(Alliance, FBgn0000533 )

Component of the extracellular signaling pathway that establishes the dorsal-ventral pathway of the embryo (PubMed:9477324, PubMed:2107028, PubMed:12493753). Three proteases; ndl, gd and snk process easter to create active easter (PubMed:9477324). Active easter defines cell identities along the dorsal-ventral continuum by activating the spz ligand for the Tl receptor in the ventral region of the embryo (PubMed:9477324).

(UniProt, P13582)

Maternal effect lethal; both recessive loss-of-function and dominant gain-of-function alleles female sterile. Embryos produced by females homozygous for recessive alleles are dorsalized; lack ventral and lateral elements similar to embryos produced by dl/dl females; dorsal folds extend around circumference of embryo; lateral head fold and ventral furrow fail to form; germ band does not extend, and cuticle forms a tube with dorsal characteristics throughout. Degree of dorsalization proportional to level of ea expression as demonstrated by hypomorphic and temperature-sensitive alleles. Temperature sensitive period as demonstrated by ea14 from the time of pole-cell formation to gastrulation; developmental Northern blots demonstrate the presence of transcript in the ovaries and increased levels during the first four hours of embryonic development followed by a marked decline between hours four and six. Partial rescue of mutant phenotype achieved by injection of cytoplasm or poly-A+ RNA from wildtype embryos or embryos from females homozygous for other dorsal-group mutants; spatial source of donor cytoplasm unimportant; degree of rescue reduced with distance from site of injection; complete rescue producing viable and fertile adults achievable with injection of purified ea+ mRNA. tw, a zygotically active member of the dorsal group of genes, is not expressed in such embryos (Thisse, Stoetzel, El Messal, and Perrin-Schmidt, 1987, Genes Dev. 1: 709-15); furthermore strong alleles allow zen expression ventrally where it is not normally observed (Rushlow, Frasch, Doyle, and Levine, 1987, Nature 330: 583-86); periodicity of ftz stripes slightly disrupted in embryos from ea mothers (Carroll, Winslow, Twombly, and Scott, 1987, Development 99: 327-32). Females heterozygous for fully penetrant dominant alleles are sterile; the offspring of eaD3/+ females display ventralization or lateralization as indicated by lateral extension of the denticle bands; patches or rings of denticles may encircle the embryo; however, the mesoderm, the most ventral pattern element, is not increased; dorsal structures such as filzkorper, antennal and maxillary sense organs are absent; field of dorsal hairs greatly reduced. eaD2/+ females are lateralized, producing embryos that lack presumptive mesoderm and have no ventral furrow, show dorsoventrally symmetrical folding at gastrulation with the lateral head fold encircling the embryo, and do not undergo germ band extension. Injection of ea-deficient embryos with 200 times the quantity of mRNA required for complete rescue does not cause ventralization, indicating that gain of function alleles are not merely hypomorphic in nature.