A completeness-independent method for pre-selection of closely related genomes for species delineation in prokaryotes

BACKGROUND

Whole-genome approaches are widely preferred for species delineation in prokaryotes. However, these methods require pairwise alignments and calculations at the whole-genome level and thus are computationally intensive. To address this problem, a strategy consisting of sieving (pre-selecting closely related genomes) followed by alignment and calculation has been proposed.

RESULTS

Here, we initially test a published approach called "genome-wide tetranucleotide frequency correlation coefficient" (TETRA), which is specially tailored for sieving. Our results show that sieving by TETRA requires > 40% completeness for both genomes of a pair to yield > 95% sensitivity, indicating that TETRA is completeness-dependent. Accordingly, we develop a novel algorithm called "fragment tetranucleotide frequency correlation coefficient" (FRAGTE), which uses fragments rather than whole genomes for sieving. Our results show that FRAGTE achieves ~ 100% sensitivity and high specificity on simulated genomes, real genomes and metagenome-assembled genomes, demonstrating that FRAGTE is completeness-independent. Additionally, FRAGTE sieved a reduced number of total genomes for subsequent alignment and calculation to greatly improve computational efficiency for the process after sieving. Aside from this computational improvement, FRAGTE also reduces the computational cost for the sieving process. Consequently, FRAGTE extremely improves run efficiency for both the processes of sieving and after sieving (subsequent alignment and calculation) to together accelerate genome-wide species delineation.

CONCLUSIONS

FRAGTE is a completeness-independent algorithm for sieving. Due to its high sensitivity, high specificity, highly reduced number of sieved genomes and highly improved runtime, FRAGTE will be helpful for whole-genome approaches to facilitate taxonomic studies in prokaryotes.

Genome-scale portrait and evolutionary significance of human-specific core promoter tri- and tetranucleotide short tandem repeats

BACKGROUND

While there is an ongoing trend to identify single nucleotide substitutions (SNSs) that are linked to inter/intra-species differences and disease phenotypes, short tandem repeats (STRs)/microsatellites may be of equal (if not more) importance in the above processes. Genes that contain STRs in their promoters have higher expression divergence compared to genes with fixed or no STRs in the gene promoters. In line with the above, recent reports indicate a role of repetitive sequences in the rise of young transcription start sites (TSSs) in human evolution.

RESULTS

Following a comparative genomics study of all human protein-coding genes annotated in the GeneCards database, here we provide a genome-scale portrait of human-specific short- and medium-size (≥ 3-repeats) tri- and tetranucleotide STRs and STR motifs in the critical core promoter region between - 120 and + 1 to the TSS and evidence of skewing of this compartment in reference to the STRs that are not human-specific (Levene's test p < 0.001). Twenty-five percent and 26% enrichment of human-specific transcripts was detected in the tri and tetra human-specific compartments (mid-p < 0.00002 and mid-p < 0.002, respectively).

CONCLUSION

Our findings provide the first evidence of genome-scale skewing of STRs at a specific region of the human genome and a link between a number of these STRs and TSS selection/transcript specificity. The STRs and genes listed here may have a role in the evolution and development of characteristics and phenotypes that are unique to the human species.

Genome-wide mining of perfect microsatellites and tetranucleotide orthologous microsatellites estimates in six primate species

Advancement in genome sequencing and in silico mining tools have provided new opportunities for comparative primate genomics of microsatellites. The SSRs (simple sequence repeats) numbers were not correlated with the genome size (Pearson, r=0.310, p=0.550), and were positively correlated with the total length of SSRs (Pearson, r=0.992, p=0.00). A total of 224,289 tetranucleotide orthologous microsatellites families and 367 single-copy orthologous SSRs loci were found in six primate species by homologous alignment. The inner mutation types of single-copy orthologous SSRs loci included the copy number variance, point mutation, and chromosomal translocation. The accumulated repeat times and average length of tetranucleotide orthologous microsatellites in Rhinopithecus roxellana, Papio anubis and Macaca mulatta were longer than Homo sapiens and Pan troglodytes, which showed the tetranucleotide orthologous SSRs loci had more repeat times and longer average length on the branches with earlier divergence time, one exception may be Microcebus murinus as a primitive monkey with a smallest morphology in Malagasy. Our conclusion indicated that single-copy tetranucleotide orthologous SSRs sequences accumulated individual mutation more slowly through time in H. sapiens and P. troglodytes than in R. roxellanae, P. anubis and M. mulatta. However, such divergence wouldn't arise uniformly in all branches of the primate tree. A comparison of genomic sequence assemblages would offer remarkable insights about comparisons and contrasts, and the evolutionary processes of the microsatellites involved in human and nonhuman primate species.