08/10/2021

PhD offer - Sorbonne University - Biomineralization and Pigmentation Sea Urchins

This job offer has closed


  • ORGANISATION/COMPANY
    LCMCP
  • RESEARCH FIELD
    Biological sciences
    ChemistryBiochemistry
  • RESEARCHER PROFILE
    First Stage Researcher (R1)
  • APPLICATION DEADLINE
    30/11/2021 16:00 - Europe/Brussels
  • LOCATION
    France › Parie
  • TYPE OF CONTRACT
    Temporary
  • JOB STATUS
    Full-time
  • HOURS PER WEEK
    35
  • OFFER STARTING DATE
    01/02/2022

OFFER DESCRIPTION

 

 

PhD offer, LCMCP, Sorbonne University (ED 397)

 

http://ed397.sorbonne-universite.fr

 

Understanding the synergy between in-vivo pigmentation and biomineralization mechanisms in sea urchins through the in-vitro opening of naphthoquinone-loaded pH-sensitive liposomes during CaCO3 precipitation

 

Topic: Biomineralization, Biochemistry, Biology, Pigmentation

Keywords: sea urchin spines, polyhydroxylated naphthoquinones, amorphous CaCO3, pH-sensitive liposomes

Host Institution: Sorbonne University, “Laboratoire Chimie de la Matière Condensée de Paris”, France

Supervisors/Contact: Marie Albéric and Nadine Nassif

Research webpage: https://lcmcp.upmc.fr/site/biomineralization/

Email: marie.alberic@sorbonne-universite.fr, nadine.nassif@sorbonne-universite.fr

Starting date: January 2022

Funding: ANR JCJC Grant – ColMhyBio

 

Project description: Although the biomineralization mechanisms (i.e. the formation of minerals by organisms) in sea urchin spines have been already studied [1,2], the pigmentation phenomena controlling the different colors of the spines have been so far overlooked. The diverse colors observed in sea urchin spines are due to a family of organic molecules, the polyhydroxylated-naphthoquinone (PHNQ) (Fig. A), which are produced within the so-called red-spherule cells (RSC) (Fig. B) [3]. PHNQs have anti-bacterial properties making the red-spherules cells part of the immune system of the urchins [3]. Our preliminary results show that when sea urchin spines fracture, RSC that actively participate to the healing of the epithelium tissues are closely located to the new growing micro-spines composed of a mixture of amorphous calcium carbonate (ACC) and calcite (Fig. C, D). In addition, micrometric vesicles containing the PHNQ molecules seem to travel from the RSC to the growing mineral surface in which they are likely incorporated (Fig. D). We also observed color variations during spine’s growth: micro-spines are at first transparent and then gradually color in light pink (Fig. E) whereas shades from brown to green can be found in mature crystalline spines. However, the origin of the color and its variations remains unclear.

 

Figs. A) Different colors of P. lividus sea urchins and PHNQ molecule structures, B) red-spherule cells at the surface of the tip of a growing spine, C) in-vivo confocal laser scanning microscopy of a calcein stained micro-spine (in green), D) focused ion beam scanning electron microscopy micrograph of a freeze substituted micro-spine in contact with a red-spherule cell and E) growing tip of a spine composed of micro-spines (CT-data).

The objective of this PhD is to improve our understanding of the mechanisms involved in the PHNQ incorporation within the growing mineral during the coupled biomineralization and pigmentation pathways in sea urchins. For this purpose, the PhD will be divided in 2 parts, which will be studied in parallel.

The first approach will be dedicated to the study of the in-vivo mechanisms leading to the PHNQs incorporation within the biominerals. Living Paracentrotus lividus sea urchins will be hosted in the aquariums of the aquatic platform of Sorbonne University. The vesicles and then the PHNQ molecules will be extracted from the red-spherule cells according to established protocols [4]. The former will be characterized by (cryo)-TEM and the later by UV-visible spectroscopy, 1H solution state NMR and HPLC/LC-MS. Moreover, pH likely plays an important role in vesicles opening and release of the PHNQs. Therefore, intra-vesicular pH measurements will be performed using pH sensitive dye that will be imaged by live-cell fluorescence microscopy [5,6] and possibly by a recent histological procedure developed for bones at the LCMCP. Live fluorescence and confocal microscopies will allow determining the relation between RSC and Ca transport, and cryo(FIB-SEM) imaging vesicles at higher magnification.

The second approach will focus on bio-mimicking the opening of naphthoquinone-loaded pH-sensitive liposomes during the precipitation of calcium carbonates. Based on established method [7-9], PHNQ-loaded pH-sensitive liposomes will be first synthesized. By varying the PHNQ composition and concentration as well as the liposome size, the effect of confinement on the color changes will be also studied. Second, liposome opening will be controlled by modifying the pH and third CaCO3 precipitation will be induced. The possibility of forming a dense 3D network of hybrid vesicles may be considered to guide CaCO3 network patterning. pH measurements, (cryo)-TEM, fluorescence and confocal microscopy as well as (cryo)-FIB-SEM will also be performed on these in-vitro systems.

 

Required skills: The candidate should have experience in research and a good academic track record. She/He should have background in (bio)chemistry, synthesis and characterization. In particular, experiences in the synthesis of liposome as well as knowledge in analytical techniques cited above will be considered. An interest in multidisciplinary work as well as in biology will be appreciated. She/He should have a good level of English (written and spoken).

 

Application modalities: Candidate should provide a CV and a cover letter. A report of the last grades, the name and email addresses of two references will also be appreciated.

 

References:

[1] Politi, et al., Sea urchin spine calcite forms via a transient amorphous calcium carbonate phase, Science 306(5699) (2004).

[2] Albéric, et al., Growth and regrowth of adult sea urchin spines involve hydrated and anhydrous amorphous calcium carbonate precursors, Journal of Structural Biology: X 1 100004 (2019).

[3] Hou, et al., Naphthoquinones of the spinochrome class: Occurrence, isolation, biosynthesis and biomedical applications, RSC Adv. 8(57) (2018).

[4] Smith, Methods for collection, handling, and analysis of sea urchin coelomocytes, Methods in Cell Biology 150 (2019).

[5] Hu, et al., Cellular bicarboate accumulation and vesicular proton transport promote calcification in the sea urchin larva, Proc. R. Soc. B. 287: 20201506. (2020).

[6] Webb, et al., pH regulation and tissue coordination pathways promote calcium carbonate bioerosion by excavating sponges, Scientific report 9:758 (2019).

[7] Monteiro, et al., Paclitaxel-Loaded pH-Sensitive Liposome: New Insights on Structural and Physicochemical Characterization, Langmuir 34 (2018).

[8] Yaroslavov, et al., a novel approach to a controlled opening of liposomes, Colloids and Surface B: Biointerfaces 190 (2020).

[9] Tester, et al., In vitro synthesis and stabilization of amorphous calcium carbonate (acc) nanoparticles within liposomes, CrystEngComm 13(12) (2011).

 

More Information

Offer Requirements

Skills/Qualifications

The candidate should have a Master degree and experience in research and a good academic track record. She/He should have background in (bio)chemistry, synthesis and characterization. In particular, experiences in the synthesis of liposome as well as knowledge in analytical techniques cited above will be considered. An interest in multidisciplinary work as well as in biology will be appreciated. She/He should have a good level of English (written and spoken). 

Specific Requirements

Candidate should provide a CV and a cover letter. A report of the last grades, the name and email addresses of two references will also be appreciated.

Map Information

Job Work Location Personal Assistance locations
Work location(s)
1 position(s) available at
Sorbonne University
France
Parie

EURAXESS offer ID: 694457

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