Seminiferous tubules physically connect to the rete testis through short segments called the transition region (TR). During fetal development, this specialized junction is considered the initial site where testis cords begin to form and to grow in length well beyond birth and into adulthood and form convoluted tubular cores. Mitotic activity of the Sertoli cell, the somatic cell of the epithelium, ceases before puberty, but modified Sertoli cells in the TR remain immature and capable of proliferation. This review presents what is known about this specialized region of the testis, with an emphasis on the morphological, molecular and physiological features, which support the hypothesis that this short region of epithelial transition serves as a specialized niche for undifferentiated Sertoli cells and spermatogonial stem cells. Also, the region is populated by an elevated number of immune cells, suggesting an important activity in monitoring and responding to any leakage of autoantigens, as sperm enter the rete testis. Several structure/function characteristics of the transition region are discussed and compared across species.

曲细精管通过称为过渡区 (TR) 的短段物理连接到睾丸网。在胎儿发育过程中，这个特殊的连接点被认为是睾丸索开始形成的初始部位，并且在出生后一直长到成年，并形成回旋的管状核心。支持细胞（上皮的体细胞）的有丝分裂活性在青春期前停止，但 TR 中修饰的支持细胞保持不成熟并能够增殖。这篇综述介绍了关于睾丸这一特殊区域的已知情况，重点是形态学、分子和生理学特征，这支持了这样的假设，即这一上皮过渡的短区域是未分化的支持细胞和精原干细胞的特殊生态位。 . 还，该区域的免疫细胞数量增加，这表明在精子进入睾丸网时监测和应对任何自身抗原泄漏的重要活动。讨论了过渡区的几个结构/功能特征，并在不同物种之间进行了比较。