Ch. 18.4, , 35.5

 Regulation of gene expression that orchestrates development  Activities of the cell depend on the genes it expresses and the proteins it produces  All cells have the same genome, but genes are regulated in each cell type ◦ Depends on activators present

 Induction: changes in the target cells (communicated via surface proteins and cell receptors)  Homeotic (Hox) genes: regulate pattern formation in the embryo (direct the developmental process)—what genes, and where located  Morphogen: determines an embryo’s axes, stimulate differentiation and development  Apoptosis: programmed cell death  Differentiation: process by which cells become specialized in structure and function  Determination: process by which a group of cells becomes committed to a particular fate  Morphogenesis: process that gives an organism its shape  Induction: changes in the target cells by environmental stimuli or other cell contact (induce differentiation)

 In multicellular organisms a fertilized egg must give rise to cells of many different types, each with different structure/function ◦ Cell  tissue  organ  organ system  organism ◦ Mutations result in abnormal development  Animal Embryonic Development…in general… Fertilization (zygote)  Cleavage (mitosis—produce blastula)  Gastrulation (folding of cells into 3 layers—gastrula)  Organogenesis (changes in cell shape/location— rudimentary organs)  Developing embryo (grow and develop, specialized cells)

 First zygote divides into a large number of cells (ball of cells--blastula) ◦ It then divides and folds to form a gastrula  Then differentiation occurs, cells become specialized (organogenesis) ◦ Results from the expression of specific genes for that tissue/organ type  Morphogenesis occurs next, specialized cells become organized into tissues and organs ◦ Occurs throughout embryo’s development

 Begins with egg cytoplasm. ◦ “Cytoplasmic Determinants”—molecules that will trigger development of different cells (unevenly distributed)  Results in division of cells with different information ◦ Induction.  Changes that induce differentiation and timing of developmental events  “Hedgehog”—signaling molecule (limb bud development) ◦ Observable differentiation marked by expression of genes for tissue specific proteins  Gives characteristic structure and function, regulated by transcription

 Body plan (cytoplasmic determinants) ◦ Spatial organization of tissues and organs  Determine where/when segments will be (embryo has cues to determine this) ◦ Controlled by “Homeotic (Hox) Genes” and “morphogens”

 Growth, morphogenesis, differentiation ◦ All controlled by gene expression  Plant organs: roots, stems, and leaves  “Root” or “Shoot” systems ◦ Made of tissue layers  Vascular (xylem and phloem)  Dermal (epidermis)  Ground

 Apoptosis: programmed cell death ◦ Cells die and are engulfed by neighboring cells  Tadpole tail  Webbing between digits  microRNAs (miRNA): bind to mRNA and blocks translation by degrading the mRNA ◦ RNA interference (RNAi): regulate gene expression at transcription  Important in development of organisms and control of cellular functions

 Single-celled organisms use signals to influence their response to the environment  Multi-cellular organisms use signals to coordinate activities within cells

 Cells most often communicate by chemical signals ◦ Secretion of messenger molecules that target nearby cells  Hormones (fight-or-flight—epinephrine)  Mating pheromones (yeast)  Quorum sensing (bacteria density)  Growth factors (stimulate division)  Neurotransmitters (signaling at synapses)  Cells also communicate via cell-cell contact ◦ Cytoplasmic materials can pass through junctions in cell wall/membrane between cells ◦ Surface molecules on membrane aid in cell recognition  Important in embryonic development and immune system!

 “Signal Transduction Pathway”—Three stages ◦ Reception: detection of a signaling molecule by the cell (binds to receptor protein in membrane) ◦ Transduction: receptor protein changes with binding of signaling molecule; converts signal to specific cellular response (sequence of changes) ◦ Response: specific cellular response is triggered

 Ligand (signaling molecule) binds to receptor protein, causing a change in shape ◦ This activates the receptor allowing it to interact with other molecules (initiates transduction) ◦ Each signaling molecule has specific target cells ◦ Some signaling molecules are small enough to pass through cell membrane and interact with proteins in the cytoplasm or nucleus

 Example: Ion-Gated Channel

 Signal is converted into a cellular response ◦ “signal transduction pathway”  The binding of the signaling molecule triggers transduction pathway ◦ A chain reaction is started that produces a “cascade”, leading to cellular response  Often controlled by phosphorylation (taking P from ATP)…this drives the reaction forward  this helps amplify the signal and response  Second messengers: small molecule that help to transmit signals (Ca ++ and cAMP); spread via diffusion

 Response at the end of the pathway that occurs in the nucleus or cytoplasm ◦ Regulate protein synthesis (on/off) ◦ Affect activity of enzymes ◦ May be altered by blocked or defective transduction pathways  Results in diseases such as diabetes, heart disease, neurological issues, autoimmune diseases, cancer, cholera

 Long distance ◦ Electrical to chemical signals—nervous system  Electrical signal travels down nerve, converted to chemical signal to stimulate other end of nerve ◦ Endocrine system and hormones  Specialized cells release molecules and travel through blood stream to target cells  Plant hormone ethylene—stimulates ripening

 Hormone: molecule secreted into bloodstream (or hemolymph) to communicate regulatory messages ◦ Each has specific receptors, only some cells have them  May either be water (amino acid based—bind to outside) or lipid-soluble (steroids—pass thru membrane to nucleus) ◦ Elicits a response from target cells ◦ Maintains homeostasis, respond to environment, regulate growth and development, trigger physical changes  Negative or positive feedback

 Pituitary gland: growth hormone, thyroid stimulating hormone, luteinizing hormone, follicle- stimulating hormone, oxytocin, antidiuretic hormone  Pineal gland: melatonin  Thyroid gland: thyroxine (T 4 ), Triiodothyronine (T 3 )

 Adrenal gland: cortisol, epinephrine  Pancreas: glucagon and insulin  Ovaries/testes: testosterone, estrogen and progesterone

 Controlled by the hormones insulin and glucagon, produced by Islets of Langerhans in pancreas ◦ negative feedback ◦ Two hormones are antagonistic  When BG is high—insulin triggers body cells to take up glucose from blood stream; also inhibits glucose production/release from liver ◦ Target cells: muscles, adipose tissue, liver  When BG is low—glucagon triggers the release of glucose from storage (liver and fatty tissue) ◦ Target cell: liver, adipose tissue

Normal blood sugar is mg/ml  Hyperglycemia: High blood sugar ◦ Symptoms include increase thirst/urination, glucose present in urine ◦ Extreme cases result in ketoacidosis (body breaking down fat for energy—releasing ketones leading to acidic blood), if untreated results in diabetic coma!  Hypoglycemia: Low blood sugar ◦ Shakiness, irritability (extreme mood changes), lightheaded, headache, seizures, unconsciousness

 Increased blood glucose, fat is broken down for energy because cells don’t take up glucose effectively or at all ◦ Ketoacidosis results (decreased blood pH, Na +, K + ) ◦ Kidneys filter some glucose and release in urine  Lots of water consumed, glucose in urine  Type 1 “juvenile diabetes” ◦ Insulin-dependent, autoimmune disorder that destroys pancreatic cells that produce insulin  Type 2 ◦ Target cells don’t respond normally to insulin, don’t take up glucose ◦ Most common type. Seen in adults mostly…resulting from excess weight.

 Thyroxine (T 4 ) and Triiodothyronine (T 3 ) ◦ Target nearly all cells in the body  Affect metabolism, growth and development ◦ Hormone production is stimulated by TSH from pituitary ◦ Iodine helps to regulate production  Absence results in overproduction of TSH and enlarged thyroid gland (goiter)  Hyperthyroidism (excess of hormone) ◦ “overactivce thyroid”; symptoms: mood changes, increased heart rate, weight loss, muscular weakness  High T 4 and low TSH  Hypothyroidism (lack of hormone) ◦ Symptoms: weight gain, fatigue; more common in women  Low T 4 and high TSH