SOMITE GENESIS IN THE CHICK. II. ANALYSIS OF NUTRIENTS FROM YOLK

¹ Department of Zoology and Entomology, University of Tennessee, Knoxville, Tennessee

1. Definitive primitive streak chick embryos have been cultured in vitro on media containing various fractions of whole yolk. Other embryos were grown on agar gels containing fractions derived by barium and alcohol fractionation of yolk and albumen dialysates. Following 22 hours of incubation, the blastoderms were mounted and examined for the development of somites.

2. The nutritional components of whole yolk are all present in the saline-soluble, dialyzable moiety, although the embryo can use the acid hydrolysate of dialyzed yolk, when accompanied by glucose, for this morphogenetic process.

3. The results, derived from an assay of barium and alcohol fractionation of both yolk and egg white, indicate that the early chick embryo can use, to limited extent, certain phosphate esters of carbohydrates in the formation of somites. There appear to be different phosphorylated materials in yolk than in albumen used by the embryo.

4. Insofar as whole yolk utilization is concerned for the formation of somites, there is evidence that the chick embryo grown in vitro uses: (1) glucose, (2) the amino acids found free in yolk, (3) a heat-labile, uncharacterized factor, and (4) certain phosphorylated carbohydrate intermediates. It may also use, but to a very limited extent, the products of proteolysis of yolk proteins.