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Localized rbp4 expression in the yolk syncytial layer plays a role in yolk cell extension and early liver development.

Li Z, Korzh V, Gong Z - BMC Dev. Biol. (2007)

Bottom Line: Knockdown of Rbp4 in the YSL resulted in shortened yolk extension as well as the formation of two liver buds, which could be due to impaired migration of liver progenitor cells. rbp4 appears also to regulate the extracellular matrix protein Fibronectin1 (Fn1) specifically in the ventro-lateral yolk, indicating a role of Fn1 in liver progenitor migration.The characteristic expression pattern of rbp4 suggests that the YSL is patterned despite its syncytial nature.YSL-expressed Rbp4 plays a role in formation of both yolk extension and liver bud, the latter may also require migration of liver progenitor cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, National University of Singapore, Singapore. g0203805@nus.edu.sg

ABSTRACT

Background: The number of genes characterized in liver development is steadily increasing, but the origin of liver precursor cells and the molecular control of liver formation remain poorly understood. Existing theories about formation of zebrafish visceral organs emphasize either their budding from the endodermal rod or formation of independent anlage followed by their later fusion, but none of these is completely satisfactory in explaining liver organogenesis in zebrafish.

Results: Expression of a gene encoding the retinol binding protein 4 (Rbp4) was analyzed in zebrafish. rbp4, which is expressed mainly in the liver in adults, was shown to be expressed in the yolk syncytial layer (YSL) during early embryogenesis. At 12-16 hpf rbp4 expression was restricted to the ventro-lateral YSL and later expanded to cover the posterior YSL. We demonstrated that rbp4 expression was negatively regulated by Nodal and Hedgehog (Hh) signalling and positively controlled by retinoic acid (RA). Knockdown of Rbp4 in the YSL resulted in shortened yolk extension as well as the formation of two liver buds, which could be due to impaired migration of liver progenitor cells. rbp4 appears also to regulate the extracellular matrix protein Fibronectin1 (Fn1) specifically in the ventro-lateral yolk, indicating a role of Fn1 in liver progenitor migration. Since exocrine pancreas, endocrine pancreas, intestine and heart developed normally in Rbp4 morphants, we suggest that rbp4 expression in the YSL is required only for liver development.

Conclusion: The characteristic expression pattern of rbp4 suggests that the YSL is patterned despite its syncytial nature. YSL-expressed Rbp4 plays a role in formation of both yolk extension and liver bud, the latter may also require migration of liver progenitor cells.

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Expression of rbp4 mRNA during early zebrafish embryogenesis. (A) RT-PCR analysis of rbp4 mRNA in wild-type embryos from 1 hpf to 14 hpf. β-actin was used as loading control. M, 100 bp DNA marker. (B, C) Ventral (B) and lateral (C) view of 12 hpf embryos with rbp4 expression as detected by WISH. (D) Ventral view of 16 hpf embryos with expression of ctsL (red) and rbp4 (blue) as detected by two-colour WISH. (E) Cross section of the two color hybridized embyos in (D) as indicated by the dashed line. (F, F') Magnified view of boxed region F in Panel (E). F, bright field. F', compound image of DIC/fluorescence reveals rbp4 expression and position of nuclei detected by DAPI staining. Arrows indicate YSL nuclei. (G), Magnified view of boxed region G in Panel (E).
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Figure 1: Expression of rbp4 mRNA during early zebrafish embryogenesis. (A) RT-PCR analysis of rbp4 mRNA in wild-type embryos from 1 hpf to 14 hpf. β-actin was used as loading control. M, 100 bp DNA marker. (B, C) Ventral (B) and lateral (C) view of 12 hpf embryos with rbp4 expression as detected by WISH. (D) Ventral view of 16 hpf embryos with expression of ctsL (red) and rbp4 (blue) as detected by two-colour WISH. (E) Cross section of the two color hybridized embyos in (D) as indicated by the dashed line. (F, F') Magnified view of boxed region F in Panel (E). F, bright field. F', compound image of DIC/fluorescence reveals rbp4 expression and position of nuclei detected by DAPI staining. Arrows indicate YSL nuclei. (G), Magnified view of boxed region G in Panel (E).

Mentions: The EST clone coding for Rbp4 (A 10) from our collection [30] was selected and sequenced completely. The complete sequence was submitted to GenBank (acc. no. EF373650) and it was almost identical (99.5%) to a sequence previously available (GenBank AJ236884, [18]). To investigate the temporal expression pattern of rbp4 in early development, rbp4 transcripts were analyzed by RT-PCR from fertilized eggs to 14 hpf. We found that rbp4 transcripts were of maternal origin and the zygotic expression of rbp4 increased from 6 hpf to reach its peak by 12 hpf (Figure 1A).


Localized rbp4 expression in the yolk syncytial layer plays a role in yolk cell extension and early liver development.

Li Z, Korzh V, Gong Z - BMC Dev. Biol. (2007)

Expression of rbp4 mRNA during early zebrafish embryogenesis. (A) RT-PCR analysis of rbp4 mRNA in wild-type embryos from 1 hpf to 14 hpf. β-actin was used as loading control. M, 100 bp DNA marker. (B, C) Ventral (B) and lateral (C) view of 12 hpf embryos with rbp4 expression as detected by WISH. (D) Ventral view of 16 hpf embryos with expression of ctsL (red) and rbp4 (blue) as detected by two-colour WISH. (E) Cross section of the two color hybridized embyos in (D) as indicated by the dashed line. (F, F') Magnified view of boxed region F in Panel (E). F, bright field. F', compound image of DIC/fluorescence reveals rbp4 expression and position of nuclei detected by DAPI staining. Arrows indicate YSL nuclei. (G), Magnified view of boxed region G in Panel (E).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2198918&req=5

Figure 1: Expression of rbp4 mRNA during early zebrafish embryogenesis. (A) RT-PCR analysis of rbp4 mRNA in wild-type embryos from 1 hpf to 14 hpf. β-actin was used as loading control. M, 100 bp DNA marker. (B, C) Ventral (B) and lateral (C) view of 12 hpf embryos with rbp4 expression as detected by WISH. (D) Ventral view of 16 hpf embryos with expression of ctsL (red) and rbp4 (blue) as detected by two-colour WISH. (E) Cross section of the two color hybridized embyos in (D) as indicated by the dashed line. (F, F') Magnified view of boxed region F in Panel (E). F, bright field. F', compound image of DIC/fluorescence reveals rbp4 expression and position of nuclei detected by DAPI staining. Arrows indicate YSL nuclei. (G), Magnified view of boxed region G in Panel (E).
Mentions: The EST clone coding for Rbp4 (A 10) from our collection [30] was selected and sequenced completely. The complete sequence was submitted to GenBank (acc. no. EF373650) and it was almost identical (99.5%) to a sequence previously available (GenBank AJ236884, [18]). To investigate the temporal expression pattern of rbp4 in early development, rbp4 transcripts were analyzed by RT-PCR from fertilized eggs to 14 hpf. We found that rbp4 transcripts were of maternal origin and the zygotic expression of rbp4 increased from 6 hpf to reach its peak by 12 hpf (Figure 1A).

Bottom Line: Knockdown of Rbp4 in the YSL resulted in shortened yolk extension as well as the formation of two liver buds, which could be due to impaired migration of liver progenitor cells. rbp4 appears also to regulate the extracellular matrix protein Fibronectin1 (Fn1) specifically in the ventro-lateral yolk, indicating a role of Fn1 in liver progenitor migration.The characteristic expression pattern of rbp4 suggests that the YSL is patterned despite its syncytial nature.YSL-expressed Rbp4 plays a role in formation of both yolk extension and liver bud, the latter may also require migration of liver progenitor cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, National University of Singapore, Singapore. g0203805@nus.edu.sg

ABSTRACT

Background: The number of genes characterized in liver development is steadily increasing, but the origin of liver precursor cells and the molecular control of liver formation remain poorly understood. Existing theories about formation of zebrafish visceral organs emphasize either their budding from the endodermal rod or formation of independent anlage followed by their later fusion, but none of these is completely satisfactory in explaining liver organogenesis in zebrafish.

Results: Expression of a gene encoding the retinol binding protein 4 (Rbp4) was analyzed in zebrafish. rbp4, which is expressed mainly in the liver in adults, was shown to be expressed in the yolk syncytial layer (YSL) during early embryogenesis. At 12-16 hpf rbp4 expression was restricted to the ventro-lateral YSL and later expanded to cover the posterior YSL. We demonstrated that rbp4 expression was negatively regulated by Nodal and Hedgehog (Hh) signalling and positively controlled by retinoic acid (RA). Knockdown of Rbp4 in the YSL resulted in shortened yolk extension as well as the formation of two liver buds, which could be due to impaired migration of liver progenitor cells. rbp4 appears also to regulate the extracellular matrix protein Fibronectin1 (Fn1) specifically in the ventro-lateral yolk, indicating a role of Fn1 in liver progenitor migration. Since exocrine pancreas, endocrine pancreas, intestine and heart developed normally in Rbp4 morphants, we suggest that rbp4 expression in the YSL is required only for liver development.

Conclusion: The characteristic expression pattern of rbp4 suggests that the YSL is patterned despite its syncytial nature. YSL-expressed Rbp4 plays a role in formation of both yolk extension and liver bud, the latter may also require migration of liver progenitor cells.

Show MeSH
Related in: MedlinePlus