Maria Milla - Academia.edu (original) (raw)

Papers by Maria Milla

Chemical Engineering Journal, 2018

The response of cells to the exposure of nanomaterials is crucial for determining their safety in... more The response of cells to the exposure of nanomaterials is crucial for determining their safety in their multiple uses; however, the majority of the in vitro experiments use monolayered cell cultures instead of comparing the behavior of the cells in 3D, a more realistic environment. Here, we have analyzed how the exposed surface of the cells, as well as the environment where cells grow, can influence the interaction and uptake of superparamagnetic iron oxide nanoparticles (SPIONs). We exposed three different cell lines (MDAMB-231, HL60 and bEnd3), which grow at different environments, to increasing concentrations of SPIONs (0-150 µg•ml-1) and we evaluated parameters analyzing the morphological changes of the cell, iron uptake and cell viability. Results showed that upon exposure to SPIONs, cell viability and morphology are more affected when cells are growing in 3D systems, indicating that the increase of exposed surface area of the cells is a strong parameter to take in account when evaluating SPIONs or other materials or drugs. Our results clearly reinforce the use of more realistic environments, such as 3D, for the design of new drug delivery systems.

Biochemistry, 2010

In previous studies with partially denatured metaphase chromosomes, we detected platelike structu... more In previous studies with partially denatured metaphase chromosomes, we detected platelike structures instead of the chromatin fibers currently considered in different structural models for chromosomes. Here we have observed that dilution of compact metaphase chromosomes with hyposmotic solutions can transform whole chromatids into extended plates formed by many layers. Since this treatment is soft and it does not change the ionic conditions, these observations indicate that native chromosomes are formed by stacked plates. This strengthens our hypothesis about the multilayer structure of chromosomes, which was originally based on results obtained using stronger denaturing conditions. We have investigated the structure of plates emanated from chromosomes using electron tomography. Our three-dimensional reconstructions demonstrate conclusively that the surface of the plates is very smooth and do not show repetitive structures supporting any regular organization of nucleosomes; even the nucleosomes in plate edges show irregular orientations. Furthermore, we have used polarizing microscopy for the study of whole chromosomes in metaphase cells in aqueous solution. Our results show that condensed chromosomes are not birefringent under structuring ionic conditions similar to those used with plates. This observation is incompatible with the existence of parallel columns of nucleosomes within chromosomes. In summary, we have not detected any regular orientation of nucleosomes, but at the same time, our results indicate that the bulk of chromatin in native chromosomes is organized forming very well-defined plates, in which the nucleosomes of the successive layers are interdigitated. Presumably, this dense structure is required for safe transfer of DNA to daughter cells.

Biophysical Journal, 2012

The three-dimensional organization of the enormously long DNA molecules packaged within metaphase... more The three-dimensional organization of the enormously long DNA molecules packaged within metaphase chromosomes has been one of the most elusive problems in structural biology. Chromosomal DNA is associated with histones and different structural models consider that the resulting long chromatin fibers are folded forming loops or more irregular three-dimensional networks. Here, we report that fragments of chromatin fibers obtained from human metaphase chromosomes digested with micrococcal nuclease associate spontaneously forming multilaminar platelike structures. These self-assembled structures are identical to the thin plates found previously in partially denatured chromosomes. Under metaphase ionic conditions, the fragments that are initially folded forming the typical 30-nm chromatin fibers are untwisted and incorporated into growing plates. Large plates can be self-assembled from very short chromatin fragments, indicating that metaphase chromatin has a high tendency to generate plates even when there are many discontinuities in the DNA chain. Self-assembly at 37°C favors the formation of thick plates having many layers. All these results demonstrate conclusively that metaphase chromatin has the intrinsic capacity to self-organize as a multilayered planar structure. A chromosome structure consistent of many stacked layers of planar chromatin avoids random entanglement of DNA, and gives compactness and a high physical consistency to chromatids.

Chemical Engineering Journal, 2018

The response of cells to the exposure of nanomaterials is crucial for determining their safety in... more The response of cells to the exposure of nanomaterials is crucial for determining their safety in their multiple uses; however, the majority of the in vitro experiments use monolayered cell cultures instead of comparing the behavior of the cells in 3D, a more realistic environment. Here, we have analyzed how the exposed surface of the cells, as well as the environment where cells grow, can influence the interaction and uptake of superparamagnetic iron oxide nanoparticles (SPIONs). We exposed three different cell lines (MDAMB-231, HL60 and bEnd3), which grow at different environments, to increasing concentrations of SPIONs (0-150 µg•ml-1) and we evaluated parameters analyzing the morphological changes of the cell, iron uptake and cell viability. Results showed that upon exposure to SPIONs, cell viability and morphology are more affected when cells are growing in 3D systems, indicating that the increase of exposed surface area of the cells is a strong parameter to take in account when evaluating SPIONs or other materials or drugs. Our results clearly reinforce the use of more realistic environments, such as 3D, for the design of new drug delivery systems.

Biochemistry, 2010

In previous studies with partially denatured metaphase chromosomes, we detected platelike structu... more In previous studies with partially denatured metaphase chromosomes, we detected platelike structures instead of the chromatin fibers currently considered in different structural models for chromosomes. Here we have observed that dilution of compact metaphase chromosomes with hyposmotic solutions can transform whole chromatids into extended plates formed by many layers. Since this treatment is soft and it does not change the ionic conditions, these observations indicate that native chromosomes are formed by stacked plates. This strengthens our hypothesis about the multilayer structure of chromosomes, which was originally based on results obtained using stronger denaturing conditions. We have investigated the structure of plates emanated from chromosomes using electron tomography. Our three-dimensional reconstructions demonstrate conclusively that the surface of the plates is very smooth and do not show repetitive structures supporting any regular organization of nucleosomes; even the nucleosomes in plate edges show irregular orientations. Furthermore, we have used polarizing microscopy for the study of whole chromosomes in metaphase cells in aqueous solution. Our results show that condensed chromosomes are not birefringent under structuring ionic conditions similar to those used with plates. This observation is incompatible with the existence of parallel columns of nucleosomes within chromosomes. In summary, we have not detected any regular orientation of nucleosomes, but at the same time, our results indicate that the bulk of chromatin in native chromosomes is organized forming very well-defined plates, in which the nucleosomes of the successive layers are interdigitated. Presumably, this dense structure is required for safe transfer of DNA to daughter cells.

Biophysical Journal, 2012

The three-dimensional organization of the enormously long DNA molecules packaged within metaphase... more The three-dimensional organization of the enormously long DNA molecules packaged within metaphase chromosomes has been one of the most elusive problems in structural biology. Chromosomal DNA is associated with histones and different structural models consider that the resulting long chromatin fibers are folded forming loops or more irregular three-dimensional networks. Here, we report that fragments of chromatin fibers obtained from human metaphase chromosomes digested with micrococcal nuclease associate spontaneously forming multilaminar platelike structures. These self-assembled structures are identical to the thin plates found previously in partially denatured chromosomes. Under metaphase ionic conditions, the fragments that are initially folded forming the typical 30-nm chromatin fibers are untwisted and incorporated into growing plates. Large plates can be self-assembled from very short chromatin fragments, indicating that metaphase chromatin has a high tendency to generate plates even when there are many discontinuities in the DNA chain. Self-assembly at 37°C favors the formation of thick plates having many layers. All these results demonstrate conclusively that metaphase chromatin has the intrinsic capacity to self-organize as a multilayered planar structure. A chromosome structure consistent of many stacked layers of planar chromatin avoids random entanglement of DNA, and gives compactness and a high physical consistency to chromatids.