Early Development: Invertebrates Brief overview of early developmental themes Early development of Sea Urchin Early development of Caenorhabditis elegans

Invertebrates? So what? Very easy to study Genetics and molecular events are highly

conserved

Cleavage initiation Maternal Factors Mitosis Promoting

Factor No Gaps at first Mid Blastula

transition-Gene activation from Zygote nucleus.

Cell and nuclear division Karyokinesis Cytokinesis Centrioles and axis

determination.

Patterns of Cell division

Gastrulation

Cell specification and Axis formation Cell-cell signaling or

acquisition of cellular factors

Bound to egg cytoplasm

Actively transported Associate with

centrioles

Sea Urchin: Initial Cleavage

Fate Mapping of Sea Urchin embryo

Global regulatory networks Maternal Factors Disheveled and b-catenin b-catenin and TCF- Micromere differentiation

Double Negative Gate

GeneA Gene B

Gene DGene C Gene E Gene F

Double Negative Gate: Micromere

Pmar1 HesC

ThrAlx1 Ets Delta

Otx/b-catenin

Double Negative Gate: Veg2 cell

Pmar1 HesC

ThrAlx1 Ets Delta

Specification of Vegetal Cells Wnt signaling; Early Signal (ES); Delta (Notch) b-catenin Blimp1 wnt autocrine;

Endoderm differentiation Pmar1 and HesC regulate ES, which leads to

mesoendoderm differentiation. Delta Mesoderm differentiation.

Axis specification Animal/Vegetal= Anterior/Posterior axis Nodal regulates Oral/Aboral axis

Gastrulation Blastula hatches from

Fertilization envelope. Skeletogenic mesenchyme

ingression. Vegetal plate involutes

beginning invagination.

Gastrulation

Gastrulation

Gastrulation

Caenorhabditis elegans

C. elegans and Initial Cleavage

Anterior-Posterior Axis Sperm Pronucleus location Cyk-4 activates GTPases

relocates PAR proteins to anterior

P-granules: Ribonucleoprotein complex RNA helicases Poly A polymerases Translation initiators

Dorsal-Ventral/Left-Right Axis formation

Specification: Autonomous Maternal cytoplasmic

factors SKN-1: EMS fate

determination. PAL-1: Differentiation

of P2 somatic descendents

PIE-1: placed into P blastomeres via PAR-1, inhibits SKN-1 and PAL-1 in P cells.

Specification: Conditional Cell-cell signaling (Juxtacrine) Paracrine signaling

Gastrulation