title: Glial cell line-derived neurotrophic factor regulation of genes essential for self-renewal of mouse spermatogonial stem cells is dependent on Src family kinase signaling.
abstract: Self-renewal and differentiation by spermatogonial stem cells (SSCs) is the foundation for continual spermatogenesis. SSC self-renewal is dependent on glial cell line-derived neurotrophic factor (GDNF); however, intracellular mechanisms stimulated by GDNF in SSCs are unknown. To investigate these mechanisms we utilized a culture system that maintains a mouse undifferentiated germ cell population enriched for self-renewing SSCs. In these cultures mRNA for the transcription factors Bcl6b, Erm, and Lhx1 are up-regulated by GDNF and decreased in its absence. The expression of all three molecules was further identified in undifferentiated spermatogonia in vivo. Using small interfering RNA to reduce expression and transplantation to quantify stem cell numbers, Bcl6b, Erm, and Lhx1 were shown to be important for SSC maintenance in vitro. Next, GDNF was shown to activate both Akt and Src family kinase (SFK) signaling in SSCs, and culture of SSCs with inhibitors to Akt or SFKs followed by transplantation analysis showed significant impairment of SSC maintenance in vitro. Apoptosis analysis revealed a significant increase in the percentage of apoptotic cells when Akt, but not SFK, signaling was impaired, indicating that multiple signaling pathways are responsible for SSC self-renewal and survival. Biochemical and gene expression experiments revealed that GDNF up-regulated expression of Bcl6b, Erm, and Lhx1 transcripts is dependent on SFK signaling. Overall, these data demonstrate that GDNF up-regulation of Bcl6b, Erm, and Lhx1 expression through SFK signaling is a key component of the intracellular mechanism for SSC self-renewal.
authors.affiliation: Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Jon M
authors.initials: JM
authors.lastname: Oatley
authors.forename: Mary R
authors.initials: MR
authors.lastname: Avarbock
authors.forename: Ralph L
authors.initials: RL
authors.lastname: Brinster
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism* / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D060850:LIM-Homeodomain Proteins; D008297:Male; D051379:Mice; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013093:Spermatogonia / Q000166:cytology / Q000378:metabolism*; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: C113027:Bcl6b protein, mouse; D004268:DNA-Binding Proteins; C513242:Etv5 protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; C499523:Lhx1 protein, mouse; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt