By David Omote

‎As the global community continues to decode the complex physiology of marine life, a leading expert in comparative molecular biochemistry and membrane transport, Esosa Omoregie, has been integral to a set of studies that fundamentally alter our understanding of how sharks manage internal water balance and the status of critical genes. 

‎‎Sharks, or elasmobranchs, maintain high internal concentrations of urea to match the salinity of seawater, a unique adaptation that requires their kidneys to efficiently reabsorb between 80 and 99% of filtered urea back into the bloodstream. This essential process of urea retention depends heavily on specialized channel proteins like the UT-1 urea transporter.  

‎‎For decades, the UT-1 protein, which facilitates this crucial urea retention, was known to be primarily or exclusively expressed in the collecting tubule (CT) segment, located towards the end of the kidney’s complex nephron structure, in species like the houndshark and bullshark.  

‎‎However, groundbreaking research co-authored by Esosa Omoregie revealed a starkly different pattern in the spiny dogfish (Squalus acanthias). The team found that the UT-1 protein was predominantly located in the Intermediate Segment 1 (IS-I) and Proximal (PIb) segments, early loops situated in the first sinus zone of the nephron.  ‎

‎‎This novel geographical shift within the kidney suggests that the spiny dogfish utilizes a fundamentally different osmoregulatory strategy for urea absorption compared to its relatives, focusing its reabsorption efforts on the sinus zone loops rather than the collecting tubule.  

‎‎The team’s work further complicated the picture by characterizing two known splice variants of UT-1 and discovering a new splice variant of a second, distinct gene, termed “Brain UT,” within the dogfish.  

‎‎Quantitative PCR analysis of kidney samples confirmed that the short variant of UT-1 was around 100 times more abundant than the long variant. This analysis also showed that the long UT-1 variant had a significantly higher level of mRNA abundance in fish acclimatized to 75% seawater, indicating a responsive role in managing salinity changes.  

‎‎Complementing this work on urea transport, Esosa’s team also investigated the status of another critical channel, Aquaporin 11 (AQP11), one of the “unorthodox” or “superaquaporins” found widely in mammalian tissues, including the kidney, liver, and brain.  

‎The initial goal of that separate study, published in the International Journal of Molecular Sciences, was to clone and sequence the AQP11 transcript, which was expected to be an easy task given the availability of sequences from related shark species.  

‎‎However, after numerous attempts to amplify the functional AQP11 cDNA from various dogfish tissues using different primers and techniques, the evidence pointed to a surprising conclusion: the AQP11 gene in the spiny dogfish may represent a pseudogene.  

‎‎The researchers employed rigorous molecular techniques, including specialized 5′ and 3′ RACE (Rapid Amplification of cDNA Ends), a process that requires the presence of functional messenger RNA. The failure of Nested RACE amplifications to sequence AQP11 fragments strongly supports the pseudogene hypothesis, suggesting a potential gene loss event in this ancient species.  

‎‎These discoveries in marine physiology are not simply academic; they form the basis for Esosa Omoregie’s broader research interest in human health. His Master’s thesis at Georgia Southern University directly links these membrane transport studies to the mechanisms of human disease.  

‎‎The thesis specifically focuses on Aquaporin 10 paralogs in the dogfish to investigate how aquaporins and solute transport contribute to tumor growth, metastasis, and general osmoregulation in human cancer cells. The underlying principle is that the same cellular machinery sharks use to manage urea and water balance is manipulated by cancer cells for survival and proliferation. 

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