Drosophila genes that affect meiosis duration are among the meiosis related genes that are more often found duplicated

Abstract

Using a phylogenetic approach, the examination of 33 meiosis/meiosis-related genes in 12 Drosophila species, revealed nine independent gene duplications, involving the genes cav, mre11, meiS332, polo and mtrm. Evidence is provided that at least eight out of the nine gene duplicates are functional. Therefore, the rate at which Drosophila meiosis/meiosis-related genes are duplicated and retained is estimated to be 0.0012 per gene per million years, a value that is similar to the average for all Drosophila genes. It should be noted that by using a phylogenetic approach the confounding effect of concerted evolution, that is known to lead to overestimation of the duplication and retention rate, is avoided. This is an important issue, since even in our moderate size sample, evidence for long-term concerted evolution (lasting for more than 30 million years) was found for the meiS332 gene pair in species of the Drosophila subgenus. Most striking, in contrast to theoretical expectations, is the finding that genes that encode proteins that must follow a close stoichiometric balance, such as polo, mtrm and meiS332 have been found duplicated. The duplicated genes may be examples of gene neofunctionalization. It is speculated that meiosis duration may be a trait that is under selection in Drosophila and that it has different optimal values in different species.

Figure 1. Jukes-Cantor corrected per site rate of non-synonymous substitutions between D. melanogaster and D. virilis for 33 meiosis genes.

For CG7676 gene this value has been extrapolated under the assumption of a molecular clock and that D. melanogaster and D. virilis have been diverging for about 40 million years while D. melanogaster and D. yakuba have been diverging for about 10 million years.

Figure 2. Relationship of the Drosophila species studied.

Adapted from http://flybase.org. Numbers are estimated divergence times in million years.

Figure 3. Bayesian phylogram of Drosophila cav-like genes.

Numbers are posterior credibility values.

Figure 4. Expression patterns of genes found to be duplicated.

G – genomic DNA; F – female gonads; M – male gonads. The cDNA of duplicated genes were sequenced in order to assure amplification specificity. In males, for genes D. virilis cav-dup, D. persimilis cav-dup, D. mojavensis mre-11-dup and D. persimilis polo-dup1 a band with the size expected for an amplification from genomic DNA is observed. In order to rule out the possibility of contamination with genomic DNA, the PCR reactions were performed three times independently starting from different cDNA aliquots and identical results were obtained. The observation that when using the same aliquot, the duplicated gene shows two bands but the genes D. virilis cav, D. persimilis cav, D. mojavensis mre-11 and D. persimilis polo show only one band of the expected size also shows that there is no contamination with genomic DNA.

Figure 5. Bayesian phylogram of Drosophila mre11-like genes.

Numbers are posterior credibility values.

Figure 6. Bayesian phylogram of Drosophila polo-like genes.

Numbers are posterior credibility values.

Figure 7. Bayesian phylogram of Drosophila mtrm-like genes.

Numbers are posterior credibility values.

Figure 8. Bayesian phylogram of Drosophila meiS332-like genes.

Numbers are posterior credibility values.