Biol168_10F_Lecture 4_1Oct2010

Biol168_10F_Lecture 4_1Oct2010 - Dr. Morris Maduro, UC...

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Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 4, page 1 Lecture #4: Drosophila : Overall development, embryonic polarity, maternal/zygotic genes, Textbook: 2nd Ed.: 48-51. 3rd Ed.: 31-34. Some figures in these notes are redrawn or reproduced from Wolpert et al. (2nd or 3rd editiosn). Importance of Drosophila The fruit fly is one of the most understood animals in terms of development and genetics. People have been working on Drosophila melanogaster since Thomas Hunt Morgan’s time in the early part of the last century. Flies are small, are easy to manipulate in the laboratory, and grow relatively quickly. As we will find out, the genes that pattern the Drosophila embryo are evolutionarily conserved. In 1995 the Nobel prize was awarded to Ed Lewis, Christiane Nüsslein-Volhard, and Eric Weishaus, the scientists that used genetics to describe how the embryo is patterned. Overview of Drosophila development This is overall life cycle of the fruit fly at 25ºC. It takes nine days to make a fly, which becomes sexually mature within two days. The female produces an egg, abo 5mm (¼ inch) long, which gets fertilized by male sperm through the micropyle at the anterior end of the egg. The haploid male an female nuclei fuse to form the diploid zygote nucleus . The nuclei undergo a series of rapid c divisions until there are thousands of nuclei along the outside surfa which constitutes the syn blastoderm stage. ut d ell ce, cytial After three hours, gastrulation starts, which is the inward movement of the future mesoderm and endoderm. The embryo hatches out as a feeding larva , which will grow and progress through two molts, or instars , before forming a pupa. The pupa metamorphoses into the adult. During this process most of the larval tissue is lost. The larvae contain tiny structures called imaginal discs which are the progenitors of adult structures such as the wings, legs and eyes. The Early Embryo After fertilization, the zygote nucleus undergoes a series of very rapid divisions ( mitosis ) in the absence of cell division (i.e. no cytokinesis ). As such, you have many nuclei sharing the same cytoplasm (a syncytium ). The nucleus undergoes 8 divisions to produce 256 nuclei (~8 min/division). The nuclei migrate to the periphery of the egg and continue to divide (at a slower rate). At division cycle 9, a small number of nuclei at the very posterior become pole cells , the progenitors of the germ line . At cycle 10,
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Dr. Morris Maduro, UC Riverside Biology 168 – 10F – Lecture 4, page 2 about 2 hours after fertilization, the embryo is referred to as the syncytial blastoderm . At cycle 11, transcription of embryonic mRNAs is first detectable. After a few more rounds of cell division (cycle 13, takes 12 min), the oocyte membranes squeeze between the nuclei to form the cellular blastoderm (~6000 cells, ~3h); transcription is greatly enhanced ( mid-blastula transition ). The
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This note was uploaded on 10/28/2010 for the course BIOL 168 taught by Professor Maduro during the Spring '10 term at UC Riverside.

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Biol168_10F_Lecture 4_1Oct2010 - Dr. Morris Maduro, UC...

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