前肢和后肢的异速生长是在脊椎动物中观察到的普遍现象。作为一种典型的早熟鸟,与前肢相比,鸭子的后肢发育更为先进,使它们在孵化后不久就能行走。这种现象与胚胎期长骨的发育密切相关。然而,控制鸭前肢和后肢骨骼异速生长的分子机制仍然难以捉摸。在这项研究中,我们采用了表型,组织学,和基因表达分析,以研究鸭胚胎中肱骨(前肢骨)和胫骨/股骨(后肢骨)之间的发育差异。我们的结果表明,从E12到E28(胚胎年龄),胫骨和肱骨之间的重量和长度差异逐渐增加。在E12时,仅在胫骨中观察到软骨内骨化,而在肱骨中未观察到。差异表达基因(DEGs)的数量在H12时逐渐增加。T12,H20vs.T20和H28vs.T28阶段与表型变异一致。在所有3个阶段共发现38个DEG。蛋白质相互作用网络分析显示HOXD基因家族成员(HOXD3/8/9/10/11/12)之间有很强的相互作用,HOXB基因家族(HOXB8/9),TBX基因家族(TBX4/5/20),HOXA11、SHOX2和MEIS2。基因表达谱分析表明,与胫骨相比,肱骨中所有HOXD基因的表达水平更高,而在肱骨中检测到的HOXA/HOXB基因的表达水平却相反。这些发现表明,HOX基因家族中的不同簇在鸭胚胎前肢和后肢的骨骼发育调节中起着不同的作用。值得注意的是,TBX4特别在胫骨中表现出高表达水平,而TBX5仅在肱骨中表现出相似的模式,如先前在其他物种研究中所见。总之,这项研究确定了在胚胎发育过程中参与鸭前肢和后肢骨骼异速生长的关键调控基因。骨骼发育是一个复杂的生理过程,需要进一步的研究来阐明候选基因在软骨内骨化中的调节作用。
Allometric growth of the
forelimb and hindlimb is a widespread phenomenon observed in vertebrates. As a typical precocial bird, ducks exhibit more advanced development of their hindlimbs compared to their forelimbs, enabling them to walk shortly after hatching. This phenomenon is closely associated with the development of long bones in the embryonic stage. However, the molecular mechanism governing the allometric growth of duck
forelimb and hindlimb bones is remains elusive. In this study, we employed phenotypic, histological, and gene expression analyses to investigate developmental differences between the humerus (
forelimb bone) and tibia/femur (hindlimb bones) in duck embryos. Our results revealed a gradual increase in weight and length disparity between the tibia and humerus from E12 to E28 (embryo age). At E12, endochondral ossification was observed solely in the tibia but not in the humerus. The number of differentially expressed genes (DEGs) gradually increased at H12 vs. T12, H20 vs. T20, and H28 vs. T28 stages consistent with phenotypic variations. A total of 38 DEGs were found across all 3 stages. Protein-protein interaction network analysis demonstrated strong interactions among members of HOXD gene family (HOXD3/8/9/10/11/12), HOXB gene family (HOXB8/9), TBX gene family (TBX4/5/20), HOXA11, SHOX2, and MEIS2. Gene expression profiling indicated higher expression levels for all HOXD genes in the humerus compared to tibia while opposite trends were observed for HOXA/HOXB genes with low or no expression detected in the humerus. These findings suggest distinct roles played by different clusters within HOX gene family during skeletal development regulation of duck embryo\'s forelimbs versus hind limbs. Notably, TBX4 exhibited high expression levels specifically in tibia whereas TBX5 showed similar patterns exclusively within humerus as seen previously across other species\' studies. In summary, this study identified key regulatory genes involved in allometric growth of duck
forelimb and hindlimb bones during embryonic development. Skeletal development is a complex physiological process, and further research is needed to elucidate the regulatory role of candidate genes in endochondral ossification.