Fluorescence imaging preparation methods for tissue scaffolds implanted into a green fluorescent protein porcine model

Detecting Green Fluorescent Protein-tagged Cryptococcus neoformans by Immunofluorescence on Paraffin-embedded Brain Sections

Cryptococcus neoformans is an important pathogen causing opportunistic fungal meningitis. The pathogenic mechanism of cryptococcal meningitis remains unclear. We aimed to describe a practical approach for studying the pathologic features of cryptococcal central nervous system infection by immunofluorescence on paraffin-embedded brain of mice using different antigen retrieval methods. After 14 days of intratracheal inoculation of green fluorescent protein-tagged C. neoformans (H99-GFP), C57BL/6J mice brains were fixed in 4% paraformaldehyde and embedded in paraffin. Antigen retrieval methods such as microwaves, 1% sodium lauryl sulfate, 1 N HCl, pepsase, and tryptase were used on 5-μm paraffin sections and the effects were compared. The green fluorescence of H99-GFP persisted with antigen retrieval using 1% sodium lauryl sulfate. After immunofluorescent staining, H99-GFP, glial fibrillary acidic protein-tagged astrocytes, and ionized calcium-binding adapter molecule 1-tagged microglia could be observed clearly. Based on our results, we provide a practical approach for the further study of the interaction between C. neoformans and brain cells.

Maintenance of Fluorescence During Paraffin Embedding of Fluorescent Protein-Labeled Specimens

Paraffin embedding is widely used in microscopic imaging for preparing biological specimens. However, owing to significant fluorescence quenching during the embedding process, it is not compatible with fluorescent-labeling techniques, such as transgenic and viral labeling using green fluorescent protein (GFP). Here, we investigate the quenching mechanism and optimize the embedding process to improve the preservation of fluorescence intensity. The results show that dehydration is the main reason for fluorescence quenching during paraffin embedding, caused by the full denaturation of GFP molecules in ethyl alcohol. To evaluate fluorescent and morphological preservation, we modified the embedding process using tertiary butanol (TBA) instead of ethyl alcohol. Fluorescence intensity following TBA dehydration increased 12.08-fold of that observed in the traditional method. We obtained uniform fluorescence maintenance throughout the whole mouse brain, while the continuous apical dendrites, spines, and axon terminals were shown evenly within the cortex, hippocampus, and the amygdala. Moreover, we embedded a whole rat brain labeled with AAV in the prelimbic cortex (Prl). With the axon terminals in different areas, such as the caudate putamen, thalamus, and pyramidal tract, the results showed a continuous tract of Prl neurons throughout the whole brain. This method was also suitable for tdTomota labeled samples. These findings indicate that this modified embedding method could be compatible with GFP and provides a potential turning point for applications in the fluorescent labeling of samples.