Gradients, cascades, and signaling pathways Chapter 31 Gradients, cascades, and signaling pathways Development of the Drosophila body plan Genetic studies One of the best understood developmental systems 13,600 genes Axis determination Signaling pathway Transcriptional and translational regulation Principles of Development 2nd edition, by Lewis Wolpert (Chapter 5) The genetics of axis specification in Drosophila The Chapter 9 of Developmental Biology by Scott Gilbert, 7th edition Chang-Gung University Dr. Li-Mei Pai

Targeted ectopic expression of the Eyeless gene --induce eyes to develop in locations such as legs and antennae Closely related genes initiate the development program for the same organ in animals separate by 500 million years of evolution

Life cycle of Drosophila 4 stages: embryo, larva, pupa, adult Culture condition: 250C and 60% humidity

Body patterning of fly One cell to an organism Fig. 31-1 Figures\Chapter09\DevBio7e09070.jpg

Homogeneous egg to asymmetry ---control of gene expression (spatial and temporal) Asymmetric division Asymmetric distribution of cytoplasmic component Maternal genes Segmentation genes Homeotic genes

Early development of Drosophila

Transgenic flies

Model of Drosophila Anterior-Posterior Pattern Formation Maternal effect genes Zygotic genes Syncytial blastoderm Figures\Chapter09\DevBio7e09081.jpg Cellular blastoderm

Maternal effect genes—( do not damage mother) preformed mRNA and proteins in the egg Zygotic genes—embryo nuclei

Polarization of the body axes during oogenesis each egg chamber: 3 types of cells Oocyte with nucleus (germinal vesicle-GV) Connected to 15 nurse cells }---germ-line Surrounded by a monolayer of about 1000 somatic follicle cells

Female sterile mutation Somatic cells Germline cells Genetic analyses Biochemical assays

Fig. 31-4

The effects of mutations in the maternal gene system Three classes Anterior Posterior terminal head and thoracic abdominal acron and telson

Three independent Genetic Pathways Interact to Form the Anterior-Posterior Axis of the Drosophila Embryo Figures\Chapter09\DevBio7e09101.jpg

Three independent Genetic Pathways Interact to Form the Anterior-Posterior Axis of the Drosophila Embryo Figures\Chapter09\DevBio7e09102.jpg

Morphogen----cell structure Quantitative---qualitative

Bicoid gene is necessary for the establishment of the anterior structure Bicoid--Transcribed in nurse cells, transported into the oocyte, localized at the anterior( 3’UTR) fertilized—translated Protein diffuses and forms morphogen gradient No head and thoracic If prick at the anterior of normal egg Partial rescued Bicoid mutant + wt anterior cytoplasm— wt head

Gene copy number

Repression of nanos mRNA translation outside of posterior Hb-repressor of transcription (of Abdominal gene) Hb is required for thorax structure, and is absent in posterior Nanos---prevent Hb translation— mRNA degraded—knirps and Giant expression

Posterior determination Nanos ( and pumilio) suppresses the translation Of the maternal mRNA of Hunchback Zygotic hb establishes a Gradient If maternal hb is absent, nanos is no more needed

Fate map Information—maternal regulators Refined—zygotic genes Region—compartment 14 parasegments (gastrulation)— Eg. 8=A2P+A3A

Every other segment

The target genes of hunchback Increase dose of hunchback – kruppel shift posteriorly Gap: 1) respond to the Bicoid 2) regulate one another

Phenotype of pair rule mutant

Expression of pair rule gene

Regulation of pair rule genes

Pair rule genes The mRNA is uniformly expressed, but protein synthesis is blocked— specific degradation of mRNA Stripes develop, transcription ceases Ftz promoter respond to other pair-rule genes Fig. 31-32

Segment polarity-engrailed

Engrailed- transcription factor homeodomain

Intercellular signaling set up PS boundary

Segment polarity A/P axis within one segment Ventral epidermis of the abdomen—ventral denticle belts (anterior) Mutation—alter the denticle pattern Wingless=Wnt hedgehog Principles of Development by Lewis Wolpert Oxford university press Second edition, 2002

Signals controlling cuticle pattern Principles of Development by Lewis Wolpert

Fig. 31-34

Cell, 127, 469, 2006

Colon cancer-APC Oncogenic-c-myc Cell, 127, 469, 2006

Wg distributed asymmetrically— less in posterior (endocytosis and degradation) Until early stage 10, Wingless spreads into the engrailed domain and then recedes sometime during stage 10. At stage 12, Wingless-containing vesicles are infrequently detected in engrailed-expressing cells. At this stage, rhomboid begins to be expressed at the posterior of each engrailed stripe, leading to the activation of EGFR signaling in and around its domain of expression. The zone of Rhomboid influence corresponds roughly to where denticles form at the end of embryogenesis, while Wingless signaling is associated with the absence of denticles (bald cuticle). PS, parasegment boundary; SB, segment boundary.

Different pathways that transduce Wnt signals Camadulin Planar polarity-hair pointed direction Cell, 109, 271, 2002

Intercellular signaling set up PS boundary Developmental Biology by Scott F. Gilbert Sinauer Associates, publishers Six edition, 2000

The domains of expression of the segment polarity genes Patched is not in en cells Principles of Development by Lewis Wolpert

The hedgehog signaling pathway Without signal—Ci is processed as a repressor into nucleus With signal---full length Ci acts as an activator in the nucleus Principles of Development by Lewis Wolpert

Reading reference : Wnt/b-Catenin signaling in Development and disease Cell, 127, 469-480, 2006