Thanks to Teresa Binstock for alerting others to this:
Dynamics of gene silencing during X inactivation using allele-specific RNA-seq
…our study provides the first comprehensive allele-specific analysis of gene silencing during X inactivation. … The molecular mechanisms by which this upregulation occur are currently unclear, but might involve transcriptional as well as posttranscriptional regulatory mechanisms.
My comment: The molecular mechanisms are nutrient-dependent and transcriptional as well as posttranscriptional regulatory mechanisms link RNA-mediated gene duplication and RNA-mediated amino acid substitutions to cell type differentiation in all genera via conserved molecular mechanisms.
During normal embryo development, X inactivation in females takes place at a very early stage. Others had already discovered that the molecule ‘Xist’ is key during X inactivation. In order to further study this process, Marks and his colleagues used embryonic stem cells as a model system to study X inactivation. With the latest technology, they were able to keep the two X chromosomes apart and measure one of them — with its 166 million base pairs — in detail. Every day they checked which parts of the chromosome had been switched off. “The whole process took about eight days,” Marks explains “and the inactivation spreads out from the centre of the X chromosome towards the ends. That doesn’t happen gradually but moves jumpwise from domain to domain.
My comment: De vries (1904) called the jumpwise changes “mutations” and claimed that “fluctuations” were not a source of evolutionary change. Schrodinger (1944) correctly placed de Vries jumps into the context of quantum biology, which links ecological variation to nutrient-dependent cell type differentiation in all cells of all individuals of all organisms. Dobzhansky (1973) linked “mutations” to an amino acid substitution that differentiates primate cell types.
Schrodinger may have realized that de Vries jumps were nutrient-dependent. Alternatively he may have realized that de Vries definition of “mutation” could not be placed into the context of any meaningful discussion of biologically-based cause and effect.
In either case, he was right. De vries definition continued to lead to even more pseudoscientific nonsense after it was used to invent and to re-invent neo-Darwinism. For contrast, Dobzhansky (1973) was placed into the context of “Combating Evolution to Fight Disease,” but few people realize what serious scientists are fighting against. They are fighting against use of de Vries definition of “mutation” and the pseudoscientific nonsense about cell type differentiation that is touted by evolutionary theorists.
Evolutionary theorists still have not determined how sex differences in cell types, or any other RNA-mediated differences in cell types arise. They attribute the differences to mutations and evolution. The differences are nutrient-dependent and controlled by the physiology of species-specific reproduction.
See for comparison: Cellular memory of stressful situations
“What we have here is a phenomenon that complies with the classic definition of epigenetics: an event where an environmental cue triggers a change in gene expression that does not entail a change in the genomic sequence, yet which is inherited for many cell divisions, even after the environmental cue has disappeared.”
My comment: X inactivation can be placed into the context of this phenomenon. The variability of the phenomenon was placed into the context of feedback loops that are nutrient-dependent and pheromone-controlled in species from microbes to man. We linked them to RNA-mediated sex difference in cell types in our 1996 Hormones and Behavior review. From Fertilization to Adult Sexual Behavior
Why hasn’t everyone else started doing that? The molecular mechanisms of cell type differentiation are conserved in all genera –not just as manifested in sex differences. Cell type differentiation is manifested in all cell types in all individuals of all genera, whether or not they sexually reproduce. In the white-throated sparrow, however, the sex differences and somatic differences in cell types are obviously due to chromosomal rearrangements.
See: Estrogen receptor α polymorphism in a species with alternative behavioral phenotypes
If theorists want to link the cell type differentiation of any species to mutations and evolution, they should try to place their claims into the context of what is known to serious scientists and stop using definitions.