Simulating The Evolution Of Introns In Invertebrate MITF Genes Using Random Mutation Base Sequences

Since the discovery of introns,researchers have gradually deepened their research on introns,and more and more intron functions have been discovered.At the same time,the evolution of intron sequences has also been explored by a large number of researchers to explore more functions of introns.The number and size of introns have changed greatly.The evolution mechanism and origin of introns have not yet been determined.There are mainly two theories with opposite positions,namely the"introns-early theory"and"Introns-late theory".Sequence simulation is an effective method to explore the evolution pattern of introns.In this study,we first designed two evolutionary models,namely the Mutation and Deletion(MD)model and the Mutation and Insertion(MI)model.On basis of the above two models,bases are allowed to be inserted in the MD model and deleted in the MI model at different frequencies,and 10 new models are constructed.For example,the MD90/10 model allows 90%base deletion and 10%base deletion The 12 models include 6 deletion-and 6 insertion-biased models.They are MD100,MD90/10,MD80/20,MD70/30,MD60/40,MD55/45,MI100,MI90/10,MI80/20,MI70/30,MI60/40 and MI55/45,all of which were used to explore intron evolution pattern through sequence simulation.The main results of this study are as follows:(1)16 invertebrate species from different phyla were selected as research objects.An intron sequence from the MITF(microphthalmia transcription factor)gene was retrieved for each species.These 16 intron sequences were subject to multiple sequence alignment and construction of phylogenetic tree using ML(maximum likelihood)method.Subsequently,5 attribute values of these 16 invertebrate intron sequences were obtained,namely:length of multiple sequence alignment(L_MSA)=3434 bp,transition and transversion ratio under T_92+G+I replacement model(R)=1.95,overall mean distance(D?)=1.425,standard error of overall mean distance SE_D?=0.119,topological score of ML phylogenetic tree(TS_ML)=32.(2)The L16(4*5)orthogonal table was employed to design 5-factor 4-level tests for the above constructed evolution models.Each test yielded 5 attribute values of the simulation sequences generated by all models.The SPSS software was used to perform statistical analysis on obtained attribute values for drawing the influence curve of each parameter on attribute values of model-generated sequences.The obtained influence curves indicate significance level of each parameter affecting the change of attribute values in each model.(3)By analyzing the influence curves in(2),according to the significance level of each parameter on attribute values of model-generated sequences,parameters were optimized for running the 12 evolution models.After parameter optimization,the attribute values obtained by running the model were subject to independent sample t-test through SPSS software.The results showed that all deletion-biased models with appropriate parameter settings could generate sequences that match the attributes of16 invertebrate introns,and all insertion-biased models with any parameter settings could not generate such sequences.The research results show that the tested invertebrate introns are likely to evolve from a longer ancestral sequence in a deletion-biased pattern,being supportive to"introns-early theory".The models constructed in this study can be used to study evolution patterns of intron sequences from other genes or other species,and is of great significance to further explore the evolution mechanism of introns.