Scott W J, Collins M D, Ernst A N, Supp D M, Potter S S
Division of Basic Science Research, Children's Hospital Research Foundation, Cincinnati, Ohio.
Dev Biol. 1994 Jul;164(1):277-89. doi: 10.1006/dbio.1994.1198.
This manuscript reports on the limb malformations and axial skeleton alterations found in legless fetuses and their heterozygote and wild-type littermates transplacentally exposed to all-trans-retinoic acid via a single intraperitoneal injection on Day 7, 8, 9, 9.5, 10, 10.5, or 11 of gestation. The most surprising aspect of the results was the temporal sensitivity of the legless mouse limb to exogenous retinoic acid. On Day 11, when both fore- and hindlimbs of nonmutant embryos can be made abnormal by retinoic acid and other teratogens, retinoic acid did not increase the frequency or severity of legless hindlimb defects and forelimb malformations were only slightly enhanced. On the other hand, retinoic acid administration on Day 7 exacerbated forelimb malformations in legless fetuses at a time when visible emergence of the affected structure is still 48 hr away. Heterozygote and wild-type fetuses had no limb malformations at this time point. A similar phenomenon was observed with hindlimb malformations after retinoic acid exposure on Day 8 except for a few mild limb malformations in heterozygotes at a high dose of retinoic acid. This early hypersensitivity of fore- and hindlimbs was followed by a period of reduced sensitivity (Day 8 forelimb; Day 9 hindlimb) when even very high doses (50 mg/kg) induced minimal changes in the typical legless malformation pattern. Subsequently, at the time of visible limb bud emergence (Day 9 forelimbs; Day 10 hindlimbs), sensitivity to exogenous retinoic acid was again detected. Surprisingly, the altered malformation patterns induced by retinoic acid in lgl mutants were nearly identical to those from earlier, pre-emergence exposure. A number of axial skeleton alterations were induced in legless fetuses by retinoic acid, especially after exposure on Days 7, 8, or 9. Posterior truncations were particularly noteworthy, showing a graded response in which frequency and severity of truncation were worst in lgl/lgl fetuses; heterozygotes gave an intermediate response, and wild-type fetuses were least affected. This exacerbation of the legless phenotype by exogenous retinoic acid coupled with the similarity between legless and retinoid malformations suggest that the legless mutation has altered endogenous retinoid homeostasis or a downstream retinoid-responsive gene.
本手稿报告了通过在妊娠第7、8、9、9.5、10、10.5或11天经腹腔单次注射，使无腿胎儿及其杂合子和野生型同窝仔经胎盘暴露于全反式维甲酸后所发现的肢体畸形和轴向骨骼改变。结果最令人惊讶的方面是无腿小鼠肢体对外源性维甲酸的时间敏感性。在第11天，当非突变胚胎的前肢和后肢都可因维甲酸和其他致畸剂而变得异常时，维甲酸并未增加无腿后肢缺陷的频率或严重程度，前肢畸形仅略有加重。另一方面，在第7天给予维甲酸会加剧无腿胎儿的前肢畸形，而此时受影响结构的明显出现仍有48小时之遥。杂合子和野生型胎儿在这个时间点没有肢体畸形。在第8天维甲酸暴露后，后肢畸形也观察到类似现象，只是在高剂量维甲酸作用下杂合子有一些轻微的肢体畸形。前肢和后肢的这种早期超敏反应之后是一段敏感性降低的时期（第8天的前肢；第9天的后肢），此时即使是非常高的剂量（50毫克/千克）也只会在典型的无腿畸形模式中引起最小的变化。随后，在可见肢体芽出现时（第9天的前肢；第10天的后肢），对外源性维甲酸的敏感性再次被检测到。令人惊讶的是，维甲酸在lgl突变体中诱导的畸形模式改变与早期、芽出现前暴露所导致的模式几乎相同。维甲酸在无腿胎儿中诱导了许多轴向骨骼改变，尤其是在第7、8或9天暴露后。后部截断尤其值得注意，呈现出一种分级反应，其中截断的频率和严重程度在lgl/lgl胎儿中最严重；杂合子表现出中等反应，野生型胎儿受影响最小。外源性维甲酸对无腿表型的这种加剧作用，以及无腿畸形与类维生素A畸形之间的相似性，表明无腿突变改变了内源性类维生素A的稳态或一个下游类维生素A反应基因。
