Defined culture systems supporting spermatogonial differentiation will provide experimental platforms to study spermatogenesis. However, germline-intrinsic signaling mechanisms sufficient to support spermatogonial differentiation without somatic cells remain largely undefined. Here, we analyzed EGF superfamily receptor and ligand diversity in rat testis cells, and delineated germline-intrinsic signaling via an ERBB3 co-transducer, ERBB2, as essential for retinoic acid-induced syncytial growth by differentiating spermatogonia. Like the ERBB2/3 agonist NRG1, we found KIT Ligand (KITL) robustly supported spermatogonial differentiation without serum or somatic cells. ERBB2 inhibitors failed to disrupt KITL-dependent spermatogonial development, and, KITL prevented ERBB3-deficient spermatogonial degeneration upon differentiation. Thus, we report NRG1 and KITL activate alternative pathways downstream of retinoic acid signaling in the germline that are essential for stem cells to undergo pre-meiotic steps of spermatogenesis in culture. Robust serum/soma-free spermatogonial differentiation opens new doors to study mammalian germ cell biology in culture, which will facilitate the discovery of spermatogenic factors that can drive meiotic progression in vitro.

中文翻译：

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NRG1和KITL信号在胚系中的维甲酸下游，以支持分化精原细胞的无体质合胞生长。

支持精原细胞分化的既定培养系统将为研究精子发生提供实验平台。然而，在没有体细胞的情况下足以支持精原细胞分化的种系内在信号传导机制仍未明确。在这里，我们分析了大鼠睾丸细胞中的EGF超家族受体和配体多样性，并通过ERBB3协同转导子ERBB2描绘了种系内在信号转导，这是视黄酸通过分化精原细胞诱导合胞体生长所必需的。像ERBB2 / 3激动剂NRG1一样，我们发现KIT配体（KITL）强有力地支持了精原细胞的分化，而没有血清或体细胞。ERBB2抑制剂未能破坏KITL依赖的精原细胞的发育，并且KITL阻止了分化后ERBB3缺陷的精原细胞的变性。从而，我们报道了NRG1和KITL激活种系视黄酸信号下游的替代途径，这对于干细胞在培养中经历精子发生的减数分裂步骤是必不可少的。强大的无血清/无瘤的精原细胞分化为研究哺乳动物生殖细胞生物学开辟了新的大门，这将有助于发现可在体外驱动减数分裂进程的生精因子。