lec 7- embryogenesis in Drosophila

Question 1

why do they study the fruit fly?

Answer 1

short life span, large number of offspring, easy to manipulate genes

Question 2

what are the stages of embryogenesis of a Drosophila?

Answer 2

-fertilized egg–> cleavage –> gastrulation

Question 3

what does the egg of the fruit fly have?

Answer 3

-it has a pattern, as well as a micropyle at the anterior end which is where the sperm enters the egg
-has dorsal appendages

Question 4

does the development of the egg occur outside of the female fly?

Answer 4

yes, fertilization is inside while the egg develops outside

Question 5

what is syncytium?

Answer 5

when the zygotic nucleus in the egg rapidly divides for several rounds , creating many nuclei in the cytoplasm of the egg

Question 6

what occurs after the syncytium?

Answer 6

after the 9th division, the nuclei move to the periphery to form the syncytial blastoderm

Question 7

what happens after the syncytial blastoderm is formed?

Answer 7

a few nuclei move to the posterior end and become surrounded by cell membranes forming pole cells

Question 8

what happens after the pole cells are formed?

Answer 8

cellular blastoderm is formed, cell membranes form around the rest of the nuclei causing pole cells to end up on the outer surface of the blastoderm, this gives rise to germ cells which produce gametes

Question 9

what are the types of cells in the blastoderm?

Answer 9

-ectoderm
-mesoderm
-endoderm
-amnioserosa
-germline

Question 10

what do the amnioserosa cells do?

Answer 10

they help with germ band extension and dorsal closure

Question 11

what occurs during gastrulation?

Answer 11

-mesoderm moves inside
-the endoderm invaginates at two places
-mesoderm migrates under the ectoderm
-ectodermal cells that form nervous system move inside the cell

Question 12

what do the cells on the ventral side of the embryo undergo?

Answer 12

-germ band extension, they move from ventral side, to posterior, to dorsal
-germ band expansion causes the cells to intercalate, making them longer and thinner

Question 13

what happens after germ band extension?

Answer 13

-the two endoderms continue to invaginate inwards and eventually fuse to form the digestive system
-invagination of the endoderm near the posterior end brings pole cells into the interior

Question 14

what happens during germ band retraction?

Answer 14

-germ band retraction brings the embryo to its final posterior position, the head, thorax, and abdomen
-germ band retraction exposes the amnioserosa, causing them to shorten and flatten

Question 15

what happens during dorsal closure?

Answer 15

-amniserosa cells contract and invaginate, causing epidermal cells to completely surround the embryo

Question 16

what are the 3 steps to dorsal closure?

Answer 16

1. an actomyosin purse strings forms at the boundary between the epithelial and amnioserosa cells
2. cells in the aniserosa undergo cell cycles of actomyosin contractions, bringing the margins of amniserosa together
3. when the epidermal cells meet at the anterior and posterior end, they fuse to create a zipper that seals the epidermis closed