Journal of Molecular Evolution

, Volume 47, Issue 3, pp 275–281 | Cite as

The Mouse Gene Encoding the Testis-Specific Isoform of Poly(A) Binding Protein (Pabp2) Is an Expressed Retroposon: Intimations That Gene Expression in Spermatogenic Cells Facilitates the Creation of New Genes

  • Kenneth C.  Kleene
  • Evan  Mulligan
  • Daniel  Steiger
  • Kevin  Donohue
  • Mary-Ann  Mastrangelo

Abstract.

The gene encoding the testis-specific isoform of mouse poly(A) binding protein (Pabp2) has been isolated and sequenced. Unexpectedly, comparison of the sequence of genomic and cDNAs demonstrated that the Pabp2 gene lacks introns, whereas all other functional Pabp genes in plants, amphibians, and mammals contain introns. Thus, the mouse Pabp2 gene is a retroposon, created by synthesizing a reverse transcriptase copy of a processed mRNA and inserting the copy into the genome. The Pabp2 retroposon is unusual because it is functional: previous work demonstrates that its promoter drives the accumulation of Pabp2 mRNA in meiotic and early haploid spermatogenic cells, and the Pabp2 mRNA encodes a protein whose size and RNA-binding specificities are characteristic of PABP in plants, yeast, and mammals (Kleene et al. 1994). Two novel factors can be implicated in the retention of function of the Pabp2 retroposon. First, the promoter of the Pabp2 gene is not derived from its intron-containing progenitor, Pabp1. Second, mRNAs encoding somatic PABP isoform, PABP1, are present at high levels in meiotic and haploid spermatogenic cells. Both features contrast with the phosphoglycerate kinase 2 retroposon, which is believed to compensate for the depletion of the somatic isoform due to X-chromosome inactivation in meiotic spermatogenic cells. We also document that more functional retroposons are expressed in meiotic and haploid spermatogenic cells than in any other tissue and speculate that transcriptional derepression in spermatogenic cells favors the creation of expressed retroposons.

Key words: Intronless gene — Retroposon — Transcriptional promiscuity — X-chromosome inactivation — Poly(A) binding protein — Spermatogenesis 

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Copyright information

© Springer-Verlag New York Inc. 1998

Authors and Affiliations

  • Kenneth C.  Kleene
    • 1
  • Evan  Mulligan
    • 1
  • Daniel  Steiger
    • 1
  • Kevin  Donohue
    • 1
  • Mary-Ann  Mastrangelo
    • 1
  1. 1.Department of Biology, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125-3393, USAUS

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