Given the task definition and input, reply with output. In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.

 The results from the present study indicate that Smad3 , Smad4 , and Smad7 , at least in part , serve as mediators linking TGF - beta1 to transcriptional regulation of IgA switching related gene and regulation of IgA class switching .

TGF - beta1