C. elegans is often a subject choice for lab testing due to there internal systems similar to that of humans. These lecture notes cover multiple lectures discussing C. elegans. Covering: an introduction to C. elegans, C. elegans adaptations to feeding, egg laying, environmental cues and development.
Adaptive physiology in C.
elegans
Introduction to C. elegans
C. elegans
Invertebrate
Belongs to phylum Nematoda
Taxonomic group: Ecdysozoa
Roundworms, non-segmented bodies
Nematodes found everywhere: parasites in animals and plants, free living, soil,
rotting fruit, water
Most abundant animals on earth (4 out of 5 animals are nematodes)
C. elegans are found in rotting fruit
Culturing C. elegans
Agar plates (Nematode Growth Media (NGM)
Food source PO50 bacteria
Maintained at 20oC
Large mixed populations
Passage between plates
Can be frozen down at -80oC for stock maintenance
Strains can be acquired in the post
C. elegans Sexual Forms
2 sexual forms: males and hermaphrodites
Hermaphrodites are prominent sex form in nature – can reproduce on their own
General overview of anatomy
1mm in length
Several key organs: pharynx, reproductive system, intestine, defecation
Cylindrical body shape
Muscle
Pharyngeal muscle
Body wall muscle
Head and neck muscle
Vulval muscle
Intestinal muscle
Anal muscle
Nervous system
302 neurons
Nerve ring and nerve cord
Somatic n.s. (282 neurons)
Pharyngeal n.s. (20 neurons)
Motoneurons, interneurons, sensory neurones (amphids and phasmids)
Polymodal neurones
, Connectome
Nomenclature
Sensory Neurones
Amphidial neurones detect external cues from the environment
There are 12 amphid neurons that are bilaterally paired
Amphids are neurons with ciliated endings that are exposed to the external
environment
Genetics
First multicellular organisms to have it’s genome fully sequenced
Genome repository: wormbase
Size of genome: 100MB
5 pairs of chromosomes, males XO and hermaphrodites XX
Experimental advantages of C. elegans genetics
Mutagenesis, transgenics and gene editing
Forward genetic screening – add mutagen – screen for a defect in the behaviour of
interest
Reverse genetic screening – mutate sequence in a known gene – what is the
phenotype and function
Microinjection – transforms worms using DNA engineered in tube
CRIPR-CAS9 – edit the genomic DNA of worms (single nucleotide resolution)
Technologies for the study of worm physiology
Visual markers – gene expression – cells and circuits (neurone function) – behaviour
Laser ablation of neurones - cells and circuits (neurone function) – behaviour
Manual observation – behaviour
Summary
Can be cultured easily in the lab
A well characterized system (eg. anatomy and sequenced genome)
Fundamental aspects of nervous system organisation is conserved
Exhibits simple behaviour that can be easily quantified
Displays adaptive physiology in response to changes in environmental cues
Is highly amenable to experimental techniques that can be used to investigate the
neurophysiological basis of adaptive behavior (eg. genetics and laser ablation)
Adaptations to feeding
Pharynx anatomy: muscle
8 muscle cell types
Muscle cells surround a hollow tube that the bacteria are moved through
pM= pharyngeal muscle
muscle can be radially orientated depending on the muscle
radial and longitudinal muscle serve different functions
muscles are linked by electrical synapses
Laser ablation studies of the pharyngeal N.S
pharynx can still pump when all neurons are killed apart from the M4 motor neurone
which is required for isthmus peristalsis
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