Mice are widely used as experimental models due to several positive characteristics and in particular their suitability for studies involving molecular biology and transgenesis. Despite the large number of mice strains currently available, the literature regarding their basic reproductive biology is still relatively scarce. Herein, we comparatively evaluated several important and correlated parameters related to testis structure and function in sexually mature male mice of inbred (C57BL/6, n = 19; BALB/c, n = 17) and outbred (Swiss, n = 17) strains, frequently utilized in research. Swiss mice presented significant variation for many parameters evaluated, including higher sperm production, mainly when compared to the C57BL/6 strain. However, some key parameters such as the duration of spermatogenesis, the Sertoli cell number per testis, and the spermatogenic efficiency were similar among the different strains. Although presenting significantly higher Leydig cell (LC) proportion and numbers per testis gram and per testis, the anogenital index was smaller in Swiss mice. Estradiol levels were lower in C57BL/6, whereas testosterone levels and 3β-HSD expression were similar among strains. Regarding the LC/macrophages relationship, in comparison to the literature, we reported a much higher contribution of macrophages to the mouse intertubule. Thus, we estimated that there are around 1.6 macrophages per LC in BALB/c mice and this intriguing finding could be relevant to testis function in overall and spermatogonial biology in particular. Taken together, our results highlight the importance of knowing more accurately the testis structure and function in the different mice strains available for research, particularly when a specific testis parameter is being investigated.

中文翻译：

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三种代表性小鼠品系的睾丸结构和功能比较

由于一些积极的特征，特别是它们适用于涉及分子生物学和转基因的研究，小鼠被广泛用作实验模型。尽管目前有大量小鼠品系可用，但有关其基本生殖生物学的文献仍然相对稀少。在此，我们比较评估了近交（C57BL/6，n = 19；BALB/c，n = 17）和远交（瑞士，n = 17）品系的性成熟雄性小鼠睾丸结构和功能相关的几个重要且相关的参数，经常用于研究。与 C57BL/6 品系相比，瑞士小鼠在许多评估参数方面表现出显着差异，包括更高的精子产量。然而，一些关键参数，例如精子发生的持续时间、每个睾丸的支持细胞数、不同菌株间的生精效率相似。尽管呈现出显着更高的 Leydig 细胞 (LC) 比例和每个睾丸克和每个睾丸的数量，但瑞士小鼠的肛门生殖器指数较小。C57BL/6 中的雌二醇水平较低，而菌株之间的睾酮水平和 3β-HSD 表达相似。关于 LC/巨噬细胞的关系，与文献相比，我们报道了巨噬细胞对小鼠小管的贡献要高得多。因此，我们估计 BALB/c 小鼠中每个 LC 大约有 1.6 个巨噬细胞，这一有趣的发现可能与睾丸的整体功能和特别是精原细胞生物学有关。综合起来，