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BOR - Papers in Press, published online ahead of print April 14, 2004.
Biol Reprod 2004, 10.1095/biolreprod.104.027730
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Submitted January 22, 2004
Returned for revision February 16, 2004
Accepted March 12, 2004

Gamete Biology


The Major Yolk Protein of Sea Urchins Is Endocytosed by a Dynamin-Dependent Mechanism

Jacqueline M. Brooks and Gary M. Wessel *

* To whom correspondence should be addressed. E-mail: rhet{at}brown.edu.

Abstract
Sea urchin oocytes grow to ten times their original size during oogenesis by both synthesizing and importing a specific repertoire of proteins to drive fertilization and early embryogenesis. During the vitellogenic growth period, the major yolk protein (MYP), a transferrin-like protein, is synthesized in the gut, transported into the ovary, and actively endocytosed by the oocytes (Brooks and Wessel, 2002; 2003). Here we begin to dissect this mechanism by first testing the hypothesis that MYP endocytosis is dynamin-dependent. We have identified a sea urchin dynamin cDNA that is highly similar in amino acid sequence, structure, and size to mammalian dynamin I: it contains an N-terminal GTPase domain, a pleckstrin-homology domain, and a C-terminal proline-rich domain. Sea urchin dynamin is enriched at the cortex of oocytes and colocalizes to MYP endocytic vesicles at the oocyte periphery. To test for a functional relationship between MYP endocytosis and dynamin, we used a dominant-negative human dynamin I mutant protein containing an alteration within the GTPase domain (hDynK44A) to specifically compete for dynamin function. Using a fluorescent MYP construct to follow its endocytosis solely, as well as a general endocytosis marker, we demonstrate that the disruption of dynamin function significantly reduces MYP uptake but does not affect fluid-phase endocytosis. Using this specific biochemical approach, we are able to separate distinct pathways of endocytosis during oogenesis and learn that dynamin-mediated endocytosis is responsible for MYP endocytosis, but not fluid-phase uptake.

Key words: Gamete Biology • Gametogenesis • Oocyte development


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C. W. Walker, L. M. Harrington, M. P. Lesser, and W. R. Fagerberg
Nutritive Phagocyte Incubation Chambers Provide a Structural and Nutritive Microenvironment for Germ Cells of Strongylocentrotus droebachiensis, the Green Sea Urchin
Biol. Bull., August 1, 2005; 209(1): 31 - 48.
[Abstract] [Full Text] [PDF]


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