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Environmental gestagens are an emerging class of contaminants that have been recently measured in surface water and can interfere with reproduction in aquatic vertebrates. Gestagens include endogenous progestogens, such as progesterone (P4), which bind P4-receptors and have critically important roles in vertebrate physiology and reproduction. Gestagens also include synthetic progestins, which are components of human and veterinary drugs, such as melengestrol acetate (MGA). Endogenous progestogens are essential in the regulation of reproduction in mammalian species, but the role of P4 in amphibian larval development remains unclear. This project aims to understand the roles and the regulatory mechanisms of P4 in amphibians and to assess the consequences of exposures to environmental gestagens on the P4-receptor signaling pathways in frogs. Here, we established the developmental profiles of the P4 receptors: the intracellular progesterone receptor (ipgr), the membrane progesterone receptor β (mpgrβ), and the progesterone receptor membrane component 1 (pgrmc1) in Western clawed frog (Silurana tropicalis) embryos using real-time qPCR. P4-receptor mRNAs were detected throughout embryogenesis. Transcripts for ipgr and pgrmc1 were detected in embryos at Nieuwkoop and Faber (NF) stage 2 and 7, indicative of maternal transfer of mRNA. We also assessed the effects of P4 and MGA exposure in embryonic and early larval development. Endocrine responses were evaluated through transcript analysis of a suite of gene targets of interest, including: ipgr, mpgrβ, pgrmc1, androgen receptor (ar), estrogen receptor α (erα), follicle stimulating hormone β (fshβ), prolactin (prl), and the steroid 5-alpha reductase family (srd5α1, 2, and 3). Acute exposure (NF 12-46) to P4 caused a 2- to 5-fold change increase of ipgr, mpgrβ, pgrmc1, and ar mRNA levels at the environmentally relevant concentration of 195 ng/L P4. Acute exposure to MGA induced a 56% decrease of srd5α3 at 1140 ng/L MGA. We conclude that environmental exposure to P4 induced multiple endocrine-related transcript responses in amphibians; however, the differential responses of MGA suggest that the effects of MGA are not mediated through the classical P4 signaling pathway in S. tropicalis.

In this case study, 15 adult laboratory Xenopus (Silurana) tropicalis (7 adult males and 8 adult females) were examinedfor nodular enlargements of the clawed digits (digits 0, I, II, and III) on the hind feet. Radiographs showed smoothly margined,rounded, peripherally mineralized lesions arising from the distal phalanges of digits 0-III with osteoproductive and osteolytic components in all frogs. Micro computed tomography (microCT) scans further revealed interphalangeal (IP),metacarpophalangeal (MCP), and metatarsophalangeal (MTP) joint osteoarthritis characterized by periarticular new bone formation, rounded mineral foci both peripherally and centrally within the joints, and more rarely, linear mineralizationpalmar/plantar to the joints in the flexor tendons. In the nonclawed digits, the shape of the distal phalanx was variablydistorted and both subluxation and malangulation of IP joints were identified. Histologically, nodules corresponded to aperipheral rim of mature cortical bone surrounding central adipose tissue, scattered hematopoietic elements, and residualbone of the distal phalanx. Occasionally, the peripheral rim of cortical bone extended proximally to encompass the distalaspect of adjacent phalanx. MCP, MTP and IP joint spaces of most digits exhibited widespread osteoarthritis characterizedby periarticular cartilaginous or osseous metaplasia, bony remodeling, and less frequently, granulomatous osteomyelitis.Nutritional analyses of the feed did not indicate imbalances nor were the lesions consistent with metabolic bone disease.The exact etiopathogenesis of these lesions is unknown; however, we hypothesize that the osteoarthritic changes are due toa combination of the frogs’ mature age, the unique structure of the Xenopus spp. claw, genetics and biomechanical forces onthe digits and distal phalanges of the hind feet.

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