title: Ultrastructural features of the differentiating thyroid primordium in the sand lizard (Lacerta agilis L.) from the differentiation of the cellular cords to the formation of the follicular lumen.
abstract: The differentiation of the thyroid primordium of lacertilian species is poorly understood. The present study reports on the ultrastructural analysis of the developing thyroid primordium in the sand lizard (Lacerta agilis) during the early stages of differentiation. The early thyroid primordium of sand lizard embryos was composed of cellular cords that contained single cells with a giant lipid droplet, which were eliminated by specific autophagy (lipophagy). The follicular lumens at the periphery of the primordium differentiated even before the division of the cellular cords. When the single cells within the cords started to die through paraptosis, the adjacent cells started to polarise and junctional complexes began to form around them. After polarisation and clearing up after the formation of the lumens, the cellular cords divided into definitive follicles. The cellular cords in the central part of the primordium started to differentiate later than those at the periphery. The cellular cords divided into presumptive follicles first and only later differentiated into definitive follicles. During this process, a population of centrally located cells was removed through apoptosis to form the lumen. Although the follicular lumen in sand lizard embryos is differentiated by cavitation similar to that in the grass snake, there were very important differences during the early stages of the differentiation of the cellular cords and the formation of the thyroid follicles.
authors.affiliation: Department of Animal Histology and Embryology, Silesian University, 9 Bankowa Str., 40-007 Katowice, Poland. Electronic address: weronika.rupik@us.edu.pl.
authors.forename: Weronika
authors.initials: W
authors.lastname: Rupik
authors.affiliation: Department of Animal Histology and Embryology, Silesian University, 9 Bankowa Str., 40-007 Katowice, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kowalska
authors.affiliation: Department of Animal Histology and Embryology, Silesian University, 9 Bankowa Str., 40-007 Katowice, Poland.
authors.forename: Elwira
authors.initials: E
authors.lastname: Swadźba
authors.affiliation: Department of Vertebrate Biology and Conservation, University of Wroclaw, 21 Sienkiewicza Str., 50-225 Wroclaw, Poland.
authors.forename: Robert
authors.initials: R
authors.lastname: Maślak
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D004625:Embryo, Nonmammalian / Q000648:ultrastructure; D008116:Lizards / Q000196:embryology*; D046529:Microscopy, Electron, Transmission; D013961:Thyroid Gland / Q000196:embryology* / Q000648:ultrastructure
keywords: Autophagy; Lizard embryos; Programmed cell death; Thyroid follicular lumen; Thyroid primordium