Today: Development

Development: differentiating cells to become an organism

Cells function differently because they express different genes.

The proper control of gene expression is critical for proper development.

Inverse relationship between smoking and weight: more smoking : less weight

Effect of smoking on fetal development and how that can affect adults

Adults exposed to smoke as fetuses have higher risk of obesity and heart disease

What is the connection?

Obesity, Diabetes, Heart Disease, High Blood Pressure, Some Cancers all may have some origins during fetal development.

Adults metabolism may react to poor nutrition as fetuses… Adaptation of Thriftiness or Catch Up Growth.

Adults metabolism may react to poor nutrition as fetuses…Adaptation of Thriftiness or Catch Up Growth. Study of babies born during Dutch famine of …

Adults metabolism may react to poor nutrition as fetuses…Adaptation of Thriftiness or Catch Up Growth. Study of babies born during Dutch famine of … 20 years later found that these babies had higher rates of obesity.

Adults metabolism may react to poor nutrition as fetuses…Adaptation of Thriftiness or Catch Up Growth. Study of babies born during Dutch famine of … 20 years later found that these babies had higher rates of obesity. Precise mechanism is not known

What about smoking? 17,000 births studied and checked at age 16 and 33. Fetuses exposed to smoking had increased rate of obesity.

What about smoking? 17,000 births studied and checked at age 16 and 33. Fetuses exposed to smoking had increased rate of obesity and more smoking meant more obesity.

What about smoking? 17,000 births studied and checked at age 16 and 33. Fetuses exposed to smoking had increased rate of obesity and more smoking meant more obesity. For Mom’s who abstained during pregnancy, no effect on fetus or as adult.

What about smoking? 17,000 births studied and checked at age 16 and 33. Fetuses exposed to smoking had increased rate of obesity and more smoking meant more obesity. Smoking during first trimester had same effect as during whole pregnancy.

What about smoking? For diabetes more than 10 cigarettes per day gave a 4 times greater risk of diabetes.

What about smoking? Risk of high blood pressure also increases with increased exposure to fetus of smoking during pregnancy

Why?

Nicotine can inhibit hunger and increase energy expenditure. This can lead to poor fetal nutrition.

Why? Nicotine causes constriction of blood vessels, and may limit blood flow to the fetus.

AAL 38.8 Mammalian circulation

Nicotine causes blood vessels to constrict

Why? CO in blood decreases delivery of O 2 to fetus.

Why? These are all indirect affects leading to “adaptation to thriftiness”… Nicotine can inhibit hunger and increase energy expenditure. Nicotine causes constriction of blood vessels, and may limit blood flow to the fetus. CO in blood decreases delivery of O 2 to fetus.

Why? Nicotine and other toxins in smoke may directly affect hormones that direct fetal development.

Hormones are molecules produced in one cell and signal another.

Why? Nicotine and other toxins in smoke may directly affect hormones that direct fetal development. Including hormones that direct brain development.

So, Smoking during pregnancy may have indirect and/or direct affects on fetal development, and these affects may manifest themselves in adults.

Correlation of weight (BMI)% Identical twins reared together80 Identical twins reared apart72 Fraternal twins reared together43 Biological siblings34 Parents and children living together26 Adopted children and parents 4 Unrelated children living together 1 Correlation of weight and relatedness The nature of environmental influences on weight and obesity: A behavior genetic analysis. Grilo, Carlos M.; Pogue-Geile, Michael F.; Psychological Bulletin, Vol 110(3), Nov pp And two books by Matt Ridley: Nature via Nurture (2003) and Genome: the Autobiography of a Species in 23 Chapters (1999)

Nature and Nurture: Are traits coded for by genes fixed while traits coded for by the environment are under our control?

What happened during development?

Fig 23.3 Developmental mutants of Drosophila melanogaster

Increases in cell number play a role… Fig 23.1

…so does cell death. Fig 23.1

CB Development of a mouse paw: yellow areas show dying cells

Development in animals is one way. Why?

Vertebrate Development: from zygote to adult

Early embryo development Fig 19.13

Totipotent: ability to differentiate into any cell-type

Totipotency is limited to early stages of animal development

Why do cells lose totipotency?

Mature, differentiated plant cells are totipotent

Why do cells lose totipotency?

Gene expression can be controlled at many points between DNA and making the final proteins. Changes in the various steps of gene expression control when and how much of a product are produced.

Why change gene expression? Different cells need different components Responding to the environment Replacement of damaged/worn-out parts

DNA packaging fluctuates… genes being expressed are unpackaged, genes not needed are tightly packaged. Fig 10.21

Normally DNA is loosely packaged During mitosis DNA is tightly packaged as chromosomes and individually visible Fig 3.8

DNA packaging fluctuates… Some of the tight packaging of DNA is irreversible. Fig 10.21

Irreversible packaging of DNA partially explains the loss of totipotency. Often in the form of DNA methylation

Stem cells still have totipotency Fig 19.13

Embryonic Stem Cells are totipotent Adult Stem Cells are pluripotent (only form some cell types) Fig 19.14

What genetic mechanisms regulate/allow development?

All humans are female for the first nine weeks of development

Fig 23.27

All humans are female for the first nine weeks of development

Flower parts: Complexity from a few simple genes 4 whorls of a flower Fig 23.23

Each whorl expresses a specific combination of three genes Fig 23.24

Fig 23.23

Changing expression of A, B, or C genes changes organ identity Fig 23.24

Flower parts: Complexity from a few simple genes 4 whorls of a flower Fig 23.23