Mesoderm-endoderm inducing factor

The induction of mesodermal organs by guinea pig bone marrow was discovered by Toivonen (1954). Later, Takata and Yamada (1960) showed that guinea pig bone marrow also induces endodermal structures. The mesoderm-endoderm-inducing factor could be extracted and partially purified (Yamada, 1962). The inducing activity is found in a protein fraction. 

So far the factor has not been separated into fractions which induce only mesodermal or endodermal organs. One factor seems to induce a combined mesoderm-endoderm anlage which segregates into a variety... 

Fig. 2. Mesodermal and endodermal tissues induced by the highly purified vegetalizing factor in isolated gastrula ectoderm of Triturm alpestries (sandwich method) (courtesy of Dr. H. Grunz). Abbreviations End, endoderm M, muscle and N, notochord.

In isolated ectoderm the factor induces mesodermal tissues (muscle, notochord, renal tubules, and blood cells) as well tissues which are derived from the endoderm like endodermal epithelium and intestine and, less frequently, liver, pancreas, stomach-, esophagus- and pharynx-epithelium (Fig. 2). 

When tested on whole gastrulae by the implantation method, the factor only induces organs which are derived from the mesoderm. The formation of endodermal tissues may perhaps be repressed by the host endoderm, or induced endodermal cells may be integrated into the host endoderm. 

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