Alveolar Type II Cell Diagram
Figure 1 : Sample diagram of an alveolar type II cell showing how simple errors in organelle position, relative sizes, incidence, transporter notation, extraneous raster images, and redundancies can misrepresent the known details. Inaccurate diagrams can become established and perpetuated in the scientifi c literature.
attention to the fact that a telomerase gene is important in surfactant production. But this presentation derails any pertinent visual associations. This double-helix icon is not only disproportionately large, but it has no T-loop/D-loop structure or proteins indicative of telomers and telomerase and is not positioned close to the inner nuclear membrane where telomers and telomerase-complexes might be found. In Figure 2 there is a considerable reduction in the size of the double helix (still inappropriately large, but better), and a generic object, colored similarly to the text (green), clearly identified as telomerase, has been added. Figure 2 also displays a diagrammatic distinction between euchromatin (shaded blue to white) and condensed chromatin (blue), which allows placement of the DNA helix and telomerase at the inner nuclear membrane near condensed chromatin where it might typically be found. Proteins . Importantly, Figure 1 strives to highlight membrane proteins known to be particularly important for surfactant production. It depicts ABCA3, a transport protein reportedly found in the limiting membrane of LBs, with a sphere and an inward pointing arrow. The lowercase text indicates mouse gene nomenclature, not human, while human protein was mentioned in the text. The same sphere-like symbol used for ABCA3 was also used for SLC34A2, the sodium- potassium symporter found on the apical plasmalemma of alveolar type II cells. Note that ABCA3 is an ATP binding cassette superfamily member, not in the same superfamily as solute carrier protein SCL34A2. Using the same symbol for both types of transporter wrongly suggests a similar function. Figure 2 uses an arrow-shape for ABCA3 (purpose- fully mimicking the structure of ABCA3, a split arrowhead).
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This provides a visual distinction between ABCA3 and SLC34A2. To indicate the location of uptake of phosphate ions from the alveolar space via proteins in the apical membrane, a sphere and single inward pointing arrow was labeled as SLC34A2 ( Figure 1 ). A single arrow is the symbol used for uniporters, but SLC34A2 is a symporter. It is likely that numerous transporters are involved in maintaining intracellular phosphate homeostasis for synthesis, reuptake, and recycling of phospholipids. An accurate depiction specific for SLC34A2 also would have shown the obligatory sodium ion import, either electrogenic or electroneutral depending on the isoform, which Figure 2 now implies with two inward pointing arrows [ 5 – 7 ]. In Figure 2 , all the icons for generic phosphate import, and parentheses for SLC34A2, are located on the apical plasmalemma with the surface
microvilli, unlike Figure 1 where the symbol lies above what is erroneously construed, by default, as lateral plasmalemma (denoted by hash marks in Figure 2 ). Endoplasmic reticulum . The endoplasmic reticulum
(ER) in Figure 1 lacks ribosomes, and by convention, then, is smooth, but its position at the nuclear membrane implies that it is rough endoplasmic reticulum. There are numerous ribosomes in the type II cell, membrane-bound and free, therefore an accurate depiction of the ER continuous with
Table 1 : Guidelines for creating scientifi c illustrations that inform and support a manuscript.
Attribute Accuracy
Audience Consistency Symbols Details Legend Best Practice
Know the facts, do the research, understand the purpose, ask questions
Identify your readership and purpose: books, schools, displays, manuscripts, museums
Note relative and absolute dimensions; indicate positions, incidence, complexity; use accepted scientific notation
Use appropriate icons, modify or create new and better symbols [ 12 , 13 ], use peer review to ascertain clarity
Choose colors, strokes, fonts, bolding, backgrounds, alignment, and arrows to emphasize critical content
Compose a comprehensive, inclusive, stand-alone legend
www.microscopy-today.com • 2017 September
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