Tae HJ et al. (2015), Temporal and spatial expression analysis of per...

XB-ART-50084

Gene Expr Patterns 2015 Jan 01;171:26-30. doi: 10.1016/j.gep.2015.01.001.

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Temporal and spatial expression analysis of peripheral myelin protein 22 (Pmp22) in developing Xenopus.

Tae HJ , Rahman MM , Park BY .

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Peripheral myelin protein 22 (Pmp22), a member of the junction protein family Claudin/EMP/PMP22, contributes to the formation and maintenance of myelin sheaths in the peripheral nervous system. Apart from the establishment and maintenance of peripheral nerves, Pmp22 and its family member have also participated in a broad range of more general processes including cell cycle regulation and apoptosis during development. Pmp22 has been identified from several vertebrate species including mouse, human and zebrafish. However, Pmp22 has not been identified from Xenopus embryos yet. In this paper, we cloned Pmp22 from Xenopus laevis and evaluated its expression during embryogenesis. We found that Pmp22 was initially expressed in the mesoderm and cement gland during the neurula stage. At early tailbud stage, strong expression of Pmp22 was detected in the trigeminal and profundal ganglia as well as developing somites and branchial arches. Later in development, Pmp22 was expressed specifically in cranio-facial cartilage, roof plate and floor plate of the developing brain, otic vesicle and lens. Pmp22 is also strongly expressed in the developing trachea and lungs. Based on its expression in facial tissues, we propose that Pmp22 may be involved in the formation of head structure in addition to the maintenance of functional peripheral nerves in Xenopus embryos.

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Species referenced: Xenopus laevis
Genes referenced: isl1 maea otx2 pmp22 sox9 wnt3a

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	pmp22 (peripheral myelin protein 22) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 15, dorsal view, anterior up.
	pmp22 (peripheral myelin protein 22) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 22, lateral view, anterior left, dorsal up.
	pmp22 (peripheral myelin protein 22) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 30, lateral view, anterior left, dorsal up.
	pmp22 (peripheral myelin protein 22) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 35, lateral view, anterior left, dorsal up.
	Fig. 1. Sequence and developmental expression of Xenopus Pmp22. (A) Amino acid sequence from human, mouse, chicken and zebrafish PMP22 were aligned using clustalW. Conserved amino acids in all five species or in at least two species are highlighted in black and gray, respectively. (B)Temporal expression of Xenopus Pmp22 was analyzed by RT-PCR. Pmp22 was first detected at stage 14 and persisted throughout development. Developmental stages were determined according to Nieuwkoop and Faber (1967). EF1α is shown as a loading control. Lane (-) shows a negative control in absence of RNA.
	Fig. 2. Expression of Pmp22 in whole-mount in situ hybridization. (A) Expression of Pmp22 at stage 15 in the cement gland. Anterior view, dorsal to top. (B) At stage 22, Pmp22 was detected in the developing somites and profundal and trigeminal nerves. (C) At stage 22 Pmp22 sense probe was used as a negative control. (D) Pmp22 was expressed in the profundal and trigeminal ganglia, cranial mesenchyme, and somites at stage 29/30, where it was also beginning to be expressed in the branchial arches. (E) Strong expression of Pmp22 was observed in the craniofacial region. (F–G, I) To confirm the tissue-specific expression of Pmp22, we also performed in situ hybridization for Sox9 and Islet1. (H, I) At stage 35, both Pmp22 and Sox9 were detected in the branchial arches. Panels (B–I), lateral view, anterior to the left. ba, branchial arches; cg, cement gland; pr, profundal ganglia; s, somites; tg, trigeminal ganglia.
	Fig. 3. Expression of Pmp22 determined by in situ hybridization of whole sections. (A) At stage 15, Pmp22 was weakly expressed in mesoderm cells. (B) At stage 30 Pmp22 sense probe was used as a negative control. (C–D) Transverse sections showing the expression of Pmp22 in the mesenchyme of the head at stage 35. Expression of Pmp22 was detected in the eye, craniofacial cartilage, trigeminal ganglia, and roof plate of the anterior neural tube, as well as floor plate of the posterior neural tube. (E) Schematic representation of the head of a stage 40 embryo as viewed from the lateral side, dorsal to top, and anterior to the left. Image was modified from Nieuwkoop and Faber (1967). (F–L) At stage 40, transverse sections revealed expression of Pmp22 in the head mesenchyme, floor plate of the developing brain, cartilage (F–I), lens (G), trigeminal ganglia (H), otic vesicle (I, L), developing trachea (J) and lungs (K). (L–O) At stage 40, expression of Pmp22 was observed in the dorsal (blue arrow) and ventral (green arrow) aspects of the developing otocyst. Islet1 (bracket) is expressed in the sensory organs of the otic vesicle (O), which did not overlap with Pmp22 (L). bc, basihyal cartilage; br, branchial cartilage; cc, craniofacial cartilage; ce, cerathoyal cartilage; di, diencephalon; et, ethmoid-trabecular cartilage; fp, floor plate; he, heart; le, lens; lu, lung; me, Meckel’s cartilage; no, notochord; ov, otic vesicle; ph, pharynx; qu, quadrate cartilage; rp, roof plate; st, stomodeum; tg, trigeminal ganglion; tr, trachea. The scale bar represents 100 μm.