Regulatory mechanism for gene expression during the development of mouse masseter muscle

神经肌肉接合处外烟碱乙酰胆碱受体（nAChR）的消除和nAChR亚基从胚胎型（α_2βγδ亚基）向成体型（α_2βεδ亚基）转换的突触发生研究尚未发表。我们通过分析发育过程中出现的δ亚基mRNA的表达水平来确定nAChR消除的时间过程，通过分析ε和γ亚基mRNA的表达水平来确定大鼠咬肌中nAChR亚基开关的时间过程。选用0 ~ 72日龄大鼠，18日龄前与母鼠同笼饲养，18日龄后饲喂颗粒饲料。采用竞争性聚合酶链反应联合反转录法测定mRNA的含量。这些亚基mrna在该大鼠咬肌中的表达谱表明，nAChR主要在7 ~ 28日龄之间被消除，nAChR主要在1 ~ 21日龄之间从胚胎型转换为成体型。由于大鼠的摄食行为似乎在19日龄后由哺乳转变为咬食，且已知咬肌在颌骨的咬动中起重要作用，因此咬肌中nAChR的消除和转换的完成可能与出生后发育过程中摄食行为的转换有关。

There are no published studies on synaptogenesis focusing on the elimination of the nicotinic acetylcholine receptor (nAChR) outside the neuromuscular junction and the nAChR subunit switch from the embryonic-type (α_2βγδ subunits) to the adult-type (α_2βεδ subunits). We analyzed the expression level of δ subunit mRNA, which was present through development, to identify the time course of the nAChR elimination, and the expression level of the ε and γ subunit mRNAs to identify the time course of the nAChR subunit switch in the rat masseter muscle. Rats from 0 to 72 days of age were used, kept in the same cages as their mothers by 18 days of age and then fed a pellet diet thereafter. The mRNA amounts were measured by competitive polymerase chain reaction in combination with reverse transcription. The expression profile of these subunit mRNAs in that rat masseter muscle indicated that the nAChR was mainly eliminated between 7 and 28 days of age and that the nAChR mostly switches from the embryonic to adult types between 1 and 21 days of age. Since the rat feeding behavior seems to switch from suckling to biting after 19 days of age and masseter muscle is known to play an important role in the biting movement of jaw, the completion of the nAChR elimination and switch in the masseter muscle may be related to the switch of the feeding behavior during the postnatal development.