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Molecular and cellular evidence for biased mitotic gene conversion in hybrid scallop.

Wang S, Zhang L, Hu J, Bao Z, Liu Z - BMC Evol. Biol. (2010)

Bottom Line: However, the exact mechanisms involved in the homogenization have been under debate.Taken together, these molecular and cellular evidences support rapid concerted gene evolution via maternally biased gene conversion.In the course of evolution, many species may have evolved involving some levels of hybridization, intra- or interspecific, the sex-biased sequence homogenization could have led to a greater role of one sex than the other in some species.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Laboratory of Marine Genetics and Breeding of Ministry of Education, Ocean University of China, Qingdao 266003, China.

ABSTRACT

Background: Concerted evolution has been believed to account for homogenization of genes within multigene families. However, the exact mechanisms involved in the homogenization have been under debate. Use of interspecific hybrid system allows detection of greater level of sequence variation, and therefore, provide advantage for tracing the sequence changes. In this work, we have used an interspecific hybrid system of scallop to study the sequence homogenization processes of rRNA genes.

Results: Through the use of a hybrid scallop system (Chlamys farreri female symbol x Argopecten irradians male symbol), here we provide solid molecular and cellular evidence for homogenization of the rDNA sequences into maternal genotypes. The ITS regions of the rDNA of the two scallop species exhibit distinct sequences and thereby restriction fragment length polymorphism (RFLP) patterns, and such a difference was exploited to follow the parental ITS contributions in the F1 hybrid during early development using PCR-RFLP. The representation of the paternal ITS decreased gradually in the hybrid during the development of the hybrid, and almost diminished at the 14th day after fertilization while the representation of the maternal ITS gradually increased. Chromosomal-specific fluorescence in situ hybridization (FISH) analysis in the hybrid revealed the presence of maternal ITS sequences on the paternal ITS-bearing chromosomes, but not vice versa. Sequence analysis of the ITS region in the hybrid not only confirmed the maternally biased conversion, but also allowed the detection of six recombinant variants in the hybrid involving short recombination regions, suggesting that site-specific recombination may be involved in the maternally biased gene conversion.

Conclusion: Taken together, these molecular and cellular evidences support rapid concerted gene evolution via maternally biased gene conversion. As such a process would lead to the expression of only one parental genotype, and have the opportunities to generate recombinant intermediates; this work may also have implications in novel hybrid zone alleles and genetic imprinting, as well as in concerted gene evolution. In the course of evolution, many species may have evolved involving some levels of hybridization, intra- or interspecific, the sex-biased sequence homogenization could have led to a greater role of one sex than the other in some species.

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Schematic presentation of the recombinant variants of the interspecific hybrid showing the origins of the sequences in the ITS region. Open bar, sequences from maternal parent; sketched bar, sequences from paternal parent. Restriction sites for Mbo I are indicated by blue arrows while restriction sites for Hae III are indicated by red arrows.
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Figure 3: Schematic presentation of the recombinant variants of the interspecific hybrid showing the origins of the sequences in the ITS region. Open bar, sequences from maternal parent; sketched bar, sequences from paternal parent. Restriction sites for Mbo I are indicated by blue arrows while restriction sites for Hae III are indicated by red arrows.

Mentions: Sequence analysis revealed that all potential recombinant regions located in the regions of 5.8S and ITS2 (Figure 3, for sequences involved in the recombinant regions, see Figure 2, shown in black background). These potential recombinant regions involved sequences of 9-116 bp, suggesting that recombinant variants may have resulted from site-specific recombination. Biased gene conversion in the hybrid may be drawn by site-specific recombination between the parental ITS sequences. Among these recombinant variants, RV1 and RV2 are mirror complement with exactly the same recombinant region: RV1 had its first part coming from the maternal allele and the second part coming from the paternal allele, while RV2 had the exactly opposite components with the first part coming from the paternal allele, and the second part coming from the maternal allele. This suggested that gene conversion tracts were bidirectional. However, the mirror complement of RV3-RV6 was not found, although no extensive efforts were devoted for the search and they could have also existed.


Molecular and cellular evidence for biased mitotic gene conversion in hybrid scallop.

Wang S, Zhang L, Hu J, Bao Z, Liu Z - BMC Evol. Biol. (2010)

Schematic presentation of the recombinant variants of the interspecific hybrid showing the origins of the sequences in the ITS region. Open bar, sequences from maternal parent; sketched bar, sequences from paternal parent. Restriction sites for Mbo I are indicated by blue arrows while restriction sites for Hae III are indicated by red arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2818637&req=5

Figure 3: Schematic presentation of the recombinant variants of the interspecific hybrid showing the origins of the sequences in the ITS region. Open bar, sequences from maternal parent; sketched bar, sequences from paternal parent. Restriction sites for Mbo I are indicated by blue arrows while restriction sites for Hae III are indicated by red arrows.
Mentions: Sequence analysis revealed that all potential recombinant regions located in the regions of 5.8S and ITS2 (Figure 3, for sequences involved in the recombinant regions, see Figure 2, shown in black background). These potential recombinant regions involved sequences of 9-116 bp, suggesting that recombinant variants may have resulted from site-specific recombination. Biased gene conversion in the hybrid may be drawn by site-specific recombination between the parental ITS sequences. Among these recombinant variants, RV1 and RV2 are mirror complement with exactly the same recombinant region: RV1 had its first part coming from the maternal allele and the second part coming from the paternal allele, while RV2 had the exactly opposite components with the first part coming from the paternal allele, and the second part coming from the maternal allele. This suggested that gene conversion tracts were bidirectional. However, the mirror complement of RV3-RV6 was not found, although no extensive efforts were devoted for the search and they could have also existed.

Bottom Line: However, the exact mechanisms involved in the homogenization have been under debate.Taken together, these molecular and cellular evidences support rapid concerted gene evolution via maternally biased gene conversion.In the course of evolution, many species may have evolved involving some levels of hybridization, intra- or interspecific, the sex-biased sequence homogenization could have led to a greater role of one sex than the other in some species.

View Article: PubMed Central - HTML - PubMed

Affiliation: Key Laboratory of Marine Genetics and Breeding of Ministry of Education, Ocean University of China, Qingdao 266003, China.

ABSTRACT

Background: Concerted evolution has been believed to account for homogenization of genes within multigene families. However, the exact mechanisms involved in the homogenization have been under debate. Use of interspecific hybrid system allows detection of greater level of sequence variation, and therefore, provide advantage for tracing the sequence changes. In this work, we have used an interspecific hybrid system of scallop to study the sequence homogenization processes of rRNA genes.

Results: Through the use of a hybrid scallop system (Chlamys farreri female symbol x Argopecten irradians male symbol), here we provide solid molecular and cellular evidence for homogenization of the rDNA sequences into maternal genotypes. The ITS regions of the rDNA of the two scallop species exhibit distinct sequences and thereby restriction fragment length polymorphism (RFLP) patterns, and such a difference was exploited to follow the parental ITS contributions in the F1 hybrid during early development using PCR-RFLP. The representation of the paternal ITS decreased gradually in the hybrid during the development of the hybrid, and almost diminished at the 14th day after fertilization while the representation of the maternal ITS gradually increased. Chromosomal-specific fluorescence in situ hybridization (FISH) analysis in the hybrid revealed the presence of maternal ITS sequences on the paternal ITS-bearing chromosomes, but not vice versa. Sequence analysis of the ITS region in the hybrid not only confirmed the maternally biased conversion, but also allowed the detection of six recombinant variants in the hybrid involving short recombination regions, suggesting that site-specific recombination may be involved in the maternally biased gene conversion.

Conclusion: Taken together, these molecular and cellular evidences support rapid concerted gene evolution via maternally biased gene conversion. As such a process would lead to the expression of only one parental genotype, and have the opportunities to generate recombinant intermediates; this work may also have implications in novel hybrid zone alleles and genetic imprinting, as well as in concerted gene evolution. In the course of evolution, many species may have evolved involving some levels of hybridization, intra- or interspecific, the sex-biased sequence homogenization could have led to a greater role of one sex than the other in some species.

Show MeSH
Related in: MedlinePlus