Sequence-Independent Assembly of Spermatid mRNAs into Messenger Ribonucleoprotein Particles

Abstract

During mammalian spermatogenesis, meiosis is followed by a brief period of high transcriptional activity. At this time a large amount of mRNA is stored as messenger ribonucleoprotein (mRNP) particles. All subsequent processes of sperm maturation occur in the complete absence of transcription, primarily using proteins which are newly synthesized from these stored mRNAs. By expressing transgene mRNAs in the early haploid spermatids of mice, we have investigated the sequence requirements for determining whether specific mRNAs in these cells will be stored as mRNP particles or be assembled into polysomes. The results suggest that mRNAs which are transcribed in spermatids are assembled into mRNP particles by a mechanism that acts independently of mRNA sequence. Our findings reveal a fundamental similarity between the mechanisms of translational control used in spermatogenesis and oogenesis.

ACKNOWLEDGMENTS

We thank D. Taylor and S. Barnett for technical assistance and training; A. Gaglio (Ventana Genetics) and J. Pierce and W. Green (University of Utah Flow Sorting Core Facility) for cell sorting; P. Flodby for suggesting the FACS separations; R. Palmiter and R. Braun for providing plasmids mP1-hGH-hGH-3′ and mP1-hGH-mP1-3′; J. Schmidt, A. Godwin, E. Leibold, C. Thummel, and K. Thomas for critically reading the manuscript; and our colleagues for thoughtful discussions.

This project was supported by the Howard Hughes Medical Research Foundation and the National Institutes of Health. E.E.S. was supported in part by the Mathers Charitable Foundation and is currently a Howard Hughes Fellow of the Life Sciences Research Foundation; E.S.H. was supported by training grant T32 DK07115 from the National Institutes of Health.