Department of Entomology
  • About
    • At a Glance
    • Welcome From the Chair
    • Code of Conduct
    • Diversity, Equity, and Inclusion >
      • DEI Working Group
      • Resources
    • Departmental History
    • For Alumni
    • Support Entomology >
      • Steinhauer Scholarship Fund
    • Proposal Resources
    • Contact >
      • Directions
  • News
    • News
    • Seminar Blog
    • Seminar Schedule
    • Awards
  • People
    • Faculty
    • Post Docs
    • Students
    • Staff
    • Alumni
  • Academics
    • Graduate >
      • Admissions
      • MS Degree Requirements
      • PhD Degree Requirements
      • Graduate Student Resources
      • Financial Assistance
      • Award & Funding Opportunities
      • Entomology Student Organization
    • Online Masters in Applied Entomology
    • Undergraduate >
      • Entomology Minor
      • Honors Program
  • Research
    • IPM & Biological Control of Agricultural, Urban & Forest Pests
    • Ecology, Conservation, Restoration, Climate Change >
      • Pollinator Science and Apiculture
    • Evolution, Systematics and Evo-Devo
    • Genetics & Genomics and Medical Entomology
  • Extension/Outreach
    • Educational Outreach
    • Insect Camp
    • Insect Drawings
    • Insect Identification
    • Pesticide Education and Assessment Program
    • Plant Diagnostic Laboratory (PDL)

How do mozzies maintain a segmented body plan after loss of a key developmental gene?

2/26/2019

 
Written by: Elizabeth Brandt, Mintong Nan, Anna Noreuil, Katie Reding

​How it is possible to maintain a segmented body plan after loss of a key developmental gene? Dr. Alys Jarvela, a biochemist, geneticist, and postdoctoral scholar in the Pick Lab at University of Maryland, presented her research to address this precise question.    
Dr. Jarvela first spoke about the body plan shared by all insects featuring a head, thorax, and abdomen, each of these regions being partitioned into smaller segmental units. The genetic mechanisms underlying Drosophila segmentation is well-studied. An egg isn’t just uniform throughout; there are specific proteins and mRNAs that are localized to different parts of the egg. As development proceeds, the embryo is broken up into more defined regions and eventually each part of the embryo is specified to make a particular kind of cell or tissue. Pair-rule genes are usually expressed in the primordia of alternate segments and are required for eventual formation of those same segments. paired (prd) is conserved as a pair-rule gene in phylogenetically diverse insects, such as in beetles and fruit flies, and is required for their normal segmentation and embryonic viability. 

When comparing segmentation mechanisms between the fruit fly, Drosophila melanogaster, and the mosquito, Anopheles stephensi, Dr. Jarvela strikingly found out that mosquitoes don’t have paired gene in their genomes. While insects typically have three pax3/7 genes, only two appeared to be in the many mosquito genomes she searched. These two genes have been identified as gooseberry (gsb) and gooseberry-neuro (gsb-n), as determined by phylogenetic analysis; neither of the pax3/7 genes found in mosquito genomes group with the paired genes (figure 1).  Furthermore, gsb and gsb-n are syntenic – they occur adjacent to each other on the same chromosome – in the Anopheles genome, just as other gsb and gsb-n genes are in other insect genomes. Of course, Anopheles embryos and larvae retain a segmented body plan and segment polarity expression of engrailed despite the loss of prd. So, how do mosquitoes maintain their segmented body plan?
 
To address this question, Dr. Jarvela sought to understand the roles of some of the other segmentation gene orthologs in A. stephensi. Might there be differences in their expression patterns that could explain mosquitoes’ loss of prd? Dr. Jarvela used a technique known as in situ hybridization staining, which allows one to visualize which cells contain mRNA of interest. Imaging revealed the expression patterns of most of the segmentation genes she examined were nearly identical to the expression patterns of these genes in Drosophila.  

She then wondered which transcription factor(s) might be taking the place of prd in the activation of engrailed, a segment polarity gene. Before she could try to identify the CREs dependent on Prd’s replacement in the mosquito, she first needed to map the Prd-dependent CREs in Drosophila. To do this, she conducted a classic enhancer-reporter screen. In this approach, a candidate CRE is placed upstream of some reporter gene, and this construct is then integrated into the Drosophila genome (Yeh et al. 1995). The ability of the candidate CRE to activate transcription of the reporter is then assayed by analyzing expression of the reporter (such as by in situ hybridization, described above). Using this technique, Dr. Jarvela was able to identify Prd-dependent engrailed regulatory regions. She then tested candidate Aste-engrailed CREs in Drosophila embryos, and was able to drive expression of a reporter in an engrailed-like pattern, demonstrating that these DNA sequences are very likely Aste-engrailed regulatory elements. Future work will look at which transcription factors might be responsible for binding these CREs in the absence of prd in mosquitoes. 
Figure 1. pax3/7 phylogeny reveals loss of prd in the lineage leading to Culicidae (mosquitoes) (Figure courtesy of Dr. Alys Jarvela, unpublished)
Figure 1. pax3/7 phylogeny reveals loss of prd in the lineage leading to Culicidae (mosquitoes) (Figure courtesy of Dr. Alys Jarvela, unpublished)
embryoFigure 2. The pR92W NR5A1 variant is able to bind DNA and disrupt segmentation only when expressed at very high levels. A) A control embryo showing the wild-type pattern of denticle belts, B) An embryo expressing the human gene NR5A1 at six times the baseline level; this reference allele causes segmentation defects when expressed in the Drosophila embryo because it is fully able to bind Ftz-f1 binding sites but cannot activate transcription of Ftz-F1 target genes, and C) An embryo expressing the NR5A1 variant p.R92W at six times the baseline level. When expressed at three times the baseline level, the same allele does not produce segmentation defects because it does not bind the DNA well enough to out-compete the endogenous Ftz-F1, compared to the reference NR5A1 allele which produces strong segmentation defects when expressed at three times the baseline level. Figure from Splinter et al (2018).
In addition to her work on mosquitoes, Dr. Jarvela also shared some of her work in Drosophila melanogaster which demonstrated the importance of the species as a model organism for understanding human genetic diseases. In a recent collaboration with the Undiagnosed Diseases Network, Dr. Jarvela and the Pick lab were contacted in an effort to use the fruit fly to study a newly identified human polymorphism in a certain transcription factor called NR5A1. In humans, this transcription factor affects the activity of several gonad development genes (Bashamboo 2016). In fruit flies, this gene is known as ftz-f1 and is a pair-rule gene, required for development of alternate segments similar to prd. The identified genetic change affects a DNA-contact point, which could either ablate or weaken DNA binding function. Dr. Jarvela could express this human NR5A1 (ftz-f1) variant allele in fruit flies and observe its effects on fruit fly embryo development. She used a driver gene system (GAL4-UAS) so she could control the level of the protein’s expression, which led her to the observation that the NR5A1 variant allele’s effects were dose-dependent - meaning high amounts of the protein were needed before segmentation defects were observed in Drosophila embryos. This is suggestive of the genetic change of the transcription factor being a partial loss of function, with some function still present. This led to a better understanding of the genetics underlying a new human syndrome (figure 2) (Bashamboo 2016, Splinter 2018). 
​
​
References
  1. Schroeder MD, Pearce M, Fak J, Fan H, Unnerstall U, et al. (2004) Transcriptional Control in the Segmentation Gene Network of Drosophila. PLOS Biology 2(9): e271. https://doi.org/10.1371/journal.pbio.0020271
  2. Osborne, PW and Dearden, PK. (2005) Expression of Pax group III genes in the honeybee (Apis mellifera). Dev Genes Evol 215: 499-508. https://doi.org/10.1007/s00427-005-0008-9
  3. Hinman, VF and Cheatle Jarvela, AM. (2014) Developmental gene regulatory network evolution: Insights from comparative studies in echinoderms. Genesis 52: 193-207. doi:10.1002/dvg.22757
  4. Splinter, K. et al. (2018). Effect of Genetic Diagnosis on Patients with Previously Undiagnosed Disease. The New England journal of medicine. 379. 10.1056/nejmoa1714458.
  5.  Bashamboo A, Donohoue PA, Vilain E, et al. (2016) A recurrent p.Arg92Trp variant in steroidogenic factor-1 (NR5A1) can act as a molecular switch in human sex development. Hum Mol Genet; 25: 5286. 


Comments are closed.

    Categories

    All
    Awards
    Colloquium
    Faculty Spotlight
    Fall 2013 Colloquium
    Fall 2014 Colloquium
    Fall 2015 Colloquium
    Fall 2016 Colloquium
    Featured
    Innovation
    News
    Publications
    Science Projects
    SESYNC
    Spring 2014 Colloquium
    Spring 2015 Colloquium
    Spring 2016 Colloquium
    Talks
    Undergraduate

    Archives

    September 2022
    August 2022
    July 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    December 2017
    November 2017
    October 2017
    September 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    January 2014
    December 2013
    November 2013
    October 2013
    September 2013

    RSS Feed

Picture
Picture
Picture
Department of Entomology 
University of Maryland 
4112 Plant Sciences Building 
College Park, MD 20742-4454
USA

Telephone: 301.405.3911 
Fax: 301.314.9290
Picture
Picture
Web Accessibility
  • About
    • At a Glance
    • Welcome From the Chair
    • Code of Conduct
    • Diversity, Equity, and Inclusion >
      • DEI Working Group
      • Resources
    • Departmental History
    • For Alumni
    • Support Entomology >
      • Steinhauer Scholarship Fund
    • Proposal Resources
    • Contact >
      • Directions
  • News
    • News
    • Seminar Blog
    • Seminar Schedule
    • Awards
  • People
    • Faculty
    • Post Docs
    • Students
    • Staff
    • Alumni
  • Academics
    • Graduate >
      • Admissions
      • MS Degree Requirements
      • PhD Degree Requirements
      • Graduate Student Resources
      • Financial Assistance
      • Award & Funding Opportunities
      • Entomology Student Organization
    • Online Masters in Applied Entomology
    • Undergraduate >
      • Entomology Minor
      • Honors Program
  • Research
    • IPM & Biological Control of Agricultural, Urban & Forest Pests
    • Ecology, Conservation, Restoration, Climate Change >
      • Pollinator Science and Apiculture
    • Evolution, Systematics and Evo-Devo
    • Genetics & Genomics and Medical Entomology
  • Extension/Outreach
    • Educational Outreach
    • Insect Camp
    • Insect Drawings
    • Insect Identification
    • Pesticide Education and Assessment Program
    • Plant Diagnostic Laboratory (PDL)