The callus growth and its organogenesis or embryogenesis can be referred into three different stages. Organogenesis and morphogenesis in fetus have been studied with explant cultures. Cell migration is also fundamental in developmental processes such as gastrulation and organogenesis. In most animals organogenesis, along with morphogenesis, results in a larva. The process of shoot organogenesis starts form the multicellular origin. Odontogenesis is a multiplex and long process of postnatal organogenesis. Before organogenesis, the process is called embryo loss. SHH plays a very important role in organogenesis and most importantly craniofacial development. Knockout mouse studies suggest roles for MAP2K4 in mediating T cell development and liver organogenesis. The structural differentiation of body and organs (organogenesis) soon follows. The organogenesis process can be studied using embryos and organoids. Plant organogenesis can be induced in tissue culture and used to regenerate plants. The risk of major defects or organogenesis is highest for infection in the first trimester. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers. Organogenesis can then occur from those cells.