Mi öröklődik a géneken kívül?

Szathmáry Eörs

Eötvös University Collegium Budapest

Units of evolution

hereditary traits affecting survival and/or reproduction

1. multiplication

2. heredity

3. variation

The formose ‘reaction’

formaldehyde

glycolaldehyde

autocatalysis

Butlerow, 1861

The reductive citric acid cycle

Von Kiedrowski’s replicator

Peptide replicator networks

Classification of replicators

Limited heredity

Unlimited heredity

Holistic formose

Modular Von Kiedrowski

genes

Limited (# of individuals) (# of types)

Unlimited (# of individuals) << (# of types)

King (1980): evolution of the coenzymes

• He looked at the metabolic maps then

• Coenzymes looked auto- and cross-catalytic

• BUT the situation is slightly more complicated

• The idea nicely links to the assumed primitive ancestry of coenzymes (related to the idea of the RNA world)

An autocatalytic cycle in the given environment

Although A is autocatalytic, it is not strictly needed

Dependent on the environment!

Autocatalysis of the pair (A, B) is more complicated, but easy to see

If this is big, you may not realize the autocatalysts

The basic question

• Could one kick-start metabolism just with external molecules and macromolecules (genes an enzymes)?

• Influx buildup of metabolism?

Metabolic networks

Membrane heredity

Principle of membrane heredity

Prions

Strain-specific prion propagation

Yeast and fungal amyloid prions

• The soluble forms of the yeast proteins Ure2p and Sup35p function in nitrogen regulation and transcription termination, respectively.

• Their amyloid forms are non-functional. Soluble Rnq1p has no known cellular function and the amyloid form can sporadically prime polymerization of Sup35p or Ure2p resulting in the generation of the [PSI+] and [URE3] prions.

• The soluble form of the HETs protein has no known function, but its amyloid form is necessary for heterokaryon incompatibility, which is a limitation on the fusion of neighbouringcolonies.

• Red domains are apparently unstructured in the native form and become amyloid in the prion form. Green shapes are natively structured domains.

Epigenetic inheritance

1. Structural inheritance (e.g. cortical inheritance in ciliates)

2. Autocatalytic gene activity

3. Chromatin marking (e.g. methylation)

Genetic and epigenetics

Regulation of gene expression by constitutive expression of a

protein

• After division the state is inherited because enough protein is around

Stable and unstable epigenetic markings

Inheritance of DNA methylation patterns

Linaria flower inheritance

Linaria (gyújtoványfű)• A naturally occurring mutant of Linaria vulgaris, originally described

more than 250 years ago by Linnaeus, in which the fundamental symmetry of the flower is changed from bilateral to radial.

• The mutant carries a defect in Lcyc, a homologue of the cycloidea gene which controls dorsoventral asymmetry in Antirrhinum.

• The Lcyc gene is extensively methylated and transcriptionally silent in the mutant.

• This modification is heritable and co-segregates with the mutant phenotype.

• Occasionally the mutant reverts phenotypically during somatic development, correlating with demethylation of Lcyc and restoration of gene expression.

• It is surprising that the first natural morphological mutant to be characterized should trace to methylation, given the rarity of this mutational mechanism

• in the laboratory. • This indicates that epigenetic mutations may play a more signi®cant

role in evolution than has hitherto been suspected.

Somatic instability of peloric plants

Types of transmitted variation

Hypermutation in derepressed operons

• Starvation for leucine in an Escherichia coli auxotroph triggers metabolic activities that specifically target the leu operon for derepression, increased rates of transcription, and mutation.

• Derepression of the leu operon was a prerequisite for its activation by the signal nucleotide, guanosine tetraphosphate, which accumulates in response to nutritional stress (the stringent response).

• A quantitative correlation was established between leuB mRNA abundance and leuB2 reversion rates.

• These investigations suggest that guanosine tetraphosphate may contribute as much as attenuation in regulating leu operon expression and that higher rates of mutation are specifically associated with the derepressed leu operon.

Types of mutation

Language is not Weismannian

germgerm germ

soma soma

germDNA

protein

DNA

protein

germNeural representation

sentence sentence

Neural representation

RNA-directed DNA methylation• Target loci (in this case tandemly repeated

sequences; coloured arrows) recruit an RNA polymerase IV complex consisting of NRPD1A and NRPD2 through an unknown mechanism, and this results in the generation of a single-stranded RNA (ssRNA) species.

• This ssRNA is converted to double-stranded RNA (dsRNA) by the RNA-dependent RNA polymerase RDR2. The dsRNA is then processed into 24-nucleotide siRNAs by DCL3. The siRNAs are subsequently loaded into the PAZ- and PIWI-domain-containing protein AGO4, which associates with another form of the RNA polymerase IV complex, NRPD1B–NRPD2. AGO4 that is ‘programmed’ with siRNAs can then locate homologous genomic sequences and guide the protein DRM2, which has de novo cytosine methyltransferase activity.

• Targeting of DRM2 to DNA sequences also involves the SWI–SNF-family chromatin remodelling protein DRD1. The NRPD1B–NRPD2 complex might generate a target transcript (ssRNA) to which the AGO4-associated siRNAs can hybridize.

• Given that siRNAs homologous to some loci are absent in drm2 mutants and ago4 mutants, it is possible that DNA methylation (blue circles) also stimulates siRNA generation and reinforces silencing.

PcG-protein-mediated silencing throughout the A. thaliana life cycle

• a, FLC is transcriptionally active in seeds and seedlings, preventing the plant from flowering and prolonging vegetative development.

• b, Exposure to a long period of cold (that is, vernalization) results in the expression of VIN3 (red), which initiates repression of FLC transcription, and the binding of the PcG protein VRN2, as well as VRN1 and LHP1 (blue). In this process, chromatin at FLC is epigenetically modified by the trimethylation of H3K27.

• c, After warmer temperatures return, FLC repression is maintained, allowing flowering to be induced by other cues.

• d, During flower development, the anthers

• and ovaries are sites of meiotic differentiation, giving rise to haploid cells known as microspores and megaspores, respectively.

• e, These meiotic products undergo mitotic proliferation to form the multicellular embryo sac and pollen gametophytes.

• f, PcG-protein-mediated repression at FLC is removed during an undefined resetting process.

• g, Then, the pollen contributes sperm nuclei to the embryo sac, and these fertilize the haploid egg cell and diploid central cell (not shown), forming the embryo and endosperm (respectively) in a new seed, in which FLC is re-expressed.

Chimpanzee culture

• Each chimpanzee community has its own unique array of traditions that together constitute the local ‘culture’.

• ‘Customary’ acts are those typical in the community, ‘habitual’ ones are less common but consistent with social transmission, and ‘absent’ acts are those missing with no apparent straightforward environmental explanation.

• Traditions are defined as behaviour patterns that are customary or habitual in at least one site but absent elsewhere.

• Transmission is attributed to social learning on the basis of a complex of circumstantial evidence, ranging from intense observation by juveniles to distributions inconsistent with alternative explanations.

The cultures of wild chimpanzees

The different social conventions of neighbours: the grooming

hand-clasp

Tool-set for harvesting termites

Selective copying

Why is language so interesting?

• Because everybody knows that only we talk

• …although other animals may understand a number of words

• Language makes long-term cumulative cultural evolution possible

• A novel type of inheritance system with showing “unlimited hereditary” potential

Design features of language

• Compositionality (meaning dependent on how parts are combined)

• Recursion (phrases within phrases)

• Symbolicism (versus icons and indices)

• Cultural transmission (rather than genetic)

• SYMBOLIC REFERENCE and SYNTAX

Three interwoven processes

• Note the different time-scales involved• Cultural transmission: language transmits itself as

well as other things, has its own dynamics