Regulation of Gene Expression

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molecule

(inducer)

Signal

transduction

pathway

Early embryo

(32 cells)

Nucleus

NUCLEUS

Signal

receptor

Slide 68

Fig. 18-15a

(a) Cytoplasmic determinants in the egg

Two different

cytoplasmic

determinants

Unfertilized egg cell

Sperm

Fertilization

Zygote

Mitotic

cell division

Two-celled

embryo

Nucleus

Slide 69

Fig. 18-15b

(b) Induction by nearby cells

Signal

molecule

(inducer)

Signal

transduction

pathway

Early embryo

(32 cells)

NUCLEUS

Signal

receptor

Slide 70

The other important source of developmental information is the environment around the cell, especially signals from nearby embryonic cells

In the process called induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells

Thus, interactions between cells induce differentiation of specialized cell types

Animation: Cell Signaling

Slide 71

Sequential Regulation of Gene Expression During Cellular Differentiation

Determination commits a cell to its final fate

Determination precedes differentiation

Cell differentiation is marked by the production of tissue-specific proteins

Slide 72

Myoblasts produce muscle-specific proteins and form skeletal muscle cells

MyoD is one of several “master regulatory genes” that produce proteins that commit the cell to becoming skeletal muscle

The MyoD protein is a transcription factor that binds to enhancers of various target genes

Slide 73

Fig. 18-16-1

Embryonic

precursor cell

Nucleus

OFF

DNA

Master regulatory gene myoD

Other muscle-specific genes

OFF

Slide 74

Fig. 18-16-2

Embryonic

precursor cell

Nucleus

OFF

DNA

Master regulatory gene myoD

Other muscle-specific genes

OFF

OFF

mRNA

MyoD protein

(transcription

factor)

Myoblast

(determined)

Slide 75

Fig. 18-16-3

Embryonic

precursor cell

Nucleus

OFF

DNA

Master regulatory gene myoD

Other muscle-specific genes

OFF

OFF

mRNA

MyoD protein

(transcription

factor)

Myoblast

(determined)

mRNA