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Life as a worm-- the nematode C. elegans

This humble animal: Revealed how cell lineage controls cell fate

This humble animal: Revealed how cell lineage controls cell fate Revealed the proteins in the RTK pathway, one of the “big Five”

This humble animal: Revealed how cell lineage controls cell fate Revealed the proteins in the RTK pathway, one of the “big Five” 3. Taught us about programmed cell death, key to neural development and mis-regulated in cancer

This humble animal: Revealed how cell lineage controls cell fate Revealed the proteins in the RTK pathway, one of the “big Five” 3. Taught us about programmed cell death, key to neural development and mis-regulated in cancer Gave us insights that led to the discovery of both RNAi and microRNAs

This humble animal: Revealed how cell lineage controls cell fate Revealed the proteins in the RTK pathway, one of the “big Five” 3. Taught us about programmed cell death, key to neural development and mis-regulated in cancer Gave us insights that led to the discovery of both RNAi and microRNAs 5. Helped us understand organogenesis at the single cell level

Life as a worm-- the nematode C. elegans

Fertilized egg to adult in ~2.5 days

Think like a geneticist! If you have a single heterozygous mutant fly or worm, how many generations till you have a homozygous mutant animal? http://www.polleverywhere.com/multiple_choice_polls/3fUwSIjK4zkVqsC

Hermaphrodites do it by themselves

An entire C. elegans hermaphrodite worm consists of exactly 959 cells EVERY SINGLE TIME, allowing one to follow the lineage of every cell in the body. Males have exactly 1,032 cells every single time!

Here’s how it works

Let’s look a bit more closely Was that too fast? Let’s look a bit more closely

Cell lineage: family trees, cellular style

Most lineages do not consist of single tissue types but the germline and the gut both arise from single founder cells

Most lineages do not consist of single tissue types but the germline and the gut both arise from single founder cells

the secret of embryonic development Within this lineage is the secret of embryonic development

Even cell death is programmed into the lineage. C. elegans was used to identify the machinery that regulates programmed cell death (apoptosis) in ALL animals

The Nobel Prize in Physiology or Medicine 2002 "for their discoveries concerning ’ genetic regulation of organ development and programmed cell death'" Sidney Brenner H. Robert Horvitz John Sulston

How can lineage control cell fate? One mechanism is through asymmetric segregation of “determinants” Determinants = mRNAs or proteins That drive cell fate decisions

Remember the P granules and how they are segregated into a single cell at each cell division? This cell is P4, The progenitor of the germline P granules DNA Gilbert 8.33

Scientists then looked for mutatns in which P granules are found in (the par mutants) in which P granules are found in ALL daughter cells wildtype par-3 mutant

We now know the Par proteins are key to making epithelial cells polarized in all animals Apical Basal Apical- towards the lumen Basal- towards underlying cells Lateral- contacting other epithelial cells 25

X New Biology career option: Worm genealogist But first you must learn to read a cell lineage diagram embryo 1st stage larva 2nd stage larva Increasing age of worm X

How do we read a cell lineage diagram? embryo 1st stage larva 2nd stage larva Increasing age of worm X What do you think is going on here?

How do we read a cell lineage diagram? Branching = cell division embryo 1st stage larva 2nd stage larva Increasing age of worm X What do you think is going on here? Branching = cell division

How do we read a cell lineage diagram? embryo 1st stage larva 2nd stage larva Increasing age of worm X What do you think is going on here?

How do we read a cell lineage diagram? X = programmed cell death embryo 1st stage larva 2nd stage larva Increasing age of worm X What do you think is going on here? X = programmed cell death

How do we read a cell lineage diagram? embryo 1st stage larva 2nd stage larva Increasing age of worm X How about here?

X How do we read a cell lineage diagram? How about here? embryo 1st stage larva 2nd stage larva Increasing age of worm X How about here? line ending = cell differentiation

Brenner and his colleagues found that mutations can alter lineages in many ways

Changes in the pattern of cell division Example #1- lin-22 Changes in the pattern of cell division

Example #1- lin-22 Changes in the pattern of cell division lin-22 is the worm version of the Drosophila pair-rule transcription factor hairy

Changes in the timing of cell division Example #2- lin-14 Changes in the timing of cell division L1 L2 L1 L2 L1 L1 L1

Scientists studying regulation of lin-14 were the first to identify functions for microRNAs

And the heterochronic regulator lin-28 can be part of the recipe for making “induced pluripotent stem cells”

The nematode also provides a great model for organogenesis: e.g., Building the vulva Vulva

Vulva Formation in C. elegans: A model for organogenesis One inducing cell Three receiving cells 22 cells One complete organ 41

The key players One gonadal anchor cell (AC) 6 vulval precursor cells (VPCs) 1° vulval precursor cell 2° vulval precursor cell 3° vulval precursor cell 43

Cell ablation helped define the key players

Cell ablation helped define the key players What can we conclude from these experiments?

The anchor cell (AC) signals to the vulval precursor cells (VPCs), telling them to adopt vulval fates Hypodermis (normal skin) Hypodermis (normal skin) Vulva

All cells are created equal Any of the VPCs can adopt 1° and 2° fates to form a vulva

Scientists also isolated “vulvaless mutants” because without signaling from the anchor cell, all cells adopt a 3° fate

Without signaling from the anchor cell, all cells adopt a 3° fate What happens in this scenario?

Without signaling from the anchor cell, a The “bag of worms” phenotype vulva cannot form The “bag of worms” phenotype

Mutational analysis also revealed that there are two steps involved in forming a vulva Step 1: Anchor cell signal reaches central 3 Vulval precursor cells (VPCs) Step 2: Central cell sends inhibitory signal to neighbors

What happens if the inhibitory signal from the 1° VPC is blocked?

What happens if the inhibitory signal from the 1° VPC is blocked? All three central VPCs adopt 1° VPC fate And three partial vulvas form!

What are the actual signals involved in vulva formation? Step 1: Anchor cell signal reaches central 3 Vulval precursor cells (VPCs) Anchor cell 1°/2° VPC

The vul mutations helped define the RTK-Ras pathway, which is mutationally activated in more than half of all human tumors

This pathway’s so important in Cancer it got 2 spots on this Table! Here’s Notch

Ras plays a central role in signal transduction downstream of receptor tyrosine kinases (RTKs)

Oncogenic Ras mutations are stuck in the ON state Ras plays a central role in signal transduction downstream of receptor tyrosine kinases (RTKs) Oncogenic Ras mutations are stuck in the ON state

What are the actual signals involved in vulva formation? Step 2: Central cell sends inhibitory signal to neighbors

Does this remind you of anything we learned earlier?

Remember me?

lin-12 is the transmembrane receptor that receives the lateral inhibition signal and it is the C. Elegans homolog of Notch