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Calcium-ATPase pumps are critical in most cells, to sequester calcium into intracytoplasmic stores and regulate general calcium signalling. In addition, cell-specific needs for calcium signals have been described and employ a diversity of calcium ATPases in adult tissues and oocytes. A major family of such calcium pumps is ATP2A/SERCA family, for Sarcoplasmic/Endoplasmic Reticulum Calcium ATPases. Although largely studied in adults, the developmental expression of the atp2a/serca genes remains unknown. Here, we provide genome organisation in Xenopuslaevis and tropicalis and phylogeny of atp2a/serca genes in craniates. We detail embryonic expression for the three X. laevis atp2a/serca genes. We found that the three atp2a/serca genes are strongly conserved among vertebrates and display complementary and tissue-specific expression in embryos. These expression patterns present variations when compared to the data reported in adults. Atp2a1/serca1 is expressed as soon as the end of gastrulation in a subset of the myod-positive cells, and later labels prospective slow muscle cells in the superficial part of the somite. In contrast atp2a2/serca2 is found in a larger subset of cells, but is not ubiquitous as reported in adults. Notably, atp2a2/serca2 is prominently expressed in the neural-related tissues, i.e. the neural plate, cement gland, but is excluded from premigratory neural crest. Finally, atp2a3/serca3 expression is restricted to the ectoderm throughout development.
Fig. 2. Atp2a1/serca1 embryonic expression compared to myod pattern in Xenopus laevis embryos. (A). Schematic of predicted Xenopus laevis SERCA1 protein structure. The different domains of the protein are indicated: Actuator (A) domain: from aa 1 to aa 34 and from aa 122 to aa 239; Nucleotide (N) domain: from aa 360 to aa 599; Phosphorylation (P) domain: from aa 318 to aa 353 and from aa 604 to aa 753 and transmembrane (TM) domains: M1 aa 57–76; M2 aa 87–103; M3 aa 260–276; M4 aa 292–310; M5 aa760–777; M6 aa 789–806; M7 aa 832–849; M8 aa 898–914; M9 aa 931–948; M10 aa 967–984. (B). Conservation of ATP2A1–3/SERCA1–3 proteins between species. Percentage of identities and positives between Xenopus laevis SERCA1, SERCA2, SERCA3 and Homo sapiens, Mus musculus, Xenopus tropicalis SERCA1, SERCA2, SERCA3. (C–D). Atp2a1/serca1 mRNA expression from cleavage to tadpole stage in Xenopus laevis. Myod and serca1 mRNA expression were compared on stagematched sibling embryos by in situ hybridization. Whole mount (a–r) and transverse sections (m′,n′,o′,p′,q′,r′) are shown for myod (b,e,h,k,m,o,q) and serca1 (c,f,i,l,n,p,r). Blastula stage embryo (stage 9) are shown in animal pole view (a, control unstained embryo, b, c). Gastrula stage embryos are shown in vegetal view with blastopore facing top (d, control unstained embryo, e, f). Neurula stage embryos are shown in dorsal view, blastopore (yellow arrowhead) to the left (j, control unstained embryo, k–n). Tadpoles are shown in side views, head to the right. Yellow arrows in m–r indicate the level of the transverse section shown in m′–r′. n′-r′ are schematic drawings of the transverse sections. Fin, np, neural plate, nt, neural tube, so, somite, no, notochord, ec, ectoderm. Green arrows indicate hypaxial muscle cells, red arrows indicate head muscles. Scale bar: a–r 0.5 mm; m′–r′ 25 μm.
Fig. 3. Atp2a2/serca2 and atpa3/serca3 embryonic expression. (A). Wholemount in situ hybridization (a–j, j′, o–r, r′) or transverse sections (g′–n and o′–v) are shown for atp2a2/serca2 (a–c, g–n) and atpa3/serca3 (d–f, o–v). Neither genes are significantly expressed at cleavage and gastrulation stages (a–f). Neurula (g–h′; o–p′) show serca2 expression in the neural tissue (arrow1) but not in the neural crest (arrow 2); while serca3 is found in the ectoderm. Tadpoles (stage 26, i–i′ and q–q′; stage 37, j–n and r–v) show dynamic serca2 expression in the neural tube (arrow 1, section in i′, i′, l), the cement gland (arrow 3), the eye (section in k), the pronephros (arrow 4, section in i′, n), the heart and branchial arches mesenchyme (arrow 6, section in m) and the proctodeum (arrow 5). Serca3 is restricted to the ectoderm (q–q′), the cement gland (arrow3, q, r, s) then to the sensory ectodermal cells (r–v). See text for details. Scale bar: a–j, j′, o–r, r′ 0.5 mm; g′–n, o′–v 0.1 mm. (B). Whole mount in situ hybridization (b,c,d) on embryos at stage 37–38 for atp2a2/serca2, nkcc2 and evi1 and scheme of the structure of the pronephros at tadpole stage (a, modified from (Raciti et al., 2008)). Atp2a2/serca2 is expressed in the proximal part of the tubule (PT); nkcc2 is expressed in the distal part of the tubule (DT); evi1 is expressed in the distal part of the tubule and in the duct (D). Scale bar: b–d 0.5 mm.
