Iet-7a, hsa-mir-21, hsa-mir-374a, hsa-mir-
367, hsa-mir-16-2, hsa-mir-154, and hsa-mir-369. In the same study, only 2
miRNAs, hsa-mir-367 and hsa-let-7a, were reported to have been up-and down-
regulated, respectively. Hsa-inir-367 has KLF4, NANOG, and LIN28 as its
potential targets. Since this niiRNA was found to be up-regulated, its target genes
will most likely be inhibited. Hsa-let-7a was the most down-regulated miRNA,
indicating that its potential targets, MYC and LIN28, and the gene it was partially
homologous with, KLF4, would be expressed. Of the 9 planarian miRNAs
conserved in humans, only one was down-regulated in hESCs. Due to low
homology score (20%), it was suggested that hsa-let-7a could have been modified
and is no longer functionally related to sme-let-7a. Therefore, humans are not
capable of regenerating major body parts because the pluripotency genes that can
give hurnans the ability to regenerate major body parts like the Schmidtea
mediterranea were not expressed.
