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The par genes (partitioning defective) are required to establish polarity in the Caenorhabditis elegans embryo. We have identified the Xenopus homologue of C. elegans PAR-6 (XPAR-6). XPAR-6 is a protein of 377 amino acids with one PDZ domain which is involved in mediating protein-protein interactions. It shares 59% and 58% amino acid identity with the mouse and Drosophila PAR-6, respectively, and 54% overall identity with C. elegans PAR-6. Xpar-6 is expressed both maternally and zygotically. Xpar-6 is first detected in the animal half of the egg, and this pattern of expression persists into the cleavage and blastula stages. At the gastrula stage, the message is detected in animal pole area and in a broad domain of ventral region, but is excluded from dorsal region. With the onset of neurulation, the localized expression of Xpar-6 becomes more obvious, leading to it being enriched in the dorsolateral region along the lateral edges of neural plate and anterior presumptive head region surrounding the anterior border of neural plate. At late tailbud stage, Xpar-6 transcripts show localized expression throughout the head, labeling the branchial arches, eyes, otic vesicles and brain, while more posteriorly Xpar-6 labels the somites, pronephros, tail tip and proctodeum. Therefore, this analysis suggests that Xpar-6 has a regionalized pattern of expression during Xenopus early embryogenesis.
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10704862
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Fig. 3. Spatiotemporal expression pattern of Xpar-6 assayed by whole-mount in situ hybridization. (A) Lateral view of an egg showing enhanced signal in the animal region, with animal pole at top. (B) Sense probe control – egg. (C) The pattern in A was confirmed by RT–PCR analysis of Xpar-6 in animal cap (AC) and vegetal pole (VP) explants from fertilized eggs. EF-1a was used as a loading control. (D,E) A stage 11 embryo viewed, ventrally and dorsally, respectively, with anterior at top. Arrowheads indicate yolk plug. (F) Vegetal view of a stage 11 embryo shows moderate staining of Xpar-6 in a yolk plug, with dorsal side at top. An arrow indicates dorsal lip of blastopore. (G) Dorsal and (H) anteroventral views, with anterior at top, of an early neurula showing Xpar-6 transcripts localized to the dorsolateral region and anterior end of the presumptive neural area. (I) Anterolateral and (J) anterodorsal views, with anterior to the left, of mid-neurula stage embryos. Xpar-6 is expressed in the lateral region along the ridges of neural fold and extreme anterior region surrounding the anterior edge of the neural plate. Bilaterally symmetric pattern of Xpar-6 expression is also observed in patches (arrowheads) in the anterior region of the neural plate. (K) Side view, with anterior to the left, of a late neurula stage embryo. (L) A late tailbudembryo viewed laterally. Xpar-6 expression is intense in the head, labeling the eyes, branchial arches, otic vesicles and brain. Posterior to the head, Xpar-6 is expressed in the somites, pronephros, tail tip and proctodeum. ov, otic vesicle; s, somite; ba, branchial arches; pd, proctodeum.
Fig. 4. Localized expression pattern of Xpar-6 from the mid-neurula to the tadpole stage by in situ hybridization on tissue sections. (A) A transverse section of a mid-neurula stage embryo. Xpar-6 transcripts are localized to the epidermal ectoderm, neural plate (arrowhead) and intermediate mesodermal region which will form the pronephros (arrows). (B) At the late tailbud stage, Xpar-6 transcripts mark the eye, otic vesicle (ov), pronephros (pn) and brain, but are excluded from the cement gland (cg). (C) A sagittal section of head region at the late tailbud stage. Xpar-6 is visible as a stripe (arrowhead) in the brain region. An arrow indicates eye. (D) A sagittal section of a tadpole stage embryo shows Xpar-6 expression outlining the somite borders (arrowhead). (E) Xpar-6 transcripts can be seen in the proctodeum (arrowhead). (F) A cross section of a late tailbud stage embryo representing Xpar-6 transcripts localized to the pronephros (pn). Magnification: B,E, ×50; A,C,F, ×100; D, ×200.
Fig. 2. RT–PCR analysis during development (stages indicated above the lanes) shows maternal and zygotic Xpar-6 transcription. ODC serves as a loading control and the –RT lane is a control of RT–PCR on stage 35 whole embryo RNA in the absence of reverse transcriptase.
pard6b (par-6 family cell polarity regulator beta) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 28, lateral view, anteriorleft, dorsal up.
pard6b (par-6 family cell polarity regulator beta) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 28, lateral view, mid sagigital section, anteriorleft, dorsal up.
pard6b (par-6 family cell polarity regulator beta) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 28, transverse section, dorsal up.
