mRNA splicing factor that regulates alternative splicing od specific genes. Has a maternal role in embryonic dorsal-ventral patterning; such role is probably indirect and due to its function as mRNA splicing factor regulator. Not present in the oocyte or early embryo. Expressed in a number of embryonic tissues at later stages. First detected at stage 9 of embryogenesis, in the epithelium of the stomodeum, which develops into the foregut and in the epithelium of the proctodeal opening. Segmentally repeated expression was observed in the mesodermal layer in stage 11. At stage 13, segmentally repeated ectodermal expression is observed. Also expressed in the epithelium of the foregut and posterior spiracles and the fat body. Detected in both nurse cells and follicle cells during oogenesis. Enriched in follicle cells adjacent to the anterior end of the oocyte. Death during embryogenesis; without displaying dorsal-ventral patterning defects. Heterozygous embryos act as a dominant maternal enhancer of dorsalizing mutation cact(E10) and display a partially dorsalized phenotype. Belongs to the ESRP family.