title: Optimization of phosphorus localization by EFTEM of nucleic acid containing structures.
abstract: Energy Filtered Transmission Electron Microscopy (EFTEM) has been used to study nucleic acids localization in unstained thin sections of virus-infected cells. For this purpose, phosphorus maps (P-maps) have been obtained by applying the N-windows Egerton model for background subtraction from data acquired by a non-dedicated TEM Jeol 1200EXII equipped with a post-column PEELS Gatan 666-9000 and a Gatan Image Filter (GIF-100). To prevent possible errors in the evaluation of elemental maps and thus incorrect nucleic acid localization, we have studied different regions of swine testis (ST) cells with similar local density containing either high concentration of nucleic acids (condensed chromatin and ribosomes) or a very low concentration (mitochondria). Special care was taken to optimize the sample preparation conditions to avoid as much as possible the traditional artifacts derived from this source. Selection of the best set of pre-edge images for background fitting was also considered in order to produce "true P-maps". A new software for interactive processing of images series has been applied to estimate this set. Multivariate Statistical Analysis was used as a filtering tool to separate the "useful information" present in the inelastic image series (characteristic signal) from the "non-useful information" (noise and acquisition artifacts). The reconstitution of the original image series preserving mainly the useful information allowed the computation of P-maps with improved signal-to-noise ratio (SNR). This methodology has been applied to study the RNA content of maturation intermediate coronavirus particles found inside infected cells.
authors.affiliation: Instituto de Microelectrónica de Madrid, CNM-CSIC, Parque tecnológico de Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Quintana
authors.forename: S
authors.initials: S
authors.lastname: Marco
authors.forename: N
authors.initials: N
authors.lastname: Bonnet
authors.forename: C
authors.initials: C
authors.lastname: Risco
authors.forename: M L
authors.initials: ML
authors.lastname: Gutiérrez
authors.forename: A
authors.initials: A
authors.lastname: Guerrero
authors.forename: J L
authors.initials: JL
authors.lastname: Carrascosa
mesh_terms: D000818:Animals; D007091:Image Processing, Computer-Assisted; D008297:Male; D008854:Microscopy, Electron / Q000379:methods*; D015999:Multivariate Analysis; D009696:Nucleic Acids / Q000032:analysis* / Q000648:ultrastructure; D010758:Phosphorus / Q000032:analysis*; D012367:RNA, Viral / Q000032:analysis* / Q000648:ultrastructure; D012984:Software; D013552:Swine; D013737:Testis / Q000648:ultrastructure / Q000821:virology; D005760:Transmissible gastroenteritis virus / Q000648:ultrastructure
chemical_list: D009696:Nucleic Acids; D012367:RNA, Viral; D010758:Phosphorus