Researchers at the University of Lublin and the Medical University of Lublin have demonstrated the first application of FT-IR imaging in zebrafish larvae, revealing that frozen samples better preserve tissue structure than chemical fixation.
A recent study conducted out of Poland explored the application of Fourier transform infrared (FT-IR) imaging in zebrafish (Danio rerio) larvae. This research collaboration, comprised of researchers from the University of Lublin and the Medical University of Lublin, yielded new information about the tissue structure of zebrafish. Their insights also showed that frozen samples better preserved zebrafish tissue structure, which was important to conduct the analysis. The findings were published in Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (1).
In the past, scientists would often use mice and rats in biological research to study the genetic causes of human diseases (2). These organisms were the experimental models for these studies, and they helped determine whether a mutation in a specific gene influences a patient’s potential symptoms (2). However, as of late, scientists have been experimenting with zebrafish for this purpose. Part of the reason for this change in animal model is because zebrafish have a genetic similarity to humans (1). According to the National Institute of Health, approximately 70% of human genes are found in zebrafish (2).
Zebrafish, which are tropical freshwater fish, also benefit from being inexpensive. Housing and maintaining mice and rats cost more money. Therefore, although more evolutionary similarities exist between mice and rats, researchers are often cash-strapped, and that makes using zebrafish more practical (2). Adult zebrafish also breed quickly and produce a ton of offspring compared to mice and rats, which allows researchers to conduct their experiments repeatedly without running out of animal models (2).
Zebrafish are also transparent, and this contributes to their utility of being an ideal model for fluorescence imaging (1). However, researchers have been searching for additional imaging techniques that can provide more detailed, label-free biochemical information. Vibrational microspectroscopy, which integrates Raman and FT-IR spectroscopy with microscopy, has emerged as a powerful tool in this regard (1).
In their study, the research team used FT-IR imaging to compare different fixation methods for 10-day post-fertilization zebrafish larvae. They examined the effects of four different preservation techniques: paraformaldehyde (PFA), glutaraldehyde (GA), low-temperature freezing, and embedding in gelatin and agarose (1).
The results obtained revealed new insights about both FT-IR and Raman mapping. Both methods showed that frozen samples better preserved tissue structure compared to chemical fixation (1). Among the chemical fixation methods, PFA showed a uniform distribution of amides, while GA treatment resulted in tissue disruptions and denser protein networks (1). These findings indicate that PFA may be a more reliable fixative for studies requiring consistent biochemical distribution, whereas GA-induced structural changes could impact data interpretation in some applications (1).
Embedding samples in gelatin or agarose also came with unique advantages. The researchers found that this method allowed them to acquire more spectral data on amides, lipids, and phosphates. However, challenges arose during handling these embedded samples. The main obstacle was that the embedded samples were very stiff at −20 °C, which resulted in difficulties maintaining sample integrity during analysis (1). Embedded samples also minimized chemical interference while preserving biochemical composition (1).
By refining tissue preservation techniques for zebrafish larvae, researchers can improve the accuracy of spectroscopic imaging analyses, leading to better insights into biological processes at the molecular level. This study also reinforces the ongoing trend of using more non-destructive, high-resolution imaging techniques in biomedical studies.
Looking ahead, the researchers suggest further studies should examine refining embedding techniques and optimize fixation protocols for various applications. By enhancing sample preservation strategies, scientists can expand the use of zebrafish models in critical areas such as neurodevelopmental disorders, cancer research, and environmental toxicology, improving patient outcomes.
