Hayashi Kanako, MacLean James A
Center for Reproductive Biology, School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA.
Department of Physiology, Southern Illinois University, Carbondale, IL 62901, USA.
Cells. 2025 Mar 22;14(7):478. doi: 10.3390/cells14070478.
The family of homeobox transcription factors comprises established regulators of gonad function, but their downstream targets have been relatively elusive, particularly in the female reproductive tract. Here, we characterize as a downstream target of the two granulosa cell-specific factors, and , in the ovary. While INS2 is classically produced by islet cells in the pancreas, we found that gene expression is present in the mural granulosa cell layer of large antral follicles, and it was not significantly reduced in -null mice. This was a surprising finding as we previously validated as a direct target of RHOX5 in Sertoli cells, the male counterpart to granulosa cells that serves the germ cell nurse function in the testis. In the ovary, RHOX8 appears to be the major driver of expression, as evidenced from the maximal activity of promoter reporter plasmids when RHOX8 protein was active within granulosa cells in vitro and the downregulation of endogenous in mice with the granulosa cell-specific knockdown of RHOX8 in vivo. RHOX5 induces expression in pre-antral granulosa cells and then becomes relatively silent in peri-ovulatory follicles. However, does not peak until after the ovulatory LH surge. The induction of by progesterone, after the normal window of RHOX5 has passed, may explain why -null female mice display apparently normal fertility, if RHOX8 is capable of the redundant stimulation of target genes that are essential for ovulation.
同源框转录因子家族包含已确定的性腺功能调节因子，但其下游靶点相对难以捉摸，尤其是在女性生殖道中。在这里，我们将INS2鉴定为卵巢中两种颗粒细胞特异性因子RHOX5和RHOX8的下游靶点。虽然INS2传统上由胰腺中的胰岛细胞产生，但我们发现INS2基因表达存在于大的窦状卵泡的壁颗粒细胞层中，并且在RHOX5基因敲除小鼠中并未显著降低。这是一个令人惊讶的发现，因为我们之前已验证INS2是睾丸支持细胞（在睾丸中为生殖细胞提供滋养功能的颗粒细胞的雄性对应物）中RHOX5的直接靶点。在卵巢中，RHOX8似乎是INS2表达的主要驱动因子，体外颗粒细胞中RHOX8蛋白激活时INS2启动子报告质粒的最大活性以及体内颗粒细胞特异性敲除RHOX8的小鼠中内源性INS2下调均证明了这一点。RHOX5在窦前颗粒细胞中诱导INS2表达，然后在排卵前卵泡中相对沉默。然而，INS2直到排卵LH峰后才达到峰值。在RHOX5的正常作用期过后，孕酮对INS2的诱导作用可能解释了为什么如果RHOX8能够对排卵所必需的靶基因进行冗余刺激，RHOX5基因敲除的雌性小鼠仍表现出明显正常的生育能力。
