Department of Biology, East Carolina University, Greenville, NC 27858, USA.
Evol Dev. 2010 Jan-Feb;12(1):45-60. doi: 10.1111/j.1525-142X.2009.00390.x.
Phylogenetic reconstructions suggest that the ancestral osteichthyan Hox paralog group 2 gene complement was composed of two genes, Hoxa2 and b2, both of which have been retained in tetrapods, but only one of which functions as a selector gene of second pharyngeal arch identity (PA2). Genome duplication at the inception of the teleosts likely generated four Hox PG2 genes, only two of which, hoxa2b and b2a, have been preserved in zebrafish, where they serve as functionally redundant PA2 selector genes. Evidence from our laboratory has shown that other telelosts, specifically striped bass and Nile tilapia, harbor three transcribed Hox PG2 genes, hoxa2a, a2b, and b2a, with unspecified function(s). We have focused on characterizing the function of the three Nile tilapia Hox PG2 genes as a model to examine the effects of postgenome duplication gene loss on the evolution of developmental gene function. We studied Hox PG2 gene function in tilapia by examining the effects of independent morpholino oligonucleotide (MO)-induced knockdowns on pharyngeal arch morphology and Hox gene expression patterns. Morphological defects resulting from independent MO-induced knockdowns of tilapia hoxa2a, a2b, and b2a included the expected PA2 to PA1 homeotic transformations previously observed in tetrapods and zebrafish, as well as concordant and unexpected morphological changes in posterior arch-derived cartilages. Of particular interest, was the observation of a MO-induced supernumerary arch between PA6 and PA7, which occurred concomitantly with other MO-induced pharyngeal arch defects. Beyond these previously unreported morphant-induced transformations, a comparison of Hox PG2 gene expression patterns in tilapia Hox PG2 morphants were indicative of arch-specific auto- and cross-regulatory activities as well as a Hox paralog group 2 interdependent regulatory network for control of pharyngeal arch specification.
系统发生重建表明，祖先硬骨鱼 Hox 同源基因簇 2 基因的组成由两个基因组成，Hoxa2 和 b2，这两个基因都在四足动物中保留下来，但只有一个基因作为第二咽弓身份（PA2）的选择基因。在硬骨鱼起源时的基因组复制可能产生了四个 Hox PG2 基因，只有两个，hoxa2b 和 b2a，在斑马鱼中被保存下来，在那里它们作为功能冗余的 PA2 选择基因。我们实验室的证据表明，其他硬骨鱼，特别是条纹鲈鱼和尼罗罗非鱼，拥有三个转录的 Hox PG2 基因，hoxa2a、a2b 和 b2a，具有未指定的功能。我们专注于描述三种尼罗罗非鱼 Hox PG2 基因的功能，作为研究基因组复制后基因丢失对发育基因功能进化影响的模型。我们通过检查独立的 morpholino 寡核苷酸（MO）诱导的 knockdowns 对咽弓形态和 Hox 基因表达模式的影响来研究 tilapia Hox PG2 基因的功能。来自 tilapia hoxa2a、a2b 和 b2a 的独立 MO 诱导 knockdown 的形态缺陷包括以前在四足动物和斑马鱼中观察到的预期的 PA2 到 PA1 同源转化，以及在后咽弓衍生软骨中出现的一致和意外的形态变化。特别值得注意的是，观察到 PA6 和 PA7 之间的 MO 诱导的额外弓，这与其他 MO 诱导的咽弓缺陷同时发生。除了这些以前未报道的形态诱导转化之外，在 tilapia Hox PG2 形态突变体中比较 Hox PG2 基因表达模式表明了特定于弓的自动和交叉调节活性，以及 Hox 同源基因簇 2 相互依赖的调节网络，用于控制咽弓指定。
