T6 AM Environmental Hypoxia
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 324-326

(CAR-1117-829710) The Response of Sheepshead Minnows to Hypoxia Exposure: Connecting Molecular and Reproductive Endpoints.

Carlson, E¹, Ryan, R¹, Manning, C¹, Karels, A¹, Mitchell, S¹, Ryan, K¹, Brouwer, M¹, ¹ University of Southern Mississippi, Ocean Springs, MS, USA

ABSTRACT- Inadequate dissolved oxygen (DO) can be a major stressor in estuarine habitats. Hypoxic conditions often result from increasing urban development, agricultural runoff, and industrial pollution. Some estuarine organisms, including the sheepshead minnow (Cyprinodon variegatus), are well adapted for survival in low DO environments. This study sought to examine the effects hypoxia exposure upon sheepshead minnow reproduction and hepatic gene expression. Hypoxia-induced alterations in gene expression were screened using cDNA microarrays containing 700 clones from hypoxia-responsive suppression subtractive hybridization and sheepshead liver cDNA libraries. In addition, several clones representing genes known to be involved in the hypoxic response of other organisms (i.e., VEGF, HIF-1 alpha) were included on the arrays. Fish were exposed to hypoxia (1.5 and 2.5 mg DO /L) or normoxia (7-8 mg DO /L) in flow-through systems and liver was sampled for RNA isolation at 10h and 2, 4, 7, and 14 d. In addition, a reproductive study was performed in which egg yield, fertilization, hatching success, and larval growth /survival were monitored for a month during continuous exposure to 1.5 mg DO /L. Microarray analysis of these exposures has revealed that several hepatic genes display clear changes in response to hypoxia including interferon inducible factor, enolase, and butyrate respiratory factor. In addition, several genes displayed sex-specific responses to hypoxia. Although hypoxia did not alter sheepshead gonado-somatic indices, egg production, or fertilization rate, significant effects were seen upon embryo and larval survival. Hypoxia-exposed larvae took an average 9 d to hatch compared to 4.5 d for normoxic controls. Furthermore, hypoxic larvae were developmentally immature at hatching with most larvae not surviving to 14 d post-hatch. Experiments examining the effects of hypoxia exposure upon embryonic development and gene expression are ongoing. Overall, it is expected that the current study will reveal gene expression patterns important for the maintenance of reproductive success during hypoxic stress. Elucidation of molecular pathways responsible for survival under prolonged hypoxia exposure may prove useful to both biomedical researchers and environmental toxicologists.

Key words: hypoxia, fish, genomics, reproduction