Localized Bicaudal‐C RNA encodes a protein containing a KH domain, the RNA binding motif of FMR1.

The Bicaudal‐C (Bic‐C) gene of Drosophila melanogaster is required for correct targeting of the migrating anterior follicle cells and for specifying anterior position. Females lacking any wild type copies of Bic‐C produce only eggshells open at the anterior end, because of the failure of the columnar follicle cells to migrate in the correct position at the nurse cell‐‐oocyte boundary. Embryos which develop from eggs produced in females with only one wild type copy of Bic‐C show defects in anterior patterning and an abnormal persistence of oskar RNA in anterior regions. We cloned Bic‐C and found that, in ovaries, Bic‐C RNA is expressed only in germline cells. Bic‐C RNA is localized to the oocyte in early oogenesis, and later concentrates at its anterior cortex. The Bic‐C protein includes five KH domains similar to those found in the human fragile‐X protein FMR1. Alteration of a highly conserved KH domain codon by mutation abrogates in vivo Bic‐C function. These results suggest roles for the Bic‐C protein in localizing RNAs and in intercellular signaling.