molecular patterning during development Flashcards
what are 3 principles governing cell differentiation?
- Generative program (The embryo does NOT contain a description of the adult, rather it contains a generative program for making it)
- Regulatory proteins work together as a “committee” to control the expression of a eukaryotic gene
- Combinations of a few gene regulatory proteins can generate many different cell types during development
what is the process of cell differentiation?
what does cell differentiation involve?
what does it achieve?
how is it charcterised?
- the process by which embryonic cells become different from one another, which happens very early on soon after fertilisation
- Involves the emergence of cell types such as muscle, nerve, skin and fat cells
- Is the achievement of a stable terminal differentiated state (not just transitory differences)
- Is characterized by the profile of proteins expressed in that cell
list the 3 steps of differentiation from a single fertilised egg to a multipotent stem cell
- single fertilised egg through cell divisions into morule stage to form totipotent stem cell
- then to blastocyst stage, there are two types of cell: placenta cells and the inner cell mass (which becomes the individual) - they are now pluripotent
- from pluripotent, they differentiate into different organ systems - they are now multipotent
what is the order of the heirarchy of stem cells?
totipotent to pluripotent to multipotent
define potency
potency - the entire repertoire of cell types a particular cell can give rise to in all environments
totipotent - define toti
pluripotent - define pluri
multipotent - define multi
-
Totipotent: ‘toti’ = whole. eg. Cells of the very early mammalian embryo;
identical and unrestricted; can give rise to any cell of the body (EMBRYONIC) -
Pluripotent: ‘pluri’ = more. eg. Inner cells of the blastocyst; less potent;
can give rise to many cell types but not all (EMBRYONIC) -
Multipotent: ‘multi’ = many. e.g. Blood stem cells;
they give rise to cells that have a particular function (ADULT)
cells are committed - this step is a decision that restricts cell fate. what are the 2 stages of commitment?
First stage: specification (reversible)
1. Capable of differentiating autonomously if placed in isolation BUT can be respecified if exposed to certain chemicals/ signals.
Second stage: determination (irreversible change)
2. Cell will differentiate autonomously even when exposed to other factors or placed in a different part of the embryo.
in what 2 ways does a naive cell (totipotent) become specified (differentiated)?
- Intrinsic signal – cell autonomous signal tells the cell ‘who is it’
-
Extrinsic signal - a chemical or molecule in the
environment gives the cell spatial information, tells the
cell ‘where it is’
what does determination imply?
Determination implies a stable change - the fate of determined cells does not change
describe the progress of a cell during development?
what is competence?
- cytoplasmic determinants or induction
- loss of competence* for alternative fates
- cell specific gene expression
competence - the ability of a cell to respond to the chemical stimuli (a cell can lose competence by changes in surface receptor or intracellular molecules)
what do patterns in chromatin determine?
what is this called?
describe this mechanism:
patterns in chromatin determine the determination of differentiation
this is known a Bivalent chromatin - mechanism basis for these fate decisions
- only occurs in developmental master regulator genes
- bivalent chromatin occurs in the promoters of these genes
- it is a pattern of either open/closed chromatin structure (chemical change of histone proteins)
- early on the genes are poised - still need to make the decision to be expressed or not^
a combination of a few regulatory proteins can generate many cell types:
where are these proteins acting within the cell?
what are the 2 factors which these sites bind onto?
where are these proteins acting within the cell:
- the promoter region
- these regulatory genes are transcription factors used to direct gene expression
note that most of the sites can bind either a stimulatory transcription or inhibitory factor but not both at once. thus the balance of stimulatory and inhibitory transcription factors in a cell determine how strongly it is expressed:
describe endochondrial ossification
- bones form as an early event
- bones are formed by forming mesochyme
- which eventually becomes hard bone with chondrocytes and osteoblasts
- ossification occurs at growth plates
describe intermembranous ossification
- Intramembraneous ossification is the formation of bone in fibrous connective tissue (which is formed from condensed mesenchyme cells)
- The process occurs during the formation of flat bones such as the mandible and flat bones of the skull
- the mesoderm is one of the early embryonic germ layers
- mesenchyme generalised embryonic connective tissue derived from mesoderm
what 2 things do HOX genes determine?
where are they expressed?
HOX genes determine the body axis + the position of limbs across it as well as the shape of bones
HOX genes are a related group of genes that are expressed along the long axis of the embryo from head to tail.
describe the descriptive terms used in embryology growth
