Ascidian follicle cells: Multifunctional adjuncts to maturation and development
Article first published online: 23 AUG 2009
© 2009 The Author. Journal compilation © 2009 Japanese Society of Developmental Biologists
Development, Growth & Differentiation
Volume 51, Issue 8, pages 677–686, October 2009
How to Cite
Lambert, C. C. (2009), Ascidian follicle cells: Multifunctional adjuncts to maturation and development. Development, Growth & Differentiation, 51: 677–686. doi: 10.1111/j.1440-169X.2009.01127.x
- Issue published online: 23 SEP 2009
- Article first published online: 23 AUG 2009
- Received 30 April 2009; revised 12 July 2009; accepted 13 July 2009.
- follicle cell;
- germinal vesicle;
Ascidians are primitive chordates, subphylum Tunicata, that are sessile filter-feeding hermaphrodites as adults. Released oocytes are enclosed within a monolayer of follicle cells, a non-cellular vitelline coat and a monolayer of test cells that cover the egg membrane. Follicle cell structure is distinctive in different groups. They originate from circulating hemoblasts with functional nuclei. They are necessary for germinal vesicle breakdown in several species and may secrete a meiosis-inducing substance to the oocyte. In some families the follicle cells are necessary for fertilization. Although all ascidians are hermaphrodites, many are not capable of self fertilization. The follicle cells seem to be involved in self, non-self discrimination. Attachment of sperm to egg involves a sperm surface glycosidase binding to an egg surface glycoside. The primary block to polyspermy involves a glycosidase released by the follicle cells. In one species with direct development, the follicle cells secrete a sticky substance that anchors the embryos in a wave-swept rocky area; a brooding solitary ascidian with a tadpole larva uses a sticky substance secreted by follicle cells to attach the brood to the atrial chamber. Several species have floating eggs due to buoyancy of their follicle cells, a result of ammonia sequestration in at least one species. Many other marine invertebrates release eggs with attached follicle cells, and all vertebrates ovulate oocytes covered with follicle cells. Comparisons are discussed between these groups and ascidians.