Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403, USA.
J Endocrinol. 2012 Sep;214(3):421-35. doi: 10.1530/JOE-12-0110. Epub 2012 Jul 3.
In mammals, parathyroid hormone-related peptide (PTHrP, alias PTH-like hormone (Pthlh)) acts as a paracrine hormone that regulates the patterning of cartilage, bone, teeth, pancreas, and thymus. Beyond mammals, however, little is known about the molecular genetic mechanisms by which Pthlh regulates early development. To evaluate conserved pathways of craniofacial skeletogenesis, we isolated two Pthlh co-orthologs from the zebrafish (Danio rerio) and investigated their structural, phylogenetic, and syntenic relationships, expression, and function. Results showed that pthlh duplicates originated in the teleost genome duplication. Zebrafish pthlha and pthlhb were maternally expressed and showed overlapping and distinct zygotic expression patterns during skeletal development that mirrored mammalian expression domains. To explore the regulation of duplicated pthlh genes, we studied their expression patterns in mutants and found that both sox9a and sox9b are upstream of pthlha in arch and fin bud cartilages, but only sox9b is upstream of pthlha in the pancreas. Morpholino antisense knockdown showed that pthlha regulates both sox9a and sox9b in the pharyngeal arches but not in the brain or otic vesicles and that pthlhb does not regulate either sox9 gene, which is likely related to its highly degraded nuclear localization signal. Knockdown of pthlha but not pthlhb caused runx2b overexpression in craniofacial cartilages and premature bone mineralization. We conclude that in normal cartilage development, sox9 upregulates pthlh, which downregulates runx2, and that the duplicated nature of all three of these genes in zebrafish creates a network of regulation by different co-orthologs in different tissues.
在哺乳动物中，甲状旁腺激素相关肽 (PTHrP，别名甲状旁腺素样激素 (Pthlh)) 作为一种旁分泌激素，调节软骨、骨骼、牙齿、胰腺和胸腺的模式形成。然而，在哺乳动物之外，关于 Pthlh 调节早期发育的分子遗传机制知之甚少。为了评估颅面骨骼发生的保守途径，我们从斑马鱼（Danio rerio）中分离出两个 Pthlh 同源物，并研究了它们的结构、系统发育和基因座关系、表达和功能。结果表明，pthlh 基因的复制起源于硬骨鱼基因组复制。斑马鱼 pthlha 和 pthlhb 呈母源性表达，并在骨骼发育过程中表现出重叠和独特的合子表达模式，与哺乳动物的表达域相呼应。为了研究复制的 pthlh 基因的调控，我们研究了它们在突变体中的表达模式，发现 sox9a 和 sox9b 在拱和鳍芽软骨中都是 pthlha 的上游基因，但只有 sox9b 在胰腺中是 pthlha 的上游基因。 形态发生素反义敲低显示，pthlha 在咽弓中调节 sox9a 和 sox9b，但在大脑或耳泡中不调节 sox9b，而 pthlhb 既不调节 sox9a 也不调节 sox9b，这可能与其高度退化的核定位信号有关。pthlha 的敲低而不是 pthlhb 的敲低导致颅面软骨中 runx2b 的过表达和骨矿化的提前发生。我们的结论是，在正常的软骨发育中，sox9 上调 pthlh，pthlh 下调 runx2，而这三个基因在斑马鱼中的复制性质创造了一个不同的组织中不同的同源物进行调节的网络。
