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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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PCR-RFLP analysis of make-up of the ITS region in the hybrid with restriction enzyme Hae III at early development. Panel A exhibits PCR-RFLP analysis at the 2-cell stage (about 1 hour after fertilization) with samples from maternal parent C. farreri (Maternal), paternal parent A. irradians (Paternal), and samples from five random selected hybrid individuals (1 through 5), and molecular weight standard (MW). Panel B exhibits PCR-RFLP analysis at the trochophore stage (about 20 hour after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel C exhibits PCR-RFLP analysis at the early umbo larva stage (about 4 days after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel D exhibits PCR-RFLP analysis at the middle umbo larva stage (about 10 days after fertilization) with samples from six random selected hybrid individuals (1 through 6), and molecular weight standard (MW). Panel E exhibits PCR-RFLP analysis at the late umbo larva stage (about 14 days after fertilization) with samples from maternal parent (Maternal), paternal parent (Paternal), and samples from four random selected hybrid individuals (1 through 4) and a sample from mixed samples of multiple individuals (5*), and molecular weight standard (MW). Molecular weight standards were 100 bp DNA ladder.
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Figure 1: PCR-RFLP analysis of make-up of the ITS region in the hybrid with restriction enzyme Hae III at early development. Panel A exhibits PCR-RFLP analysis at the 2-cell stage (about 1 hour after fertilization) with samples from maternal parent C. farreri (Maternal), paternal parent A. irradians (Paternal), and samples from five random selected hybrid individuals (1 through 5), and molecular weight standard (MW). Panel B exhibits PCR-RFLP analysis at the trochophore stage (about 20 hour after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel C exhibits PCR-RFLP analysis at the early umbo larva stage (about 4 days after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel D exhibits PCR-RFLP analysis at the middle umbo larva stage (about 10 days after fertilization) with samples from six random selected hybrid individuals (1 through 6), and molecular weight standard (MW). Panel E exhibits PCR-RFLP analysis at the late umbo larva stage (about 14 days after fertilization) with samples from maternal parent (Maternal), paternal parent (Paternal), and samples from four random selected hybrid individuals (1 through 4) and a sample from mixed samples of multiple individuals (5*), and molecular weight standard (MW). Molecular weight standards were 100 bp DNA ladder.

Mentions: PCR-RFLP analysis of ITS sequences provides a rapid diagnostic tool for species identification of C. farreri and A. Irradians [14]. In the hybrid generated by crossing C. farreri female with A. irradians male, the restriction patterns using restriction enzyme Hae III differentiate the maternal ITS from paternal ITS. The C. farreri maternal ITS should produce three PCR-RFLP fragments of 526 bp, 117 bp and 98 bp (741 bp in total), while the paternal A. irradians ITS should produce three PCR-RFLP fragments of 343 bp, 244 bp and 182 bp (769 bp in total). In order to assess dynamic variation of ITS constitution in the hybrid, PCR-RFLP was conducted at various early developmental stages. As shown in Figure 1, the proportion of the maternal and paternal alleles varied greatly with development. At the 2-cell stage, both the maternal and the paternal alleles were equally present (Figure 1A); at the trochophore stage (approximately 20 hours after fertilization), most larvae harbored alleles from both parents, while some (less than 5%) harbored only the maternal ITS (Figure 1B); at the early stage of umbo larvae (approximately 4 days after fertilization), most larvae still harbored alleles from both parents, but signal intensities of the restriction fragments representing the paternal A. irradians became significantly lower in some larvae, and the proportion of the larvae that possessed only the maternal ITS allele was increased (Figure 1C); at the middle stage of umbo larvae (approximately 10 days after fertilization), most larvae possessed only the maternal ITS allele, and even in those that still possessed the parental ITS allele (less than 30%), signal intensities of the restriction fragments representing the paternal allele of A. irradians were significantly lower (Figure 1D). At the late stage of umbo larvae (approximately 14 days after fertilization), the vast majority of larvae harbor only the maternal ITS allele as paternal allele was not evident when samples were analyzed individually (lanes 1 through 4, Figure 1E), although the restriction fragments from the paternal A. irradians allele could still be detected when multiple larvae were simultaneously included in PCR-RFLP analysis (lane 5, Figure 1E). In general, the proportion of the paternal ITS allele decreased gradually in the hybrid during the development. At the 14th day after fertilization, the paternal allele representation became extremely low (Figure 1).


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)

PCR-RFLP analysis of make-up of the ITS region in the hybrid with restriction enzyme Hae III at early development. Panel A exhibits PCR-RFLP analysis at the 2-cell stage (about 1 hour after fertilization) with samples from maternal parent C. farreri (Maternal), paternal parent A. irradians (Paternal), and samples from five random selected hybrid individuals (1 through 5), and molecular weight standard (MW). Panel B exhibits PCR-RFLP analysis at the trochophore stage (about 20 hour after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel C exhibits PCR-RFLP analysis at the early umbo larva stage (about 4 days after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel D exhibits PCR-RFLP analysis at the middle umbo larva stage (about 10 days after fertilization) with samples from six random selected hybrid individuals (1 through 6), and molecular weight standard (MW). Panel E exhibits PCR-RFLP analysis at the late umbo larva stage (about 14 days after fertilization) with samples from maternal parent (Maternal), paternal parent (Paternal), and samples from four random selected hybrid individuals (1 through 4) and a sample from mixed samples of multiple individuals (5*), and molecular weight standard (MW). Molecular weight standards were 100 bp DNA ladder.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: PCR-RFLP analysis of make-up of the ITS region in the hybrid with restriction enzyme Hae III at early development. Panel A exhibits PCR-RFLP analysis at the 2-cell stage (about 1 hour after fertilization) with samples from maternal parent C. farreri (Maternal), paternal parent A. irradians (Paternal), and samples from five random selected hybrid individuals (1 through 5), and molecular weight standard (MW). Panel B exhibits PCR-RFLP analysis at the trochophore stage (about 20 hour after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel C exhibits PCR-RFLP analysis at the early umbo larva stage (about 4 days after fertilization) with samples from six random selected hybrid samples (1 through 6), and molecular weight standard (MW). Panel D exhibits PCR-RFLP analysis at the middle umbo larva stage (about 10 days after fertilization) with samples from six random selected hybrid individuals (1 through 6), and molecular weight standard (MW). Panel E exhibits PCR-RFLP analysis at the late umbo larva stage (about 14 days after fertilization) with samples from maternal parent (Maternal), paternal parent (Paternal), and samples from four random selected hybrid individuals (1 through 4) and a sample from mixed samples of multiple individuals (5*), and molecular weight standard (MW). Molecular weight standards were 100 bp DNA ladder.
Mentions: PCR-RFLP analysis of ITS sequences provides a rapid diagnostic tool for species identification of C. farreri and A. Irradians [14]. In the hybrid generated by crossing C. farreri female with A. irradians male, the restriction patterns using restriction enzyme Hae III differentiate the maternal ITS from paternal ITS. The C. farreri maternal ITS should produce three PCR-RFLP fragments of 526 bp, 117 bp and 98 bp (741 bp in total), while the paternal A. irradians ITS should produce three PCR-RFLP fragments of 343 bp, 244 bp and 182 bp (769 bp in total). In order to assess dynamic variation of ITS constitution in the hybrid, PCR-RFLP was conducted at various early developmental stages. As shown in Figure 1, the proportion of the maternal and paternal alleles varied greatly with development. At the 2-cell stage, both the maternal and the paternal alleles were equally present (Figure 1A); at the trochophore stage (approximately 20 hours after fertilization), most larvae harbored alleles from both parents, while some (less than 5%) harbored only the maternal ITS (Figure 1B); at the early stage of umbo larvae (approximately 4 days after fertilization), most larvae still harbored alleles from both parents, but signal intensities of the restriction fragments representing the paternal A. irradians became significantly lower in some larvae, and the proportion of the larvae that possessed only the maternal ITS allele was increased (Figure 1C); at the middle stage of umbo larvae (approximately 10 days after fertilization), most larvae possessed only the maternal ITS allele, and even in those that still possessed the parental ITS allele (less than 30%), signal intensities of the restriction fragments representing the paternal allele of A. irradians were significantly lower (Figure 1D). At the late stage of umbo larvae (approximately 14 days after fertilization), the vast majority of larvae harbor only the maternal ITS allele as paternal allele was not evident when samples were analyzed individually (lanes 1 through 4, Figure 1E), although the restriction fragments from the paternal A. irradians allele could still be detected when multiple larvae were simultaneously included in PCR-RFLP analysis (lane 5, Figure 1E). In general, the proportion of the paternal ITS allele decreased gradually in the hybrid during the development. At the 14th day after fertilization, the paternal allele representation became extremely low (Figure 1).

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