Drosophila Emrbyonic Stages

Question 1

Stage 4

Answer 1

• 50 minutes
• syncytial blastoderm stage
• blastoderm nuclei perform last 4 cleavage divisions (10-13)
• blastoderm nuclei to outside = clear rim with visible nuclei
• pole cells form, to posterior

Question 2

First cells to form in the embryo

Answer 2

pole cells

Question 3

Stage 4 key events

Answer 3

• syncytial divisions 10-13

* pole cell formation

Question 4

Stage 5

Answer 4

• blastoderm nuclei elongate
• pole cells start to move to dorsal sides
• membrane furrows separate the individual blastoderm nuclei
• nuclei sperical to elongate

Question 5

Stage 5 key event

Answer 5

cellularization

Question 6

Stage 6

Answer 6

• gastrulation - invagination of mesoderm initiated
• endoderm - anterior and posterior midgut invaginate
• blastoderm cells at posterior form a dorsal plate under pole cells - onset of germ band elongation
• cephalic furrow visible at 65% (from post)

Question 7

Stage 6 key events

Answer 7

• onset of gastrulation
• formation of ventral and cephalic furrow
• dorsal shift of pole cells

Question 8

Stage 7

Answer 8

• gastrulation completed
• midgut and hindgut invaginatele cells tilts inward
• posterior dorsal plate that carries the pole cells tilts inward and forms a pocket
• whole pocket called proctodeal invagination (part of anal passage)
• 3 folds - cephalic, anterior, posterior furrows
(only cephalic lasts til stage 9)

Question 9

Stage 7 key events

Answer 9

• completion of gastrulation

* pole cells in a pocket

Question 10

Stage 8

Answer 10

• rapid germ band elongation

* posterior tip of the germ band to 60% egg length (from posterior)

Question 11

Germ band elongation

Answer 11

the gradual extension of the germ band over the dorsal side of the embryo

Question 12

Stage 8 key events

Answer 12

rapid phase of germ band extension to 60% egg length

Question 13

Stage 9

Answer 13

• first neural stem cells (neuroblasts) segregate from the outer ectoderm
• by the end, the germ band exhibits a 3-layered architecture

Question 14

Three layered architecture

Answer 14

mesoderm
neuroblasts
outer ectoderm
(stage 9)

Question 15

Stage 9 key events

Answer 15

• germ band elongation to 70% egg length

* beginning of nervous system formation

Question 16

Stage 10

Answer 16

• appearance of stodeum
• germ band continues to stretch to 75%
• yolk sac

Question 17

Stodeum

Answer 17

gives rise to foregut and annexes
• formed by cells that are internalized at the anterior ventral side of the embryo
• site of internalization = stomodeal invagination

Question 18

Stage 10 key events

Answer 18

• germ band elongates to 75% egg length

* stomodeum invaginatees

Question 19

Stage 11

Answer 19

• first signs of germ band retraction
• segmental furrows that subdivide the germ band into metameric units
• thorax and abdomen boundaries = deep folds
• head’s gnathan segments visible ventral to cephalic furrow
• cephalic furrow becomes shallower and disappears

Question 20

Stage 11 key events

Answer 20

segmentation becomes visible

Question 21

Stage 12

Answer 21

• shortening of the germ band
- segmentation becomes prominent
- yolk sac pushed to dorsal side and is covered by amnioserosa
• anterior and posterior midgut meet at 60% egg length
• ventral cord separates completely from the epidermis= first axons in the ventral nerve cord appear

Question 22

Stage 12 key events

Answer 22

• onset of germ band retraction

* fusion of anterior and posterior midgut

Question 23

Stage 13

Answer 23

• initiated by completion of germ band shortening
• cells in primordial organs start to differentiate
• after germ band retraction = dorsal closure and head involution
• midgut primordium forms 2 longitudinal plates flanking the central yolk that fuse to form closed tubes

Question 24

Dorsal closure

Answer 24

• starts in stage 13
• epidermal primordium from ventral to dorsal
• closes the gap in the dorsal part

• begins at both ends, towards middle

Question 25

Stage 13 key events

Answer 25

• start of organ differentiation and dorsal closure

Question 26

Stage 14

Answer 26

• begins with onset of head involution
• 3 major morphogenetic events
- progression of dorsal closure
- closure of the midgut
- head involution

• epidermis covers 80% of embryo (leaving small part on dorsal side)
• most head structures (inc gnathal segments) brought inside
• obv by involution of clypeolabrum - nose shaped at front
• midgut plates fuse ventrally and dorsally to form closed tubes

Question 27

Gnathal segments

Answer 27

mandible, maxilla, and labium

Question 28

Clypeolabrum

Answer 28

part of the mouth

Question 29

Stage 14 key events

Answer 29

• progression of dorsal closure

* head involution

Question 30

Stage 15

Answer 30

• gut forms a closed tube, encloses the yolk sac, develops 3 constrictions
• anterior and posterior, midgut lumen is continuous w/ the lumen of the foregut and hindgut
• dorsal closure is complete
• head involution continues

Question 31

Stage 15 key events

Answer 31

dorsal closure of epidermis and midgut

Question 32

Stage 16

Answer 32

• 3 circular midgut constrictions become visible that subdivide the midgut into 4 chambers
• head involution is completed
• shortening of the ventral nerve cord - posterior tip to about 60% egg length

Question 33

Stage 16 key events

Answer 33

• subdivision of the midgut

* shortening of the ventral nerve cord

Question 34

Stage 17

Answer 34

• until the hatching
• differentiation of the organs complete
• fully developed tubes of the digestive system are visible
• movements of the embryos w/i the egg shells can be observed

Question 35

Stage 17 key events

Answer 35

• completion of organogenesis

* movements of the embryo w/i the vitelline envelope