Early development in Drosophila

Drosophila as model

Small size, Short life cycle, High Fecundity, Many genetic tools, Development processes conserved

Fertilization

gives organism new genome

Cleavage

series of mitotic division

Gastrulation

cell rearrangement, mitotic division slow, blastomere undergo dramatic movement

Organogenesis

cells in different germ layer exchange chemicla signal, cell interaction and rearrangement produce specific organs at specific sites

Formation body axes

Anterior posterior, Dorsal ventral, Lateral medial

Drosophila early development stages

Fertilization, Cleavage, Gastrulation, Organogenesis, Formation body axes

Fertilization in Drosophila

Sperm enter already activated egg, enter through micropyle, membrane do not fuse only pronuclei fuse

Micropyle

only site where sperm can enter Drosophila egg, likely prevent polyspermy

Superficial cleavage

most insect, Karyokinesis (nuclear) with cytokinesis (cell), creates syncytium

Drosophila 9th cycle

5 nuclei reach posterior pole, enclosed by cell membrane to generate pole cells

Energids

nuclei and their associated cytoplasmic island of cytoskeletal protein

Drosophila 10th cycle

nuclei move toward the periphery

Drosophila after 13th cycle

Cell membrane fold inward, partition off each energid into own cell formation of cellular blastoderm, single layered jacket around yolky core

Syncytial blastoderm

describe only cellular division, no cell membranes separating nuclei

Cellular blastoderm formation

Microtubules and actin filament, Phase I → Invagination between nuclei (furrow canals), Phase II →Invagination increase and actin constrict at basal end of cell

Mid blastula transition in Drosophila

slowdown of nuclear division, cellularization, increase new RNA transcription (maternal to zygotic)

Maternal effect genes

genes in maternal genome, produce mRNA or protein localized in region of egg, affect embryonic development

Maternal messages

maternal mRNA in oocytes

Maternal to zygotic transition in Drosophila

embryonic control switch from store maternal mRNA to transcribed mRNA from zygote, begin at cycle 11 and enhanced at cycle 14

Gastrulation in Drosophila

after mid blastula transition, segregate presumptive meso/endo/ecto derm, prospective mesoderm folds inwards (Ventral furrow)

Ventral Furrow (Gastrulation)

prospective mesoderm folding inward, active myosin and actin accumulate at midline forming connection through adherens junctions, transmit contractile forces causing apical constriction, pinch off into ventral tube

Anterior- Posterior Midgut invagination (Gastrulation)

Ventral furrow pinch off into ventral tube, pole cell internalized, presumptive endoderm invaginates to form 2 pockets, presumptive ectoderm bend to form cephalic furrow

Cephalic furrow

presumptive ectoderm bend to form, separate future head and trunk regions

Germ band extension (Gastrulation)

surface ectodermal and mesoderm undergo convergence and extension, migrate toward ventral midline, form germ band, extends posteriorly and wraps around dorsal surface of embryo, marks end of gastrulation

Germ Band

collection of cell along ventral midline, all cell that will form the trunk

Part of Drosophila gastrulation

Ventral furrow, Cephalic furrow, Midgut invagination, Pole cell internalization, Germ band extension

Drosophila organogenesis and segmentation

dividing of ectoderm and mesoderm, after 3 germ layer formed (gastrulation)

Dorsal Closure

after germ band retract → expose dorsal surface, 2 side of epidermis brough together

Drosophila body plan

consistent across life stages, repeating segmental units between head and tail, thorax has 3 segment and abdomen has 8