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

神经肌肉接头外烟碱型乙酰胆碱受体亚基从胚胎型(α_2βγδ亚基)向成人型(α_2βεδ亚基)的转换是突触发生研究的热点。通过对发育过程中δ亚单位基因表达水平的分析，确定大鼠咬肌中ε和γ亚单位的表达水平，以确定大鼠咬肌中nAChR亚单位转换的时间进程。实验动物为0~72日龄大鼠，18日龄时与其母鼠饲养在相同的笼子中，之后喂以颗粒饲料。用竞争性聚合酶链式反应结合逆转录法测定mRNA的含量。这些亚单位在大鼠咬肌中的表达谱表明，nAChR在7日龄至28日龄主要被消除，nAChR在1日龄至21日龄主要由胚胎型转变为成年型。由于大鼠的摄食行为在19日龄后似乎从哺乳转变为咬合，而咬肌在咬合运动中起着重要的作用，咬肌nAChR的清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.