“IMPORTANT” GENES

　　Preimplantation Development

• Oct4 – transcription factor expressed in ICM, necessary for development of ICM and proliferation of trophectoderm (via of regulation of Fgf4 expression). (Autonomous)

• Fgf4 - transcription factor expressed in ICM that is crucial for trophectoderm proliferation (non-autonomous – activated by Oct4)

• White/c-kit – receptor tyrosine kinase crucial for neural crest cell and primordial germ cell migration, binds to steel which functions as chemoattractant – defects are cell autonomous

• Steel/c-kit ligand – secreted protein crucial for neural crest cell and primordial germ cell migration, binds to c-kit on surface of migrating cells – defects are cell non-autonomous

• Bicoid – transcription factor localized to anterior pole of Drosophila egg, anterior localization controls gene expression in anterior of syncitial embryo (formation of transcription factor gradients before cellularization)

• Nanos – posterior determinant of Drosophila egg, localized to posterior pole

• Hunchback – transcription factor whose level along a/p axis of Drosophila embryo is controlled by bicoid and nanos – threshold level of bicoid required to activate hunchback transcription, translation of hunchback mRNA inhibited by nanos (high level in anterior, low levels in posterior) – controls expression of gap genes (acts and activator and repressor of the same genes based on concentration)

• Kruppel – gap gene (transcription factor), repressed by high [hunchback], activated at intermediate [hunchback]

• Knirps – gap gene (transcription factor), repressed by hunchback but active at low [hunchback] – also has anterior stripe elements controlled by different enhancers and transcription factors – expression repressed by tailless at posterior end

• Giant – gap gene (transcription factor), repressed by hunchback, only active and very low [hunchback] - also has anterior stripe elements controlled by different enhancers and transcription factors - expression repressed by tailless at posterior end

• Dorsal – transcription factor whose expression is uniform throughout Drosophila embryo but has graded nuclear localization (localized to nucleus on ventral side, not localized on dorsal side) – activates ventrally expressed genes (twist/snail), represses dorsally expressed genes – nuclear localization prevented on dorsal side by gurken (secreted growth factor) from dorsal embryo, which signals follicular cells and prevents secretion of molecules mediating dorsal nuclear localization Spatzle/Toll à (Tolloid, Zorknult, Decapentalogic)

• Pair rule genes – primary pr genes regulated by gap genes, secondary pr genes regulated by primary pr genes, expression of primary and secondary pr genes is “out of phase,” creating unique expression pattern in each row of cells

• Hairy – Drosophila pair rule gene, single gene expressed in 7 stripes with each stripe controlled by a different enhancer through combination of activation and repression – transcription factor – stripe 6： activated by knirps and repressed by kruppel

• Even-skipped – Drosophila pair rule gene – transcription factor – stripe 2： activated by bicoid and hunchback, repressed by giant and kruppel

• Segment polarity genes – encode extracellular signalling proteins, transmembrane proteins, serine-threonine kinases, transcription factors, adhesion proteins – expressed just prior to cellularization and throughout embryogenesis, expressed in identical patterns in each segment (Ex. Engrailed (transcription factor) and hedgehog (signalling molecule) in anterior, wingless (signalling molecule) in posterior – expression of all 3 is interdependent)

• Homeotic genes – transcription factors – expression controlled by gap, pair rule, and segment polarity genes – spatial (a/p) and temporal expression patterns regulate structures in each segment (Ex. Scr controls a/p localization of salivary gland formation)