Download Bauplan and Morphogenesis

Bauplan and Morphogenesis
Drosophila early embryonic development:
•maternal and zygotic gene activity patterns in the early embryo.
•antero-posterior patterning
•dorso-ventral patterning
Dr. Don Newgreen
[email protected]
Refs. from:
Wolpert, Beddington, Jessell, Lawrence, Meyerowitz and Smith (2002)
“Principles of Development” 2nd edition (Oxford University Press)
Gilbert (2003) “Developmental Biology” 7th edition (Sinauer Associates,
Sunderland, MA)
Also:
Alberts, Johnson, Lewis, Raff, Roberts and Walter (2002)
“Molecular Biology of the Cell” 4th edition (Garland Science, New York)
Nüsslein-Volhard and Wieschaus (1980) Mutations affecting segment number and
polarity in Drosophila. Nature 287:795-801
Lawrence (1992) The making of a fly (Blackwell Scientific Publishing)
Pattern formation : “The process by which spatial and temporal
patterns of cell activities is organized within the embryo so that a well-ordered
structure develops.” – Wolpert p.10
Development of a body plan, axes
(rostral)
(caudal)
Wolpert: “The early development of Drosophila is probably the best
understood developmental system of all animals, at the molecular
level. This is due largely to a saturation mutagenesis screen for
embryonic pattern defects carried out in the 1970s by C. NussleinVolhard and E. Wieschaus. Approximately 100 genes were identified
which can account for most of the pattern formation and
morphogenetic events of the early embryo. This set of genes
complement a different set of genes studied by E. Lewis, whose
activities were involved in specifying the identity of segments
observable in the adult fly. Together, these genes became the Rosetta
stones that allowed fly development to be deciphered. At the time, no
one suspected that they would provide the keys to understanding
development in all animals, yet that is what has occurred; even
humans use the genetic networks first discovered in flies, albeit in
sometimes very different ways. For this reason, Drosophila
development deserves special attention in studies in developmental
biology.”
Overview: Drosophila early embryogenesis #1
W5
G9
Overview: Drosophila early embryogenesis #2
Ant. terminus:acron
Head
Thorax
Abdomen
Post. terminus:telson
G9
G9
Similarities between Insects and Vertebrates
•Many common genes/molecules
•Maternal “determinants” in oocyte
•Nuclear and cell division
•“Mid-blastula transition”—slow down of nuclear/cell division
•Molecular gradients and signals
•Antero-posterior patterning
•Dorso-ventral patterning
•Morphogenetic movements—eg. gastrulation
(Apparent) Differences between Insects and Vertebrates
•Syncytial blastoderm in insects vs cellular blastoderm in verts.
•Gradients within single cytoplasm vs gradients between cells
•Insects are upside down (or maybe we are?)
Nuclear division and cell division
(cleavage) NOT necessarily
synchronised 1:1.
Cleavage influenced by:
• amount and position of yolk (yolk
impedes cleavage).
•other molecules that govern angle
of microtubular mitotic spindle
Species variations in these means
that there are many detailed
cleavage patterns
G8
Antero-Posterior Patterning
Klaus Sander 1960s-1970s---”classic” embryological experiments
Ligation of embryo
to produce 2 parts
A
M
P
A
P
The later the ligation, the more
larval middle segments develop.
1. Postulated an opposing double-gradient model of antero-posterior patterning.
RNA destruction at ant pole resulted in lack of anterior and double-posterior embryo.
2. Gradient(s) involved mRNA localisation.
Maternal effect genes: mutations in the mother produce patterning
defects in the offspring. Christianne Nüsslein and Eric WieschausNobel Prize 1995
W5
Anterior…
Bicoid mutants have A-P defects:
double posterior
Bicoid is a
transcription
factor.
G9
G9
Bicoid mRNA and
protein is at right
time and place to
affect A-P pattern (A
⋄ P gradient).
W5
Bicoid mRNA “rescues” Bicoid mutants.
G9
Posterior…
Nanos mRNA and protein with P⋄ A gradient.
Nanos protein is a translation repressor.
Caudal protein with P⋄ A gradient.
Caudal is a transcription factor.
P
A
G9
W5
Putting A and P determinants together…..
Zygotic
hunchback
hunchback
mRNA
Hunchback
protein
G9mod
Making and holding the A-P gradients in a syncytium….
G9
Termini: Torso (RTK) signalling.
Note: Torso activation has different
outcomes in Bicoid and Caudal
contexts. Former leads to acron
formation, latter leads to telson
formation.
G9
(Groucho)
End lect #1