Where the telomere came from?
<Where the telomere came from?>
Yoonyoung Lee
Introduction
Telomere is a certain DNA portion which has repeated sequence and locates in end point of chromosome. It protects DNA during DNA replication process. Then, how this important portion evolved? I will show some hypothesis and suggest experimental approach. I may show two hypothesis. One is about centromere and other is about transposable elements.
Body
1. Telomere and centromere
Centromere is a certain DNA portion which regulate distribution of sister chromatids during mitosis and meiosis to opposite site of cell. [1] I think centromere and telomere are related to each other and maybe telomere came from centromere. There are three evidences for this hypothesis.
First evidence is that both centromere and telomere are has repeated sequence. For example, human repetitive telomere sequence is ‘TTAGGG’ with the complementary DNA strand sequence is ‘AATCCC’. [2] Similar to these sequences, repetitive sequence of human centromere is ‘GGAAT’. [3]
Second evidence is structure type of centromere. [1] Centromere has four types of structure; metacentric, submetacentric, acrocentric and telocentric. Metacentric is indicates that centromere is locate in the middle portion of chromosome (Meta = Middle). Submetacentric means centromere is not on the middle side, rather than it is on the portion which is more near to one end of chromosome. Acrocentric is that centromere is on almost end portion of one side of chromosome. Last, telocentric is that centromere is on the end portion of chromosome. I think these telocentric can be the original form of telomere.
2. Transposable elements
Transposable elements are the certain DNA portions that move from one site of DNA to other sites. There are two types of transposable elements: Retrotransposons and DNA transposons. Retrotransposons transport via reverse transcription of an RNA intermediate. DNA transposons move directly to other position without using RNA intermediate. [4]
Some retrotransposons and DNA transposons have certain important portion for transposition, called ‘long terminal repeat (LTR - TAATC)’ and ‘inverted repeats (IR - GGTGTACAAGT)’. These inverted repeat sequence position can be replicated during transposition process. So, It can may related to telomere in the case of multiple repeated sequence.
Also, transposable elements maintain the length of Drosophila chromosomes. In every cycle of cell division, transposable elements move around to other position and prevent shortening of chromosome. [4]
Reference
[1] http://study.com/academy/lesson/centromere-definition-structure-quiz.html
[2] https://en.wikipedia.org/wiki/Centromere
[3] http://www.pnas.org/content/89/5/1695.full.pdf
(Highly conserved repetitive sequences are present at human centromeres, Biochemistry, Vol. 89, p. 1695-1699, March 1992)
[4] Genetics from gene to genomes, 5th edition, p. 427 - 430 Leland H. Hartwell.
