miRNA miRNA ancient form

of regulation. Protection against

viral pathogens Quick regulation and

turnover of mRNA.

Drosophila Development: Genetics at work!

Development of Drosophila

Closer look at Early Development of Drosophila.

Cellularization

Gastrulation and Segmentation

Anterior-Posterior Polarity in Oocyte Starts during oogenesis Gurken mRNA

transferred to oocyte. Signal sent back to

oocyte post Gurken/Torpedo interaction.

Par-1 mediated organization of microtubules to posterior side of oocyte via Oskar. Minus end (posterior) and plus end (anterior).

Dorsal-Ventral Patterning in Oocyte.

Dorsal Gradient

Anterior-Posterior Polarity in Embryo

Syncytial Specification in Drosophila

Anterior-Posterior Polarity in Embryo

Translational Regulation Stored oocyte mRNAs-

selective inhibition of translation.

Genes turned on quickly post-fertilization.

Relies on the recruitment of proteins involved in making a polyA tail.

Drosophila Bicoid gene product.

Gap Genes Role in early

segmentation Transcriptional

regulators

Pair-rule Genes Another set of

Transcriptional Regulators.

Develops the precursors for the actual segments.

Zebra-stripe pattern of expression.

Stripe position determined by which enhancer is bound.

Pair-rule Genes

Segment Polarity Genes Wingless (Wnt) and

Hedgehog signal pathway proteins.

Paracrine signaling maintains segmentation.

Homeotic Selector Genes (Hox) Regulated by Pair-

rule and Gap genes. Antennapedia

Complex and bithorax complex.

AbdA and AbdB repressed by Hunchback and Kruppel.

Repression maintained by Polycomb, activation maintained by Trithorax.

Epigenetic Memory Trithorax- keeps genes active.

Counteract Polycombs Modify nucleosomes Keep H3K4 trimethylated

Polycomb- keeps genes inactivated. H3K27 methylase Bind meH3 tails

Hox Genes in Other Species Mouse Limb

development-deletion of Hoxd11, Hoxd12, Hoxd13 causes polydactyly

Zebra fish, loss of H3K27 demethylase activity and subsequent Hox gene disregulation- poor tail development