A. (2019) Selfassembling peptide-based hydrogel: regulation of mechanical stiffness and thermal stability and 3D cell culture of fibroblasts. ACS Applied Bio Materials, 2 (12). pp. 5235-5244.
Lipid droplets (LDs), reservoirs of cholesterols and fats, are organelles that
hydrolyse lipids in the cell. In zebrafish embryos, the actomyosin complex and
filamentous microtubules control the periodic regulation of the LD geometry.
Contrary to the existing hypothesis that LD transport involves the
kinesin-microtubule system, we find that their recruitment to the blastodisc depends
on the actomyosin turnover and is independent of the microtubules. For the first
time we report the existence of two distinct states of LDs, an inactive and an
active state, that occur periodically, coupled weakly to the cleavage cycles. LDs
are bigger, more circular and more stable in the inactive state in which the
geometry of the LDs is maintained by actomyosin as well as microtubules. The active
state has smaller and irregularly shaped LDs that show shape fluctuations that are
linked to actin depolymerization. Because most functions of LDs employ surface
interactions, our findings on the LD geometry and its regulation bring new insights
to the mechanisms associated with specific functions of LDs, such as their storage
capacity for fats or proteins, lipolysis etc.
Differentiation of monocytes entails their relocation from blood to the tissue, hence accompanied by an altered physicochemical micro-environment. While the mechanism by which the biochemical make-up of the micro-environment induces differentiation is known, the fluid-like to gel-like transition in the physical micro-environment is not well understood. Monocytes maintain non-adherent state to prevent differentiation. We establish that irrespective of the chemical makeup, a 3D gel-like micro-environment induces a positive-feedback loop of adhesion-MAPK-NF-κβ activation to facilitate differentiation. In 2D fluid-like micro-environment, adhesion alone is capable of inducing differentiation via the same positive-feedback signaling. Chemical inducer treatment in fluid-like micro-environment, increases the propensity of monocyte adhesion via a brief pulse of p-MAPK. The adhesion subsequently elicit differentiation, establishing that adhesion is both necessary and sufficient to induce differentiation in 2D/3D micro-environment. MAPK, and NF-κβ being key molecules of multiple signaling pathways, we hypothesize that biochemically inert 3D gel-like micro-environment would also influence other cellular functions.
SUMMARYAll-trans retinoic acid (RA) is a key player in many developmental pathways. Most methods used to study its effects in development involve continuous all-trans RA activation by incubation in a solution of all-trans RA or by implanting all-trans RA-soaked beads at desired locations in the embryo. Here we show that the UV-driven photo-isomerization of 13-cis RA to the trans-isomer (and vice versa) can be used to non-invasively and quantitatively control the concentration of all-trans RA in a developing embryo in time and space. This facilitates the global or local perturbation of developmental pathways with a pulse of all-trans RA of known concentration or its inactivation by UV illumination. In zebrafish embryos in which endogenous synthesis of all-trans RA is impaired, incubation for as little as 5 minutes in 1 nM all-trans RA (a pulse) or 5 nM 13-cis RA followed by 1-minute UV illumination is sufficient to rescue the development of the hindbrain if performed no later than bud stage. However, if subsequent to this all-trans RA pulse the embryo is illuminated (no later than bud stage) for 1 minute with UV light (to isomerize, i.e. deactivate, all-trans RA), the rescue of hindbrain development is impaired. This suggests that all-trans RA is sequestered in embryos that have been transiently exposed to it. Using 13-cis RA isomerization with UV light, we further show that local illumination at bud stage of the head region (but not the tail) is sufficient to rescue hindbrain formation in embryos whose all-trans RA synthetic pathway has been impaired.
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