SOX2-positive cells are stem/progenitor cells that supply hormone-producing cells; they are found in the anterior lobe of the rodent pituitary gland. However, they are likely composed of several subpopulations. In rats, a SOX2-positive cell populations can be distinguished by the presence of S100β. We identified the novel markers cluster of differentiation (CD) CD9 and CD81, members of the tetraspanin superfamily, for the identification of S100β/SOX2-positive cells. Recently, CD9/CD81 double-knockout mice were generated. Although they grew normally until 3 weeks after birth, they exhibited atrophy of the pituitary gland. These findings suggested that CD9/CD81/S100β/SOX2-positive cells in the mouse pituitary are adult stem/progenitor cells. To substantiate this hypothesis, we examined CD9 and CD81 expression in the adult and developing anterior lobe. Immunohistochemistry showed that CD9/CD81-positive cells began appearing from postnatal day 0 and settled in the stem cell niches (marginal cell layer and parenchyma) of the adult anterior lobe while expressing S100β. We next isolated CD9 -positive cells from the adult anterior lobe, using the anti-CD9 antibody for cell characterisation. The cells in culture formed free-floating three-dimensional clusters (pituispheres); moreover, induction into all types of hormone-producing cells was successful. Furthermore, reduction of CD9 and CD81 mRNAs by siRNAs inhibited cell proliferation. These findings indicate that CD9/CD81/S100β/SOX2-positive cells may play a role as adult stem/progenitor cells in SOX2-positive subpopulations, thus supplying hormone-producing cells in the postnatal anterior lobe. Furthermore, CD9 and CD81 are implicated in cell proliferation. The current findings provide novel insights into adult pituitary stem/progenitor cells.

SOX2 阳性细胞是提供激素产生细胞的干细胞/祖细胞；它们存在于啮齿动物脑垂体的前叶。然而，它们很可能由几个亚群组成。在大鼠中，S100β 的存在可以区分 SOX2 阳性细胞群。我们鉴定了新的分化标记簇 (CD) CD9 和 CD81，即四跨膜蛋白超家族的成员，用于鉴定 S100β/SOX2 阳性细胞。最近，产生了 CD9/CD81 双基因敲除小鼠。尽管它们在出生后 3 周前都正常生长，但它们表现出脑垂体萎缩。这些发现表明小鼠垂体中的 CD9/CD81/S100β/SOX2 阳性细胞是成体干细胞/祖细胞。为了证实这个假设，我们检查了成人和发育中的前叶中 CD9 和 CD81 的表达。免疫组织化学显示 CD9/CD81 阳性细胞从出生后第 0 天开始出现，并在表达 S100β 的同时定居在成人前叶的干细胞壁龛（边缘细胞层和薄壁组织）中。我们接下来从成人前叶分离 CD9 阳性细胞，使用抗 CD9 抗体进行细胞表征。培养中的细胞形成自由漂浮的三维簇（垂体球）；此外，成功地诱导了所有类型的激素产生细胞。此外，siRNAs 减少CD9 和CD81 mRNAs 抑制细胞增殖。这些发现表明 CD9/CD81/S100β/SOX2 阳性细胞可能在 SOX2 阳性亚群中作为成体干细胞/祖细胞发挥作用，从而为出生后的前叶提供产生激素的细胞。此外，CD9 和 CD81 与细胞增殖有关。目前的发现为成人垂体干/祖细胞提供了新的见解。