Abstract
BackgroundOocyte quality decreases with aging, thereby increasing errors in fertilization, chromosome segregation, and embryonic cleavage. Oocyte appearance also changes with aging, suggesting a functional relationship between oocyte quality and appearance. However, no methods are available to objectively quantify age-associated changes in oocyte appearance.ResultsWe show that statistical image processing of Nomarski differential interference contrast microscopy images can be used to quantify age-associated changes in oocyte appearance in the nematode Caenorhabditis elegans. Max–min value (mean difference between the maximum and minimum intensities within each moving window) quantitatively characterized the difference in oocyte cytoplasmic texture between 1- and 3-day-old adults (Day 1 and Day 3 oocytes, respectively). With an appropriate parameter set, the gray level co-occurrence matrix (GLCM)-based texture feature Correlation (COR) more sensitively characterized this difference than the Max–min Value. Manipulating the smoothness of and/or adding irregular structures to the cytoplasmic texture of Day 1 oocyte images reproduced the difference in Max–min Value but not in COR between Day 1 and Day 3 oocytes. Increasing the size of granules in synthetic images recapitulated the age-associated changes in COR. Manual measurements validated that the cytoplasmic granules in oocytes become larger with aging.ConclusionsThe Max–min value and COR objectively quantify age-related changes in C. elegans oocyte in Nomarski DIC microscopy images. Our methods provide new opportunities for understanding the mechanism underlying oocyte aging.
Highlights
Oocyte quality decreases with aging, thereby increasing errors in fertilization, chromosome segregation, and embryonic cleavage
Mm value reflects age‐associated changes in the cytoplasmic texture of C. elegans oocytes To quantify age-associated changes in oocyte appearance, we used Nomarski differential interference contrast (DIC) microscopy to observe the oocytes of 1, 2, and 3-day-old C. elegans adults
Mm Max–min value (Value) did not differ significantly between Days 1 and 2. These results suggest that the Mm Value decreases with aging and can be used to quantitatively characterize the age-associated changes in the cytoplasmic texture of C. elegans oocytes
Summary
Oocyte quality decreases with aging, thereby increasing errors in fertilization, chromosome segregation, and embryonic cleavage [1,2,3]. The nematode Caenorhabditis elegans is a leading model for studying aging because of its short lifespan (~ 3 weeks) and the conservation of longevity pathways from C. elegans to humans [4]. C. elegans has been developed as a model for studying agerelated decline in fertility [5]. Mutant analyses using C. elegans have revealed various genes and signaling pathways that affect aging [6,7,8]. The molecular processes involved in the age-related regulation of oocyte quality are shared between C. elegans and mammals [9]
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