In ovo thyroxine exposure alters later UVS cone loss in juvenile rainbow trout

Abstract

a thyroid hormone) induces precocious SWS1 downregulation and UVS cone degeneration, whereas TH attenuation via propylthiouracil (PTU) delays SWS1 downregulation and UVS cone loss, suggesting that endogenous T4 initiates these processes naturally during development (Browman and Hawryshyn, 1992;Browman and Hawryshyn, 1994 Accepted 17 March 2011 SUMMARY Thyroid hormones (THs) play a vital role in vertebrate neural development, and, together with the beta isoform of the thyroid hormone receptor (TR), the development and differentiation of cone photoreceptors in the vertebrate retina. Rainbow trout undergo a natural process of cone cell degeneration during development and this change in photoreceptor distribution is regulated by thyroxine (T4; a thyroid hormone). In an effort to further understand the role of T4 in photoreceptor ontogeny and later developmental changes in photoreceptor subtype distribution, the influence of enhanced in ovo T4 content on the onset of opsin expression and cone development was examined. Juvenile trout reared from the initial in ovo-treated embryos were challenged with exogenous T4 at the parr stage of development to determine if altered embryonic exposure to yolk THs would affect later T4-induced short-wavelength-sensitive (SWS1) opsin transcript downregulation and ultraviolet-sensitive (UVS) cone loss. In ovo TH manipulation led to upregulation of both SWS1 and long-wavelength-sensitive (LWS) opsin transcripts in the prehatch rainbow trout retina and to changes in the relative expression of TR. After 7days of exposure to T4, juveniles that were also treated with T4 in ovo had greatly reduced SWS1 expression levels and premature loss of UVS cones relative to T4-treated juveniles raised from untreated eggs. These results suggest that changes in egg TH levels can have significant consequences much later in development, particularly in the retina.

Effects of Low‐Dose Embryonic Thyroid Disruption and Rearing Temperature on the Development of the Eye and Retina in Zebrafish

“…Our results are consistent with published reports showing that photoreceptors, optic primordia, optic nerve development, and opsin expression are influenced by thyroid function (Gamborino et al, 2001;Gan and Novales Flamarique, 2010;Fischer et al, 2011;Pinazo-Duran et al, 2011;Raine et al, 2011). Previous studies have shown that treatment with phenylthiourea can decrease zebrafish dorsal retina and lens due to its effects on thyroid peroxidase .…”

Detection and localization of the thyroid hormone receptor beta mRNA in the immature olfactory receptor neurons of chum salmon

“…In salmonid fish, TR genes have been detected in various organs (brain, intestine, gill, liver, muscle, kidney, ovary, skin, etc.) of rainbow trout ( O. mykiss ) ( Jones et al., 2002 ; Raine et al., 2005 , 2011 ), coho salmon ( Harada et al., 2008 ), and Atlantic salmon ( Salmo salar ) ( Marchand et al., 2001 ). However, TR gene expression in the peripheral olfactory system has not been widely studied in vertebrates, including teleost.…”

Prefertilization Exposure of Rainbow Trout Eggs to Per‐ and Polyfluoroalkyl Substances to Simulate Accumulation During Oogenesis

“…Fertility of rainbow trout oocytes and survival to the eyed stage of development were the same or better following storage in Cortland's solution when compared to storage in coelomic fluid or fertilization prior to storage (Goetz & Coffman, 2000). Coelomic fluid has been shown to be an effective delivery medium in this and other studies (Raine et al, 2004, 2011; Raine & Leatherland, 2003), but Cortland's solution provides a logistically simpler medium to use and appears to work quite successfully in this application.…”

“…This suggests that this method of exposure is a viable and practical procedure to study in ovo developmental effects of PFAS on large‐bodied species of fish. This exposure method has been used previously to deliver thyroid hormones, cortisol, and bisphenol A into prefertilization rainbow trout oocytes using coelomic fluid as the exposure medium (Aluru et al, 2010; Birceanu et al, 2015; Coffin et al, 2012; M. Li et al, 2010; Raine et al, 2004, 2011; Raine & Leatherland, 2003). Coelomic fluid is difficult to obtain in quantity, and its association with the oocytes makes it difficult to prepare treatment solutions in advance of an experiment.…”