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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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Alignment of parental and 6 recombinant variants' sequences. Cf: C. farreri; Ai: A. irradians; RV1-6: recombinant variants 1-6. Potential recombinant regions in recombinant variants are shown in black background. Asterisks show identical bases; dashes indicate alignment gaps. (ITS1: 34-350 bp; 5.8S: 351-506 bp; ITS2: 507-805 bp). Restriction sites for Mbo I GATC are indicated by a blue box while restriction sites for Hae III GGCC are indicated by a red box.
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Figure 2: Alignment of parental and 6 recombinant variants' sequences. Cf: C. farreri; Ai: A. irradians; RV1-6: recombinant variants 1-6. Potential recombinant regions in recombinant variants are shown in black background. Asterisks show identical bases; dashes indicate alignment gaps. (ITS1: 34-350 bp; 5.8S: 351-506 bp; ITS2: 507-805 bp). Restriction sites for Mbo I GATC are indicated by a blue box while restriction sites for Hae III GGCC are indicated by a red box.

Mentions: Recombinant Variants and Potential Recombinant Regions: When PCR product of multiple larvae at the trochophore stage was cloned, 6 recombinant variants were identified in about 200 randomly selected colonies with PCR-RFLP technique (restriction enzymes Hae III and Mbo I). The frequencies of the six variants are 6% (RV1), 3% (RV2), 1.5% (RV3), 1.5% (RV4), 1% (RV5) and 2% (RV6). These recombinant variants are composed of segmental sequences of C. farreri and A. irradians. These recombinant variants were probably intermediates of the paternal ITS undergoing biased gene conversion. Of the six recombinant variants, RV1, RV3, and RV4 had their first part of the amplified ITS region containing sequences from the maternal parent, and their second part of the amplified ITS region containing sequences from the paternal parent. In contrast, RV2 and RV6 contained their first part of the amplified ITS region containing sequences from the paternal parent, and the second part of the amplified ITS region containing sequences from the maternal parent. For RV5, the two terminal parts of the amplified ITS region containing sequences from the maternal parent, whereas the middle segment of approximately 50 bp containing sequences from the paternal allele (Figure 2).


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)

Alignment of parental and 6 recombinant variants' sequences. Cf: C. farreri; Ai: A. irradians; RV1-6: recombinant variants 1-6. Potential recombinant regions in recombinant variants are shown in black background. Asterisks show identical bases; dashes indicate alignment gaps. (ITS1: 34-350 bp; 5.8S: 351-506 bp; ITS2: 507-805 bp). Restriction sites for Mbo I GATC are indicated by a blue box while restriction sites for Hae III GGCC are indicated by a red box.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Alignment of parental and 6 recombinant variants' sequences. Cf: C. farreri; Ai: A. irradians; RV1-6: recombinant variants 1-6. Potential recombinant regions in recombinant variants are shown in black background. Asterisks show identical bases; dashes indicate alignment gaps. (ITS1: 34-350 bp; 5.8S: 351-506 bp; ITS2: 507-805 bp). Restriction sites for Mbo I GATC are indicated by a blue box while restriction sites for Hae III GGCC are indicated by a red box.
Mentions: Recombinant Variants and Potential Recombinant Regions: When PCR product of multiple larvae at the trochophore stage was cloned, 6 recombinant variants were identified in about 200 randomly selected colonies with PCR-RFLP technique (restriction enzymes Hae III and Mbo I). The frequencies of the six variants are 6% (RV1), 3% (RV2), 1.5% (RV3), 1.5% (RV4), 1% (RV5) and 2% (RV6). These recombinant variants are composed of segmental sequences of C. farreri and A. irradians. These recombinant variants were probably intermediates of the paternal ITS undergoing biased gene conversion. Of the six recombinant variants, RV1, RV3, and RV4 had their first part of the amplified ITS region containing sequences from the maternal parent, and their second part of the amplified ITS region containing sequences from the paternal parent. In contrast, RV2 and RV6 contained their first part of the amplified ITS region containing sequences from the paternal parent, and the second part of the amplified ITS region containing sequences from the maternal parent. For RV5, the two terminal parts of the amplified ITS region containing sequences from the maternal parent, whereas the middle segment of approximately 50 bp containing sequences from the paternal allele (Figure 2).

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