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Biol168_10F_Lecture 5_4Oct2010

Biol168_10F_Lecture 5_4Oct2010 - Dr Morris Maduro UC...

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Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 5, page 1 Lecture #5: Drosophila : Maternal genes and gap genes Textbook: 2nd Ed.: 143-151; 161-165. 3rd Ed.: 32-47; 57-61. Some figures in these notes are redrawn from Wolpert et al. (2nd edition). Maternal Genes Fall into Three Classes In their screens, the maternal patterning mutants of the early embryo fell into three classes: Anterior , Posterior , and Terminal . The textbook summarizes the genes involved in maternal patterning of the Drosophila embryo (about 30); we will look at only examples of each class. All of these genes act before about 3hrs after fertilization, just as the embryo becomes cellularized and cells become specified. With severe defects, the mutants often do not hatch, or they die within a few hours of hatching. [ The phenotypes and roles are often much more complex than described here or in the textbook. ] The goal for us here is to understand how these genes function together, and how changes in their expression and/or localization leads to phenotypes. bicoid ( bcd ) – The phenotype of embryos from bcd- mutant mothers is the absence of Head and Thorax, and the replacement of the Acron with a duplicated Telson. bcd- mutants can be partially rescued by addition of anterior cytoplasm from wild-type embryos. The bcd gene encodes a putative transcription factor, and is therefore a candidate for the anterior determinant. By in situ hybridization, the mRNA for bcd is localized to the anterior pole of the embryo. By antibody staining, the bcd protein is present in a gradient from anterior to posterior. Although the mRNA is sharply localized, the translation of that mRNA and the diffusion of the protein allow the establishment of a smooth gradient from anterior to posterior. Further proof that bicoid is the anterior determinant comes from transplant experiments using bcd mRNA. Injection of bcd mRNA at the anterior of bcd- embryos can rescue them, while injection at middle or posterior sites can induce the head structures to form there. bcd- antibody staining in situ hybridization (The minus sign here means that the embryo did not inherit functional bicoid from its mother, because bicoid is maternal.) nanos ( nos ) nos- embryos are shorter than wild-type and lack the abdominal segments. nanos
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