Quantitatively Investigating the Genetic Response of the Euryhaline Sailfin Molly (Poecilia latipinna) to Manipulations of Environmental and Dietary Magnesium

Magnesium (Mg2+) plays vital roles including aiding in DNA replication, cell signaling, hormone production, and musculoskeletal health. To date, research into the function and regulation of genes suspected to be involved in Mg2+ homeostasis has lacked a holistic approach. I therefore sought to quantitatively investigate the regulation of a multitude of genes including solute carriers (slc) slc41a1, slc41a2, cyclin m3 (cnnm3), transient receptor potential melastatin 7 (trpm7), as well as two Na+/K+-ATPase (nka) isoforms nka-1α, nka-2α in the gills, intestines, and kidneys of euryhaline sailfin mollies (Poecilia latipinna) during manipulations of environmental salinity and dietary Mg2+. I further investigated how these manipulations would affect plasma Mg2+ levels using Ion Selective Microelectrodes (ISME) to better understand the function of these genes and the responses to salinity in this species. All Mg2+ transporters were ubiquitously expressed across all tissues examined, regardless of environmental salinity. Furthermore, saltwater acclimation alone did not affect plasma Mg2+ levels, but downregulation of slc41a1, cnnm3, and trpm7 was observed in the gills and intestines, and downregulation of cnnm3 and trpm7 was observed in the kidneys. Increasing dietary Mg2+ led to acute elevation of plasma Mg2+ that was quickly normalized in both salinities. Freshwater-acclimated fish seemed to adapt to dietary manipulations by decreasing intestinal absorption, whereas saltwater-acclimated fish seemed to favour increased renal transport and decreased intestinal transport. This study was the first of its kind to quantitatively investigate the integrated roles of these genes in cellular Mg2+ homeostasis across multiple ionoregulatory epithelia in a euryhaline fish and highlight the need for more wholistic investigations in other species.