Positive Selection and Functional Divergence at Meiosis Genes That Mediate Crossing Over Across the Drosophila Phylogeny

Meiotic crossing over ensures proper segregation of homologous chromosomes and generates genotypic diversity. Despite these functions, little is known about the genetic factors and population genetic forces involved in the evolution of recombination rate differences among species. The dicistronic meiosis gene, mei-217/mei-218, mediates most of the species differences in crossover rate and patterning during female meiosis between the closely related fruitfly species, Drosophila melanogaster and D. mauritiana. The MEI-218 protein is one of several meiosis-specific mini-chromosome maintenance (mei-MCM) proteins that form a multi-protein complex essential to crossover formation, whereas the BLM helicase acts as an anti-crossover protein. Here we study the molecular evolution of five genes— mei-218, the other three known members of the mei-MCM complex, and Blm— over the phylogenies of three Drosophila species groups— melanogaster, obscura, and virilis. We then use transgenic assays in D. melanogaster to test if molecular evolution at mei-218 has functional consequences for crossing over using alleles from the distantly related species D. pseudoobscura and D. virilis. Our molecular evolutionary analyses reveal recurrent positive selection at two mei-MCM genes. Our transgenic assays show that sequence divergence among mei-218 alleles from D. melanogaster, D. pseudoobscura, and D. virilis has functional consequences for crossing over. In a D. melanogaster genetic background, the D. pseudoobscura mei-218 allele nearly rescues wildtype crossover rates but alters crossover patterning, whereas the D. virilis mei-218 allele conversely rescues wildtype crossover patterning but not crossover rates. These experiments demonstrate functional divergence at mei-218 and suggest that crossover rate and patterning are separable functions.

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Origin and Evolution of a New Gene Descended From alcohol dehydrogenase in Drosophila

Genetics ◽

10.1093/genetics/145.2.375 ◽

1997 ◽

Vol 145 (2) ◽

pp. 375-382

Author(s):

David J Begun

Keyword(s):

Molecular Evolution ◽

Alcohol Dehydrogenase ◽

Functional Divergence ◽

Sequence Divergence ◽

Origin And Evolution ◽

Repleta Group ◽

Adh Genes ◽

New Gene ◽

Terminal Amino ◽

Adh Activity

Drosophila alcohol dehydrogenase (Adh) is highly conserved in size, organization, and amino acid sequence. Adh-ψ was hypothesized to be a pseudogene derived from an Adh duplication in the repleta group of Drosophila; however, several results from molecular analyses of this gene conflict with currently held notions of molecular evolution. Perhaps the most difficult observations to reconcile with the pseudogene hypothesis are that the hypothetical replacement sites of Adh-ψ evolve only slightly more quickly than replacement sites of closely related, functional Adh genes, and that the replacement sites of the pseudogenes evolve considerably more slowly than neighboring silent sites. The data have been presented as a paradox that challenges our understanding of the mechanisms underlying DNA sequence divergence. Here I show that Adh-ψ is actually a new, functional gene recently descended from an Adh duplication. This descendant recruited ∼60 new N-terminal amino acids, is considerably more basic than ADH, and is evolving at a faster rate than Adh. Furthermore, though the descendant is clearly functional, as inferred from molecular evolution and population genetic data, it retains no obvious ADH activity. This probably reflects functional divergence from its Adh ancestor.

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Molecular Evolution and Diversification of Proteins Involved in miRNA Maturation Pathway

Plants ◽

10.3390/plants9030299 ◽

2020 ◽

Vol 9 (3) ◽

pp. 299

Author(s):

Taraka Ramji Moturu ◽

Sansrity Sinha ◽

Hymavathi Salava ◽

Sravankumar Thula ◽

Tomasz Nodzyński ◽

...

Keyword(s):

Molecular Evolution ◽

Rna Polymerase Ii ◽

Functional Divergence ◽

Functional Characterization ◽

Sequence Divergence ◽

Mirna Biogenesis ◽

Specific Sequence ◽

Mirna Genes ◽

Expression Of Genes ◽

Function Relationship

Small RNAs (smRNA, 19–25 nucleotides long), which are transcribed by RNA polymerase II, regulate the expression of genes involved in a multitude of processes in eukaryotes. miRNA biogenesis and the proteins involved in the biogenesis pathway differ across plant and animal lineages. The major proteins constituting the biogenesis pathway, namely, the Dicers (DCL/DCR) and Argonautes (AGOs), have been extensively studied. However, the accessory proteins (DAWDLE (DDL), SERRATE (SE), and TOUGH (TGH)) of the pathway that differs across the two lineages remain largely uncharacterized. We present the first detailed report on the molecular evolution and divergence of these proteins across eukaryotes. Although DDL is present in eukaryotes and prokaryotes, SE and TGH appear to be specific to eukaryotes. The addition/deletion of specific domains and/or domain-specific sequence divergence in the three proteins points to the observed functional divergence of these proteins across the two lineages, which correlates with the differences in miRNA length across the two lineages. Our data enhance the current understanding of the structure–function relationship of these proteins and reveals previous unexplored crucial residues in the three proteins that can be used as a basis for further functional characterization. The data presented here on the number of miRNAs in crown eukaryotic lineages are consistent with the notion of the expansion of the number of miRNA-coding genes in animal and plant lineages correlating with organismal complexity. Whether this difference in functionally correlates with the diversification (or presence/absence) of the three proteins studied here or the miRNA signaling in the plant and animal lineages is unclear. Based on our results of the three proteins studied here and previously available data concerning the evolution of miRNA genes in the plant and animal lineages, we believe that miRNAs probably evolved once in the ancestor to crown eukaryotes and have diversified independently in the eukaryotes.

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Molecular Evolution of Duplicated Amylase Gene Regions in Drosophila melanogaster: Evidence of Positive Selection in the Coding Regions and Selective Constraints in the cis-Regulatory Regions

Genetics ◽

10.1093/genetics/157.2.667 ◽

2001 ◽

Vol 157 (2) ◽

pp. 667-677

Author(s):

Hitoshi Araki ◽

Nobuyuki Inomata ◽

Tsuneyuki Yamazaki

Keyword(s):

Drosophila Melanogaster ◽

Molecular Evolution ◽

Positive Selection ◽

Natural Populations ◽

Sliding Window ◽

Selective Constraint ◽

Proximal Region ◽

Coding Regions ◽

Asian Populations ◽

Flanking Region

Abstract In this study, we randomly sampled Drosophila melanogaster from Japanese and Kenyan natural populations. We sequenced duplicated (proximal and distal) Amy gene regions to test whether the patterns of polymorphism were consistent with neutral molecular evolution. Fst between the two geographically distant populations, estimated from Amy gene regions, was 0.084, smaller than reported values for other loci, comparing African and Asian populations. Furthermore, little genetic differentiation was found at a microsatellite locus (DROYANETSB) in these samples (Gst′=−0.018). The results of several tests (Tajima's, Fu and Li's, and Wall's tests) were not significantly different from neutrality. However, a significantly higher level of fixed replacement substitutions was detected by a modified McDonald and Kreitman test for both populations. This indicates that positive selection occurred during or immediately after the speciation of D. melanogaster. Sliding-window analysis showed that the proximal region 1, a part of the proximal 5′ flanking region, was conserved between D. melanogaster and its sibling species, D. simulans. An HKA test was significant when the proximal region 1 was compared with the 5′ flanking region of Alcohol dehydrogenase (Adh), indicating a severe selective constraint on the Amy proximal region 1. These results suggest that natural selection has played an important role in the molecular evolution of Amy gene regions in D. melanogaster.

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Analysis of Sequence Divergence in Mammalian ABCGs Predicts a Structural Network of Residues That Underlies Functional Divergence

International Journal of Molecular Sciences ◽

10.3390/ijms22063012 ◽

2021 ◽

Vol 22 (6) ◽

pp. 3012

Author(s):

James I. Mitchell-White ◽

Thomas Stockner ◽

Nicholas Holliday ◽

Stephen J. Briddon ◽

Ian D. Kerr

Keyword(s):

Substrate Specificity ◽

Functional Divergence ◽

3D Structure ◽

Sequence Divergence ◽

Conformational Flexibility ◽

Substrate Selectivity ◽

Multiple Sequence ◽

Atp Binding Cassette Transporters ◽

Structural Network ◽

Wide Substrate Specificity

The five members of the mammalian G subfamily of ATP-binding cassette transporters differ greatly in their substrate specificity. Four members of the subfamily are important in lipid transport and the wide substrate specificity of one of the members, ABCG2, is of significance due to its role in multidrug resistance. To explore the origin of substrate selectivity in members 1, 2, 4, 5 and 8 of this subfamily, we have analysed the differences in conservation between members in a multiple sequence alignment of ABCG sequences from mammals. Mapping sets of residues with similar patterns of conservation onto the resolved 3D structure of ABCG2 reveals possible explanations for differences in function, via a connected network of residues from the cytoplasmic to transmembrane domains. In ABCG2, this network of residues may confer extra conformational flexibility, enabling it to transport a wider array of substrates.

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