Comprehending Development: Generating New Cells and Organs

Lange

BIOL 370 – Developmental Biology

Topic #1

The focus in BIOL 370 – Developmental Biology is to understand the physiological principles that guide development in multicellular organisms.

This course will pull information from a wide array of approaches to study biology including…. •physiology, •genetics, •anatomy, •and cellular biology.

V.M. - Amphibian Life Cycle

Developmental history of the leopard frog, Rana pipiens

Embryogenesis – the stages of the life cycle from fertilization through hatching (or parturition in mammals).

Gametogenesis – the period of time(s) where germ cell lines are in production in some form

(Note that in the above, the purple color is showing times of strong germ cell development, whereas the beige is showing times of strong somatic cell development.)

Heinz Christian Pander Russian biologist, has been credited for the discovery of the three germ layers that form during

embryogenesis.

•Pander received his doctorate in zoology from the University of Wurzburg in 1817. •He began his studies in embryology using chicken eggs, which allowed for his discovery of the ectoderm, mesoderm and endoderm. •Due to his findings, Pander is sometimes referred to as the "founder of embryology".

Early development of the frog Xenopus laevis

Amplexus – the mating behavioral displayed by frogs where the male will grasp the female around the belly and deposit sperm onto eggs as they are released.

Notes:

a)Yolk is in greenb)Adults matingc)Laid eggsd – i) Development beyond the fertilized egg

Continued development of Xenopus laevis

Continued development showing a variety of stages.

Note:

i) – mature tadpole that has hatched from the egg

Metamorphosis of the frog

Metamorphosis - biological process by which an animal physically develops after birth or hatching that involves a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation.

Various insects, amphibians, molluscs, crustaceans, Cnidarians, echinoderms and tunicates may undergo metamorphosis.

Most examples of metamorphosis are also accompanied by a change in habitat and/or behavior.

Summary of meiosis

In your review of meiosis, be sure to note the following:

Homologus chromosomes - chromosome pairs of the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the organism's mother; the other from the organism's father. They are not identical, but carry the same type of information.

Homologus chromatids - sister chromatids are generated when a single chromosome is replicated into two copies of itself, these copies being called sister chromatids.

Summary of meiosis

The resulting production of gametes is the method by which sexually reproducing species produce haploid cells that can be mixed together to create offspring with greater genetic diversity than is seen in asexual reproduction.

Depictions of chick developmental anatomy

When we examine chick development, we can see a variety of interesting anatomical aspects.

Depictions of chick developmental anatomy (Part 1)

Classic Drawing by Malpighi (1672)

Depictions of chick developmental anatomy (Part 2)

Lillie, 1908

Depictions of chick developmental anatomy (Part 3)

Eduard d’Alton

Depictions of chick developmental anatomy (Part 4)

Dividing cells of the fertilized egg form three embryonic germ layers

As development progresses beyond the zygote and blastula, you see greater differentiation in the gastrula stage.

Dividing cells of the fertilized egg form three embryonic germ layers (Part 1)

Ectoderm:

Differentiates to form the nervous system (spine, peripheral nerves and brain), tooth enamel and the epidermis. It also forms the lining of mouth, anus, nostrils, sweat glands, hair and nails.

Dividing cells of the fertilized egg form three embryonic germ layers (Part 2)

Mesoderm:

Forms mesenchyme (connective tissue), mesothelium, blood cells and coelomocytes (immune cells in worms and spiders)

Mesothelium lines coeloms; forms the muscles in a process known as myogenesis.

Dividing cells of the fertilized egg form three embryonic germ layers (Part 3)

Endoderm:

Parts of the alimentary canal), the lining cells of all the glands which open into the digestive tube, general respiratory tract, the trachea, bronchi, and alveoli, general endocrine glands and organs, parts of the auditory system (the epithelium of the auditory tube and tympanic cavity), urinary system (the urinary bladder and part of the urethra).

The notochord is an interesting structure that is seen only during embryological development. In early development, it defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc.

This image is showing a computer enhanced image of the vertebrate head (in this case a salamander) early in development. The purple colored regions indicate what are called:

Pharyngeal Arches (Branchial Arches).

In the next slide, look at how these structures develop into various parts of the skeletal bones of the head in different vertebrates.

Evolution of pharyngeal arch structures in the vertebrate head

Notochord in chick development

Notochord - guides development of of the nervous system (neural tube/groove)

Somites – vertebrae, ribs, skeletal muscle.

Above – chickTo the right - frog

Similarities and differences among vertebrate embryos during development

Fate Maps and Cell Lineages:

Unlike in adults, the cells in the embryo tend to move and shift. Therefore, in developmental biology it is cruicial to identify the following two types of cells:

Epithelial cells – cells that are very tightly connected to each other and form sheets of tissue or tubes of tissue.

Mesenchymal cells – cells that ARE NOT connected to each other and function as independent units.

Fate map for Drosophila sp. eggs.

Morphogenesis – a limited range of variations in processes of a cell within epithelial and mesenchymal cells. Types of morphogenic variations include:

•Direction and number of cell divisions

versus

Additional morphogenic variations:

•Cell shape changes

•Cell migrations

•Cell growth

•Cell death – (programmed cell death is called apoptosis)

•Cell membrane changes

•Secretion changes by cells

Fate maps of vertebrates at the early gastrula stage

Fate Maps – maps of early developmental stages showing a tracing (or map) of cell lineages through developmental time. Important for both descriptive and experimental embryology.

Edwin Grant Conklin - traced the formation of organs to their origins in the egg cell and embryo. Conklin also investigated the

physical mechanism of cell division.

Tunicates are marine filter feeders with a sac-like body structure. In their respiration and feeding they take in water through an incurrent siphon and expel the filtered water through an excurrent siphon.

Most adult tunicates are sessile and attached to rocks or similarly suitable surfaces on the ocean floor.

Common names for specific examples of species of tunicates include sea squirts, sea pork or sea tulips.

Fate map of the tunicate embryo

This diagram highlights two different ways to represent a fate map…

b) Shows a cellular fate map

c) Shows a linear fate map

Walter Vogt - the first "fate map" of a vertebrate embryo -- a description of how cells move from their original positions in the early embryo to their ultimate destination.

Vital dye staining of amphibian embryos

Fate mapping using a fluorescent dye

A more modern take on Vogt’s approach:

Fluorescence Staining

Hilde Mangold

Hans Spemann

Embryologists who first successfully transplanted embryonic tissues to form chimeric embryos.

Chick resulting from transplantation of a trunk neural crest region from an embryo of a pigmented strain of chickens into the same region of an embryo of an unpigmented strain

Genetic markers as cell lineage tracers

Genetic Markers

Two more modern takes on ’s Mangold & Spemans’s approach:

Genetic Markers

Fate mapping with transgenic DNA shows that the neural crest is critical in making the bones of the frog jaw

Transgenic Labeling

Larval stages reveal the common ancestry of two crustacean arthropods

Similar Appearance Early On Very Different Later

Homologies of structure among human arm, seal forelimb, bird wing, and bat wing

Development of bat and mouse

Selectable variation through mutations of genes that work during developmental

Developmental anomalies caused by genetic mutation

Piebaldism - a disorder caused by the KIT gene which regulates production of the KIT protein which guides proliferation and migration of neural crest cells among other cells.

Individuals affected often experience fertility issues, anemia, underpigmentation of skin and hair, problems with the digestive systems and auditory issues.

BE ABLE TO RELATE THIS TO HOW THE NEURAL CREST PROLIFERATES INTO THESE REGIONS.

Developmental anomalies caused by an environmental agent

Environmental exposure to chemicals can affect development in a myriad of ways. The gentleman above was exposed to Thalidamide in-utero, and this resulted in his phocomelia (insufficient limb growth).

End.