Life Cycles and Evolution of Developmental Patterns

Frog Development Overview of development

Frog Life Cycle

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

Cleavage amphibian cleavage Xenopus cleavage

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

Gastrulation gastrulation in cross-section external gastrulation gastrulation in Xenopus

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

Organogenesis Neurulation

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

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

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

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

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

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

Evolution of Multicellular Organisms Life cycle of Dictyostelium

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

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?

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

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

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