title: Calcium transport into the cells of the sea urchin larva in relation to spicule formation.
abstract: We investigated the manner in which the sea urchin larva takes up calcium from its body cavity into the primary mesenchymal cells (PMCs) that are responsible for spicule formation. We used the membrane-impermeable fluorescent dye calcein and alexa-dextran, with or without a calcium channel inhibitor, and imaged the larvae in vivo with selective-plane illumination microscopy. Both fluorescent molecules are taken up from the body cavity into the PMCs and ectoderm cells, where the two labels are predominantly colocalized in particles, whereas the calcium-binding calcein label is mainly excluded from the endoderm and is concentrated in the spicules. The presence of vesicles and vacuoles inside the PMCs that have openings through the plasma membrane directly to the body cavity was documented using high-resolution cryo-focused ion beam-SEM serial imaging. Some of the vesicles and vacuoles are interconnected to form large networks. We suggest that these vacuolar networks are involved in direct sea water uptake. We conclude that the calcium pathway from the body cavity into cells involves nonspecific endocytosis of sea water with its calcium.
authors: Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel.
authors: Netta
authors: N
authors: Vidavsky
authors: Life Sciences Core Facilities, Weizmann Institute of Science, 76100 Rehovot, Israel.
authors: Sefi
authors: S
authors: Addadi
authors: Global Applications Support, Carl Zeiss Microscopy GmbH, 73447 Oberkochen, Germany.
authors: Andreas
authors: A
authors: Schertel
authors: Israel Oceanographic and Limnological Research, National Center for Mariculture, Eilat 88112, Israel.
authors: David
authors: D
authors: Ben-Ezra
authors: Israel Oceanographic and Limnological Research, National Center for Mariculture, Eilat 88112, Israel.
authors: Muki
authors: M
authors: Shpigel
authors: Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel.
authors: Lia
authors: L
authors: Addadi
authors: Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel; steve.weiner@weizmann.ac.il.
authors: Steve
authors: S
authors: Weiner
keywords: SPIM imaging; biomineralization; cryo-FIB-SEM; endocytosis; in vivo imaging