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Comparative Analysis of the Shared Sex-Determination Region (SDR) among Salmonid Fishes.

Faber-Hammond JJ, Phillips RB, Brown KH - Genome Biol Evol (2015)

Bottom Line: This variation results from the movement of the sex-determining gene, sdY, throughout the salmonid genome.We found approximately 4.1 kb of orthologous sequence common to all three species, which contains the genetic content necessary for masculinization.The regions contain transposable elements that may be responsible for the translocations of the SDR throughout salmonid genomes and we examine potential mechanistic roles of each one.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Portland State University School of Biological Sciences, Washington State University Vancouver.

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A simplified hypothetical model of retrotransposition of the SDR facilitated by RNA-directed DNA polymerase from mobile element jockey-like. (A) A promoter upstream of sdY acts as recognition site for an RNA polymerase, and (B) transcription occurs until a termination site in the retrotransposon is recognized. All internal transcripts in the SDR are naturally transcribed in the opposite direction. (C) The retro-TE flanks the SDR transcript and recognizes a target insertion site elsewhere in the genome. (D) The SDR is reverse transcribed, (E) a template jump occurs, and the complementary DNA strand is synthesized. (F) The nonhomologous flaps of DNA are removed, gaps are filled in and ligated by an unknown series of enzymes. The result is duplication of the SDR with the flanking retrotransposon, and a formation of a new Y chromosome. Males with two Y chromosomes may pass one, both, or neither to offspring with a 25% chance of normal XY male offspring with a new sex-chromosome pair.
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evv123-F9: A simplified hypothetical model of retrotransposition of the SDR facilitated by RNA-directed DNA polymerase from mobile element jockey-like. (A) A promoter upstream of sdY acts as recognition site for an RNA polymerase, and (B) transcription occurs until a termination site in the retrotransposon is recognized. All internal transcripts in the SDR are naturally transcribed in the opposite direction. (C) The retro-TE flanks the SDR transcript and recognizes a target insertion site elsewhere in the genome. (D) The SDR is reverse transcribed, (E) a template jump occurs, and the complementary DNA strand is synthesized. (F) The nonhomologous flaps of DNA are removed, gaps are filled in and ligated by an unknown series of enzymes. The result is duplication of the SDR with the flanking retrotransposon, and a formation of a new Y chromosome. Males with two Y chromosomes may pass one, both, or neither to offspring with a 25% chance of normal XY male offspring with a new sex-chromosome pair.

Mentions: Based on the orientation of alignment to the predicted protein structures, transcription of this element would occur in the 3′- to 5′-direction relative to the SDR scaffolds if it were functional. The gene sits in the same orientation in both species, so that if an RNA copy of the SDR were transcribed in the 3′- to 5′-direction (again, relative to the genomic scaffolds) this non-LTR element could serve as a terminator sequence for transcription, a site of insertion of the SDR sequence into a genomic target, and a site of initiation for reverse transcription of the SDR (fig. 9). Even if the non-LTR element could not produce a functional reverse transcriptase enzyme, it is possible that fully functional retrotransposon machinery from elsewhere in the genome recognized a still-intact promoter and target sequence for retrotransposition of the SDR. Similar phenomena have been observed in vitro for other types of mobile elements (Casacuberta and Santiago 2003; Bolton et al. 2005). It is also possible that the translated retrotransposon had partial functionality, lacking of endo/exonuclease activity which was compensated for by other cis or trans elements (Gilbert et al. 2002, de Boer et al. 2007).Fig. 9.—


Comparative Analysis of the Shared Sex-Determination Region (SDR) among Salmonid Fishes.

Faber-Hammond JJ, Phillips RB, Brown KH - Genome Biol Evol (2015)

A simplified hypothetical model of retrotransposition of the SDR facilitated by RNA-directed DNA polymerase from mobile element jockey-like. (A) A promoter upstream of sdY acts as recognition site for an RNA polymerase, and (B) transcription occurs until a termination site in the retrotransposon is recognized. All internal transcripts in the SDR are naturally transcribed in the opposite direction. (C) The retro-TE flanks the SDR transcript and recognizes a target insertion site elsewhere in the genome. (D) The SDR is reverse transcribed, (E) a template jump occurs, and the complementary DNA strand is synthesized. (F) The nonhomologous flaps of DNA are removed, gaps are filled in and ligated by an unknown series of enzymes. The result is duplication of the SDR with the flanking retrotransposon, and a formation of a new Y chromosome. Males with two Y chromosomes may pass one, both, or neither to offspring with a 25% chance of normal XY male offspring with a new sex-chromosome pair.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4524489&req=5

evv123-F9: A simplified hypothetical model of retrotransposition of the SDR facilitated by RNA-directed DNA polymerase from mobile element jockey-like. (A) A promoter upstream of sdY acts as recognition site for an RNA polymerase, and (B) transcription occurs until a termination site in the retrotransposon is recognized. All internal transcripts in the SDR are naturally transcribed in the opposite direction. (C) The retro-TE flanks the SDR transcript and recognizes a target insertion site elsewhere in the genome. (D) The SDR is reverse transcribed, (E) a template jump occurs, and the complementary DNA strand is synthesized. (F) The nonhomologous flaps of DNA are removed, gaps are filled in and ligated by an unknown series of enzymes. The result is duplication of the SDR with the flanking retrotransposon, and a formation of a new Y chromosome. Males with two Y chromosomes may pass one, both, or neither to offspring with a 25% chance of normal XY male offspring with a new sex-chromosome pair.
Mentions: Based on the orientation of alignment to the predicted protein structures, transcription of this element would occur in the 3′- to 5′-direction relative to the SDR scaffolds if it were functional. The gene sits in the same orientation in both species, so that if an RNA copy of the SDR were transcribed in the 3′- to 5′-direction (again, relative to the genomic scaffolds) this non-LTR element could serve as a terminator sequence for transcription, a site of insertion of the SDR sequence into a genomic target, and a site of initiation for reverse transcription of the SDR (fig. 9). Even if the non-LTR element could not produce a functional reverse transcriptase enzyme, it is possible that fully functional retrotransposon machinery from elsewhere in the genome recognized a still-intact promoter and target sequence for retrotransposition of the SDR. Similar phenomena have been observed in vitro for other types of mobile elements (Casacuberta and Santiago 2003; Bolton et al. 2005). It is also possible that the translated retrotransposon had partial functionality, lacking of endo/exonuclease activity which was compensated for by other cis or trans elements (Gilbert et al. 2002, de Boer et al. 2007).Fig. 9.—

Bottom Line: This variation results from the movement of the sex-determining gene, sdY, throughout the salmonid genome.We found approximately 4.1 kb of orthologous sequence common to all three species, which contains the genetic content necessary for masculinization.The regions contain transposable elements that may be responsible for the translocations of the SDR throughout salmonid genomes and we examine potential mechanistic roles of each one.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Portland State University School of Biological Sciences, Washington State University Vancouver.

Show MeSH
Related in: MedlinePlus