Department of Poultry Science, University of Georgia, Athens, GA 30602, USA.
Department of Poultry Science, University of Georgia, Athens, GA 30602, USA.
Poult Sci. 2024 Nov;103(11):104174. doi: 10.1016/j.psj.2024.104174. Epub 2024 Aug 5.
Somatotropic gene expression has been altered by genetic selection, and developmental changes in insulin-like growth factor (IGF) and IGF binding protein (IGFBP) expression may contribute to rapid growth and muscle accretion in commercial broilers. The objective of this study was to evaluate changes in somatotropic axis activity between embryonic day (e) 12 and post-hatch day (d) 21. Liver and breast muscle (pectoralis major) were collected to measure gene expression, and blood was collected post-hatch to measure circulating IGFs. Liver IGF1 rose rapidly post-hatch and, in muscle, IGF1 exhibited a dynamic expression pattern. Levels decreased from e14 to e20, returned to e14 levels at d3, decreased again at d10, and stayed low thereafter. In both tissues, mRNA levels of several IGFBPs changed between embryogenesis and post-hatch. Liver IGFBP2 increased between e12 and e20, returned to e12 levels on d1, and remained low. Conversely, liver IGFBP4 expression was greater post-hatch than during embryogenesis. Expression of select IGFBPs was depressed in liver during the peri-hatch period. Liver IGFBP1, IGFBP3, IGFBP5, and IGFBP7 mRNA levels all decreased around this time and returned to embryonic levels by d3. In breast muscle, expression of both IGFBP2 and IGFBP4 was reduced after hatch. Circulating insulin-like growth factor IGF1 and IGF2 levels did not change between hatch and d21. These data suggest that post-hatch IGF effects are likely modulated by target tissue IGFR1 and IGFBP expression rather than changes in circulating hormone levels, with promotion or restriction of IGF-receptor binding regulating growth. Downregulation of several IGFBPs synthesized in the liver may facilitate the metabolic transition from utilizing yolk lipids to dietary carbohydrates. Several IGFBPs produced in breast muscle appear to have growth-promotive effects during embryogenesis but restrict growth of this tissue after hatch, as their post-hatch downregulation could facilitate local IGF signaling. These developmental gene expression patterns suggest that somatotropic hormonal signaling regulating growth and muscle accretion might be controlled through differential actions of IGFBPs and provide a basis for future functional studies.
生长激素基因的表达已被遗传选择改变，胰岛素样生长因子 (IGF) 和 IGF 结合蛋白 (IGFBP) 表达的发育变化可能有助于商业肉鸡的快速生长和肌肉积累。本研究的目的是评估胚胎期第 12 天 (e) 至孵化后第 21 天 (d) 之间生长轴活性的变化。采集肝脏和胸肌 (胸大肌) 以测量基因表达，并在孵化后采集血液以测量循环 IGF。肝脏 IGF1 在孵化后迅速上升，在肌肉中，IGF1 表现出动态表达模式。水平从 e14 到 e20 下降，在 d3 回到 e14 水平，再次在 d10 下降，此后保持低位。在这两种组织中，几种 IGFBP 的 mRNA 水平在胚胎发生和孵化后之间发生变化。肝 IGFBP2 在 e12 到 e20 之间增加，在 d1 回到 e12 水平，并保持低位。相反，肝 IGFBP4 的表达在孵化后高于胚胎发生期。围孵化期肝脏中某些 IGFBP 的表达受到抑制。肝 IGFBP1、IGFBP3、IGFBP5 和 IGFBP7 的 mRNA 水平均在此时下降，并在 d3 时恢复到胚胎水平。在胸肌中，孵化后 IGFBP2 和 IGFBP4 的表达均减少。孵化后至 d21 期间，循环 IGF1 和 IGF2 水平没有变化。这些数据表明，孵化后 IGF 的作用可能是通过靶组织 IGF1R 和 IGFBP 表达的调节，而不是循环激素水平的变化来调节的，促进或限制 IGF-受体结合调节生长。肝脏中合成的几种 IGFBP 的下调可能有助于从利用卵黄脂质向膳食碳水化合物的代谢转变。在胚胎发生期间，胸肌中产生的几种 IGFBP 似乎具有促进生长的作用，但在孵化后限制该组织的生长，因为它们孵化后的下调可能促进局部 IGF 信号传导。这些发育基因表达模式表明，调节生长和肌肉积累的生长激素激素信号可能通过 IGFBP 的不同作用来控制，并为未来的功能研究提供基础。
