Cell Differentiation and Specialization How cells become tissues and organs Interactions between external stimuli and regulated gene expression result in specialization of cells, tissues and organs

Overview Atoms  Molecules  Cells  Tissues  Organs Cells becomes specialized (for one purpose). This occurs through the differentiation of cells. There are 220 types of cells in the human body.

What causes cell specialization? Differentiation is triggered in 3 ways: Internal cues from the cell its that turn genes on/off Thereby changing proteins made / phenotype expressed External cues from adjacent cells that turn genes on/off Environmental cues / stimuli that turn genes on/off

In the beginning… All cells begin as stem cells (baby cells) Not specialized yet Can become any of the 220 types of human cells Have the exact same DNA After the fertilization of egg & sperm, Becomes a zygote

Life continues… A zygote is totipotent Has the ability to generate a whole organism As the zygote becomes a blastula, Becomes pluripotent Can development any cell But cannot become a whole organism Then, differentiation happens Becomes unipotent Cannot become any other cell

Development Summary

What causes differentiation? Internal cues Based on cell’s location in the organism (or body) Express only certain genes in the genome Other genes will methylate (add CH3) – turn off Cues are called transcription factors Chemical that causes DNA  mRNA Makes amino acids then proteins

What causes differentiation? External cues (from adjacent cells) Example: At 6 weeks, all embryos are female At this time, the Y chromosome becomes activated SRY gene turns on (sex-determining Y region) In males, the gonads will start to produce male hormones Act as a signal to be sent to all cells Make male proteins Controls gene regulation

What causes differentiation? Environmental Stimuli Examples: Heat Shock Factor Cell sense a change in temperature Changes physical properties of the cell to protest itself Examples can occur with lack of oxygen too Galapagos Tortoise Eggs Incubation at a particular time in embryo development trigger protein production on the Y chromosomes Temp can change gender

Using this technology today… Therapeutic Cloning (tissues and organs for transplant) Embryological sources of stem cells are controversial because of “when does life begin?” issues

However…good news We can do this WITHOUT the use of embryonic stem cells! iPS cells Turns adult cells back into pluripotent stem cells Use the same transcription factors to give cell signals

Videos to watch… http://www.ted.com/talks/anthony_atala_growing _organs_engineering_tissue.html http://www.ted.com/talks/anthony_atala_printing_ a_human_kidney.html Bozeman Science – Cellular Specialization