Pseudogene - Possible Resurrection of A Pseudogene

Possible Resurrection of A Pseudogene

The duplicated pseudogenic DNA can be resurrected to a functional protein in certain cases as a rare or occasional evolutionary event and may enable sampling of more sequence space for a protein or protein family. The pseudogenes or parts of pseudogenes may be re-utilized once they have been drifted randomly without being subjected to selection pressure for certain period of evolution. Koch, for the first time, postulated an idea about such "untranslatable intermediates" in the evolution of protein. Occasionally, this mechanism may yield a shorter evolutionary route to another desirable or favorable evolutionary energetic minimum although one would generally expect it to produce unviable or unfavorable leaps in sequence space. A longer time will be available to search sequence space by the pseudogene resurrection, but it is believed that it rarely brings in to existence the proteins with new functions. The repair of lesions could be achieved by the reinsertion of a deleted segment, the removal (in frame) of an inserted segment, or other events that are likely to be improbable like gene conversion. Conversion of a pseudogene with a functional gene as a donor might improve the probability of pseudogene reactivation provided enough of the pseudogene sequence must be preserved throughout the course to maintain the benefits of expanding the sequence space explored after duplication.

There are several examples that can be used to support such resurrection. The Bovine Seminal Ribonuclease, which had lain dormant for about 20 million years as a pseudogene, appears to have been resurrected into a functional gene. It is believed that the event called gene conversion may be the cause of such resurrection. The large group of pseudogenes for olfactory receptors (ORs) in metazoans, where 60% of the ORs in the human genome are pseudogenic, are resurrectable may be due to gene conversion events. In a cluster of ORs which contains 16 OR genes and 6 OR pseudogenes on chromosome 17, is appeared to be subjected to many number (20) of gene conversion events over the course of primate evolution. These gene conversion events in OR gene clusters may aid to bring diversity in binding capability at the odorant binding site. Finally, the resurrection of a pseudogene also led to the diversity of immunoglobulin heavy chain variable-region gene segments in the chicken which appears to be brought by the gene conversion event of a single functional gene with more than 80 pseudogenic gene segments.

The era of molecular paleontology is just beginning. The surface of the pseudogene strata is barely studied, but if scientists conduct more research, they may be able to identify many more pseudogenes. The data mining process of large scale identification of pseudogenes is dynamic. The ancient and decayed pseudogenes are escaping from detection, although the recently generated pseudogenes are readily identified by the current techniques which are heavily based on the sequence comparison to well characterized genes. Characterization of pseudogenes will likely be improved as well since the sequence and annotation of the human genome itself are refined and updated. Modern clues may point to some possibilities of pseudogene resurrection- a dead gene become a living one and making a functional protein exist with the evidence.

In addition to the seminal ribonuclease enzyme, the other incidents like slight differences in the pseudogene complements of individual people have also been found. For instance, in most people the olfactory receptor pseudogenes are dead but in few they are intact and functional genes. Some studies also suggested that however that in yeast, certain cell surface protein pseudogenes are resurrected due to stressful new environment challenged the organism. The two processed pseudogenes called the rat RC9 cytochrome c pseudogene and the mouse L 32 ribosomal protein pseudogene rpL32-4A are implied to be potentially functional. From the recent experiments, they found that in a bacterial genome a considerable segment of the intergenic regions are actively transcribed. From the ENCODE project, scientists have found about 20% of the TARS were produced from previously unidentified ‘potential unborn genes’ which says that there are functional pseudogenes inside these regions. To make sure that do the pseudogenes are transcribed in to RNA and to ascertain their functionality the studies on mouse oocyte are very useful where the small interfering RNAs (siRNAs) derived from pseudogene are found to be functional in regulating gene expression. Some pseudogenes are dead yet with some functions strengthen the fact that they are not ‘junk DNA". With the embedded picture of genome annotation the real evolutionary history of pseudogenes will be revealed out in the near future of research.