Imaging Flashcards
Marcello Malpighi
Marcello Malpighi was the first to use the light microscope to study tiny biological entities widely considered the founder of histology
- Analysed wide variety of organisms, including bats and frogs
- When studying lung structure under the microscope, he identified membranous alveoli and hair-like connections between arteries and veins, which he called capillaries
o Important discovery it established how oxygen breathed in circulates through the bloodstream and provides for the body
- Enos et al (1953)
demonstrated this by looking at bodies of deceased US soldiers from the Korean War. Although their average age was only 22, histological analysis revealed there were already clear signs of lesions and arterial wall thickening.
Braak et al. (1991)
demonstrated very little neuroanatomical and temporal correlation between amyloid plaques and neurodegeneration; plaques were mainly found in the precuneus and frontal lobes, while neuronal death began and occurred most readily in the entorhinal cortex and hippocampus.
- Wade-Martins et al. (2009)
used electron microscopy to report a new role for this gene in regulating autophagy
o They transfected cell lines with a BAC construct containing wild-type LRRK2-Ypet.
o They used immune-electron microscopy with anti-GFP antibodies to demonstrate specific localisation of cytoplasmic LRRK2 in lysosomal-autophagic organelles, such as autolysosomes.
o siRNA-mediated knockdown of LRRK2 significantly increased LC3-II turnover, which indicated increased autophagic activity; this suggested that LRRK2 may act as a negative regulator of autophagy.
o Indeed, the R1441C mutation in a BAC construct significantly increased accumulation of autophagic organelles, which contained incompletely digested material.
- This indicates that the mutant LRRK2 impaired the normal lysosomal-autophagic pathway.
Trzaskoma et al. (May 2020
published an exciting Nature paper in which they combined electron microscopy with DNA in situ hybridisation to visualise the detailed 3D chromatin folding structures of the human genome, which had not been previously possible.
- They used this combination approach on human lymphoblastoid cells and were able to visualise many distinctive 3D chromatin folding structures at targeted genomic regions with ultra-resolution
- They uncovered significant heterogeneity of chromatin folding ultrastructures in individual nuclei, indicating these 3D chromatin states are very fluid need to try and further understand these dynamic changes and their potential role in gene expression
- Hirota et al (2004)
inactivated condensin I and II by CAP-D2 and CAP-D3 depletion respectively in prophase-cells using siRNAs (CAP-D2 found in condensin I only, and CAP-D3 only in condensin II).
o DAPI staining and subsequent immunofluorescence and time-lapse confocal microscopy revealed that condensin II is required for chromosome condensation in early prophase, whereas condensin I appears to be dispensable at this stage.
o By contrast, condensin I was required for the complete dissociation of cohesin from chromosome arms, chromosome shortening and for normal timing of progression through prometaphase and metaphase, whereas normal condensin II levels are dispensable for all three of these processes.
o Moreover, after depletion of both, the onset of chromosome condensation was delayed until the end of prophase, but is then initiated rapidly before nuclear envelope breakdown, so it appears that compaction can still occur in the absence of condensin.
- Compaction occurs in absence of condensin due to small expression of condensins not fully targeted by RNAi?
- Important to note that this work is based on RNAi experiments, whilst genetic knock-downs of both condensin complexes may give a more penetrant phenotype.
o But genetic KO = difficult as it is an essential gene
Qin et al May 2020
published a paper in Nature explaining how they have developed a 2-photon fluorescence microscopy method to image the retina in vivo, which had never been previously achieved before.
- They developed an adaptive optics two-photon excitation fluorescence microscopy (AO-TPEFM) system to achieve subcellular resolution for in vivo imaging of the mouse retina, without optic aberrations of the eye degrading the image resolution (which had previously prevented visualisation of the retina at such a resolution previously)
- They were able to demonstrate simultaneous functional calcium imaging of neuronal somas and dendrites
- And in a mouse model of retinal disorder, they were also able to image the dynamics of microglia
- This system is therefore a highly promising tool for non-invasive retinal imaging, and can be used to understand eye diseases in vivo
Chow et al. 2020
- Currently, optical access to brains in adult vertebrates is limited
- This group show that three-photon (3P) imaging through the heads of living adult zebrafish allows structural + functional imaging through the telencephalon and deep into the cerebellum and optic tectum, at a cellular resolution
- So with 3P imaging, we can noninvasively image the large portions of the brain from embryo to adult in this vertebrate model
2014, the Schizophrenia Working Group of the Psychiatric Genomics Consortium
published an analysis of almost 37,000 pts and 113,000 controls investigating SNPs associated with SCZ
- The strongest association was with the MHC locus, particularly near the multi-allelic C4 gene (encoding complement component 4), but little was known about the molecular mechanisms
- Sekar et al. (2016):
): investigated this site using super-resolution microscopy technique called structured illumination microscopy (SIM)
o Using IHC, and high-resolution structured illumination microscopy (SIM) imaging, they determined that neuronal dendrites, axons and synapses expressed C4. For example, it co-localises w presynaptic markers VGLUT1/2 and postsynaptic marker PSD-95
o C4 was then shown to promote synapse elimination in mice during the developmentally timed maturation of a neuronal circuit
o So this indicates complement activity has a clear role in the developing brain and synaptic connectivity, and excessive complement activity could explain the reduced synapses in the brains of people with schizophrenia
Mogilner et al. (1993
used MEG to map the somatotopic hand area in S1 (primary somatosensory cortex) in two individuals with syndactyly (webbed fingers).
o The presurgical maps displayed shrunken and ill-defined cortical organisation. After surgery and separation of their digits, significant cortical reorganisation occurred over 3-9mm in the somatosensory hand area to produce better-defined digit representations, and these findings correlated with improved functional status of their separated digits.
Volkow et al. (2005)
o They administered 11[C]-raclopride a (radiolabelled D2 antagonist) to cocaine addicts and visualised their dorsal striatum with PET imaging.
o They split the cocaine addicts into two groups. One group were shown innocuous images (for example of nature scenes) whilst the other group were shown images of cocaine purchase and preparation.
o The authors observed a smaller signal in the dorsal striatum of the group shown cocaine images due to greater displacement of the radioligand by dopamine, showing that lots of dopamine was released in the addicts shown the cocaine images
- So not only can meaningful insights be obtained from functional imaging studies in humans, but moreover some human disorders such as cocaine addiction would not naturally be found in animal models.
Abi-Dargham et al. (2000)
used SPECT with [123I]-IBZM to measure baseline dopamine occupancy of D2 receptors.
o Schizophrenic patients and control subjects were administered alpha-methyl-para-tyrosine to deplete endogenous dopamine. The decrease in receptor occupancy was significantly greater for schizophrenic patients (19% compared to 9%), indicating greater receptor occupancy at baseline, which supports the mesolimbic hyperdopaminergic theory of schizophrenia.
(Feb 2020) by Zhang et al.
• In this paper, they showed that a machine-learning algorithm the authors designed can predict antidepressant response in major depression by analysis electroencephalographic signatures!
o A big challenge in treating depression is that only ~30-40% of patients respond to antidepressant monotherapy, leaving 60-70% of patients who do not respond optimally, partly because clinical diagnosis of depression encompasses biologically heterogeneous conditions
o So ability to predict treatment response could help match patients to appropriate treatment more rapidly
o Here, the authors designed a machine-learning algorithm tailored for resting-state EEG and applied it to data from the largest image-coupled, placebo-controlled antidepressant study, which involved 309 participants
o From the EEG alone, this algorithm was able to robustly predict symptom improvement for sertraline (an SSRI) versus placebo
o This sertraline-predictive EEG signature both reflected general antidepressant responsivity and related differentially to a rTMS (repetitive transcranial magnetic stimulation) treatment outcome
(March 2020) in Nature, Tixier et al
identified a new exciting use for FDG-PET images of tumours: they showed that PET radiomics can reveal cancer transcriptomics!***
o Their study included 45 patients with locally advanced head and neck cancer who had undergone FDG-PET scans at the time of diagnosis and transcriptome analysis using RNAs from both cancer and healthy tissues on microarrays
o Using Genomica software, they identified relationships between PET radiomics and genes involved in the cell cycle, disease, DNA repair, the immune system, metabolism, extracellular matrix organisation and signal transduction pathways
