Larval cement gland of frogs: Comparative development and morphology

Abstract

The cement gland (CG) is a transient mucus-secreting organ, found in most anuran embryos and early larvae and located normally on the anteroventral side of the head. Its sticky secretion allows newly hatched larvae to attach to the egg jelly or to another support and remain hidden and stationary until feeding starts. Analysis of CG morphology in 20 anuran species from six families using scanning electron microscopy revealed five distinct patterns of development, which partly related to families. The five patterns are described, as well as additional details such as CG surface ciliation and asymmetry. Three species lacked a CG. This was expected in two cases, a late-hatching phyllomedusine hylid and a direct-developing eleutherodactylid, but not in the foam-nesting Leptodactylus fuscus, which hatches at the same stage as many species that develop a CG. Lack of the CG in L. fuscus suggests that its posthatching period in the foam nest may be obligate. In both L. fuscus and the phyllomedusine hylid, there remain morphological traces of CG development.

Conservation, development, and function of a cement gland-like structure in the fish Astyanax mexicanus

“…These data are consistent with the idea that Bmp4 is permissive for CG formation but conflict with the proposal that the CG forms "at a conserved anterior position, where embryonic ectoderm and endoderm touch" (25). In fact, the position of the CG is not conserved even among different frog species (14). The CG happens to correspond to the "anterior extreme" in Xenopus (1, 2), but its position probably is not a defining feature-although the anterior position is indeed a conserved feature for the stomodeum (26).…”

“…The available molecular data on anuran CG are derived exclusively from studies of X. laevis. However, most frogs possess a CG, even though some species that are direct developers, hatch late, or spend the posthatching period in foam nests do not (14), most probably because they have lost it. In urodeles (anuran sister group), there is no CG per se, but the balancers are developmentally related, if not homologous, to the CG (16).…”

“…The study of the amphibian CG has been confined mainly to the Xenopus laevis species, although a recently published, complete survey of the existence and morphology of the CG in 20 anuran species discusses the CG with regard to the species' habitat, behavior, and mode of development (14). The balancers of urodele amphibians have been suggested to be related evolutionarily to the anuran CG, and some support for this idea comes from the description of trigeminal innervation and Otx5 expression in the balancers (5,15,16).…”

21st Century neontology and the comparative development of the vertebrate skull

“…Although extensive effort has been made to understand ectodermal subdivisions within the neural plate, there has been a much less of an effort to understand early regional pattern within the cephalic surface ectoderm outside of those investigations examining the origination of the neural crest, the cranial placodes, and some perhaps generally underappreciated work involving the cement gland in amphibians (Gammill and Sive, 1997, 2000Fang and Elinson, 1999;Baker and Bronner-Fraser, 2001;Schweickert et al, 2001;Sauka-Spengler et al, 2002;Wardle and Sive, 2003;Streit, 2004;Nokhbatolfoghahai and Downie, 2005). Analyses of the development of the early vertebrate epiblast have typically been concerned either with (1) when and how the distinction between neural and non-neural ectoderm is established or (2) how is positional information, i.e., anterior (head) and posterior (trunk), within the neural plate established Stern, 2002Stern, , 2005Wilson and Houart, 2004), and have lead to several questions, including: Is the epiblast ubiquitously competent to become either neurectodermal or surface ectodermal, and if so, is the specification and eventual commitment to neural and surface ectodermal achieved simultaneously, or does one precede the other?…”

Cement gland as the adhesion organ in Xenopus laevis embryos

“…There are data that the embryo's cement gland is fixed to the internal surface of the vitellin sheath even before hatching. In the point of action of the enzyme produced by the hatching gland (it is located in the front of the embryo above the cement gland and has an inversed V form), the vitellin sheath breaks and the embryo is driven from it by the fluid head but remains fixed on it (Bles, 1905-cited from Nochbatolfoghahai andDownie, 2005).…”