Molecular Patterning During Development

Question 1

What is cell differentiation

Answer 1

process by which embryonic cells become different from one another, it is characterised by the profile of proteins in that cell.

Question 2

What is totipotent?

Answer 2

Cells of very early embryo. These can give rise to any cell of body.

Question 3

What is pluripotent?

Answer 3

inner cells of blastocyte, can give rise to many cells but not all.

Question 4

What is multipotent? (adult)

Answer 4

Blood stem cells, can give rise to cells that have a particular function

Question 5

Describe the two stages of commitment

Answer 5

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.

Question 6

What is cell fate?

Answer 6

Fate of a cell describes what it will become in the course of normal development.

Question 7

Define potency

Answer 7

The entire repertoire of cell types a particular cell can give rise too in all possible environments

Question 8

What is bivalent chromatin?

Answer 8

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.

Question 9

Describe the development of a dermatome and myotome

Answer 9

Somites (paired aggregations of the paraxial mesoderm) subdivide into sclerotomes and dermomyotomes. Dermomyotomes give rise to dermatomes and myotomes.

Question 10

When does primary and secondary ossification begin?

Answer 10

Primary - at 12 weeks pregnant. Secondary - begins are birth

Question 11

What is intramembranous ossification?

Answer 11

The formation of bone in fibrous connective tissue. It occurs during the formation of flat bones, eg, skull or mandible.

Question 12

What is the role of HOX genes? and what do they regulate?

Answer 12

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)

Question 13

Growth is regulated along what axes?

Answer 13

1) proximo-distal axis.
2) Antero-posterior axis.
3) Dorso-ventral axis

Question 14

When do the upper and lower limb buds appear?

Answer 14

Upper limb buds appear on dy 24 (between somites C5 and T1) Lower limb buds appear on day 28 (between L1 and S2).

Question 15

What occurs in week 7 of development?

Answer 15

Forelimbs rotate 90 degrees laterally and hindlimbs rotate 90 degrees medially.

Question 16

What does a limb bud consist of?

Answer 16

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.

Question 17

What is the role of the apical ectoderm ridge?

Answer 17

It controls the proximo-distal development. It induces underlying tissue to remain undifferentiated, rapidly proliferating cells (progress zone)

Question 18

What results in the proximo-distal development?

Answer 18

The differentiation of cells into cartilage and muscle as they move away from the AER

Question 19

What is the antero-posterior axis regulated by?

Answer 19

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.

Question 20

Describe what the Dorso-ventral axis is controlled by

Answer 20

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.

Question 21

What is amelia, meromelia. phocomelia and micromelia

Answer 21

Amelia - Complete absence of limbs.
Meromelia - partial absence of limbs.
Phocomelia - absence of long bones.
Micromelia - segments are abnormally short.

Question 22

What is the effects of thalidomide?

Answer 22

It causes limb abnormalities such as phocomelia which is associated with intestinal atresia and cardiac abnormalities

Question 23

What is Holt Oram Syndrome?

Answer 23

A mutation in the TBX5 gene which leads to upper limb deformities and heart defects

Question 24

What is; Brachydactyly, Syndactyly, polydactyly and cleft foot

Answer 24

Bradydactyly - short digits.
Syndactyly - fused digits (failure of apoptosis).
Polydactyly - extra digits.
Cleft foot - lobster claw deformity.