Developmental biology BVETMED1 (D100) Lecture notes

DEVELOPMENTAL BIOLOGY

WEEK 1 ............................................................................................................................................................................. 2
INTRODUCTION TO DEVELOPMENTAL BIOLOGY ....................................................................................................................... 2
GASTRULATION ................................................................................................................................................................ 3
MAJOR EARLY EVENTS 1 ................................................................................................................................................... 5
MAJOR EARLY EVENTS 2 ................................................................................................................................................... 7
DEVELOPMENT AND EVOLUTION ....................................................................................................................................... 9
CELL DIVISION AND DIFFERENTIATION ............................................................................................................................. 11

, WEEK 1

INTRODUCTION TO DEVELOPMENTAL BIOLOGY
Describe the animal models used in developmental biology and their advantages and disadvantages.

Describe how cell division and cleavage occurs in the fertilised egg during the formation of the blastocyst.

Describe changes in the organisation of the blastula following implantation.

Model organisms

Invertebrates Vertebrates (anamniotes)
- Drosophila (fruit flies) - Develop external to mother
- Short life span - Large eggs
- Not vertebrate - Transparent
- Easy to handle large numbers - Easy to mutate
- Easily mutated - Sequenced genomes
- Genome sequenced



Fertilisation and formation of embryo

- 2 germ cells meet and fuse → forms zygote
- Primordial germ cells come from ovary/testis → diploid (2n)
- Germ cells → haploid (1n) through meiosis
- Entry of sperm → formation of zygote → oocyte becomes impenetrable (prevents polyspermy)

Cleavage stage

- Cells divide, becoming smaller → called blastomeres
- Each cell touches zona pellucida (outer membrane)
-
- Reorganises to create inner and outer layer of cells
- Inner core = cells form inner cell mass. Become the embryo
- Outer core = cells are trophoblasts. Become extra-embryonic membranes → placenta

Blastocyst stage

- Cells on outside pump fluid into embryo → Forms blastocyst cavity
- Now called blastula

Blastocyst hatching

- Breaks out of Zona pellucida → begins to grow
- After hatching, implantation occurs → implants in uterine wall (requires nutrients/waste excretion)

Inner cell mass

- Undergo reorganisation into 2 specific cell layer s
- Epiblast layer = makes embryonic tissues, columnar cells
- Hypoblast layer = face yolk sac, cuboidal cells