Establishment of polarity in egg and embryo (Orb)

mRNA localization plays a central role in the establishment of polarity axes in the Drosophila egg and embryo. A key component of the mRNA localization system is encoded by the orb gene. orb is essential for determining both the A-P and D-V axes of the developing egg chamber, and mutations in orb are found to prevent the proper localization of mRNAs required for these polarity axes such as osk, Bic-D, K(10), and gurken. orb encodes a germ-line specific RRM type RNA binding protein which is homologous to the Xenopus CPEB protein. In Xenopus, the CPEB protein controls the translation of masked mRNAs in developing oocytes. We have found that localized mRNAs such as osk, K(10), and Bic-D are not translated in orb mutant ovaries. In favor of a direct role in regulating the localization/translation of these mRNAs, we have found that Orb protein binds to their 3'UTRs both in vivo and in vitro. One of the mRNAs bound by Orb protein in vivo is orb itself. Recent results indicate that Orb protein autoregulates its own on site expression by binding to localized orb mRNA and activating translation. The orb gene is weakly haploinsufficient and we taken advantage of this haploinsufficiency to devise genetic screens for other genes involved either in orb autoregulation or in the establishment of polarity.


Nathaniel Hafer - Graduate Student

Li Chin Wong - Graduate Student




Costa, A. et al., The Drosophila fragile X protein functions as a negative regulator in the orb autoregulatory pathway. Dev. Cell, 2005. 8(3): p.331-42.

Chang et al., (2001) Functioning of the Drosophila orb gene in gurken mRNA localization and translation. Development 128, 3169-3177.

Tan et al., (2001) An autoregulatory feedback loop directs the localized expression of the Drosophila CPEB protein Orb in the developing oocyte. Development 128: 1159-1169.

Chang et al., (l999) The Drosophila CPEB homolog, orb, is required for oskar protein expression in oocytes. Dev Biol. 215. 91-106.

Christerson, L., V. Lantz, J. Chang, P. Schedl, D. McKearin (1995). In Localized RNA. (Ed H. Lipschitz), R.G. Landes Co., Austin, TX, pp. 87-98.

Lantz, V., J.S. Chang, J. Horabin, D. Bopp, and P. Schedl (1994). The Drosophila orb RNA binding protein is required for the formation of the egg chamber and establishment of polarity. Genes and Devel., 8:598-613.

Lantz, V. and P. Schedl (1994). Multiple cis-acting targeting sequences are required for orb mRNA localization during Drosophila oogenesis. MCB, 14:2235-2242.

Lantz, V., L. Ambrosio and P. Schedl (1992). The Drosophila orb gene is predicted to encode sex-specific germline RNA binding proteins and has localized transcripts in ovaries and early embryos. Devel. 115:75-88.



people  chromatin sex determination germline

  Molecular Biology Department