title: The role of MATER in endoplasmic reticulum distribution and calcium homeostasis in mouse oocytes.
abstract: Ca(2+) oscillations are a hallmark of mammalian fertilization and play a central role in the activation of development. The calcium required for these oscillations is primarily derived from the endoplasmic reticulum (ER), which accumulates in clusters at the microvillar subcortex during oocyte maturation. The migration of the ER to the cortex during maturation is thought to play an important role in rendering the ER competent to generate the calcium transients, and the redistribution of ER is believed to be primarily mediated by microtubules and microfilaments. We have previously shown that the oocyte- and early embryo-restricted maternal effect gene Mater (Nlrp5) localizes to, and is required for, formation of the oocyte cytoplasmic lattices, a tubulin-containing structure that appears to play an important role in organelle positioning and distribution during oocyte maturation. Given these observations, we hypothesized that Mater may also be required for ER redistribution and Ca(2+) homeostasis in oocytes. To test this hypothesis, we first investigated ER localization in metaphase-II Mater(tm/tm) (hypomorph) oocytes and found ER clusters to be less abundant at the microvillar cortex when compared to wild type oocytes. To examine the potential mechanisms by which MATER mediates ER redistribution, we tested whether tubulin expression levels and localization were affected in the mutant oocytes and found that the Triton-insoluble fraction of tubulin was significantly decreased in Mater(tm/tm) oocytes. To identify potential functional defects associated with these ER abnormalities, we next set out to investigate if the pattern of Ca(2+) oscillations was altered in Mater(tm/tm) oocytes after fertilization in vitro. Intriguingly, Ca(2+) oscillations in Mater(tm/tm) oocytes exhibited a significantly lower first peak amplitude and a higher frequency when compared to wild type oocytes. We then found that the Ca(2+) oscillation defect in Mater(tm/tm) oocytes was likely caused by a reduced amount of Ca(2+) in the ER stores. Taken together, these observations support the hypothesis that MATER is required for ER distribution and Ca(2+) homeostasis in oocytes, likely due to defects in lattice-mediated ER positioning and/or redistribution.
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Boram
authors.initials: B
authors.lastname: Kim
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA; State Key Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing 210029, China. Electronic address: zhxuesen@gmail.com.
authors.forename: Xuesen
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Kan
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Roy
authors.initials: R
authors.lastname: Cohen
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Chinatsu
authors.initials: C
authors.lastname: Mukai
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Travis
authors.affiliation: Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. Electronic address: sac269@cornell.edu.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Coonrod
mesh_terms: D000818:Animals; D000941:Antigens / Q000378:metabolism*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology*; D047468:Immunoprecipitation; D008677:Metaphase / Q000502:physiology*; D051379:Mice; D018613:Microscopy, Confocal; D008870:Microtubules / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism
chemical_list: D000941:Antigens; D004527:Egg Proteins; C416503:Nalp5 protein, mouse; D014404:Tubulin; D002118:Calcium
keywords: Calcium homeostasis; Endoplasmic reticulum; MATER; Oocyte maturation; Tubulin