Molecular Patterning During Development Flashcards
What is cell differentiation
process by which embryonic cells become different from one another, it is characterised by the profile of proteins in that cell.
What is totipotent?
Cells of very early embryo. These can give rise to any cell of body.
What is pluripotent?
inner cells of blastocyte, can give rise to many cells but not all.
What is multipotent? (adult)
Blood stem cells, can give rise to cells that have a particular function
Describe the two stages of commitment
1) specification (reversible) - Cells can be respecified if exposed so certain chemicals
2) Determination (irreversable) - cells will differentiate autonomously even if expose to certain chemicals.
What is cell fate?
Fate of a cell describes what it will become in the course of normal development.
Define potency
The entire repertoire of cell types a particular cell can give rise too in all possible environments
What is bivalent chromatin?
Segments of DNA on histone proteins that are poised. They can repress or activate epigenetic regulators which determine if a gene is silenced or expressed.
Describe the development of a dermatome and myotome
Somites (paired aggregations of the paraxial mesoderm) subdivide into sclerotomes and dermomyotomes. Dermomyotomes give rise to dermatomes and myotomes.
When does primary and secondary ossification begin?
Primary - at 12 weeks pregnant. Secondary - begins are birth
What is intramembranous ossification?
The formation of bone in fibrous connective tissue. It occurs during the formation of flat bones, eg, skull or mandible.
What is the role of HOX genes? and what do they regulate?
To determine the body axis and the position of limbs along the body axis. They regulate the transcription of other genes (TBX5 (fore limbs) and TBX4 (hind limbs)
Growth is regulated along what axes?
1) proximo-distal axis.
2) Antero-posterior axis.
3) Dorso-ventral axis
When do the upper and lower limb buds appear?
Upper limb buds appear on dy 24 (between somites C5 and T1) Lower limb buds appear on day 28 (between L1 and S2).
What occurs in week 7 of development?
Forelimbs rotate 90 degrees laterally and hindlimbs rotate 90 degrees medially.
What does a limb bud consist of?
Core of mesenchyme (derived from lateral plate mesoderm) and ectoderm which covers the surface. Ectoderm is thickened at the apex of the developing limb to for the AER.
What is the role of the apical ectoderm ridge?
It controls the proximo-distal development. It induces underlying tissue to remain undifferentiated, rapidly proliferating cells (progress zone)
What results in the proximo-distal development?
The differentiation of cells into cartilage and muscle as they move away from the AER
What is the antero-posterior axis regulated by?
The Zone of Polarising Activity (ZPA), it is a cluster of cells near the posterior boarder. It ensures thumb is on anterior side of limb and expresses protein sonic headgehog.
Describe what the Dorso-ventral axis is controlled by
BMPs in the ventral ectoderm. It represses WNT7, limiting its expression to dorsal limb ectoderm. WNT7 induces LMX1 which specifies the cells to be dorsal.
What is amelia, meromelia. phocomelia and micromelia
Amelia - Complete absence of limbs.
Meromelia - partial absence of limbs.
Phocomelia - absence of long bones.
Micromelia - segments are abnormally short.
What is the effects of thalidomide?
It causes limb abnormalities such as phocomelia which is associated with intestinal atresia and cardiac abnormalities
What is Holt Oram Syndrome?
A mutation in the TBX5 gene which leads to upper limb deformities and heart defects
What is; Brachydactyly, Syndactyly, polydactyly and cleft foot
Bradydactyly - short digits.
Syndactyly - fused digits (failure of apoptosis).
Polydactyly - extra digits.
Cleft foot - lobster claw deformity.
