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Genomic theory goes directly from DNA to adult morphology, ignoring role of epigenetic mechanisms competent to control intervening and more complex developmental stages
Epigenetics refers to the entire series of interactions among cells and cell products, leading to morphogenesis. Thus, all cranial development is epigenetic, by definition.
Mechanical loads regulate skeletal muscle phenotype, and chronic muscle stimulation can change its phenotype.
Mechanical epigenetic factors (function) significantly control musculoskeletal growth, development, and maintenance of structural and physiological attributes
Function over form.
Nevertheless, epigenetic processes and events are the immediately proximate causes of development, and as such they are the primary agencies of growth and development
Mechanical loading influences gene expression.
Cell shape changes.
Genomic (formal cause) and Epigenetic (efficient cause) factors are both necessary.
Only the interactions of the two provide the necessary and sufficient cause of morphogenesis.
Functional appliances can alter the musculature, and therefore may lead to growth and development modification, which is VERY NICE for patients with skeletal malocclusions.
Epigenetic Event (Muscle Contraction)
Signals down through cellular and molecular levels to bone cell genome
Signals back up through histologic levels to the event of gross bone form adaptational changes
The cranial skeleton's growth and development is primarily dictated temporally and directionally by their related non-skeletal cells, tissues, and organs (ie the functional matrices)
Genomic hypothesis: the genome contains all the info needed to generate a diversity of cell types in the precise pattern of tissues and organs
Material (With what?)-Intrisic
Formal (by what rules?)- Intrinsic
Efficient (How?)- Extrinsic
Epigenetic hypothesis: the outside environment influence the growth and development of an organism
Both intrinsic causes are prior, meaning they exist before the creation of some specific state or structure.
Efficient cause is proximate, meaning its operation immediately causes the creation of a new state or attribute
Includes all epigenetic factors!
or
Emergence- at each higher and more complex level, new attributes/properties arise whose existance could not be predicted from lower levels. Not Genetically Controlled
Claim of genomic control of molecular sytheses underlying the formation of skeletal tissue 'building blocks' does not substantiate the further claim that the genome regulates the growth and development of the gross anatomical bone.
Periosteal Functional Matrix Stimulus
Signals (ionic or mechanical) hierarchically moves down to osteocytes
Leads to the regulation of the genomic activity of its strained skeletal unit bone cell, thus effecting phenotypic expression
Mechanoreception-extracellular stimulus-->receptor cell
Mechanotransduction- transforms the content of the transmitted stimulus into an intRAcellular signal
Bone adaptation requires subsequent intERcellular signals
Bone cells are not specialized--can evoke multiple responses
aneural
bone adaptation confined within each bone independently (ie every bone for himself)