Evaluation of candidate spermatogonial markers ID4 and GPR125 in testes of adult human cadaveric organ donors

Abstract

The optimal markers for human spermatogonial stem cells (SSCs) are not known. Among the genes recently linked to SSCs in mice and other animals are the basic helix-loop-helix transcription factor ID4 and the orphan G-protein coupled receptor GPR125. While ID4 and GPR125 are considered putative markers for SSCs, they have not been evaluated for co-expression in human tissue. Further, neither the size nor the character of the human spermatogonial populations that express ID4 and GPR125, respectively, are known. A major barrier to addressing these questions is the availability of healthy adult testis tissue from donors with no known reproductive health problems. To overcome this obstacle, we have employed healthy testicular tissue from a novel set of organ donors (n=16; aged 17-68 years) who were undergoing post-mortem clinical organ procurement. Using immunolabeling, we found that ID4 and GPR125 are expressed on partially overlapping spermatogonial populations and are more broadly expressed in the normal adult human testis. Additionally, we found that expression of ID4 remained stable during aging. These findings suggest that ID4 and GPR125 could be efficacious for identifying previously unrecognized human spermatogonial subpopulations in conjunction with other putative human stem cell markers, both in younger and older donors.

Spermatogonial stem cells and spermatogenesis in mice, monkeys and men

“…Some A pale have a transition phenotype similar to larger chain A al spermatogonia in rodents (e.g., GFRa1+/SOHLH1+/NGN3+/cKIT+) (Hermann et al, 2009; Ramaswamy et al, 2014). Markers of undifferentiated spermatogonia that are conserved from rodents to nonhuman primates to humans include GFRa1, UTF1, PLZF, SALL4 and LIN28 (van Bragt et al, 2008; Meng et al, 2000; Costoya et al, 2004; Buaas et al, 2004; Hobbs et al, 2012; Eildermann et al, 2012a; Gassei & Orwig, 2013; Zheng et al, 2009; Hermann et al, 2009; Ramaswamy et al, 2014; Aeckerle et al, 2012; Lin et al, 2015; Di Persio et al, 2017; Valli et al, 2014; Zheng et al, 2014; Sachs et al, 2014) (See UTF1 staining of monkey and human testis cross sections in Fig. 4C and D).…”

“…4C and D). ID4 is conserved in the undifferentiated spermatogonia of rodents (Oatley et al, 2011) and humans (Sachs et al, 2014), but has not been described in nonhuman primates. cKIT appears to be a conserved marker of differentiated spermatogonia, marking the transition to A1 spermatogonia in rodents; B1 spermatogonia in nonhuman primates and B spermatogonia in humans (Hermann et al, 2009; Valli et al, 2014).…”

Regulation of spermatogonial stem cell self-renewal and spermatocyte meiosis by Sertoli cell signaling

“…The functional interactions and feedback loops of GDNF signaling with other SSC self-renewal regulators will be the focus of future studies and will be useful for dissecting this unique process. Human orthologs of mouse SSC maintenance genes, such as RET, GFRA1, ETV5, ID4, and BCL6B, are highly enriched in human spermatogonia relative to somatic cells , Sachs et al 2014. Whether these genes contribute to SSCs self-renewal in humans will require further investigation via in vitro studies.…”

Spermatogonial stem cells: Current biotechnological advances in reproduction and regenerative medicine

“…Apparently, SSEA-4 seems to be conserved in humans [48] . SSCs from humans also express GPR125 [49] , besides GFRα1 [50] . Another human SSC marker that adds to the known panel is ITGA6 [51] .…”