Table 2.

Distribution and functions of different IRS isoforms.

Isoforms	Distribution	Activation	Function
IRS1	Widely expressed in various tissues	PI3K, SHP2, and Grb2	Cell differentiation and glucose homeostasis [59]
IRS2	Widely expressed in various tissues	PI3K, SHP2, and Grb2	Cell growth and differentiation, mainly participate in glucose homeostasis in liver [59]
IRS3	Adipocytes and brain	PI3K and SHP2	Cell growth of adipocytes [60]
IRS4	Embryonic tissues	PI3K and Grb2	Cell proliferation and differential and reproductive capacity [61]
IRS5	Mainly in kidney and liver	Undetected	Undefined [62, 63]
IRS6	Skeletal muscle	Undetected	Undefined [63]