DEVELOPMENTAL BIOLOGY Wright Atlas – Chapter 1

Chapter 1 – Atlas/Introduction Developmental Biology The study of the formation of a new organism Development includes; Growth Differentiation Metamorphosis Tissue repair Regeneration Most organisms go through similar (general) stages of development during their life cycle

Model Organisms It is unethical to experiment on human embryos Must study model organisms to gain insights into human development No one single organism can give this These models include Plant (Arabidopsis thaliana) Fruit Fly (Drosophila melanogaster) Nematode (Caenorhabditis elegans) Zebra Fish (Brachydanio rerio) Frog (Xenopus tropicalis) Mouse (Mus musculus)

Model Organisms Many model organisms are Dioecious Exist as separate sexes Some exist are Sexually Dimorphic Sexes are distinguished externally Embryonic classification is made by examining the early formation of the gut Protostomes Mouth area opens first Deuterostomes Anus area opens first

Protostomes and Deuterostomes

Gastrulation and Formation of Blastopore

Protostomes and Deuterostomes

Phylogeny of the Model Organisms

Mollusca Dioecious – exist as separate sexes One – distinctly female Other – distinctly male Majority of animal species (some plants)

Nematoda Adults live as males and self-fertilizing hermaphrodites (Ascaris is sexually dimorphic) Caenorhabditis elegans 3 days to mature

Arthropoda Fertilization is internal and females lay up to 100 oocytes/day Drosophila melanogaster Dioecious and sexually dimorphic 6 days to full sexual maturity

Drosophila Melanogaster Excellent model to study Polytene chromosomes Arise in non-dividing cells Repeated DNA replication 100s of identical copies Identical banding patterns

Echinodermata Classic embryology specimen - Echinoidea Lytechinus pictus Excellent model to study fertilization Produces millions of gametes in one season Dioecious, but not sexually dimorphic

Echinodermata Asteroidea Dioecious, but Not sexually dimorphic Asterias Dioecious, but Not sexually dimorphic Seasonal spawning with transparent oocytes shed from ovaries Important in studying meiotic maturation

Chordata Characteristics Phylum Chordata Lancets, tunicates, vertebrates, …. Presences of Dorsal hollow nerve cord Notochord Pharyngeal slits Muscular postanal tail (at some time during embryonic development) Cephalochordata Front brain development Lancelet (branchiostoma)

Chordata Characteristics Pharyngeal slits Notochord Dorsal hollow nerve cord Postanal tail

Diagram of Adult Lancet Notochord Nerve cord Intestine Anus Pharyngeal slits Atriopore Gonads Buccal cirri

Zebrafish Osteichthyes (Actinopterygii) Tropical freshwater fish i.e. zebrafish (Brachydanio rerio) Release 100s of oocytes per day Develop rapidly ~3 days ; sexually mature ~3 months

Amphibia Frogs and salamanders Large / robust embryos Develop externally Easily undergo microsurgery Rana pipens & Xenopus laevis

Aves Domestic chicken Gallus gallus & Gallus domesticus Dioecious and sexually dimorphic Large & robust embryo Survive surgical manipulations

Mammalia Most widely used is mouse model Mus musculus Internal fertilization Oocytes easily undergo in vitro fertilization Develops asynchronously for about a week Sexual maturity in = 4 weeks Gestation 19 – 21 days Lives up to 3 years Transgenic Mice, Mouse knockouts, Genetically Engineered Mice

Mammalia Used to teach mammalian embryology Domestic pig Sus scrofa Makes anatomy easier to interpret from embryology

Model Organisms

Overview of Developmental Embryology Models

Types of Cell Division

Cell Cycle

Fertilization

Early Domains of Zygotic Genes

Cleavage

Classification of Morphogenetic processes

Embryogenesis

Axis of Symmetry

Cortical Rotation

Early Domains of Zygotic Genes

Gastrulation

Comparative Development of Mesoderm

Neurulation

Tailbud Stage

Stages of Xenopus Development

Xenopus Fate Mapping

In Vitro Preparations of Sense mRNA or Antisense Hybridization

Methods of Inhibition

End of Wright Chapter 1