Differential contribution of the MTOR and MNK pathways to the regulation of mRNA translation in meiotic and postmeiotic mouse male germ cells.
Translation of stored mRNAs accounts for protein synthesis during the transcriptionally inactive stages of spermatogenesis. A key step in mRNA translation is the assembly of the initiation complex EIF4F, which is regulated by the MTOR (mammalian target of rapamycin) and MNK1/2 (MAP kinase-interacting kinase 1 and 2) pathways. We investigated the expression and activity of regulatory proteins of these pathways in male germ cells at different stages of differentiation. All translation factors analyzed were expressed in germ cells throughout spermatogenesis. However, while EIF4G and PABP1 (poly[A]-binding protein 1) were more abundant in postmeiotic cells, MTOR and its target EIF4EBP1 (4E-BP1) decreased steadily during spermatogenesis. In vivo labeling showed that pachytene spermatocytes display higher rates of protein synthesis, which are partially dependent on MTOR and MNK activity. By contrast, haploid spermatids are characterized by lower levels of protein synthesis, which are independent of the activity of these pathways. Accordingly, MTOR and MNK activity enhanced formation of the EIF4F complex in pachytene spermatocytes but not in round spermatids. Moreover, external cues differentially modulated the activity of these pathways in meiotic and haploid cells. Heat shock decreased MTOR and MNK activity in pachytene spermatocytes, whereas round spermatids were much less sensitive. On the other hand, treatment with the phosphatase inhibitor okadaic acid activated MTOR and MNK in both cell types. These results indicate that translational regulation is differentially dependent on the MTOR and MNK pathways in mouse spermatocytes and spermatids and suggest that the late stages of germ cell differentiation display constitutive assembly of the translation initiation complex.
Messina
Valeria
V
Section of Anatomy, Department of Public Health and Cell Biology, University of Rome Tor Vergata, Rome, Italy.
Di Sauro
Annarita
A
Pedrotti
Simona
S
Adesso
Laura
L
Latina
Alessia
A
Geremia
Raffaele
R
Rossi
Pellegrino
P
Sette
Claudio
C
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D039562:Eukaryotic Initiation Factor-4F / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D008540:Meiosis / Q000502:physiology*; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013090:Spermatocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D013091:Spermatogenesis / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D004791:Enzyme Inhibitors; D039562:Eukaryotic Initiation Factor-4F; D012333:RNA, Messenger; D019319:Okadaic Acid; C106281:Mknk1 protein, mouse; C106282:Mknk2 protein, mouse; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases