The pineal gland is a neuroendocrine organ responsible for production of the nocturnal hormone melatonin. A specific set of homeobox gene-encoded transcription factors govern pineal development, and some are expressed in adulthood. The brain-specific homeobox gene (Bsx) falls into both categories. We here examined regulation and function of Bsx in the mature pineal gland of the rat. We report that Bsx is expressed from prenatal stages into adulthood, where Bsx transcripts are localized in the melatonin-synthesizing pinealocytes, as revealed by RNAscope in situ hybridization. Bsx transcripts were also detected in the adult human pineal gland. In the rat pineal gland, Bsx was found to exhibit a 10-fold circadian rhythm with a peak at night. By combining in vivo adrenergic stimulation and surgical denervation of the gland in the rat with in vitro stimulation and transcriptional inhibition in cultured pinealocytes, we show that rhythmic expression of Bsx is controlled at the transcriptional level by the sympathetic neural input to the gland acting via adrenergic stimulation with cyclic AMP as a second messenger. siRNA-mediated knockdown (>80% reduction) in pinealocyte cultures revealed Bsx to be a negative regulator of other pineal homeobox genes, including paired box 4 (Pax4), but no effect on genes encoding melatonin-synthesizing enzymes was detected. RNA sequencing analysis performed on siRNA-treated pinealocytes further revealed that downstream target genes of Bsx are mainly involved in developmental processes. Thus, rhythmic Bsx expression seems to govern other developmental regulators in the mature pineal gland.

中文翻译：

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Bsx 同源框基因在成人松果体中的昼夜节律调节和分子作用。

松果体是负责产生夜间激素褪黑激素的神经内分泌器官。一组特定的同源框基因编码的转录因子控制松果体的发育，有些在成年期表达。大脑特异性同源框基因 (Bsx) 属于这两类。我们在这里检查了 Bsx 在大鼠成熟松果体中的调节和功能。我们报告 Bsx 从产前阶段表达到成年期，其中 Bsx 转录本位于合成褪黑激素的松果体细胞中，正如 RNAscope 原位杂交所揭示的那样。在成人松果体中也检测到 Bsx 转录物。在大鼠松果体中，发现 Bsx 表现出 10 倍的昼夜节律，并在夜间达到峰值。通过将大鼠体内肾上腺素能刺激和腺体手术去神经与体外刺激和培养的松果体细胞中的转录抑制相结合，我们表明 Bsx 的节律性表达在转录水平上由通过肾上腺素作用的腺体的交感神经输入控制。以环 AMP 作为第二信使的刺激。松果体细胞培养物中 siRNA 介导的敲低（>80% 减少）显示 Bsx 是其他松果体同源框基因的负调节因子，包括配对框 4 (Pax4)，但未检测到对编码褪黑激素合成酶的基因有影响。对 siRNA 处理的松果体细胞进行的 RNA 测序分析进一步揭示了 Bsx 的下游靶基因主要参与发育过程。因此，