Evaluation of the stages of the seminiferous epithelium cycle in the testis of Chinchila lanigera according to the acrosomic system

The Chinchila lanigera is a rodent endemic in Andes, South America and is considered critically endangered due to the large use of its fur in the market. Despite its economic importance, there are only few reports about its reproductive biology. So far, some peculiar characteristics have been described, for instance, the puberty in male chinchillas takes place at 3 months of age (mo) and the sexual maturity is reached at 17 mo, a very long period of time when compared to other mammals. In this context, the main objective was to determine the stages of the seminiferous epithelium cycle according to the acrosomic system in order to provide the basis for other studies in this species. Therefore, four adult chinchillas were utilized. Testes were perfused-fixed with glutaraldehyde and processed for histological analyses. Sections stained with PAS were used to better determine the size and position of the acrosome. The stages were characterized based on the presence, angle and size of the acrosome, shape and location of spermatid nuclei, presence of meiotic divisions, and overall seminiferous epithelium composition. In order to help the stages determination, the angles of the acrosome were measured from 10 photos per animal and 20 spermatids per photo in stages IV to VII using Image J 1.47t. Based on the acrosomic system, 11 stages of the seminiferous epithelium cycle were found for chinchilla. Stages I to VI had two generations of spermatids (round and elongate spermatids), while stages VII to XI had only one generation. In stage I, early round spermatids (step 1) were found with no acrosomal vesicle, some elongate spermatid bundles were located deeply within the epithelium. Young pachytene primary spermatocytes were situated between round spermatids and the basal lamina. Subsequently, in stages II/III it was possible to see, in the same cross section, round spermatids with one or more granules on their nuclear surfaces (step 2) or with one rounded acrosomal vesicle on it (step 3), making it difficult to designate as stages II or III, separately. The stage IV is characterized by the presence of step 4 round spermatids. The acrosomal vesicle starts to spread over the nuclear membrane, depicting an angle (~65°±0.04). Bundles of elongated spermatids had started to move toward the seminiferous tubule lumen. Also, pachytenes were found more distant from the basal lamina in this stage. The acrosome in round spermatids (step 5) kept developing over the nucleus in the stage V, and its angle mean was ~77°±0.05. Elongated spermatid bundles continued moving toward the lumen. Next, in stage VI, nuclei of elongated spermatids were located along the lumenal surface of the seminiferous epithelium as long as the spermiation occurs at this stage. Many residual bodies were found just below elongated spermatids. Also, the angle depicted by the acrosome over the round spermatid (step 6) nucleus was around 107°±0.05. After spermiation, only one spermatid generation was occurring in the epithelium. Hence, the angle formed over the round spermatids nuclei (step 7) by the acrosome vesicles represented ~130±0.05 degrees. In stage VIII, step 8 spermatids nuclei began the elongation process and started to be organized with the acrosome side facing the basal lamina. Two types of primary spermatocytes (leptotene and pachytene) were found at the bottom of the epithelium. Spermatids at the step 9 were present in the stage IX and they were more elongated compared with the same cells of the previous stage. Nuclear condensation has started at this stage. Leptotene and pachytene spermatocytes were observed at this stage as well. The nuclear condensation of elongated spermatids (step 10) was more evident than the precedent cells. Also, these cells were arranged in bundles, with the acrosomal side facing the basal lamina. Zygotene and diplotene corresponded to the spermatocytes present in the seminiferous epithelium at the stage X. In stage XI, it was possible to see meiosis I and meiosis II cells. Besides that, zygotene and secondary spermatocytes were also observed. Eventually, diplotene spermatocytes were still present at this phase of the seminiferous epithelium cycle. The spermatogonia were present along the 11 stages of the seminiferous epithelium cycle. However, ongoing studies are being performed in order to thoroughly characterize these cell types and their generations.