University Museum of Zoology and Department of Zoology, Downing Street, Cambridge, CB2 3EJ, UK.
Dev Genes Evol. 2010 Sep;220(3-4):117-22. doi: 10.1007/s00427-010-0329-1. Epub 2010 Jun 22.
The arthropod head problem has puzzled zoologists for more than a century. The head of adult arthropods is a complex structure resulting from the modification, fusion and migration of an uncertain number of segments. In contrast, onychophorans, which are the probable sister group to the arthropods, have a rather simple head comprising three segments that are well defined during development, and give rise to the adult head with three pairs of appendages specialised for sensory and food capture/manipulative purposes. Based on the expression pattern of the anterior Hox genes labial, proboscipedia, Hox3 and Deformed, we show that the third of these onychophoran segments, bearing the slime papillae, can be correlated to the tritocerebrum, the most anterior Hox-expressing arthropod segment. This implies that both the onychophoran antennae and jaws are derived from a more anterior, Hox-free region corresponding to the proto and deutocerebrum of arthropods. Our data provide molecular support for the proposal that the onychophoran head possesses a well-developed appendage that corresponds to the anterior, apparently appendage-less region of the arthropod head.
节肢动物头部问题困扰动物学家一个多世纪。节肢动物成虫的头部是一个复杂的结构,由不确定数量的体节的修饰、融合和迁移而来。相比之下,可能是节肢动物姊妹群的有爪动物具有相对简单的头部,由三个体节组成,在发育过程中定义明确,并发育出具有三对口器的成虫头部,这些口器专门用于感觉和食物捕获/操作。基于前 Hox 基因 labial、proboscipedia、Hox3 和 Deformed 的表达模式,我们表明这些有爪动物的第三个体节,具有粘液乳头,可与 tritocerebrum(最前部的 Hox 表达节肢动物体节)相关联。这意味着有爪动物的触角和颚都来自于一个更靠前的、没有 Hox 的区域,与节肢动物的原脑和后脑相对应。我们的数据为有爪动物头部具有与节肢动物头部显然无附肢的前部相对应的发达附肢的观点提供了分子支持。