CDB 312-DB Bootcamp Goals: Learn the basics on the development of the model organisms used at Vanderbilt. Descriptive embryology (not experimental zoology, developmental biology, genetic manipulation, etc) Care and feeding Compare and contrast Course Management Director: David Bader Student Director: Rachel Skelton Student Director (in training): Abby Olena Coordinator: Kim Kane Grades Attendance. Asking questions/Participation. Getting into it. Final “Exam”
Volvox carteri -This is one of the first multicellular organisms seen in nature. -Two cell types: inner gamates (around 12-16) and outer epithelium (a few thousands). -The epithelium resembles Chlamydomonas. -Asexual reproduction is most common. -Sexual reproduction occurs with stress and is stimulated by one of the most bioactive compounds found in nature. What comes with multicellularity?
Death of the individual first appears in the life cycle. Separation from the environment is possible. Body compartments are formed. Cell diversification is possible. Multicellularity also introduces embryology. Volvox has a peculiar event in its developmental program.
Inversion of V. carteri is a critical step in its embryology. With asexual reproduction, a haploid cell divides. Two cell types are generated. Epithelial cells form an embryonic sphere. SEM on left and standard histology on right. (From D. Kirk) Here’s the story: Haploid embryos have gonidia on outside and epithelium with flagella on inside. A phialopore forms and the epithelium “inverts” so that flagella are outside. Gonidia are translocated to the inside of the adult. Even in this simplest of organisms, development is highly complex.
Anatomical Positions Organisms, organ systems, and organs have names for the different surfaces and positions. In Thursday’s lab, use the right terms when you examine embryos.
What “larger” questions in biology are best approached by Developmental Biology? Differentiation Morphogenesis Growth Reproduction Evolution Nature/Nurture Repair??? how one cell gives rise to many different cell types generation of ordered forms comprised of organized cells regulated cell growth is essential instructions must be passed between generations species diversity with colinearity of mechanism and genes how the environment influences developmental processes
Things don’t always look as they seem. Embryology is a moving target in terms of?? Morphogenesis Cell division and migration Gene expression and cell diversification Reaction with the environment Bottom line: Sometimes you can’t predict what you will see.
What is the relationship to mom during these processes? What are the major stages/events in embryogenesis? Fertilization Cleavage Morula Blastula Gastrulation Partitioning of germ layers Organogenesis Growth Sexual maturation Reproduction Death
Stages of early vertebrate embryogenesis zygote single cell cleavage many cells morula ball of cells blastula hollow ball of cells gastrula cells move inside to fill cavity neurula neural plate/neural tube form organogenesis maturation/differentiation of organs THE BIG POINT: All/nearly all embryos go through these phases with conservation of the process and variation.
blastomeres micromeres macromeres Cleavage holoblastic, equal divisions: holoblastic, unequal divisions:
mouse, human, ascidian, amphioxus holoblastic/equal = cleavage plane goes through cell meiolecithal = little to no yolky cytoplasm
mouse, human, ascidian, amphioxus frog holoblastic/unequal = different size blastomeres result mesolecithal = medium amount of yolky cytoplasm
mouse, human, ascidian, amphioxus frog meroblastic = cleavage plane only goes partly through cell macrolecithal = large amount of yolky cytoplasm fish chick
yolky cells meiolecithal mesolecithal amphioxus frog Blastodisc yolk macrolecithal chick Blastula: Ball of cells with a space (blastocoel) The relationship of blastocoel and yolk/yolk-carrying cells is critical in understanding descriptive development and potential signaling pathways.
Early mammalian development inner cell mass compaction blastocyst
Gastrulation: The most simple form.
Let’s discuss: 1. The movement of cells to form germ layers 2. Partitioning of mesoderm. 3. The vertebrate body plan and how it explains adult function.
How do embryos move cells around? How do these cells form organs? As epithelial sheets. As single cells. Examples??? Next, compartmentalize mesoderm
This basic structure is preserved in vertebrates, even in the adult. Compartmentalization of mesoderm is critical. From Meier, JEEM, 1980 Note the structure of epithelia. Let’s fold the ‘bro.
Epithelial movements to make the gut Can this really explain gut structure and function? Note the retention of epithelial orientation. Does epithelium ever move over epithelium?
Mesodermal/endodermal relationships: retention of those relationships? Structure varies, abruptly, throughout the alimentary canal in response to function.
Esophagus What comes from what? What is exocrine? What is endocrine?
zygote single cell cleavage many cells morula ball of cells blastula hollow ball of cells gastrula cells move inside to fill cavity neurula neural plate/neural tube form organogenesis maturation/differentiation of organs