Behavior and Functional Roles of CD34+ Mesenchymal Cells in Mammalian Testes

Abstract

Mammalian testes consist of seminiferous tubules within which Sertoli cells line up at the periphery and nurse germ cells, and of interstitia that harbor various cells such as peritubular myoid cells (PMCs), Leydig cells (LCs), vascular endothelial cells, immune cells such as macrophages, and mesenchymal (stromal) cells. Morphological studies have recently reported the presence of telocytes with telopodes in the interstitium of adult mouse, rat, and human testes. CD34+PDGFRα+ telocytes with long and moniliform telopodes form reticular networks with various cell types such as LCs, PMCs, and vessels, indicating their potential functions in cell–cell communications and tissue homeostasis. Functional studies have recently been performed on testicular interstitial cells and CD34+ cells, using 3D re-aggregate cultures of dissociated testicular cells, and cell cultures. Direct observation of CD34+ cells and adult LCs (ALCs) revealed that CD34+ cells extend thin cytoplasmic processes (telopodes), move toward the LC–CD34+ cell-re-aggregates, and finally enter into the re-aggregates, indicating the chemotactic behavior of CD34+ telocytes toward ALCs. In mammalian testes, important roles of mesenchymal interstitial cells as stem/progenitors in the differentiation and regeneration of LCs have been reported. Here, reports on testicular telocytes so far obtained are reviewed, and future perspectives on the studies of testicular telocytes are noted.

The Molecular Signature of Human Testicular Peritubular Cells Revealed by Single-Cell Analysis

“…PDGFRA and CD34, but of note not ACTA2, are thought to be typical for telocytes, and they have been reported in the human testis [ 57 , 58 ]. The present results, thus, do not indicate that they are present in the cultured HTPCs.…”

Unlocking Genetic Mysteries during the Epic Sperm Journey toward Fertilization: Further Expanding Cre Mouse Lines

“…In addition to spermatogenic, Leydig, and Sertoli cells, various other cell types have been well established in the testes, including T cells, endothelial cells, peritubular myoid cells, mesenchymal (stromal) cells, macrophages, tenocytes, two pericyte subpopulations (with either smooth muscle or ECM-secreting properties), and a Leydig cell precursor population [151][152][153]. However, the functional characteristics of these cells contributing to spermatogenesis are yet to be elucidated, and their protein expression patterns have not been identified.…”

“…Despite reports of the recombination efficiency of Cre, evidence supporting its ability to eliminate specific genes in testicular macrophages remains lacking. Other cell types identified through single-cell sequencing in the testes, such as T cells, mesenchymal (stromal) cells, and tenocytes [151][152][153], have been poorly studied in terms of their regulation of germ cell development, and a detailed description of the cKO strategy is not provided.…”

Telocytes and Other Interstitial Cells 2.0: From Structure to Function

“…Telocytes were also described in turtle, mouse, rat, and adult human testes [15][16][17][18]. Regarding this topic, Shin-ichi Abe assembled a valuable review and proposed an in vitro system to examine the functions of telocytes in spermatogenesis [19]. He and his group elaborated and studied the reconstruction of in vitro seminiferous tubule-like structures, in which they dissociated testicular cells deprived of interstitial cells and peritubular cells and concluded that, in the absence of all the above-mentioned components, dysmorphic structures are formed [20].…”

“…He and his group elaborated and studied the reconstruction of in vitro seminiferous tubule-like structures, in which they dissociated testicular cells deprived of interstitial cells and peritubular cells and concluded that, in the absence of all the above-mentioned components, dysmorphic structures are formed [20]. They decided that all the cell components are indispensable for the reconstruction of seminiferous tubule-like structure and that this model scientist will be able to investigate the role of Leydig cells, as well as interstitial and peritubular cells, such as CD34+PDGFR+ mesenchymal cells (telocytes), immune cells, and endothelial cells, by knocking out some genes at a time [19].…”