Limb Development Flashcards Preview

CBNS169 Human Embryology > Limb Development > Flashcards

Flashcards in Limb Development Deck (20):
1

Development of the limbs

LIMB PRIMORDIA
PROCESSES INVOLVED IN LIMB DEVELOPMENT
DIFFERENTIATION
SPECIFICATION OF LIMBS
HOX GENES IN LIMB DEVELOPMENT
LIMB ABNORMALITIES

A image thumb
2

LIMB PRIMORDIA

LATERAL PLATE MESODERM
BONES
TENDONS AND LIGAMENTS
VASCULATURE
SOMITE MESODERM
LIMB MUSCLES
NCC
DERMIS
MELANOCYTES
SCHWANN CELLS
NEURAL TUBE
NEURONS

 

ORGANOGENESIS - DEVELOMENT OF ORGANS - MAJOR EVENT OF EMBRYONIC AND FETAL PERIODS

WILL LOOK AT DEVELOMENT OF THE LIMB AS ANEXAMPLE OF ORGANOGENSIS

THIS SLIDE SHOWS PRIMORDIA THAT GIVE RISE TO THE LIMBS

 

 

Morphogenesis-deelopment of form

NCC= Neural Crest Cells

A image thumb
3

Schematic of myoblast migration from ventrolateral dermomyotome into limb buds

Figure 3 (A) Schematic of myoblast migration from ventrolateral dermomyotome into limb buds. (B) Immunostaining of transverse section of HH stage 20 chicken embryo. PAX3 (red) -positive cells are shown delaminating and entering limb bud (red arrowheads). (C) Schematic of dorsal and ventral muscle masses formed by limb bud myoblasts. Undifferentiated precursors (some of which will give rise to satellite cells in adult muscles) are shown in red with differentiated myotubes shown in green. (D) Immunostaining of transverse section of HH stage 24 chicken embryo. PAX3 (red) cells are restricted to the dorsal and ventral regions of the limb bud. My, myotome; Dm, dermomyotome; P, proximal; D, distal; dmm, dorsal muscle mass; vmm, ventral muscle mass; AER, apical ectodermal ridge of limb bud. 

A image thumb
4

myotome cells blue migrating into limb bud

A image thumb
5

DEVELOPMENTAL PROCESSES INVOLVED IN LIMB MAKING

MORPHOGENESIS
MITOSIS
CELL MIGRATION
CELL RECOGNITION
CELL ADHESION
DIFFERENTIATION*
INDUCTION*
CELL SIGNALING*
APOPTOSIS
PATTERN FORMATION*
AXIS FORMATION*

 


MOLECULES INVOLVED:
GROWTH FACTORS
MORPHOGENS
TRANSCRIPTION FACTORS

 

 

 

 

MITOSIS - NEEDED FOR GROWTH OF LIMB

CELL MIGRATION - SOMITE MESODERM MIRGATES INTO LIMB AND BECOMES MUSCLE

CELL RECOGN AND ADHESION/ IMPORTANT IN HISTOGENESIS - FORMATION OF TISSUES WITHIN THE LIMB

DIFFERENTIATION - DEVELOPMENT OF MESENCHYME INTO TISSUES SUCH AS MUSCLE OR BONE

INDUCTION - INFLUENCE OF ONE TISSUE ON DEVELOPMENT OF ANOTHER

CELL SIGNALING - INVOLVED IN INDUCTIONS
APOPTOSIS - CELL DEATH - IN LIMB - DESTROYS WEBBING BETWEEN DIGITS
 

A image thumb
6

DETERMINATION AND DIFFERENTIATION

GENERATION OF CELL DIVERSITY

 

DUE TO DIFFERENTIAL GENE EXPRESSION

HOUSEKEEPING GENES ARE ON IN ALL CELLS

CERTAIN GENES GET TURNED ON IN MUSCLE TO GIVE IT THE CHARACTERISTICS OF MUSCLE

ACTIN AND MYOSIN - LUXURY PROTEINS EXPRESSED IN MUSCLE

IF BONE WERE PRODUCED, A DIFFERENT SET OF GENES WOULD BE TURNED ON
 

 

determination: transcription factor(s) dictate to (mesenchymal) cells that it will become (muscle), even though it looks the same, it's determined to be something else

 

Differentiation-when cells can actually be determined to be different

 

 

A image thumb
7

GENES INVOLVED IN MAKING A SKELETAL MUSCLE--MyoD GENE FAMILY

Myf5

MyoD

Myogenin

MRF4
 

 PERTAINS TO SKELETAL MUSCLE

ONE OF BEST UNDERSTOOD SYSTEMS FOR DETERMINATION- DIFFERENTIATION

IS REGULATED BY THE MYOD GENE FAMILY - GROUP OF MYOGENIC REGULATAORY FACTORS (MRF)
TRANS FACTORS THAT TURN ON MUSCLE LINEAGE DURING DEV
THE MYOD GENES ENCODE  HELIX LOOP HELIX (HLH)  TYPE TRANSCRIPTION FACTORS
BIND TO CANNTG SEQUENCE IN PROMOTERS OR ENHANCERS OF OTHER GENES AND TURN THEM ON
MASTER SWITCHES -

MYOD GENES - TWO FUNCTIONS:
COMMITS UNDETERMINED CELL TO MUSCLE LINEAGE
ACTIVATES GENE THAT PRODUCE MUSCLE SPECIFIC PROTEINS

  
WHERE DOES THIS HAPPEN?
IN SOMITES – SPECIFICALLY IN THE MYOTOME OF SOMITES
MYF5 IS EXPRESSED IN THE DORSAL-MEDIAL SOMITE – LATER BECOMES MUSCLE OF BACK (EPAXIAL)
MYOD IS EXPRESSED IN DORSALATERAL SOMITE – LATER BECOMES MUSCLE OF BODY WALL AND LIMB

BOTH MYF5 AND MYOD ARE TURNED ON BY WNT PROTEINS (SIGNALING) FROM DORSAL NEURAL TUBE AND SURFACE EPIDERMIS     RESPECTIVELY

 


 

 

 

 

 

 

 

 

MyoD encodes transcription factors

1st transcription factors during myogenesis (Muscle formation): Myf5 or MyoD

KO MyoD--> mice still had Myf5, made muscle

KO Myogenin-->no muscle

A image thumb
8

In situ hybridisation of MYF5 in HH stage 16 embryos

Figure 2 (A) In situ hybridisation of MYF5 in HH stage 16 embryos. Anterior is towards the top, posterior is towards the bottom. Expression is seen in anterior somites starting in the epaxial myotome and then spreading more widely through the somite. Posterior somites (I–VI) do not express muscle-specific genes. (B) In situ hybridisation of MYF5 in HH stage 22 embryos. Expression is seen in all muscle types including myogenic cells in somites (s), limb buds (lb) and head. Tongue muscle precursors are seen in the hypoglossal cord (hgc), jaw and facial muscles in the branchial arches (ba) and extraocular muscles (eom) around the eye. 

A image thumb
9

Comparison of the signalling pathways leading to MRF expression and myogenesis in epaxial and hypaxial somite, limb, head and neck, and adult

Figure 4 Comparison of the signalling pathways leading to MRF expression and myogenesis in epaxial and hypaxial somite, limb, head and neck, and adult. In grey boxes are the core network of MRFs in activating myogenesis from different tissues. Positive regulatory signals are shown in red, and inhibitory signals are shown in blue. Black arrows show genetic interactions. (A) Epaxial somite: DACH2, SIX1/4, EYA2, PAX3, MYF5 and MRF4 induce MYOD, thus leading to myogenin (MYOG) expression and myogenesis. WNT1, WNT3A and SHH up-regulate MYF5 expression, and WNT7A up-regulates MYOD. BMP4 negatively regulates MYOD but is itself inhibited by noggin. (B) Hypaxial somite: DACH2, SIX1/4 and EYA2 are capable of inducing PAX3. Subsequently, PAX3 induces MYF5 and MRF4, which in turn activate MYOD expression, followed by MYOG expression and myogenesis. BMP and WNT7A positively regulate MYF5 and MYOD expression. (C) Limb: DACH2, SIX1/4, EYA2, PAX3, MEOX2 and PITX2 are capable of inducing MYF5 and MYOD; subsequently, MYOD induces MYOG expression and myogenesis. MSX1 can inhibit MYOD expression. BMP and HGF up-regulate PAX3 expression, and WNT regulates MSX1. (D) Head and neck: PITX2 and TBX1 induce each other and MYF5. TBX1 is capable of inducing MYF5 expression (and MRF4 in those head muscles which express it) before activating MYOD expression. Subsequently, MYOD induces MYOG expression followed by myogenesis, but inhibitory signals from WNT and BMP can also regulate MYOG expression. (E) Adult: PAX3/7 directly induce MYF5 expression, whereas SIX1/4 can induce MRF4, MYF5 and MYOG. MRF4 and MYOD activate MYOG expression followed by myogenesis.

 

A image thumb
10

TRANSFECTION OF NON-MUSCLE CELL WITH MyoD

REVIEW EXPERIMENT

SHOWS MyoD IS SUFFICIENT TO CAUSE MUSCLE CELL DIFFERENTIATION

KNOCKOUTS
KO MYOD IN MICE
EXPECT - NO MUSCLE
GET MUSCLE OK
OTHER GENES IN MYOD FAMILY CAN SUBSTITUTE   FOR MYOD  EG. MYF-5 CAN SUB FOR MYOD

KO MYOGENIN - DEVELPOMENT STOPS - NO BACKUP

IN LIMB, MUSCLE DEVELOPS FROM SOMITE MESENCHYME THAT
MIGRATES INTO LIMB BUD

MESENCHYME FROM LP FORMS CARTILAGE, BONES, BLOOD, CT

A image thumb
11

INDUCTION

HANS SPEMMAN AND HILDE MANGOLD
1924

PRIMARY INDUCTION = INDUCTION OF NEURAL TUBE FORMATION BY PS AND NOTOCHORD

SPEMMAN AND MANGOLD DISCOVERED

DRAW ON BOARD EXPT SHOWING DISCOVERY

MANY OTHER INDUCTIONS TAKE PLACE DURING DEVELOPMENT - THESE = SECONDARY INDUCTIONS

SECONDARY INDUCTIONS MAY BE RECIPROCAL

 

Image is recriprocal induction

A image thumb
12

INDUCTION – WAYS IT MAY OCCUR

A image thumb
13

LIMB BUDS (INDUCTION)

A image thumb
14

INDUCTION DURING LIMB DEVELOPMENT

EXPTS SHOWING RECIPROCAL INDUCTION BETW LIMB MESENCHYME AND AER

1. NO LIMB
CONCLUDE : MESENCHYME IS NEC FOR LIMB FORMATION

2. LIMB MESENCHYME AT ECTOPIC SITE INDUCES FORMATION OF AER AND A NEW  LIMB FORMS
CONCLUDE: MESEN HAS INFO TO DIRECT LIMB FORMATION; CAN INDUCE FORMATION OF AER AND CAN INSTRUCT AER AT ECTOPIC SITE

3. WHEN HINDLIMB MESEN AND FORELIMB MESEN ARE COMBINED A HIND LIMB FORMS
CONCLUDE: MESEN CLOSEST TO AER CONTROLS WHAT DEVELOPS
EVIDENCE FOR INTERACTION OF MESEN W/ ECTODERM

 

 

 

 

growing limb bud has only mesenchyme, surrounded by a layer of ectoderm which thickens at the tip-->apical ecodermal ridge

A image thumb
15

INDUCTION DURING LIMB DEVELOPMENT AER EXPERIMENTS

EXPTS WITH ECTODERM

1. NO NEW LIMB FORMS IF AER GRAFTED TO NEW SITE
CONCLUDE: ECTODERM ALONE WILL NOT PROMOTE LIMB DEVELOPMENT

2. IF AER REMOVED, LIMB DEVELOPMENT STOPS
CONCLUDE: AER IS ALSO NEC FOR LIMB DEVELOPMENT
AER INFLUENCES MESENCHYME
RECIPROCAL INDUCTION

3. EXTRA STRUCTURE FORMS
CONCLUDE: ECTODERM EXERTS INFLUENCE ON MESENCHYME
RECIPROCAL INDUCTION

OVERALL CONCLUSIONS:
A. MESENCHYME INDUCES FORMATION OF AER AND INSTRUCTS AER TO  PRODUCE A CERTAIN TYPE OF LIMB
B. BUT AER IS NEC FOR SUSTAINED LIMB DEVELOPMENT AND GROWTH

A image thumb
16

SUMMARY OF LAST EXPERIMENTS ON INDUCTION

MESENCHYMAL CELLS:
INDUCE AND SUSTAIN THE AER
DETERMINE THE TYPE OF LIMB FORMED

AER
RESPONSIBLE FOR SUSTAINED
OUTGROWTH AND DEVELOPMENT
    OF THE LIMB
 

17

REGIONAL SPECIFICITY OF INDUCTION

DERMIS OF SKIN COMES FROM MESODERM
EPIDERMIS OF SKIN COMES FROM ECTODERM

RECOMBINATION EXPTS:

1. MESODERM DETERMINES WHICH CUTANEOUS STRUCTURE FORMS

2. ECTODERM DEVELOPS ACCORDING TO THE REGION FROM WHICH THE MESODERM WAS TAKEN

3.MESENCHYME IS INSTRUCTIVE CAUSES DIFFERENT GENES TO BE TURNED ON IN RESPONDING CELLS

A image thumb
18

GENETIC SPECIFICITY OF INDUCTION

THE MESENCHYME CAN INSTRUCT THE ECTODERM AND TELL IT WHAT SET OF GENES TO TURN ON BUT THE  MESENCHYME CAN COMPLY ONLY WITH WHAT IS IN IT GENOME!


 

A image thumb
19

GENETIC SPECIFICITY OF INDUCTION CONTINUED

CHICK BRANCHIAL ARCHES HAVE NOT MADE TEETH IN 10 MILLION YEARS

CHICK ECTODERM STILL RETAINS GENE FOR TOOTH MAKING

CHICK MUST HAVE LOST MOLECULES THAT INDUCE EXPRESSION OF TOOTH MAKING GENES DURING EVOLUTION - SO THEY NO LONGER MAKE TEETH

THE MOUSE MESENCHYME SUPPLIED THE INDUCER SO TEETH WERE MADE

INTERESTING INSIGHT INTO HOW EVOLUTION OCCURS
NOT NECESSARY TO LOSE GENE TO LOSE A STRUCTURE
HERE A STRUCTURE WAS LOST  BEC/ THE INDUCER WAS LOST!!

A image thumb
20

REVIEW OF LIMB DEVELOPMENT

LIMB PRIMORDIA
PROCESSES IN  MORPHOGENESIS
DIFFERENTIATION
INDUCTION EXPTS
TRANSPLANTATION EXPTS
FGF10 – AS AN INDUCER
SPECIFICATION OF LIMBS
TBX GENES
LIMB ELONGATION
FGF 10 AND FGF8/RECIPROAL INDUCTION
HOMEOTIC GENES/HOX GENES