frog development

Question 1

rRNA in early frog embryo

Answer 1

rRNA not needed from zygotic genome, maternal contribution makes up for it (frog will later die without ribosomal rna but for eary gasturla mom’s rRNA is enough)

Question 2

blastomere

Answer 2

segment of a blastula (ie: split twice…4 blastulas)

Question 3

blastula–> gastrula cell size

Answer 3

cells are dividing but quantity of cytoplasm stays the same up until the gastrula phase

Question 4

how does beta catenin induce the D/V axis?

Answer 4

beta catenin can only act as TF when localized in the nucleus, can only be localized in the nucleus when WNT pathway active

1) DSH is displaced to the dorsal region upon fertilization/cortical rotation
2) WNT pathway is only active dorsally, so beta catenin only localized in the nucleus dorsally

Question 5

what does spemanns organizer secrete?why? **

Answer 5

• wnt inhibitors secreted, eventually localized anteriorily and bmp inhibitors secreted eventually localized dorsally
• organizer is region where wnt and bmp are both inhibited made up of the first cells to invaginate eventually become head
• if you have two organizers you will have another anterior posterior axis and another head ie: conjoined twins

Question 6

Neural tube formation (cytoskeleton factors)

Answer 6

microtubules elongate from the apical to basal domain
adhesion belts constricts making the cells of the invaginating cells thin at the top and wide at the bottom, further, the differential cadherin expression allows the cells pinching off to bind to each other with n-cadherin instead of binding to e cadherin

Question 7

E-Cadherin/ Beta Catenin

Answer 7

• E-Cadherin suppresses tumor suppressors because forces cells to be attached to one another
• E-Cadherin overexpression means more beta catenin serving as an adhesion protein instead of as a transcription factor so decreases proliferation

Question 8

Why are the first cleavages of embryogenesis synchronized?

Answer 8

All of the mitosis promoting factor is shared within the egg until mid-blastula transition, therefore because equal amounts of MPF and MPF RNA–> cleavage will be synchronized

Question 9

Maternally Expressed Traits [maternal mRNA translation]

Answer 9

Maternally expressed genes (mRNA/ proteins laid in the egg) derived from the DNA during metaphase 1 ie: the DNA is 2n, egg will have two copies of the mutant allele

Question 10

How does notochord induce overlying ectoderm to become neural tube ?

Answer 10

Secretes BMP Inhibitors allowing differential expression of cadherin (e-cadherin to n-cadherin)

Question 11

Why is the Organizer induced and not the entire dorsal side of the embryo

Answer 11

siamois protein (wnt) + nodal protein (vegT + VG1) = goosecoid protein (MRG for organizer)