Isolation, Identification and Enrichment of Type A Spermatogonia from the Testis of Chinese Cross-Bred Buffaloes (Swamp × River)

Optimized Recovery of Immature Germ Cells after Prepubertal Testicular Tissue Digestion and Multi-Step Differential Plating: A Step towards Fertility Restoration with Cancer-Cell-Contaminated Tissue

Undifferentiated germ cells, including the spermatogonial stem cell subpopulation required for fertility restoration using human immature testicular tissue (ITT), are difficult to recover as they do not easily adhere to plastics. Due to the scarcity of human ITT for research, we used neonatal porcine ITT. Strategies for maximizing germ cell recovery, including a comparison of two enzymatic digestion protocols (P1 and P2) of ITT fragment sizes (4 mm3 and 8 mm3) and multi-step differential plating were explored. Cellular viability and yield, as well as numbers and proportions of DDX4+ germ cells, were assessed before incubating the cell suspensions overnight on uncoated plastics. Adherent cells were processed for immunocytochemistry (ICC) and floating cells were further incubated for three days on Poly-D-Lysine-coated plastics. Germ cell yield and cell types using ICC for SOX9, DDX4, ACTA2 and CYP19A1 were assessed at each step of the multi-step differential plating. Directly after digestion, cell suspensions contained >92% viable cells and 4.51% DDX4+ germ cells. Pooled results for fragment sizes revealed that the majority of DDX4+ cells adhere to uncoated plastics (P1; 82.36% vs. P2; 58.24%). Further incubation on Poly-D-Lysine-coated plastics increased germ cell recovery (4.80 ± 11.32 vs. 1.90 ± 2.07 DDX4+ germ cells/mm2, respectively for P1 and P2). The total proportion of DDX4+ germ cells after the complete multi-step differential plating was 3.12%. These results highlight a reduced proportion and number of germ cells lost when compared to data reported with other methods, suggesting that multi-step differential plating should be considered for optimization of immature germ cell recovery. While Poly-D-Lysine-coating increased the proportions of recovered germ cells by 16.18% (P1) and 28.98% (P2), future studies should now focus on less cell stress-inducing enzymatic digestion protocols to maximize the chances of fertility restoration with low amounts of cryo-banked human ITT.

Nanoscale level gelatin-based scaffolds enhance colony formation of porcine testicular germ cells

The extracellular matrix is important in cell growth, proliferation, and differentiation. Gelatin, a support for adhering cells, is used for coating culture plate surfaces of several primary and stem cells. However, gelatin characteristics on culture plates and its cell interactions are not understood. Here, we aimed to identify the effect of gelatin topography on culture plates on the proliferation and colony formation of porcine spermatogonial germ cells (pSGC). To generate different surface topographies, gelatin powder was dissolved in H₂O at varying melting temperatures (40, 60, 80, and 120 °C) and coated on the surface of the culture plates. At 40 °C, the pores of the gelatin scaffold were regular ellipses 5-6 μm in diameter and 10-30 nm in thickness. However, at 120 °C, irregular pores 20-30 μm in diameter and 10-20 nm in thickness were obtained. Additionally, the number of attached cells and pSGC colonies were significantly more at 40 °C than at 120 °C after a week of culture. Interestingly, the feeder cells did not settle properly at 120 °C but detached easily from the culture dishes. PSGC colonies were 100 μm in diameter at 40 °C, with small and detached colonies observed at 120 °C. Thus, optimal topography of gelatin was obtained at 40 °C, which was sufficient for the proliferation of feeder cells and the formation of pSGC colonies. Thus, gelatin scaffold conditions at 40 °C and 60 °C were optimal for the derivation and culture of pSGC, and gelatin surface morphology is important for the maintenance of supportive feeder cells for pSGC proliferation and colony formation.

Current scenario and challenges ahead in application of spermatogonial stem cell technology in livestock

PURPOSE

Spermatogonial stem cells (SSCs) are the source for the mature male gamete. SSC technology in humans is mainly focusing on preserving fertility in cancer patients. Whereas in livestock, it is used for mining the factors associated with male fertility. The review discusses the present status of SSC biology, methodologies developed for in vitro culture, and challenges ahead in establishing SSC technology for the propagation of superior germplasm with special reference to livestock.

METHOD

Published literatures from PubMed and Google Scholar on topics of SSCs isolation, purification, characterization, short and long-term culture of SSCs, stemness maintenance, epigenetic modifications of SSCs, growth factors, and SSC cryopreservation and transplantation were used for the study.

RESULT

The fine-tuning of SSC isolation and culture conditions with special reference to feeder cells, growth factors, and additives need to be refined for livestock. An insight into the molecular mechanisms involved in maintaining stemness and proliferation of SSCs could facilitate the dissemination of superior germplasm through transplantation and transgenesis. The epigenetic influence on the composition and expression of the biomolecules during in vitro differentiation of cultured cells is essential for sustaining fertility. The development of surrogate males through gene-editing will be historic achievement for the foothold of the SSCs technology.

CONCLUSION

Detailed studies on the species-specific factors regulating the stemness and differentiation of the SSCs are required for the development of a long-term culture system and in vitro spermatogenesis in livestock. Epigenetic changes in the SSCs during in vitro culture have to be elucidated for the successful application of SSCs for improving the productivity of the animals.

Homologous transplantation of fluorescently labelled enriched buffalo (Bubalus bubalis) spermatogonial stem cells to prepubertal recipients

Spermatogonial stem cell transplantation provides a unique opportunity to study the biology of spermatogenesis and also offers an alternative approach for genetic modification in large animals. The present study aimed to extend this technique to the water buffalo. Spermatogonial stem cells (SSCs) were isolated from prepubertal buffalo testes (3-6 months of age) using two-step enzymatic digestion method and enriched by differential plating and Percoll density gradient centrifugation. The enriched SSCs expressed numerous spermatogonial transcriptional markers, viz. ID4, THY1, BCL6B, UCHL1, ETV5 and REX1 which confirmed their bonafide SSC identity. Subsequently, the enriched SSCs were labelled with a fluorescent dye PKH26 and transplanted into buffalo calves under ultrasound guidance. The recipient testes were recovered after 7-8 weeks by castration and their fluorescence microscopebased examination exhibited the persistence and localization of the fluorescent donor cells within the recipient seminiferous tubules. Further validation was done by the flow cytometric evaluation of PKH26 labeled donor cells among those isolated by two-step enzymatic digestion of recipient testicular parenchyma. In conclusion, we demonstrated the feasibility of SSC transplantation technique in the water buffalo.

Successful transplantation of transfected enriched buffalo (Bubalus bubalis) spermatogonial stem cells to homologous recipients

Genetic modification of spermatogonial stem cells (SSCs) is an alternative method to pronuclear microinjection and somatic cell nuclear transfer for transgenesis in large animals. In the present study, we optimized the process of homologous SSC transplantation in the water buffalo (Bubalus bubalis) using transfected enriched SSCs generated by a non-viral transfection approach. Firstly, the SSC enrichment efficiencies of extracellular matrix components viz. collagen, gelatin, and Datura stramonium agglutinin (DSA) lectin were determined either individually or in combination with Percoll density gradient centrifugation. The highest enrichment was achieved after differential plating with DSA lectin followed by Percoll density gradient centrifugation. Nucleofection showed greater transfection efficiency (68.55 ± 4.56%, P < 0.05) for enriched SSCs in comparison to fugene HD (6.7 ± 0.25%) and lipofectamine 3000 (15.57 ± 0.74%). The transfected enriched SSCs were transplanted into buffalo males under the ultrasound guidance and testis was removed by castration after 7-8 weeks of transplantation. Persistence and localization of donor cells within recipient seminiferous tubules was confirmed using fluorescent microscopy. Further confirmation was done by flow cytometric evaluation of GFP expressing cells among those isolated from two-step enzymatic digestion of recipient testicular parenchyma. In conclusion, we demonstrated for the first time, generation of buffalo transfected enriched SSCs and their successful homologous transplantation in buffaloes. This study represents the first step towards genetic modifications in buffaloes using SSC transplantation technique.

Spermatogonial stem cells identified by molecular expression of PLZF, integrin β1 and reactivity to Dolichos biflorus agglutinin in alpaca adult testes

The identification system of spermatogonial stem cell (SSC) was established in alpaca using the molecular expression as well as the reactivity pattern to Dolichos biflorus agglutinin (DBA) by flow cytometry. Twenty-four testicles with their epididymis were recovered from adult alpacas at the slaughterhouse of Huancavelica-Perú. Samples were transported to the Laboratory of Reproductive Physiology at Universidad Nacional Mayor de San Marcos. Testes were selected for our study when the progressive motility of epididymal spermatozoa (ESPM) was above 30%. Isolation of SSC was performed with two enzymatic digestions. Finally, sperm viability was evaluated by means of the trypan blue vital stain in spermatogonial round cells. Samples with more than 80% viability were selected. Isolated cells cultured for 2 days were used for identifying the presence of SSCs by the expression of integrin β1 (116 bp) and PLZF (206 bp) genes. Spermatogonia were classified according to the DBA reactivity. Spermatogonia with a strong positive to DBA (sDBA⁺ ) were classified as SSC (Mean ± SEM=4.44 ± 0.68%). Spermatogonia in early differentiation stages stained weakly positive with DBA (wDBA⁺ ) (Mean ± SEM=37.44 ± 3.07%) and differentiated round cells as DBA negative (Mean ± SEM=54.12 ± 3.18%). With the use of molecular and DBA markers, it is possible to identify easily the spermatogonial stem cells in alpaca.

Simplified isolation and enrichment of spermatogonial stem-like cells from pubertal domestic cats (Felis catus)

The efficiency of spermatogonial stem cell (SSC) isolation and culture from pubertal donors is currently poor primarily, because of contamination with other testicular cells. This study aimed to purify SSC-like cells using different extracellular matrixes and a discontinuous gradient density. In experiment 1, testes (n=6) were analyzed for histology and SSC-related protein expressions (laminin, SSEA-4, DDX-4 and GFRα-1). After enzymatic digestion, the cell suspension was plated onto either a laminin- or gelatin-coated dish. The number of SSC-like cells was determined at 15, 30 and 60 min of culture (experiment 2). Experiment 3 was performed to test whether or not the additional step of Percoll gradient density centrifugation could really improve purification of SSC-like cells. Testicular histology revealed complete spermatogenesis with laminin expression essentially at the basal lamina of the seminiferous tubules. SSEA-4 and GFRα-1 co-localized with DDX-4 in the spermatogonia. The relative percentage of SSC-like cells, as determined by cells expressing SSEA-4 (59.42 ± 2.18%) and GFRα-1 (42.70 ± 1.28%), revealed that the highest SSC-like cell purity was obtained with the 15-min laminin-coated dish compared with other incubation times and gelatin treatment (P<0.05). Percoll treatment prior to laminin selection (15 min) significantly improved SSC-like cell recovery (91.33 ± 0.14%, P<0.001) and purity (83.82 ± 2.05% for SSEA-4 and 64.39 ± 1.51% for GFRα-1, P<0.05). These attached cells demonstrated a typical SSC-like cell morphology and also expressed POU5F1, RET and ZBTB16 mRNA. In conclusion, double enrichment with Percoll gradient density centrifugation and laminin plating highly enriched the SSC-like cells population.

Spermatogonial stem cells from domestic animals: progress and prospects

Spermatogenesis, an elaborate and male-specific process in adult testes by which a number of spermatozoa are produced constantly for male fertility, relies on spermatogonial stem cells (SSCs). As a sub-population of undifferentiated spermatogonia, SSCs are capable of both self-renewal (to maintain sufficient quantities) and differentiation into mature spermatozoa. SSCs are able to convert to pluripotent stem cells during in vitro culture, thus they could function as substitutes for human embryonic stem cells without ethical issues. In addition, this process does not require exogenous transcription factors necessary to produce induced-pluripotent stem cells from somatic cells. Moreover, combining genetic engineering with germ cell transplantation would greatly facilitate the generation of transgenic animals. Since germ cell transplantation into infertile recipient testes was first established in 1994, in vivo and in vitro study and manipulation of SSCs in rodent testes have been progressing at a staggering rate. By contrast, their counterparts in domestic animals, despite the failure to reach a comparable level, still burgeoned and showed striking advances. This review outlines the recent progressions of characterization, isolation, in vitro propagation, and transplantation of spermatogonia/SSCs from domestic animals, thereby shedding light on future exploration of these cells with high value, as well as contributing to the development of reproductive technology for large animals.