Normal development in Xenopus laevis: A complementary staging table for the skull based on cartilage and bone

Abstract

Background: Xenopus laevis is a widely used model organism in the fields of genetics and development, and more recently evolution. At present, the most widely used staging table for X. laevis is based primarily on external features and does not describe the corresponding skull development in detail. Here, we describe skull development in X. laevis, complete with labeled figures, for each relevant stage in the most widely used staging table.Results: We find skull development in X. laevis is, for the most part, distinct at each of the previously established stages based on external anatomy. However, variation does exist in the timing of onset of ossification of certain bones in the skull, which results in a range of stages where a skull element first ossifies. The overall sequence of ossification is less variable than the timing of ossification onset. Conclusions: While events in skull development vary somewhat between specimens, and in comparison, to external events, this staging table is useful in showing both when bones first appear and for documenting the range of temporal variance in X. laevis skull development more accurately than previously done. Furthermore, when only skull data are available, the approximate stage of a specimen can now be determined.

The interglenoid tubercle of the atlas is ancestral to lissamphibians

“…The anterior‐most vertebrae of Xenopus laevis first appear with the chondrification of the atlas neural arch between Nieuwkoop and Faber (NF) stages 48 and 51 (MacKenzie et al, 2022; Nieuwkoop & Faber, 1994; Smit, 1953; Trueb & Hanken, 1992). The atlas centrum has been observed to chondrify as early as NF stage 53 (Trueb & Hanken, 1992), and ossification of the neural arch and centrum begins as early as NF stage 54 (Smit, 1953).…”

“…The atlas centrum has been observed to chondrify as early as NF stage 53 (Trueb & Hanken, 1992), and ossification of the neural arch and centrum begins as early as NF stage 54 (Smit, 1953). Ossification of the anterior vertebrae of X. laevis is consistently present by NF stage 56 (MacKenzie et al, 2022) and metamorphosis is complete at NF stage 66 (Trueb & Hanken, 1992). For this reason, we observed 36 cleared and Alizarin red S (bone) stained specimens and 15 cleared and double stained (Alizarin red S and Alcian blue [cartilage]) specimens between NF stages 56 and 66 (specimen count by stage summarized in Table 1).…”

“…The tadpoles used herein were initially cleared and either stained for bone with Alizarin red S (Sigma-Aldrich A5533) or double stained for bone and cartilage with Alizarin red S and Alcian blue (8GX, Acros Organics A3157) for a study of cranial development of Xenopus laevis (MacKenzie et al, 2022; specimens summarized here in Table 1). The detailed methods of husbandry, staging, fixation, clearing, and staining were described by MacKenzie et al (2022). All procedures were conducted in accordance with the Canadian Council of Animal Care and the Carleton Animal Care Committee-approved animal use protocols.…”

“…While observing a growth series of the frog Xenopus laevis (MacKenzie et al, 2022), we were surprised to observe a structure resembling the TI of salamanders on the atlantes of some tadpoles. Here, we describe the observed occurrence of this TI-like structure in tadpoles of X. laevis and explore its occurrence among fossil relatives to test the hypothesis that this structure may represent a synapomorphy of Lissamphibia (see Parsons and Williams [1963], McGowan and Evans [1995], and Gardner [2001]).…”

Phenotype–genotype relationships in Xenopus sox9 crispants provide insights into campomelic dysplasia and vertebrate jaw evolution

“…The upper jaw (palatoquadrate) cartilages were deformed, the lower jaw (Meckel's) cartilages were bent inward, and the ceratohyal cartilages were bent inward and reduced. The branchial/gill cartilages were reduced but not so severely deformed compared to the jaw cartilages (Figure 4b, lower panels) (MacKenzie et al, 2022;Sadaghiani & Thiébaud, 1987). Transverse sections of the representative tadpoles stained with Alcian blue and Mayer's hemalum solution showed a decrease in palatoquadrate, ceratohyal, and branchial chondrocytes lining the deformed buccal cavity compared to uninjected tadpoles (Figure 4c).…”