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Mechanism of an Alternate Type of Echinoderm Blastula Formation: The Wrinkled Blastula of the Sea Urchin Heliocidaris erythrogramma
Author(s) -
Henry Jonathan J.,
Wray Gregory A.,
Raff Rudolf A.
Publication year - 1991
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.1991.00317.x
Subject(s) - blastula , blastomere , blastocoel , sea urchin , cleavage (geology) , polarity in embryogenesis , microbiology and biotechnology , biology , gastrulation , anatomy , embryo , embryogenesis , paleontology , fracture (geology)
While most indirect‐developing echinoderms (possessing a feeding larval stage) form a hollow, smooth‐walled blastula, most direct‐developing species form a wrinkled blastula. The process of wrinkled blastula formation was examined in the direct‐developing sea urchin, Heliocidaris erythrogramma . Approximately 5 hrs after fertilization the blastula epithelium contains folds along one, two or three orthogonal planes, which superficially appear like 2‐, 4‐ or 8‐cell stages, respectively. Microinjection of fluorescent dye into individual blastomeres of 2‐, 4‐ and 8‐cell embryos revealed that the wrinkles correspond with the first, second and third cleavage planes. Two factors appear to generate the wrinkled blastula epithelium. First, blastomeres undergo a partial separation along the first, second and third cleavage planes during early cleavage. Subsequent cell divisions are oriented such that the blastula epithelium is constructed with deep creases along these planes of cell separation. Second, there is no room for the expansion of the developing blastoderm within the tightly fitting fertilization envelope. Prior to hatching from the fertilization envelope, wrinkles in the blastula epithelium disappear, due to an increased packing and elongation of the cells. In addition, a substantial volume of cellular material is removed as lipids are secreted into the blastocoel in an apocrine fashion.