Tag Archives: evolution

Bowdish lab research on the evolution of MARCO featured in the New York Times

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Our research on the scavenger receptor MARCO was featured in an article “Air Pollution, Evolution, and the Fate of Billions of Humans” by Carl Zimmer in the New York Times. In this manuscript we collaborated with Dr. Brian Golding, an expert in evolutionary biology in order to understand the evolution of this macrophage receptor. MARCO (or macrophage receptor with collagenous structure) is expressed on macrophages where it binds bacteria and particles such as those found in dust and air pollution. We had hypothesized that because it is the receptor for two pathogens, Streptococcus pneumoniae and Mycobacterium tuberculosis, that have played a major part in driving human evolution, that we might find evidence of areas of the receptor that were undergoing rapid evolution to protect us from this pathogen.

In order to determine which regions of the protein were changing we performed a phylogenetic analysis of the sequence of MARCO from humans, our close ancestors, the Denisovians and Neanderthals, and primates. We found a few interesting things. There was one mutation, which we call F282S (282 refers to the 282nd amino acid in the protein, the F = phenylalanine and the S= serine), had changed very rapidly. All our primate, Denisovian and Neanderthal relatives had a serine residue in that position but fully 83% of the human genomes we analyzed had a phenylalanine. The fact that this mutation spread so quickly through the population means that there must have been very strong selection pressure. We cloned both variants and found that the human specific variant was indeed better at binding inert particles and bacteria. There were a few other interesting mutations we characterized (see article below) but the take home message is that some of the evolutionary adaptations we have made to deal with pathogens may have influenced our ability to handle air pollution or, since the savannah was predicted to be a dry and dusty place, the adaptations we’ve made to deal with particulates in the air may have changed our response to pathogens.

To read the full article, see below.

Human-specific mutations and positively-selected sites in MARCO confer functional changes. Novakowski KE, Yap NVL, Yin C, Sakamoto K, Heit B, Golding GB, Bowdish DME. Mol Biol Evol. 2017 Nov 20. doi: 10.1093/molbev/msx298.
PMID: 2916561

Kyle Novakowski is the Bowdish lab’s newest PhD!

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Kyle Novakowski successfully defended his thesis “IDENTIFICATION AND  FUNCTIONAL CHARACTERIZATION OF CONSERVED RESIDUES AND DOMAINS IN THE MACROPHAGE SCAVENGER RECEPTOR MARCO”  to become the Bowdish lab’s 4th PhD student. He’ll be joining Turnstone Biologics as a PhD scientist. We wish him very well in his future endeavours. Congratulations Dr. Novakowski!

Publication: Human-specific mutations and positively-selected sites in MARCO confer functional changes.

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First author on the publication, PhD student Kyle Novakowski of Dr. Dawn Bowdish’s lab.
A common element that links ancient fish that dwell in the darkest depths of the oceans to land mammals, Neanderthals, and humans is the necessity to defend against pathogens. Hundreds of millions of years of evolution have shaped how our innate immune cells, such as macrophages, detect and destroy microorganisms.

In a new study led by Dr. Dawn Bowdish (in collaboration with Dr. Brian Golding) and her PhD student Kyle Novakowski, the team identified novel sites within a macrophage receptor, MARCO, that are under positive selection and are human-specific. The team demonstrated the importance of these sites by site-directed mutation and showed a reduction in cellular binding and uptake of pathogens. These findings demonstrate how small genetic changes in humans can influence how we defend ourselves against pathogens.

Read the full publication in Oxford University Press.

Human-specific mutations and positively-selected sites in MARCO confer functional changes. Novakowski KE, Yap NVL, Yin C, Sakamoto K, Heit B, Golding GB, Bowdish DME. Mol Biol Evol. 2017 Nov 20. doi: 10.1093/molbev/msx298.
PMID: 2916561

Publication: A naturally occurring transcript variant of MARCO reveals the SRCR domain is critical for function

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Macrophages play a critical role in innate immunity by detecting, engulfing and destroying pathogenic bacteria and alerting neighbouring immune cells to join the fight against infection. They have many different receptors on their cell surface that allow them to carry out these important processes. A particular group of receptors called Scavenger Receptors are vital to this response. A recent study published in Immunology and Cell Biology by PhD student Kyle Novakowski from the laboratory of Dr. Dawn Bowdish has uncovered a mechanism by which a specific scavenger receptor contributes to macrophage-specific antibacterial immunity.

Scavenger Receptors are evolutionarily ancient and have evolved to recognize a wide array of pathogens by detecting ligands that are common across many pathogenic organisms. A particularly important Scavenger Receptor is Macrophage Receptor with Collagenous Structure, or MARCO. MARCO has been shown to significantly contribute to the clearance of Streptococcus pneumoniae colonization of the nose and in models of pneumococcal pneumonia. The NSERC-funded study took a unique approach to functionally characterizing how MARCO contributes to innate immunity by studying a naturally-occurring variant of the receptor. The study highlighted the importance of a particular domain of the receptor that is required for macrophages to bind and internalize ligands. The study also showed that the domain is necessary to enhance the pro-inflammatory response to pathogenic Streptococcus pneumoniae and can enhance cellular adhesion; both vital to proper macrophage functions.

To read the article, please click here.

“The Evolution of the Class A Scavenger Receptors” 2012. Whelan et al. BMC Evol Biol

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Whelan et al. BMC Evolutionary Biology 2012, 12:227 http://www.biomedcentral.com/1471-2148/12/227

The scavenger receptors are an evolutionarily ancient family of proteins required for host defence and homeostasis but teasing apart their function and even their structure has been challenging. The goal of this manuscript was to use evolution as a guide to discover how the class A scavenger receptor family was formed and to identify regions of conservation and hence probable functional importance for future study. Phagocytic receptors such as the class A scavenger receptors are integral members of the innate immune response, which is conserved in all classes of life and after reproduction and nutrient acquisition is probably the major most fundamental requirement for survival.

There are essentially only four basic mechanisms of the innate immune system – agglutination (e.g. lectins), lysis/neutralization (e.g complement, antimicrobial peptides), phagocytosis (e.g. scavenger receptors), and pro-inflammatory signalling (e.g. the toll like receptors). The fact that these processes are ancient and have been so strongly preserved is a testament to their importance. Of these, phagocytosis is likely the most ancient process and was probably adapted from its original purpose of nutrient ingestion . One might hypothesize that phagocytosis was truly the genesis of the immune system since our single celled ancestors had to distinguish  between “self” and “non-self” in order to distinguish between food and their own daughter cells.  From there phagocytosis became essential to fundamental processes such as embryonic development, pathogen recognition, and homeostatic clearance of senescent cells. Without phagocytosis, the transition to more complicated life forms could not have occurred.

Although there have been excellent evolutionary analyses of the lectins, toll like receptors and complement pathways, very little is known about the evolution of the phagocytic receptors. The class A scavenger receptors are an excellent example of these multifunctional receptors as they are involved in both host defence and homestasis. Since the phagocytic receptors in general and the scavenger receptors in particular are a diverse group of proteins,it has been challenging to understand how members within a group are related. Indeed, the first goal of this manuscript was to definitively demonstrate that the members of the class A scavenger receptors, which had been grouped together based on a ragtag combination of ligand binding and some degree of amino acid similarity, were actually a family at all.  Since we were able to trace a probable path of gene duplication and consequent functionalization, we are confident that the 5 members (SRAI/II, MARCO, SCARA3/4/5) are actually related.  Interestingly the class A scavenger receptors may have acquired their long stalk like form with a single scavenger receptor cysteine rich domain (SRCR) around the time of the evolution of fish since, although SRCR domain can be found in invertebrates and single celled organisms, we could not find anything that resembled a modern class A scavenger receptor in any genomes of evolutionarily more ancient organisms such as jellyfish, lampreys and insects.

Because elucidating the function of the specific domains of the scavenger receptors has been so challenging (even the function of the SRCR domain is unclear), ultimately we want to use evolution as a guide to which domains are functionally important (i.e. conserved). In this regard we found that there is a common conserved region in the collagenous domain, which in the type member SRAI, is believed to be the ligand binding domain. In addition conserved domains were identified in the cytoplasmic tail and the coiled-coiled domain. Future experiments will be performed to determine if these domains are necessary for structure, expression, cellular localization or phagocytic function.

 

Extra, Extra, Read all about it! The Bowdish lab elucidates the evolution of the class A scavenger receptors.

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Congratulations to Fiona Whelan (MSc) for publishing her first manuscript “The Evolution of the class A scavenger receptors” in BMC Evolutionary Biology. The scavenger receptors are an evolutionarily ancient family of proteins required for host defence and homeostasis but teasing apart their function and even their structure has been challenging. The goal of this manuscript was to use evolution as a guide to discover how the class A scavenger receptor family was formed and to identify regions of conservation and hence probable functional importance for future study. Phagocytic receptors such as the class A scavenger receptors are integral members of the innate immune response, which is conserved in all classes of life and after reproduction and nutrient acquisition is probably the major most fundamental requirement for survival.

There are essentially only four basic mechanisms of the innate immune system – agglutination (e.g. lectins), lysis/neutralization (e.g complement, antimicrobial peptides), phagocytosis (e.g. scavenger receptors), and pro-inflammatory signalling (e.g. the toll like receptors). The fact that these processes are ancient and have been so strongly preserved is a testament to their importance. Of these, phagocytosis is likely the most ancient process and was probably adapted from its original purpose of nutrient ingestion . One might hypothesize that phagocytosis was truly the genesis of the immune system since our single celled ancestors had to distinguish  between “self” and “non-self” in order to distinguish between food and their own daughter cells.  From there phagocytosis became essential to fundamental processes such as embryonic development, pathogen recognition, and homeostatic clearance of senescent cells. Without phagocytosis, the transition to more complicated life forms could not have occurred.

Although there have been excellent evolutionary analyses of the lectins, toll like receptors and complement pathways, very little is known about the evolution of the phagocytic receptors. The class A scavenger receptors are an excellent example of these multifunctional receptors as they are involved in both host defence and homestasis. Since the phagocytic receptors in general and the scavenger receptors in particular are a diverse group of proteins,it has been challenging to understand how members within a group are related. Indeed, the first goal of this manuscript was to definitively demonstrate that the members of the class A scavenger receptors, which had been grouped together based on a ragtag combination of ligand binding and some degree of amino acid similarity, were actually a family at all.  Since we were able to trace a probable path of gene duplication and consequent functionalization, we are confident that the 5 members (SRAI/II, MARCO, SCARA3/4/5) are actually related.  Interestingly the class A scavenger receptors may have acquired their long stalk like form with a single scavenger receptor cysteine rich domain (SRCR) around the time of the evolution of fish since, although SRCR domain can be found in invertebrates and single celled organisms, we could not find anything that resembled a modern class A scavenger receptor in any genomes of evolutionarily more ancient organisms such as jellyfish, lampreys and insects.

Because elucidating the function of the specific domains of the scavenger receptors has been so challenging (even the function of the SRCR domain is unclear), ultimately we want to use evolution as a guide to which domains are functionally important (i.e. conserved). In this regard we found that there is a common conserved region in the collagenous domain, which in the type member SRAI, is believed to be the ligand binding domain. In addition conserved domains were identified in the cytoplasmic tail and the coiled-coiled domain. Future experiments will be performed to determine if these domains are necessary for structure, expression, cellular localization or phagocytic function.

The best part of our paper is that it is Open Access so you can enjoy reading it in provisional form today at http://www.biomedcentral.com/1471-2148/12/227/abstract. If you have questions, comments or thoughts, please feel free to contact Dr. Dawn Bowdish at bowdish@mcmaster.ca or on her Google+ account. Dr. Bowdish is always interested in talking with undergraduate or graduate students interested in pursuing studies that use bioinformatics to answer questions about the scavenger receptors, phagocytosis, and structure/function relationships.

A summary of the common motifs in the class A scavenger receptor protein sequences. Conserved motifs present in the protein sequences of these receptors are indicated with coloured boxes at their approximate position within the protein with shout out boxes used to show the level of conservation across the aligned Homo sapiens sequences. From Whelan et al. BMC Evol Biol. BMC Evolutionary Biology 2012, 12:227