Oliver B, Kim Y-J, Baker B S. the number of cells that expressed BAM protein was increased 5- to 10-fold in the germarium regions of mutants. These results suggest that RBP9 protein binds to mRNA to down regulate BAM protein expression, which is essential for the initiation of cystocyte differentiation into functional egg chambers. In hypomorphic mutants, cystocytes differentiated into egg chambers; however, oocyte determination and Rabbit Polyclonal to Ezrin positioning were perturbed. Therefore, the concentrated localization of RBP9 protein in the oocyte of the early egg chambers may be required for proper oocyte determination or positioning. RBP9 is usually a RNA binding protein that shares a high level of sequence similarity with ELAV (41) and human Hu proteins (HuC, HuD, Hel-N1, and HuR) (26, 29, 48). Proteins in this family are known to be expressed in the nuclei of neuronal cells right after the completion of mitotic division. RBP9 is usually expressed predominantly in the nuclei of cells of the central nervous system (CNS), after the CNS metamorphosis that occurs during the pupal period (19). The related human Hu proteins are also expressed primarily in neurons and are localized preferentially in the nuclei (8). Hu proteins are absent in neuroblasts but appear in subsequent early-lineage neurons and maturing neuronal cells. Thus, it has been suggested that proteins in this family are required for neuronal maturation. A role for in Acetyl-Calpastatin (184-210) (human) neurogenesis is usually further suggested by the fact that ELAV is usually expressed specifically in the nuclei of all neurons (41), and loss-of-function alleles of are embryonic lethal, causing abnormal CNS development (40). Recently, was suggested to regulate neuron-specific splicing of pre-mRNA (24), which is Acetyl-Calpastatin (184-210) (human) usually consistent with the presence of RNA binding motifs in the ELAV protein and its nuclear localization pattern. However, in vitro studies suggest mRNA stability rather than pre-mRNA splicing as a functional target of the Hu Acetyl-Calpastatin (184-210) (human) proteins. For example, Hu proteins were shown to bind to stretches of U residues (the AU-rich element), and this conversation increases the stability of the bound reporter mRNAs in a cell culture system (5, 9, 21, 26, 28, 32, 37). Given that Hu protein is usually localized mainly in the nucleus, the cytoplasmic function of mRNA stabilization appears to be accomplished by the shuttling of nuclear Hu proteins to the cytoplasm (9). Because Hu protein binding sequences are often found in mRNAs that encode cell growth regulators, it has been suggested that this Hu proteins control Acetyl-Calpastatin (184-210) (human) cell proliferation by regulating the stability of mRNAs that encode cell proliferation and/or differentiation transmission proteins (3, 4, 5, 15, 21, 26, 32). For example, the in vitro binding of Hel-N1 protein to the 3 untranslated region (UTR) of mRNA, which encodes a transcriptional repressor abundant in undifferentiated neuronal precursor cells, suggests the involvement of Hel-N1 in the regulation of nerve cell development (21). Recently, we found that RBP9 down regulates the expression of (homolog of mRNA (36). These results indicate that this RBP9 family of proteins binds to mRNAs and functions in the regulation of cell growth and differentiation. In addition to the two putative functions of the Hu protein gene family discussed above, the expression of certain Hu proteins in nonneuronal tissues indicates the presence of additional physiological functions. In vertebrates, four closely related Hu homologs are expressed in a distinct developmental pattern. For example, in adult frogs, elrC and elrD are expressed exclusively in nerve cells during specific developmental stages, whereas elrA is usually expressed in all tissues throughout development. In particular, elrB is usually expressed in testis and ovaries, in addition to its stage-specific expression in the brain (13). Therefore, each of the related Hu homologs appears to participate in the regulation of unique developmental processes. In this paper, we present the results of experiments designed to decipher the function(s) of RBP9. We show that RBP9 protein is usually expressed in the cytoplasm of ovaries, as well as in the nuclei of neuronal cells. Analysis of mutants revealed.