Walter BE and Henry JJ (2004), Embryonic expression of pre-initiation DNA repl...

XB-ART-2764

Gene Expr Patterns 2004 Nov 01;51:81-9. doi: 10.1016/j.modgep.2004.06.005.

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Embryonic expression of pre-initiation DNA replication factors in Xenopus laevis.

Walter BE , Henry JJ .

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We examined the expression of various DNA replication factors, including: cdc45, the factors of the GINS heterotetramer (Sld5, Psf1, Psf2, Psf3), and PCNA, in Xenopus laevis during embryonic development via whole mount in situ hybridization. For the most part, these factors were expressed in similar patterns, with some subtle variations, throughout development within the anterior CNS, pharyngeal arches, and various placodes. More significant variations were also observed, including expression of only Psf1 and Psf2 in the pronephros and unique Psf2 expression in the somitic mesoderm. Overall, these results suggest that common regulatory mechanisms are involved in the transcriptional deployment of these factors. Significantly, expression of these factors does not directly coincide with elevated patterns of DNA replication, suggesting that different replication factors are utilized in different developmental regions.

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Species referenced: Xenopus laevis
Genes referenced: cdc45 gins1 gins2 gins3 gins4 pcna ret tap1 tap2

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	gins1 (GINS complex subunit 1 (Psf1 homolog)) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 26 lateral view, anterior left, dorsal up.


	Fig. 1. Expression of cdc45. Embryos in (A) as well as (F–H) are oriented anterior to the left and dorsal to the top. (A) Stage 13 embryo. Arrowheads demarcate expression within the region which will become the sensory placodes. (B) Stage 13 embryo, anterior view with the dorsal side to the top. Arrowheads demarcate higher intensity of expression within the anterior CNS and retinal rudiments. (C) Stage 22 embryo, dorsal view, anterior toward the top. Note dorsal stain associated with the CNS with increased intensity anteriorly in the optic regions. Faint signal is also present in the posterior end of the embryo. (D) Stage 32 embryo, dorsal view, anterior toward the top. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. Note the gradient of expression in the CNS. (E) Stage 37 embryo, dorsal view, anterior toward the top. Intense stain is located in the ventricular region of the forebrain. (F) Stage 26 embryo. (G) Stage 32 embryo. (H) Stage 37 embryo. (I) Oblique section through the forebrain region of a stage 37 embryo Note the intense stain in the ventricular zone of the forebrain as well as the ciliary marginal zone of the retina. cmz: ciliary marginal zone of the retina, for: forebrain, lens: lens, mid: midbrain, nc: neural crest, oc: optic cup, ot: otic vesicle, ov: optic vesicle, pa: pharyngeal arches, phx: pharynx, vz: ventricular zone. (J) Sense control stage 22 embryo. (K) Sense control stage 37 embryo. The scale bar in (H) equals 380 mm in (A and B), 760 mm in (C) 200 mm in (D) and (E), 550 mm in (F–H), (J and K), and 125 mm for (I).
	Fig. 2. Expression of Sld5. All embryos are oriented anterior to the left and dorsal to the top, except those in (C) and (D), which are dorsal views oriented anterior toward the top. (A). Stage 14 embryo. As compared to cdc45 (see Fig. 1A), note the low intensity of expression which is barely detectable in this figure. (B) Stage 22 embryo. (C) Stage 26 embryo. (D) Stage 37 embryo. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. (E) Stage 26 embryo. (F) Stage 31 embryo. (G) Stage 37 embryo. (H) Section through a stage 37 embryo at the level of the midbrain, with the dorsum oriented to the left. (I) Sense control stage 31 embryo. (J) Sense control stage 37 embryo. m/h: midbrain/hindbrain boundary, olf: olfactory placode, ret: retina. All other labels follow that listed in the legend to Fig. 1. The scale bar in (G) equals 380 mm in (A), 550 mm in (B) and (E–G), (I and J), 200 mm in (C) and (D) and 100 mm in (I).
	Fig. 3. Expression of Psf1. All embryos are oriented anterior to the left and dorsal to the top, except those in (C) and (D), which are dorsal views oriented anterior to the top. (A) Stage 13 embryo. Arrowheads demarcate anterior regions of expression. (B) Stage 22 embryo. Arrowheads demarcate posterior expression of Psf1. (C) Stage 33 embryo. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. (D) Stage 37 embryo. (E) Stage 26 embryo. (F) Stage 33 embryo. (G) Stage 37 embryo. (H) Section through a stage 37 embryo at the level of the forebrain, with the dorsum oriented to the left. Note the intense stain in the ventricular zone of the CNS, and a lesser degree of expression within the rest of the CNS. Expression can also be seen in the lens, the lining of the pharynx, and the ciliary marginal zone of the retina. (I) Sense control stage 33 embryo. (J) Sense control stage 37 embryo. m/h: midbrain/hindbrain boundary, pn: pronephros. All other labels follow that listed in the legend to Fig. 1. The scale bar in (G) equals 380 mm in A, 550 mm in (B), (E–G), (I and J), 200 mm in (C) and (D), and 100 mm in (H).
	Fig. 4. (A–H) Expression of Psf2 during development. Embryos in (A), (F–H) are oriented anterior to the left and dorsal to the top; those in (C–E) which are dorsal views with the anterior to the top. (A) Stage 14 embryo. Arrowheads demarcate weaker regions of expression outside the neural plate, within the presumptive placodal regions. (B) Stage 22 embryo, anterior view with the dorsal side to the top. (C) Stage 22 embryo. (D) Stage 31 embryo. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. (E) Stage 37. (F) Stage 26. (G) Stage 31 embryo. (H) Stage 35 embryo. (I) Transverse section of a stage 31 embryo, dorsal to the left, showing expression in the optic cup, lens, and ventricular zone of the CNS. (J–M) Expression of Psf2 during cornea-lens transdifferentiation. Arrowheads demarcate the region of stain in (J–L) (J) Relatively diffuse Psf2 expression in the cornea overlying the pupillary space three days after lens-ectomy. This stain does not appear directly over the pupillary space due to the differential contractions of the eye muscles resultant from the fixation process. (K and L) Expression six days after lens-ectomy, localized within the newly forming lens vesicle. (M) Undisturbed, control eye showing no detectable expression of Psf2 in the cornea. (N) Sense control stage 23 embryo. (O) Sense control stage 31 embryo. (P) Sense control stage 37 embryo so: somites. All other labels follow that listed in the legends to Figs. 1–3. The scale bar in (M) equals 380 mm in (A and B), 760 mm in (C), 200 mm in (D and E), 550 mm in (F–H), (N–P), 240 mm in (I), and 400 mm in (J–M).
	Fig. 5. Expression of Psf3. All embryos are oriented anterior to the left and dorsal to the top, except those in (C and D) which are dorsal views oriented anterior to the top. (A) Stage 13 embryo. Arrowheads demarcate anterior and posterior regions of neural expression. (B) Stage 22 embryo. (C) Stage 32 embryo. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. (D) Stage 37 embryo. (E) Stage 26 embryo. (F) Stage 32 embryo. (G) Stage 37 embryo. (H) Section through a stage 37 embryo at the level of the hindbrain, with the dorsum oriented to the left. Note the consistent levels of expression in the dorsal CNS compared to Psf1 (Fig. 3H) and Psf2 (Fig. 4I). (I) Sense control stage 30 embryo. (J) Sense control stage 37 embryo. All labels follow that listed in the legend to Fig. 1. The scale bar in G equals 380 mm in (A), 550 mm in (B) and (E–G), (I–J), 200 mm in (C and D), and 125 mm in (H).
	Fig. 6. Expression of PCNA. The embryos in (A and C), (H), and (J and K) are oriented anterior to the left and dorsal to the top; (B) is a dorsal view, oriented anterior to the left; those in (E–G) are dorsal views oriented anterior toward the top. (A) Stage 20 embryo. (B) Stage 22 embryo. (C) Stage 26 embryo. (D) Stage 26 embryo, anterior view with dorsal located to the top. (E) Stage 28 embryo. Arrowheads demarcate stronger signal in the tailbud region. (F) Stage 28 embryo. (G) Stage 37 embryo. The bracket demarcates the right half of the CNS, and the left margin of the bracket aligns with the inner boundary of the ventricular zone. (H) Stage 37 embryo. The stain in the midbrain is located at the midbrain–hindbrain boundary. (I) Section through a stage 37 embryo at the level of the midbrain/hindbrain boundary, with the dorsum oriented to the left. This section was taken from the temporal margins of the optic cup, and therefore does not include any ciliary marginal zone stain. (J) Sense control stage 23 embryo. (K) Sense control stage 37 embryo. cg: cement gland, cns: central nervous system, m/h: midbrain/hindbrain boundary. All other labels follow that listed in the legend to Fig. 1. The scale bar in (G) equals 430 mm in (A and B), 550 mm in (C), 250 mm in (D), 690 mm in (E), 780 mm in (F), and 200 mm in G, 380 mm in (H),(J and K), and 100 mm in (I).
	Fig. 7. Summary of expression in selected tissues between stages 28–30 and 35–37.