Image Glossary > Chromatin

The complex of DNA and DNA-binding protein that makes up a eukaryotic chromosome.  The DNA is wrapped around histone proteins, each of which is composed of four core histones, H2A, H2B, H3 and H4.  The wrapping of the DNA around histones effectively packages over 2 meters of human DNA into compacted nucleosomes. The chromatin can exist in two forms:  tightly coiled chromatin called heterochromatin that is not actively transcribed or loosely coiled chromatin called euchromatin that is actively transcribed. 

In mature, fully differentiated somatic cells, several of the genes that encode for the iPS reprogramming factors are located within the heterchromatin and are therefore considered transcriptionally silent.  Because the reprogramming factors are not actively expressed, scientists must induce the expression of these genes artificially using transgenic strategies.  International research efforts are currently exploring alternative methods to help unlock necessary reprograming genes that are located within the tightly packed heterochromatin.

Retrovirus An RNA virus that fuses to surface receptors located within the host cell's plasma membrane. After binding, the membrane of the... Read More

Reverse Transcriptase A DNA polymerase enzyme that transcribes single-stranded RNA into double-stranded DNA which is then integrated into the host ... Read More

Transcription Factor A regulatory protein that binds to DNA and affects the transcription of specific genes. The four reprogramming factors, Oct-4, SOX2, Klf-4... Read More

Cellular Reprogramming Cellular reprogramming describes the process where a fully differentiated, specialized cell type is induced to transform into a different... Read More

Stem Cell There are many different types of stem cells within our body. Each type of stem cell is defined by the group of specialized cells it give ... Read More

Induced Pluripotent Stem Cell A somatic cell that has been reprogrammed to exhibit pluripotent stem cell properties. Many somatic cells have been... Read More

iPS Colony Refers to the tightly packed homogenous cluster of induced pluripotent cells. Undifferentiated embryonic stem cells and... Read More

Fibroblast A type of cell in loose connective tissue that secretes the protein ingredients of the extracellular matrix. Many somatic cells have been ... Read More

Reprogramming Factors In 2006, the Yamanaka lab identified four factors that, when co-transfected and expressed in mouse adult fibroblast cells, caused.... Read More