Fibronectin mediates correct positioning of the interrenal organ in zebrafish

Abstract

Background: Fibronectin (Fn) forms a centripetal gradient during the fetal adrenal gland organogenesis, and modulates hormone responsiveness of adrenocortical cells in the primary culture. However, how Fn is involved in organ formation of the adrenal gland remains unclear. Results: In this study, we found that Fn accumulates around migrating ff1b-expressing interrenal cells, which were marked by the ff1b promoter-driven transgenic fluorescence, during the course of interrenal organ assembly. The interrenal cells displaying the migratory phenotype were absent in the fn1 mutant, while specification and kidney association of the interrenal tissue remained normal. The Fn deposition in the interrenal microenvironment was severely reduced in the vessel-deficient ets1b morphant, implying its origin of synthesis from the peri-interrenal vasculature. In the fn1 mutant, early-migrating chromaffin cells were capable of interacting with steroidogenic interrenal cells, yet continuous migration and midline convergence of chromaffin cells were disrupted. Migration defects of both interrenal and chromaffin lineages, in the absence of Fn, thus led to incomplete interrenal organ assembly in aberrant positions. Conclusions: Our results indicate that Fn is essential for patterning interrenal organ formation, by modulating the migratory behavior of both steroidogenic interrenal and chromaffin cells. Developmental Dynamics 242:432-443, 2013. V C 2013 Wiley Periodicals, Inc.Key words: zebrafish; adrenal; interrenal; steroidogenic; chromaffin; fibronectin Key Findings:Fibronectin accumulates around migrating steroidogenic cells, which are detected by a steroidogenic cell-specific zebrafish transgenic line, during the course of interrenal organ assembly. Migration but not specification of steroidogenic interrenal cells is defective in the zebrafish fibronectin mutant. Fibronectin distribution in the zebrafish interrenal microenvironment is at least in part contributed by the neighboring vasculature. The assembly of zebrafish interrenal organ is aberrant in the absence of Fibronectin, due to migration defects of both steroidogenic and chromaffin cells.

The Hemodynamically-Regulated Vascular Microenvironment Promotes Migration of the Steroidogenic Tissue during Its Interaction with Chromaffin Cells in the Zebrafish Embryo

“…Consistent with the findings of our earlier study [19], the integration of the two cell populations was detected as early as 36 hpf (Figure 7A–A'), and was not affected in tnnt2a morphants (Figure 7B–B'), while interrenal medial migration and organ assembly were observed at 56 hpf and 3 dpf (Figure 7C–C', E–E'), respectively. Since the medial extension of steroidogenic tissue was inhibited in tnnt2a morphants, chromaffin cells that reached the interrenal region remained closely associated with steroidogenic cells, and were located to the right of the midline (Figure 7D–D', F–F').…”

“…The obstruction of blood flow in the zebrafish embryo produced a phenotype similar to that of the fn1 mutant [19] (Figure 7), providing evidence that the interrenal Fn-enriched microenvironment is regulated by hemodynamic forces (Figure 4). However, while blood flow-deficient embryos have similar defects in steroidogenic and chromaffin cell migration, 20%–30% of fn1 mutants exhibit a more severe phenotype, where the bilateral fusion of early interrenal tissues is unsuccessful (Figure 7).…”

“…A lower concentration of 2,3-BDM (2 mM) caused a 26% decrease in heart rate and a visibly weakened blood flow (Video S3). To examine the morphology of the DA adjacent to the kidney and interrenal regions, 2,3-BDM was applied to Tg(kdrl: EGFP) s843 embryos that express GFP in the developing blood vascular structure [40], which were then harvested at 2.5 dpf, when the migration of interrenal cells can be clearly observed [19]. Treatment with 2 or 6 mM 2,3-BDM suppressed interrenal medial extension across the midline (Figure 2B, B'', C, C''), with similar effects observed at both concentrations (Figure 2D).…”

“…The initiation of IRV angiogenesis requires deposition of Fn at the ventral DA near the interrenal tissue, and the accumulation of this protein in the local microenvironment supports IRV extension [21]. While the interrenal tissue is closely associated with both the DA and the IRV, vessel-derived Fn functions at the tissue-vessel interface and thus modulates the migration of steroidogenic cells [19]. Therefore, it is possible that the vascular microenvironment established during IRV angiogenesis is regulated by blood flow, which in turn modulates the migration of steroidogenic cells.…”

“…The integration of these two cell types occurs between 1.5 and 3 days post-fertilization (dpf), which is immediately followed by de novo cortisol synthesis in response to stress [18], [19], [20]. Within the same temporal window, the interrenal vessel (IRV) is patterned along with a vessel-derived, Fibronectin (Fn)-enriched microenvironment [21], which is essential for IRV growth, steroidogenic tissue morphogenesis, and positioning the interrenal organ.…”