Developmental Biology

1. Developmental Biology Life Cycles and Developmental Stages

2. Developmental Stages • Dividing embryogenesis into stages allows for easier description of embryonic events • Stages should follow logical, observable changes in the embryo • Refinement of classical embryological stages with the advent of molecular technology has occurred

3. Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

4. Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Attraction of sperm to egg species specificity attraction at a distance Fusion of sperm and egg activation of egg to complete meiosis prevention of polyspermy Fusion of pronuclei Rearrangement of cortical cytoplasm Developmental Stages

5. Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Rapid cell divisions Drosophila 8’, Xenopus 20’ no transcription S and M phases only mammals 12-24 hr, chick 6-12 hr transcription occurs Produces a hollow embryo blastocoel mesoderm induction signals from endoderm induce ectodermal cells Developmental Stages

6. Formation of gut Complex cell movements to arrange trilaminar embryo and set up body plan Major movements are of the mesodermal cells Positioning of mesodermal cells to interior of embryo Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

7. Cell movements occur in distinct ways in different genera Invertebrates invagination of cells on the future ventral side Vertebrates fish & amphibians spherical embryos involution of mesoderm on future dorsal side at blastopore lip Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

8. Vertebrates Reptiles, birds and some mammals (humans) disc embryos delamination of ectoderm to form endoderm & mesoderm delaminating cells involute at Henson’s node, primitive streak and groove form & progresses along dorsal midline mammals (mouse) cup embryos ingression at the dorsal midline (primitive streak) as in chick and human Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

9. Invertebrates Echinoderms unusual CNS Arthropods form CNS from region from neural cells that are displaced from the neuroectoderm Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

10. Vertebrates Dorsal ectoderm is induced by the notochord to become neural tissue Ectoderm turned into neural tissue is called the neural plate Neural plate cells change shape & fold into neural tube Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

11. neural crest transition zone between neural plate & ectoderm becomes neural crest crest cells leave dorsal neural tube & migrate throughout embryo differentiating into multiple cell types melanocytes – pigment cells peripheral nervous system – sensory and motor nerves adrenal gland Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

12. Invertebrates Highly variable depending on phyla Arthropods (insects) Imaginal discs Specialization of segments Developmental Stages • Early Development • Fertilization • Cleavage • Gastrulation • Neurulation • Later Development • Organogenesis • Larval molts • Metamorphosis • Aging

13. Vertebrates Complete body plan is apparent at end of neurogenesis Pharyngula All vertebrate embryos similar appearance Major landmarks branchial arches/visceral arches/pharyngeal pouches segmented neural tube segmented axial mesoderm – somites Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

14. Forming organs gut tube, proctodeum (anus), stomodeum (mouth) pronephros (kidney) dorsal aortas heart liver diverticulum eye anlagen otic vesicles (ears/tympanic membranes) cartilage deposition Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

15. Invertebrates Arthropods and Nematodes Series of larval stages Several orders of magnitude increases in organismal size Ecdysysis – shedding of exoskeleton/epiderm Holometabolous arthropods Imaginal discs Precursor to adult organ Hormonally induces to develop during larval stages Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

16. Arthropods Evagination of imaginal tissues Echinoderms Massive revision of body plan Chordates Tunicates Loss of chordate structures Cephalochordates Amphibians Major changes to respiratory system & digestive tract Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages

17. Cell senescence Regeneration Early Development Fertilization Cleavage Gastrulation Neurulation Later Development Organogenesis Larval molts Metamorphosis Aging Developmental Stages