Smith Kathleen K
Department of Biology, Duke University, Durham, North Carolina 27708, USA.
Dev Dyn. 2006 May;235(5):1181-93. doi: 10.1002/dvdy.20676.
Biologists have long studied the evolutionary consequences of the differences in reproductive and life history strategies of marsupial and eutherian mammals. Over the past few decades, the impact of these strategies on the development of the marsupial embryo and neonate has received attention. In this review, the differences in development in the craniofacial region in marsupial and eutherian mammals will be discussed. The review will highlight differences at the organogenic and cellular levels, and discuss hypotheses for shifts in the expression of important regulatory genes. The major difference in the organogenic period is a whole-scale shift in the relative timing of central nervous system structures, in particular those of the forebrain, which are delayed in marsupials, relative to the structures of the oral-facial apparatus. Correlated with the delay in development of nervous system structures, the ossification of the bones of the neurocranium are delayed, while those of the face are accelerated. This study will also review work showing that the neural crest, which provides much of the cellular material to the facial skeleton and may also carry important patterning information, is notably accelerated in its development in marsupials. Potential consequences of these observations for hypotheses on constraint, evolutionary integration, and the existence of developmental modules is discussed. Finally, the implications of these results for hypotheses on the genetic modulation of craniofacial patterning are presented.
长期以来，生物学家一直在研究有袋类哺乳动物和有胎盘类哺乳动物在生殖和生活史策略上的差异所带来的进化后果。在过去几十年里，这些策略对有袋类胚胎和新生儿发育的影响受到了关注。在这篇综述中，将讨论有袋类哺乳动物和有胎盘类哺乳动物颅面区域发育的差异。该综述将突出器官发生和细胞水平上的差异，并讨论重要调控基因表达变化的假说。器官发生期的主要差异在于中枢神经系统结构，特别是前脑结构的相对发育时间发生了全面变化，相对于口面部器官的结构，有袋类动物的前脑结构发育延迟。与神经系统结构发育延迟相关的是，神经颅骨的骨化延迟，而面部的骨化加速。这项研究还将回顾一些研究成果，这些成果表明，为面部骨骼提供大量细胞物质并且可能还携带重要模式信息的神经嵴，在有袋类动物中的发育明显加速。讨论了这些观察结果对有关限制、进化整合以及发育模块存在的假说的潜在影响。最后，阐述了这些结果对颅面模式遗传调控假说的意义。
