Spermatogonial Stem Cell Markers and Niche in Equids

Abstract

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and are located in a highly dynamic microenvironment called “niche” that influences all aspects of stem cell function, including homing, self-renewal and differentiation. Several studies have recently identified specific proteins that regulate the fate of SSCs. These studies also aimed at identifying surface markers that would facilitate the isolation of these cells in different vertebrate species. The present study is the first to investigate SSC physiology and niche in stallions and to offer a comparative evaluation of undifferentiated type A spermatogonia (Aund) markers (GFRA1, PLZF and CSF1R) in three different domestic equid species (stallions, donkeys, and mules). Aund were first characterized according to their morphology and expression of the GFRA1 receptor. Our findings strongly suggest that in stallions these cells were preferentially located in the areas facing the interstitium, particularly those nearby blood vessels. This distribution is similar to what has been observed in other vertebrate species. In addition, all three Aund markers were expressed in the equid species evaluated in this study. These markers have been well characterized in other mammalian species, which suggests that the molecular mechanisms that maintain the niche and Aund/SSCs physiology are conserved among mammals. We hope that our findings will help future studies needing isolation and cryopreservation of equids SSCs. In addition, our data will be very useful for studies that aim at preserving the germplasm of valuable animals, and involve germ cell transplantation or xenografts of equids testis fragments/germ cells suspensions.

Characterization of spermatogonial markers in the mature testis of the dogfish (Scyliorhinus canicula L.)

“…Tissue expression studies have shown that PLZF is expressed in testis of different species such as the carp (Mohapatra et al 2010) and the mouse (Kokkinaki et al 2010), as observed in the dogfish, even if its expression was higher in the liver and eye than in the testis. In dogfish, plzf was detected not only in undifferentiated spermatogonia, in agreement with observations in various mammals and in zebrafish (Hermann et al 2009, Kokkinaki et al 2010, Ozaki et al 2011, Costa et al 2012, but also in differentiated spermatogonia, a larger expression pattern also described in humans and monkeys (Hermann et al 2009). Surprisingly, plzf expression in dogfish meiotic germ cells and young spermatids was a unique case in the studied species.…”

“…As the highest expression level of gfra1 was found in dogfish brain, we can hypothesize a similar function in S. canicula. In testis cells, GFRa1 was reported to be a marker of undifferentiated spermatogonia in many mammalian models (Suzuki et al 2009, Costa et al 2012. GFRa1 and its co-receptor RET stimulate SSC self-renewal in response to the GDNF (Naughton et al 2005).…”

“…Spermatogonia subpopulations were well described in various species on the basis of morphological criteria (De Rooij & Russell 2000, Leal et al 2009) and their molecular characterization is continuously improving (Costa et al 2012, for review, Nagano & Yeh (2013 Figure 7 Evolution of the expression pattern of spermatogonial markers in Osteichthyes and Chondrichthyes. The protein expression patterns (bars) reported in mice for GFRa1, PLZF (Suzuki et al 2009), C-KIT (Tokuda et al 2006), and POU5F1 (Wu et al 2010), in medaka for Pou2 (Sanchez-Sanchez et al 2010), in zebrafish for Plzf (Ozaki et al 2011) and in tilapia for Gfra1 (Lacerda et al 2013) were compared with transcript expression in dogfish (pou2, gfra1, plzf, hmgb3, and mcm6) and C-kit protein expression pattern (Loppion et al 2008).…”

Maintenance of Potential Spermatogonial Stem Cells In Vitro by GDNF Treatment in a Chondrichthyan Model (Scyliorhinus canicula L.)1

“…For example, the GFRα1 (GDNF Family Receptor α1) has been described as a marker of undifferentiated spermatogonia in mouse [7], equids [8], buffalo [9] or collared peccary [10] and more recently in fishes such as the Nile tilapia [5]. Other undifferentiated spermatogonial markers were identified in various species such as the cell surface marker Thy1 (Thymus cell antigen 1) in mouse [11], bull [12] and carp [13] or the following transcriptional factors: PLZF (Promyelocytic Leukaemia Zinc Finger protein) in mouse [7], equids [8] and zebrafish [14], POU2/POU5F1 in mouse [15], buffalo [9] and carp [13] and ID4 (Inhibitor of DNA binding 4), a more selective marker of SSCs than Thy1, in the mouse [16]. Some of these defined markers were used to improve in vitro culture systems by selecting undifferentiated spermatogonia from the testicular cell population, including potential SSCs, using the MACS technology (Magnetic-Activated Cell Sorting) in mammals as well as in Teleosts.…”

Spermatogonial stem cells from domestic animals: progress and prospects

“…Similarly, promyelocytic leukemia zinc-finger protein (PLZF, also known as ZBTB16), a transcription factor essential for the maintenance and self-renewal of SSCs, is initially found to be expressed by mouse undifferentiated spermatogonia (Buaas et al 2004, Costoya et al 2004. Later, its expression in a sub-population of gonocytes and SSCs/progenitors in pigs, cattle, sheep, goats, and equids is verified (Luo et al 2006, Borjigin et al 2010, Reding et al 2010, Costa et al 2012, Zheng et al 2013a.…”