Untitled

• Developmental biology studies how a single cell, specifically a fertilized egg, develops into a new organism.
• A fertilized human egg develops into an embryo with recognizable features in just over seven weeks.
• Developmental biology encompasses events after birth, including postnatal growth and aging, not just embryonic development.
• Developmental mechanisms are involved in regeneration, the ability of an adult organism to replace missing parts.
• Evolutionary developmental biology, or evo-devo, is a very active research area because development is fundamental to evolution.
• Developmental biology knowledge has applications in medicine and agriculture due to its understanding of how organisms develop.
• Cancer uses the same mechanisms as development, making developmental biology relevant to understanding diseases.
• Understanding how cells and tissues build organs in embryos may provide new ways to repair or replace damaged tissues in regenerative medicine.
• Model organisms are essential in studying developmental mechanisms through their embryos.
• Chickens and amphibians like frogs and newts were widely studied because their eggs are easily available and manipulated.
• Fruit flies, mice, thale cress, zebrafish, and nematode worms facilitate studying the genetics of development.

Discovery of the Organizer

• A key advancement was the discovery of the organizer, a small group of cells in the early amphibian embryo that controls the laying down of the main body axis.
• Transplanting the organizer leads to the host tissue creating a second body axis through cell-cell interactions.
• A twinned tadpole results from an organizer transplant, highlighting the importance of cell-cell interactions in development.

First Clues of Genetic Basis

• Studying mutants of the fruit fly, Drosophila, provided clues to the genetic basis of developmental biology with body part replacements.
• The study of body plan changes led to the discovery of Hox genes, a subset of homeobox genes that specify regions of the body plan along animals' head-tail axis.
• Vertebrates, including humans, have related complexes of genes that function similarly to those in flies, which specify regional identity of segments, and determine the type of appendages.
• Developmental genes provide a direct link to clinical genetics, with fruit fly mutants and genes responsible for human conditions converging as the same.
• The mouse became a mammalian genetic model for development alongside advances in fruit fly genetics.
• Establishing in vitro fertilization in humans, which can be used to treat infertility, was founded by maintaining the earliest stages of development in culture, and then successfully implanting the embryos into a surrogate mother producing live births.

Inner Cell Mass

• Approximately three days post-fertilization, a blastocyst with an internal cavity will form, where cells on one side of the cavity can be seen.
• The cells are known as the inner cell mass, from which the embryo forms.
• The cells of the inner cell mass are pluripotent embryonic stem cells that can give rise to cells of the body.

Stem Cells

• Stem cells self-renew, and are not only found in embryos, but also in adult tissues such as skin, the lining of the gut, and blood.
• Adult stem cells can only differentiate into a limited number of cell types.

New Opportunities with Genomics

• Genomics, the ability to sequence whole genomes, has led to opportunities to examine non-coding regions such as regulatory sequences of DNA.
• The genomes of all model organisms used in studying developmental biology have been sequenced
• Genomics is impacting evo-devo studies through studying the evolution of genes and their regulation.

Human life cycle

• Development in humans begin when the blastocyst is implanted into the uterus.
• Gastrulation involves the rearrangement of cells to generate 3 main body layers.
  • Controlled by the node, specific to mammals.
• Organogenesis takes places between 4 and 8 weeks.
  • The vascular system is one of the first systems develop.
• The embryo is known as a fetus after about 8 weeks when all the body parts are laid down.

Transcription and translation

• Newly organic information is encoded in the DNA.
• The information is transcribed into RNA, then translated into proteins.
• The proteins determine the cell's activities.

Cell Activity

• Cell activity has a repertoire of cell activity, and turn genotype into phenotype during development.
• Activities include, proliferation, death, change shape, move, attach, and interacts with other cells.
• Major processes of four that cell activity are involved in are; Growth, morphogenesis, cell differentiation, and pattern formation.

Growth of the human embryo and foetus

• Growth is a result of cell proliferation, outstripping cell death and an increase in size.
• Growth is controlled by both extrinsic and intrinsic factors.

Morphogenesis

• Development does not only involve getting bigger, but changing shape.
• 30 years ago, the genetic control of cell death was discovered by studies on the nematode worm.
• The ability of cells to change shape is another important cell involved in shaping the embryo.
• Computer modeling is often used to provide insights into morphogenesis.

Cell Migration

• Cell migration is key for gastrulation.
• A protein can be genetically encoded into cells at random so behavior can be tracked.

Cell differentiation

• Cell differentiation involves gene expressions.

Differential gene expression and pattern formation

• Localized cytoplasmic determinants and asymmetric cell divisions are ways gene expression can be controlled.
• Cells inherit cytoplasmic determinants inherit different cytoplasmic determinants when they divide to make the two daughter cells different.
• Cells become different by extracellular signals. Transcription factors control the expression of particular genes.
• Some, known as master genes, encode the transcription factors which act as major switches in cell differentiation
• Heritability of cell differentiation is important for cells to maintain their integrity.
• Cell differentiation does not affect gene sequences, but involves modifications in the chromatin.
• Cloning has also been carried out in mammals, most famously Dolly the Sheep.
• During the experiment it shows how the pattern activity in the nucleus of a different cell can be reversed.
• Landmark discoveries show now adult skin fibroblasts can be reprogrammed to pluripotent stem cells by introducing genes that encode embryonic stem cell-specific transcription factors.
• The cells produced are known as pluripotent stem cells.

Pattern Formation

• Pattern formation is an important issue in cell differentiation during development because it shows how it is spatially generated.
• The ways tissues and cells can be spatially generated are Reaction-diffusion, Positional information, Sorting out, and Clock-like mechanisms.
• Lewis Wolpert's Mechanism illustrates the stripes are stripes of different colors with positional information.
• It considers how lines of cells turn into a French Flag.

Chick wing development

• The developing chick wing had been one of the models for investigating how pattern formation occurs.
• Cell differentiate in the wing to for the skeleton with three didgits called 2, 3, and 4.

Cell-cell interactions

• Interactions identified are apical ectodermal ridge which is used to cover the lid bud controlling growth.
• Polarizing region is used. as an organizer to patter the digits.
• When grouping cells from the wing and grafting on the opposite, a dramatic effect is had.
• Six digits developed instead of the normal three, creating an image symmetry with a set of different cells.

Morphogen gradient model for the chick wing bud

• This proposal that the polarizing region makes a substance that impacts the cellular development, setting up a cells across the wings' bud.
• Following the polarizing U gradient to make a symmetrical pattern. Mouse limbs have 5 digits.

What is is the morphogen?

• It's known that Shh is responsible for polarizing.
• Beasd soaked in Shh induce an mirror image pattern of the digits.
• Shh and been implicated in different types of tumors.

Digits 4 and 5

• Digits 4 and 5 is specified by the timing mechanism, linked to the length of time cells sonic hedgehog.
• The activator acts locally and triggers a response, leading to structures like didgets,
• The inhibitor is diffused, working its role for acting over the area.

Cis-regulatory

• This gives insights into clinical medicine and evolution with a 1 megabse away from Sonic.
• regulatory shows how long range control will be expressed.
• Sasquatch the sequencve has been shown expression for sonic.

Snakes Shh

• Mutations cause a loss of sonic hedgehog in polarizing, rather than the sides of limbs.
• The expression and development are impacted.
• Without limbs and expression, the limbs become truncated.

Environmental agents

• Environmental and infections can also interfere with teratogens to limbs' development.
• The best is thalidomide which causes mothers to treat sickness.

Final comments

• Future areas of focus include evolutionary, and ecological with potential in regenerative medicine.