1

Bantenghttp://www.rowlandward.com

Gene RegulationLecture 12, Part 1

2

Much of the text material in the lecture notes is from our textbook, “Essential Biology with Physiology” by Neil A. Campbell, Jane B.

Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship. Other sources were sometimes used, and are noted.

3

Outline

• Cellular differentiation and gene expression• Reproductive and therapeutic cloning• Embryonic and adult stem cells• Gene regulation• Genetic basis of cancer• Lifestyle and cancer risk• Words and terms to know• Possible test items

4

Cellular Differentiation

• Every cell in an organism started with one zygote that has gone through many rounds of mitosis.

• Each body cell contains an identical DNA pattern because mitosis dupli-cates the entire genome.

• During embryonic development, the genes regulate how unspecialized cells develop into different structures and functions.

• These cells are called stem cells, and the process is known as cellular differentiation.

An ovum 1-to-3 hours after sperm penetration, just prior to the fusion of genetic material from the mother and

father.

http

://w

ww

.lum

c.nl

5

Gene Expression

• In transcription, the genes in DNA determine the nucleotide sequences in mRNA molecules.

• In translation, mRNA determines the amino acid sequences to synthesize the polypeptides that form protein molecules.

• This flow of genetic information from genes to proteins—from genotype to phenotype—is known as genetic expression.

6

Different Pathways

• Cells follow different pathways to develop as different tissues during early embryonic development.

• Examples include neurons, muscle cells, blood cells, and skin cells, among many others.

Intestinal cellsht

tp:/

/foc

us.h

ms.

harv

ard.

edu

7

Genetic Potential of Cells

• Although different body cells have different functions, they each have the same complete set of DNA.

• Each body cell has the potential to act like any other body cell if the pattern of gene expression could be altered.

8

Patterns of Gene Expression

Four genes are shown in three types of cells—different combinations of genes are expressed.

Gene Panc rea s c e lls Le ns ce lls o f the embr yonic e ye

Neu rons

Glyc olys is e nzyme Act ive Act ive Act ive

Crys tallin Inact ive Act ive Inact ive

Ins ulin Act ive Inact ive Inact ive

Hemoglob in Inact ive Inact ive Inact ive

9

Genetic Potential of Plant Cells

• Many plants cuttings can develop due to the genetic potential of their cells.• A single cell removed from a carrot root and placed in a growth medium

begins dividing (through mitosis) and eventually grows into a mature plant.• This technique is used to produce thousands of genetically-identical plants,

or vegetative clones.

10

Plant Cuttings

http://www.infovisual.com

http://www.salvialight.com

11

Vegetative Cloning

• In using vegetative cloning, commercial growers can propagate large numbers of plants that have high yield or are resistant to viral diseases.

• Vegetative cloning illustrates that cellular differentiation does not lead to irreversible changes in the DNA.

Tomato plants growingin a hothouse

http

://w

ww

.hou

wel

ings

.com

12

Animal Cloning

• Animal cells that do not normally regenerate body parts retain their full genetic potential.

• In the 1950s, the nuclei of frog eggs were replaced with nuclei from the intestinal cells of tadpoles.

• The embryos developed into tadpoles and then into frogs.• The process—called nuclear transplantation—has been used in cloning

a variety of animal species.

http

://c

ache

.eb.

com

13

Hello Dolly

Dolly, the first cloned sheep, was born in 1996.

http://www.hawaii.edu

14

First Mammal Cloning

• Dolly was cloned using the nucleus from an adult somatic cell inserted into an egg cell that had its nucleus removed.

• The cell was grown in a culture medium.• The developing embryo was then implanted into the uterus of a surrogate

mother.• Dolly resembled her genetic parent—but not the egg donor mother or the

surrogate mother. • Nuclear transplantation has also been used in cloning mice, cows, goats,

pigs, cats, and other animals.

15

Cloned Kittens

http://www.biotechnologyonline.gov.au

Would you clone your favorite pet?

16

Why Clone?

• Farm animals with desirable phenotypes have been cloned to produce complete herds with the same physical traits.

• Researchers have used cloned animals to assure genetically-identical populations to control for extraneous variables in scientific experiments.

• Pharmaceutical companies have explored the use of cloned animals for potential medical uses.

• Some biologists have explored how cloned animals could help restock populations of endangered wildlife.

17

Banteng

In 2003, a baby banteng was produced by the cloning of frozen skin cells from an adult male that died in 1990. The nuclei from the banteng cells were inserted into cow eggs, and one was brought to term

by the cow.

http://www.smh.com.au

http://www.rowlandward.com

18

A Tale of Three Cats

http://www.nature.com

Nucleus donor to the left, and surrogate mother and cloned kitten to the right.

The clone resembles its one parent, on the left, although she has a somewhat different personality—environmental

factors are at work.

19

Therapeutic Cloning

• The goal of therapeutic cloning is to generate stem cells for producing new body tissues.

• Stem cells in early embryonic life produce all differentiated cells in the body—these cells are said to be ‘pluripotent.’

• Embryonic stem cells can divide seemingly indefinitely when grown in a laboratory environment.

20

Possible Uses

• One possibility is to grow differentiated cells in a laboratory culture for the repair of injured or diseased organs.

• Embryos might be produced using cell nuclei from a human patient.• The stem cells from these embryos could be harvested and induced

to develop entire organs that can be transplanted.• The harvesting of stem cells, and other aspects of reproductive and

therapeutic cloning, are part of an ongoing debate about ethics and morality.

Just because we are able to achieve something technologically, is it okay to do so?

21

Human Blastocyst

http://www.iscr.ed.ac.uk

Embryonic stem cells cells are found in the inner cell mass of the blastocyst. These pluripotent cells give rise to all of

specialized cells of an organism.

22

Embryonic Stem Cells

http://www.csa.com

Zygote

Blastocyst

NeuronsCardiac muscle

Red blood cells

Pluripotent stem cells

Eight-cell embryo

23

Adult Stem Cells

• Adult stem cells are partially differentiated, and therefore can only give rise to a few types of cells.

• The stem cells in bone marrow produce many different types of blood cells.

• Although adult stem cells are more difficult to grow in a lab culture, their medical use may result in less debate.

Bone marrow stem cells(false color electron micrograph)

http

://e

pige

nom

e.ed

u

24

Gene Regulation…

• The process from genes in the DNA to synthesis of functioning proteins is complex.

• The process can be regulated to turn-on, turn-off, speed-up, or slow-down the expression of genes.

• Points of regulation in the cell nucleus include:

25

…In the Nucleus

• Unpacking of the DNA from the chromatin• Transcription of DNA to RNA• RNA splicing to remove introns• Addition of a cap and tail to form mRNA

26

…In the Cytoplasm

• Translation of mRNA to polypeptides (proteins) in the ribosomes• Breakdown of mRNA over time into its individual nucleotides• Changes in the physical shape of protein structures• Breakdown of proteins over time into its individual amino acids

27

Lactose and Lactase

• Lactose is a sugar in dairy products as we discussed earlier in the course. • Lactase is an enzyme produced by the bacteria, Escherichia coli (E. coli),

in the small intestine.• A surge of lactose occurs when milk or other dairy products are ingested.• In response, E. coli express three genes for producing lactase and other

enzymes to absorb and digest lactose.

http

://im

ages

.jupi

terim

ages

.com

28

Repressor Protein

• Once the lactose is digested, the E. coli stop producing the enzymes by turning-off the three genes.

• The on-off mechanism is controlled by a repressor protein that blocks the activation sites on the genes.

29

DNA Packing

• Recall from a previous lecture that DNA is densely packed in chromatin.• The highly-compacted chromatin prevents gene expression because the

enzymes for transcription cannot physically come in contact with the DNA molecules.

• DNA packing is a biological process used in the long-term inactivation of certain genes.

Computer-generated imagehttp://www.cgl.ucsf.edu

DNA shown in orange and proteins in blue

30

X Chromosome and DNA Packing

• In female mammals, one X chromosome of the 23rd pair is compacted in chromatin to inactivate it.

• The inactivation occurs at random in the cells early in embryonic develop-ment.

• The pattern is inherited by each cell’s descendants through the process of mitosis.

31

Tortoise-Shell and Calico Cats

• A female cat who is heterozygous for an X-linked trait of fur color will have populations of cells that express different alleles.

• The random inactivation of one allele produces orange and black patches of fur in tortoise-shell cats.

• Calico cats follow the same pattern although they also have white patches of fur determined by another gene.

32

X Chromosome Inactivation

http://www.eagle.ca

Tortoise-shell and calico cats are almost always

female.

http://upload.wikimedia.org

33

Cell Signaling

• Gene regulation can also extend across cell boundaries in multicellular organisms.

• A cell can produce and secrete chemicals that regulate other cells.• In the receptor cell, a gene is transcribed from DNA to RNA in response

to the chemical signal.• Cell signaling is a key mechanism in the differentiation and development

of a complex organism from a single-cell zygote.

34

Cell Signaling

• Cell signaling is also important in coordination of intercellular activities in a mature organism.

• A signal molecule binds to a receptor molecule in the plasma membrane, which can activate a signal transduction pathway in the cell.

• Signal molecules include estrogen, testosterone, thyroid hormones, and others. �

35

Genetic Basis of Cancer

• Cancer is a collection of diseases in which cells are no longer effectively controlled by the mechanisms that normally limit division through mitosis.

• The absence of a normal cell cycle control system is due to changes in some of the genes, or possibly the way that certain genes are express-ed.

Cancerous squamous cell with cross-sectional cuthttp://www.wellcome.ac.uk

36

Mechanisms

• The abnormal behavior of cancer cells was observed long before anything was known about either the cell control cycle or the role of genes in tumor formation.

• Some viruses can carry cancer-causing genes in their DNA or RNA, which they insert into host cells.

37

Oncogenes and Proto-Oncogenes

• A gene that causes a cell to be cancerous is called an oncogene, or ‘tumor gene.’

• A normal gene with the potential to become an oncogene is known as a proto-oncogene.

• A proto-oncogene results from mutations or changes in gene expression.

38

Genes and Growth Factors

• Many of the genes involved in cancer code for growth factors—proteins that stimulate cell division in the cell control cycle.

• These proteins normally keep the rate of mitotic cell division at an appro-priate level.

• Uncontrolled cell growth can result when the formation of these proteins malfunctions.

Cell control cycle

http://www.answers.com

Mitotic phase

G2 phase

S phase

G1 phase

39

Tumor-Suppressor Genes

• Other genes may inhibit rampant cell division by suppressing the division and growth of cancerous cells.

• Tumor-suppressor genes are a focus of research as a promising cancer treatment.

A protein produced by a tumor-suppressor gene surrounding a

segment of DNA.

Computer-generated imagehttp://www.cosmosmagazine.com

40

Colon Cancer Cells

http://www.wellcome.ac.uk

False-color electron micrograph

41

Colon Cancer

• Almost 150,000 people in the United States were diagnosed with colon or rectal cancer in 2003.

• Colon cancer—a well-understood type of human cancer—illustrates a key principle of how cancer develops:

More than one mutation is needed to produce a full fledged-cancer cell.

42

Progressive Mutations

• Colon cancer begins as an unusually-frequent mitotic division of normal- appearing cells in the lining of the colon wall.

• Cellular changes result in DNA mutations at the initial stage, and at later stages.

• The number of progressive mutations before the cancer is evident—at least four—explains why some cancers can take a long time to develop.

• Cancerous cells are grossly altered in their appearance by the time of the fourth mutation.

43

Progressive Mutations

http://science.kennesaw.edu

Normal cell

44

Role of Heredity

• Cancer is a genetic disease (but usually not inherited) since it results from mutations in the DNA.

• Most mutations that lead to cancer arise in the organ where the malignant tumor starts.

• These genetic mutations are not passed from parent to child if they do not affect the ova or sperm cells.

• In some families, mutations in one or more genes can be passed to their offspring and may predispose them to cancer.

• These cancers usually don’t appear unless the person acquires additional mutations.

45

Breast Cancer

• One out of ten women in the United States will be diagnosed with breast cancer in their lifetimes.

• The large majority of cases appears to have nothing to do with inherited mutations.

• A very small number of breast cancer cases is related to mutations in the BRCA1 gene.

• Research suggests the protein encoded by a normal BRCA1 gene acts as a tumor suppressor.

• Clinical tests are available for detecting the presence of mutations in the BRCA1 gene.

• Unfortunately, few options currently exist if positive test results are found.

46

Cancer Risk

• Cancer is the leading cause of death in most developed countries including the United States.

• Death rates for some types of cancer have declined, but the overall rate is on the rise.

• Cancer-causing agents—carcinogens—lead to DNA changes and cellular mutations.

• In some instances, the mutagenic effects may require years of exposure to the carcinogen.

• Lifestyle factors have a role in at least 50 percent of all cases of cancer.

47

Cancer in the United States

Rank Cancer Known or likely carcinogen of factor Estimated

cases (2003)

Estimated deaths (2003)

1 Prostate Testosterone, possibly dietary fat 220,900 28,900

2 Breast Estrogen, possibly dietary fat 212,600 40,200

3 Lung Tobacco smoke 171,900 157,200

4 Colon and rectum High dietary fat, low dietary fiber 147,500 57,100

5 Lymphatic system Viruses for some types 61,000 24,700

6 Skin Ultraviolet light 58,800 9,800

7 Bladder Tobacco smoke 57,400 12,500

8 Uterus Estrogen 40,100 6,800

9 Kidney Tobacco smoke 31,900 11,900

10 Pancreas Tobacco smoke 30,700 30,000

11 Leukemias X-rays, benzene, viruses for some types 30,600 21,900

12 Ovary Large number of ovulation cycles 25,400 14,300

13 Stomach Table salt, tobacco smoke 22,400 12,100

14 Mouth and throat Tobacco including smokeless tobacco; alcohol 20,600 5,500

15 Brain / nervous system Physical trauma, x-rays 18,300 13,100

16 Liver Alcohol, hepatitis virus 17,300 14,400

17 Cervix Viruses, tobacco smoke 12,200 4,100

All other cancers 154,500 92,000

Totals 1,334,100 556,500

48

Then and Now

Early-1960s

http://abc.news.com

21st century

http://www.siliconeer.com

49

Tobacco is a Carcinogen

• Tobacco use and secondhand smoke are carcinogenic despite many years of public denial by tobacco companies.

• Tobacco is known to cause more cases and types of cancer than any other carcinogen.

• ‘Smokeless’ tobacco can result in profound disfigurement and be just as deadly.

50

Health Risks

• Smoking cigarettes, cigars, and pipes can result in cancers including of the lungs, bladder, kidney, pancreas, stomach, mouth, throat, and cervix.

• Not all smokers develop a cancer, but the rate is much higher than for non-smokers.

• The risk of other diseases is much higher including emphysema, heart attacks, and stroke.

51

Glamour

http://uberoriginal.blogspot.com

Lauren Bacall and

James Dean

http://blog.beliefnet.com

52

Lung Cancer

http

://w

ww

.hom

e-ai

r-pu

rifie

r-ex

pert

.com

http

://w

ww

.esu

bulle

tin.c

om

Healthy and cancerous lungs

53

Brain Cancer

Cancerous cells in the lungs can metastasize to the brain.

http://www.uthsc.edu

54

Image Marketing

http://www.euro-cig.com

http://paulho91.files.wordpress.com

55

About 1950

Before Marlboro was rebranded as the ‘rugged’ smoke.

http

://w

ww

.qui

tsm

okin

gpai

nles

slyn

ow.c

om

56

Youth-Oriented Marketing

http://www.notmytribe.com

A counter-advertising campaign

http://farm1.static.flickr.com

Fifteen years ago, most five-year-old children

could identify Joe Camel.

57

Other Lifestyle Factors

• Excessive exposure to UV light, a potent carcinogen, can cause skin cancer, or melanoma.

• Consumption of too much animal fat has been associated with colon cancer—reduced fat consumption is a good idea for several health reasons.

• Consuming about 20 to 30 grams of plant fiber daily—about twice the U.S. average—can reduce the risk of colon cancer.

• Fruits and vegetables are good sources of soluble and insoluble fiber.

58

Other Lifestyle Factors

• Vitamins including C, E, and A may offer some protection against some cancers (but some recent research suggests that this may be question-able).

• Determining how dietary factors can result in cancer is a major focus of medical research.

59

Words and Terms to Know

• Adult stem cell• Carcinogen• Cellular differentiation• Cell signaling• Embryonic stem cell• Gene regulation• Genetic expression• Genetic potential

• Oncogene• Proto-oncogene• Reproductive cloning• Somatic mutation• Therapeutic cloning• Tumor-suppressor gene• X chromosome inactivation

60

Possible Test Items

1. Describe how genetic expression regulates an organism’s phenotype.2. Explain the basic biological principles of how animal cloning works.3. Should the use of embryonic stem cells be permitted for therapeutic

reasons? Please include biological and social perspectives.4. Explain how seemingly normal cells can mutate into cancerous forms.