1. Life Cycles and Evolution of Developmental Patterns

2. Frog Development
Overview of development

3. Frog Life Cycle

4. Gametogenesis and Fertilization
What role do hormones play in these processes?
estrogen and vitellogenin
progesterone and meiosis
Seasonal effects
females
males
estrogen stimulates production of yolk proteins in liver (vitellogenin)
Progesterone restarts meiosis at metaphase of first meiotic division. At end of first division, egg released from ovary
Photoperiod and temperature influences hormone production and egg laying.
In leopard frog all sperm is made in summer

5. Cleavage
amphibian cleavage
Xenopus cleavage

6. Cleavage
D – yolk shown as yellow and green – cytoplasmic rearrangement during first cleavage of Xenopus
E – end of first cleavage
F – 8 cell embryo
G – early blastula, smaller cells same overall volume
H – late blastula
I – cross section of late blastula

7. Gastrulation gastrulation in cross-section external gastrulation
gastrulation in Xenopus

8. Gastrulation Xenopus A – dorsal view B – ventral view
C – blastopore and yolkplug stage
D – beginning of neurulation
E – beginning of neural groove
F – neural tube is forming

9. Organogenesis
Neurulation

10. Developmental Patterns Unicellular Protists
How were acetabularia used to illustrate the role of the nucleus in development?
Hammerling’s experiments – 1930’s

11. Developmental Patterns Unicellular Protists
material coded by nucleus and stored in tip shown to be m-RNA
factors in cytoplasm influence translation of m-RNA

12. Developmental Patterns Unicellular Protists
Conjugation in paramecia
Allows for combining genes from two individuals
form cytoplasmic bridge
micronuclei undergo meiosis
macronuclei degenerate
all but one micronucleus in each degenerates
microneuclei divide to form stationary and migratory
migratory crosses cytoplasmic bridge and fertilizes stationary
diploid nucleus divides and generates a new macronucleus

13. Developmental Patterns Unicellular Protists
sexual reproduction in chlamydomonas
Zygote is only diploid cell
No structural difference between gametes.
Recognition between mating types occurs via flagella

14. Evolution of Multicellular Organisms
beginnings of differentiation
Representatives of Volvocales
A – Chlamydomonas
B- Gonium
C- Pandorina
D – Eudorina
E - Pleodorina, posterior cells differentiate as reproductive cells gonidia
F - Volvox

15. Evolution of Multicellular Organisms
simplest organisms with sperm and eggs
Sexual reproduction in Volvox
requires sexual inducer protein to form eggs and sperm – stimulated by heat
Zygotes resist drying, heat and cold

16. Evolution of Multicellular Organisms
Life cycle of Dictyostelium

17. Evolution of Multicellular Organisms
Life cycle of Dictyostelium
Aggregation occurs when food supply is diminished.
slug = grex
grex migrates in dark, moist environment
migration ceases in illuminated area and differentiation into fruiting body begins
anterior cells form stalk
posterior cells become spore cells

18. Evolution of Multicellular Organisms
c-AMP causes aggregation.
Cells respond to C-AMP by moving toward it and releasing c-AMP – get spiral wave of c-AMP
What causes the myxamoebae to aggregate?

19. Evolution of Multicellular Organisms
What kinds of molecules promote cell adhesion in dictyostelium?
gp 24 protein seen after mitosis stops; gp 80 seen in streming amoeba; gp150 present in migrating grex

20. Evolution of Multicellular Organisms
What controls differentiation in dictyostelium?
internal & external influences:
internal – nutritional status, cell size, cell cycle phase at starvation, intracellular calcium levelss
external – ammonia and c-AMPstimulates prespore gene expression; high calcium and lipid, DIF-1 stimulates pre-stalk pathway
other proteins involved in final differentiation

21. Overview of Metazoan Development
Porifera – not true metazoans; no real organs; three major cell types
diplobasts
radial versus bilateral symmetry
protostomes versus deuterostomes
molters versus spiral cleavage
amniote egg helped transition to land