The submandibular gland (SMG) of newborn mice has no mature acini but has the rudiments of acini called terminal tubules (TT). The TT are composed of TT cells with dark secretory granules and proacinar cells with lighter secretory granules, the latter being considered the immediate precursor of mature acinar cells. TT cells contain a specific secretory protein, submandibular gland protein C (SMGC) and they decrease in number postnatally at a higher rate in males than in females. In the present study, in order to clarify the biological roles of TT cells and their secretory product SMGC, we generated a knockout (KO) mouse strain deficient in SMGC. The KO mice of both sexes grew normally, had normal reproductive capacity and had normal acinar and duct systems in the SMG in adult ages. However, through the neonatal and early postnatal stages, the KO mice were deficient not only in the production of SMGC but also in TT cells. With electron microscopy of the SMG of newborn KO mice, TT cells with characteristic granules were absent and replaced by undifferentiated ductal cells, whereas proacinar cells were normal. These results suggested that the absence of SMGC inhibits the development of TT cells and that the absence of SMGC and TT cells has no notable influence on the postnatal development of the acinar and duct systems in the SMG.

中文翻译：

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下颌下腺蛋白C缺陷小鼠下颌下腺终末小管细胞缺失

新生小鼠的下颌下腺 (SMG) 没有成熟的腺泡，但具有称为终末小管 (TT) 的腺泡的雏形。TT由具有深色分泌颗粒的TT细胞和具有较浅分泌颗粒的原腺泡细胞组成，后者被认为是成熟腺泡细胞的直接前体。TT 细胞含有一种特定的分泌蛋白，即下颌下腺蛋白 C (SMGC)，并且它们在出生后的数量在男性中以比女性更高的速度减少。在本研究中，为了阐明 TT 细胞及其分泌产物 SMGC 的生物学作用，我们生成了 SMGC 缺陷的敲除 (KO) 小鼠品系。两性的 KO 小鼠生长正常，具有正常的生殖能力，成年后 SMG 中的腺泡和导管系统正常。然而，通过新生儿和产后早期阶段，KO 小鼠不仅缺乏 SMGC，而且缺乏 TT 细胞。通过对新生 KO 小鼠 SMG 的电子显微镜检查，没有具有特征颗粒的 TT 细胞并被未分化的导管细胞取代，而原腺泡细胞是正常的。这些结果表明，SMGC 的缺失抑制了 TT 细胞的发育，并且 SMGC 和 TT 细胞的缺失对 SMG 中腺泡和导管系统的出生后发育没有显着影响。