Glial Cell-Line Derived Neurotrophic Factor-Mediated RET Signaling Regulates Spermatogonial Stem Cell Fate1

Abstract

Normal spermatogenesis is essential for reproduction and depends on proper spermatogonial stem cell (SSC) function. Genes and signaling pathways that regulate SSC function have not been well defined. We report that glial cell-line-derived neurotrophic factor (GDNF) signaling through the RET tyrosine kinase/GFRA1 receptor complex is required for spermatogonial self-renewal in mice. GFRA1 and RET expression was identified in a subset of gonocytes at birth, was restricted to SSCs during normal spermatogenesis, and RET expressing cells were abundant in a cryptorchid model of SSC self-renewal. We used the whole-testis transplantation technique to overcome the limitation of neonatal lethality of Gdnf-, Gfra1-, and Ret-deficient mice and found that each of these genes is required for postnatal spermatogenesis and not for embryological testes development. Each mutant testis shows severe SSC depletion by Postnatal Day 7 during the first wave of spermatogenesis. These defects were due to lack of SSC proliferation and an inability of SSCs to maintain an undifferentiated state. Our results demonstrate that GDNF-mediated RET signaling is critical for the fate of undifferentiated spermatogonia and that abnormalities in this pathway may contribute to male infertility and testicular germ cell tumors.

Ret receptor tyrosine kinase sustains proliferation and tissue maturation in intestinal epithelia

“…In contrast to known Ret functions in other progenitor cell types—for example, in spermatogonia or the hematopoietic system (Naughton et al , 2006; Hofmann, 2008; Fonseca‐Pereira et al , 2014)—Ret is not required for the survival of adult somatic stem cells in the intestine, but sustains both their homeostatic and regenerative proliferative capacity. Our gain‐ and loss‐of‐function experiments point to the existence of positive feedback between Ret and Wg signalling.…”

“…It is now well established that the endogenous activity of Ret is required for the formation and/or maintenance of a variety of cell types including neuronal, kidney, lymphoid, hematopoietic and testis germ cells (Schuchardt et al , 1994; Naughton et al , 2006; Veiga‐Fernandes et al , 2007; Ibanez, 2013; Fonseca‐Pereira et al , 2014). In these cells, Ret signalling is involved in a diverse range of developmental processes including proliferation, migration survival and/or differentiation (Sasselli et al , 2012; Ibanez, 2013).…”

Transcriptome analysis of differentiating spermatogonia stimulated with kit ligand

“…Indeed, Plzf is expressed in gonocytes, and in undifferentiated spermatogonia, but it is thought not to be expressed in kit positive spermatogonia in the adult testis (Oatley et al, 2006). However, Plzf is co-expressed with kit in a subset of spermatogonial stem cells during the first wave of spermatogenesis (Naughton et al, 2006). Moreover, recent data in our laboratory indicate that one of the mechanisms through which Plzf maintains the stem cell phenotype is the suppression of kit expression (Filipponi et al, 2007).…”

Gdnf signaling pathways within the mammalian spermatogonial stem cell niche

“…Similarly, the ablation of Ret or Gfrα-1 is neonatally lethal, preventing the analysis of a lack of receptor activation on SSC maintenance and self-renewal. To overcome the problem of neonatal mortality, Naughton and colleagues transplanted Gdnf, Gfrα-1 and Ret deficient neonatal testes under the back skin of immunodeficient mice, and subsequently monitored the development of the grafted testes (Naughton et al, 2006). This strategy revealed that any disruption of Gdnf-mediated Ret signaling results in a lack of spermatogonial stem cell self-renewal and induces the progressive loss of spermatogenesis by germ cell depletion.…”