Young Investigator Sara Casado Zapico
January 18, 2022 | Human ID and Forensics

Young Investigator Sara Casado Zapico on estimation of age-at-death

The Young Investigator Community is a forum for young forensic researchers and graduate students. The new Investigator blog is an opportunity to meet one of these talented researchers in a place where they can share their achievements and aspirations with peers, friends and colleagues. Read on to find out what first drew this month’s blogger to forensic science. Share with them the excitement of discovery that sustains a passionate commitment to their work.

This new Investigator blog introduces Sara Casado Zapico. Sara is currently a Research Collaborator at the Smithsonian Institution and an Assistant Professor at the New Jersey Institute of Technology in the department of Chemistry and Environmental Science where she teaches while continuing her research work in epigenetics.

1. Tell us about your background and how you became interested in forensic science?

Since I was a child, I wanted to be a forensic scientist. I really enjoyed playing with my microscope, and I had a small detective's kit, like a miniature crime lab. Also, I was an eager reader of the Sherlock Holmes stories and Agatha Christie's novels. For that reason, I decided to study biology and biochemistry at the University of Oviedo, in my home country, Spain. During this time, I read the book "Death's Acre" by Dr. Bill Bass. (Dr. Bass established the Forensic Anthropology Center at The University of Tennessee Knoxville in 1987, beginning with the Anthropology Research Facility, also known as The Body Farm.) I became fascinated with the world of forensic anthropology and the problems to overcome for human identification and the estimation of postmortem interval.

Unfortunately, opportunities to conduct forensic science research in Spain are scarce. I did my Ph.D. in Biomedical Sciences, and at the same time, I studied for a Master’s degree in Forensic Anthropology and Genetics. At the end of my Ph.D. I decided to redirect my career to forensic sciences. I was very fortunate to be awarded a postdoctoral fellowship with the Peter Buck Fellowship Program at the Smithsonian Institution’s National Museum of Natural History, working under the supervision of Dr. Douglas Ubelaker. The fellowship gave me the opportunity to apply the knowledge from my Ph.D. in oxidative stress and its implications in aging to improving estimation of age-at-death in forensic anthropology. I am continuing with this line of research, focusing right now on applications of DNA methylation for age-at-death estimation.

2. Can you provide a summary of the project you are working on?

The first part of this project was developed during my short stay at Catholic University Leuven, Belgium. We demonstrated the correlation between DNA methylation levels of certain genes with age in dentin samples, leading to more accurate age-at-death estimation in forensic anthropology compared with current standards. I have recently published a continuation of this project, but in this case with pulp tissue. Right now, I am trying to identify more genes relevant for aging in both tissues, hopefully leading to even better estimates.

3. Please describe your typical day in the lab.

It depends on the day. If I have to extract DNA, it will take the whole day. Since I am working with dentin and pulp, I have to be so precise to cut and separate both tissues from cementum and enamel. Although I have an established protocol for this, it takes time. The results in terms of DNA yield are great. If I move to the next steps of the project, bisulfite conversion and target amplification, my day is more relaxing. Although, between PCRs I am preparing classes, grading,......

4. What do you find most interesting about your project? Have you seen any surprising results?

The most interesting thing about my project is the difference in terms of gene targets between dentin and pulp. These are two different tissues but at the same time related, and as a result, the genes that play a role in age estimation are different. In fact, I found one of my surprising results with pulp. The methylation analyses of five genes gave age estimates of +/- 1.5 years with respect to the real age. In dentin, the estimates were +/- 4.8 years, and the only gene that both tissue analyses have in common is ELOVL2.

5. What are the benefits of your project?

The ultimate goal of my project is to be able to apply this technique to forensic cases, giving an accurate age-at-death estimation of the victim. With current anthropological techniques, age-at-death can be estimated with a range of +/- 10 years. When you create a biological profile from skeletal remains and try to compare with missing persons' reports, a gap of 10 years on the estimation of age-at-death can make possible identification difficult. Right now, the most accurate biochemical technique for age estimation is aspartic acid racemization in dentin. This method has some drawbacks. I am hoping to improve my current results and be able to apply them to forensic cases, overcoming some of the disadvantages of aspartic acid racemization.

6. What are the major challenges faced while working on your project and how do you overcome them?

One of the major challenges is getting enough DNA yield to perform bisulfite conversion. Although I have an efficient workflow for DNA extraction from dentin and pulp, sometimes it is difficult to obtain enough DNA. At present, I am working with clinical samples. I normally work with third molars as these give better DNA yields depending on the tooth and its condition. It is possible that I may not be able to get third molars when translating this into a forensic scenario. In these cases, I mostly recover more DNA from dentin.

7. Which QIAGEN products do you use and what do you like about the products?

I use the DNeasy Blood and Tissue Kit for DNA extraction from dentin and pulp. I really like the column system as it makes sure to trap the DNA during the cleaning steps. For bisulfite conversion, I use the EpiTect Fast Bisulfite Conversion Kit. Again, the cleaning using columns is one of the advantages of the product. For amplification, I use the 2x PyroMark PCR Kit Master Mix. Its efficiency of amplification, even with low amounts of DNA, is great. Finally, for Pyrosequencing I use the PyroMark Q48 Advanced Reagents. I really like that the PyroMark Q48 Autoprep and its reagents are easy to use and provide high sequencing efficiency.

8. Outside of forensic science, what are your hobbies?

I love learning in general, especially new languages. I love traveling, when we could do it, and learning the language of the country I visit. I love reading, writing, going for long walks and practicing kick-boxing.

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