Abbott B D, Hill L G, Birnbaum L S
Systemic Toxicology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Teratology. 1990 Mar;41(3):299-310. doi: 10.1002/tera.1420410307.
All-trans-retinoic acid (RA) is teratogenic to the embryonic mouse, producing malformations in many developing systems, including the limb bud and palate. High incidences of limb defects and cleft palate are induced at doses which are not maternally toxic and do not increase resorptions. Exposure to RA on gestational day (GD) 10 results in small palatal shelves, which fail to make contact on GD 14. The formation of small shelves could be a consequence of increased cell death, reduced proliferation, a combination of these effects, or some other effect such as inhibition of extracellular matrix production. After exposure to 100 mg RA/kg on GD 10, proliferation in mesenchymal cells of the palatal shelves was not reduced from GD 12 to GD 14 and the levels of cell death in control and treated shelves did not differ when observed by light and electron microscopy. The present study examines the effects of RA on cell death and proliferation from GDs 10-12 and compares the effects in palatal shelves and limb buds. Embryonic mice were exposed to RA suspended in corn oil (100 mg/kg on GD 10), a dose that was teratogenic but not maternally toxic or embryolethal. Embryos were collected at 4, 12, 24, 36, or 48 hr postexposure, and tissues which form the palate or limb were dissected from the embryos, stained by a modified Feulgen procedure, and whole mounted on slides. Mitotic index (MI) and percentage dead cells were determined for mesenchymal cells of the first visceral arch, maxillary process, or palatal shelf (depending on stage of development) and forelimb buds. In the palatal tissues from GD 10 to GD 12, RA did not significantly alter MI and percentage dead cells was significantly increased only at 4 hr postexposure. Some whole embryos were prepared for scanning electron microscopy (SEM). At 48 hr (GD 12) a reduction in the size of the shelves was not apparent on SEM. In the limb buds, RA did not increase percentage dead cells, but MI was significantly decreased. A decreasing rate of proliferation was detected in control facial tissues as development progressed, and this agrees with findings in rat and chick. Thus it appears that mesenchymal cell death and reduced proliferation are not responsible for the small palatal shelves seen on GD 14. RA did not increase cell death but inhibited proliferation in the limb bud, and this effect may contribute to the retarded development and malformations occurring in the limb.
全反式维甲酸（RA）对胚胎期小鼠具有致畸性，会在许多发育系统中导致畸形，包括肢芽和腭部。在不会引起母体中毒且不会增加吸收的剂量下，会诱导出高发生率的肢体缺陷和腭裂。在妊娠第10天（GD10）接触RA会导致腭突变小，在GD14时无法接触。腭突变小可能是细胞死亡增加、增殖减少、这些效应的综合作用，或者是其他效应（如细胞外基质产生受到抑制）的结果。在GD10给予100mg RA/kg后，从GD12到GD14，腭突间充质细胞的增殖没有减少，通过光学显微镜和电子显微镜观察，对照组和处理组腭突的细胞死亡水平没有差异。本研究考察了RA在GD10 - 12期间对细胞死亡和增殖的影响，并比较了在腭突和肢芽中的效应。将胚胎期小鼠暴露于悬浮在玉米油中的RA（GD10时为100mg/kg），该剂量具有致畸性，但不会引起母体中毒或胚胎致死。在暴露后4、12、24、36或48小时收集胚胎，从胚胎中解剖出形成腭部或肢体的组织，采用改良的福尔根染色法进行染色，然后整体封片于载玻片上。测定第一鳃弓、上颌突或腭突（取决于发育阶段）以及前肢芽的间充质细胞的有丝分裂指数（MI）和死细胞百分比。在从GD10到GD12的腭部组织中，RA没有显著改变MI，仅在暴露后4小时死细胞百分比显著增加。一些完整胚胎被制备用于扫描电子显微镜（SEM）观察。在48小时（GD12）时，在SEM下未观察到腭突大小减小。在肢芽中，RA没有增加死细胞百分比，但MI显著降低。随着发育进展，在对照面部组织中检测到增殖速率降低，这与在大鼠和鸡中的研究结果一致。因此，似乎间充质细胞死亡和增殖减少并不是GD14时所见腭突变小的原因。RA没有增加细胞死亡，但抑制了肢芽中的增殖，这种效应可能导致肢体发育迟缓和畸形。
