| Abstract | MHC molekule važna su komponenta imunosti. Njihova uloga jest predočavanje fragmenata antigena limfocitima T. Geni koji kodiraju MHC molekule članovi su multigenske porodice. To znači da imaju zajedničko porijeklo i sličnog su DNA slijeda. MHC regija podijeljena je na tri regije, regiju koja kodira MHC molekule skupine I, regiju koja kodira MHC molekule skupine II, a između se nalazi tzv. MHC regija III. Evolucija gena multigenskih porodica, kao što su porodica rRNA gena, histona, imunoglobulinska porodica, porodica MHC molekula, proučavana je već dugi niz godina, pa su se tako javili različiti modeli koji objašnjavaju njihovu evoluciju. Neko se vrijeme smatralo da su geni koji kodiraju MHC molekule evoluirali prema modelu usklađene evolucije. Prema tom modelu uzrok evolucije su spontane mutacije koje se kopiraju i šire po porodici gena nizom uzastopnih nejednolikih krosingovera ili genskom konverzijom. Iako prisutnost tih pojava nije upitna, nema dokaza da su ti događaji dovoljno učestali i važni da su uzrok evolucije čitave porodice. Geni koji kodiraju MHC molekule, čini se, evoluirali su prema modelu nastanka i nestanka gena gdje geni nastaju duplikacijama. Neki se geni 'sačuvaju', a neki se deletiraju ili inaktiviraju, odnosno nestanu. Filogenetičke analize, koje se danas vrše zahvaljujući sve većem broju sekvenciranih sljedova DNA u različitim vrstama, potvrđuju upravo taj obrazac evolucije. Daljnjim sekvenciranjem gena koje kodiraju MHC molekule u što više različitih vrsta može se dobiti potpunija slika evolucije tih gena, ali i gena multigenskih porodica općenito. |
| Abstract (english) | The MHC molecules are important part od immunity. Their function is presenting peptide fragments of antigens to T-cells. Genes coding for the MHC are a part of the multigene family. This means that they are of the same origin and have a similar DNA sequence. MHC region is divided in three regions, one that codes for MHC-I, second that codes for MHC-II and the third one, MHC-III, which is positioned between the first two regions. Evolution of multigene families, like the rRNA genes, histone genes, immunoglobulin gene family, MHC gene family, has been studied for a long time, consequently different models explaining their evolution appeared. For a certain time, it was believed that the evolution of the MHC followed a pattern called concerted evolution. According to this model, the cause of evolution are spontanious mutations arising in a repeat unit and are then spread rapidly throughout the multigene family by unequal crossing-over or gene conversion. Although these occurrences are not questionable, there is no evidence that they are occuring often enough or even important enough to have a role in gene evolution of the entire multigene family. The MHC genes apparently evolved following birth-and-death evolution, where new genes are created by gene duplication. While some genes are maintained for a long time, others are deleted or become nonfunctional by deleterious mutations. Phylogenetic analyses, which are run thanks to an increasing number of identified DNA sequences in different species, confirm this model od evolution. Continued application of phylogenetic analysis produces not only a broader picture of evolution of these genes, but also evolution of multigene families in general. |
