Lipid Distribution and Metabolic Gene Expression throughout Embryogenesis

(A-E) Bright field images show yolk utilization from 0 hpf to 5 dpf.

(F-I) ORO staining shows that there were no deposits of neutral lipid in the head of the embryo at 24 hpf (F), but lipid was present at 48 hpf in the forebrain (arrow, G) and around the eye and underneath the otic vesicle (arrowhead, G), at 72 hpf around the eye (arrowhead, H), and at 5 dpf at a low amount (I).

(J) c/ebpα expression was present at 24 hpf in the developing liver and gut (arrowhead).

(K-M) c/ebpα expression increased in these organs from 48 hpf to 5 dpf (arrowhead).

(N-Q) fabp11a expression was located in the forebrain (arrow), in the eye and in the hindbrain (arrowhead) from 24 hpf to 5 dpf.

(R-U) lpl was present in the developing liver (arrowhead) from 24 to 5 dpf.

(V) pparγ was not detected in the embryo at 24 hpf.

(W and X) At 48 and 72 hpf, pparγ was expressed in the developing gut (arrowheads).

(Y) At 5 dpf, expression increased in the liver (arrow) and gut (arrowhead) and was present in the swim bladder. E, eye; G, gut; L, liver; Y, yolk.

See also Figure S1.

BODIPY-Labeled Lipid Injections Were Incorporated into New Lipids in the Yolk Sac

(A, B, D, and E) BODIPY-labeled FFA and PC were injected into yolk sac of the embryos at 24 hpf. Fluorescent imaging shows spreading of fluorescent FFA (A) and PC (D) at 1 hpi (as marked by dotted white lines) that continued to spread throughout the yolk sac at 6 hpi (B and E).

(C) TLC of BODIPY-labeled FFA injections, with lipid standards in pale orange, shows fluorescent bands in yolk sac samples at 1, 3, and 6 hpi (white arrowheads) and a band at 6 hpi in the body sample (asterisk) that correspond to the TG standard. Bands below the TG bands are present in yolk sac samples at 1, 3, and 6 hpi (open arrowheads) while a similar band is only detected at 6 hpi in the body sample (pound sign). Groupings of four bands, just above the cholesterol standard, were present in yolk samples at 1 hpi and 3 hpi (brackets). One band only was detected in the adjacent area in body samples at 1 hpi and 3 hpi (cross). At 6 hpi, another band is detected above these bands in both the yolk sac and body samples that were not present at earlier time points (circle) demonstrating a temporal dynamic evolution of lipid during development.

(F) TLC of BODIPY-labeled PC injections produced a pair of bands between the TG and FFA standards only in the yolk sac samples at 1, 3, and 6 hpi (arrows, parentheses). These bands were never detected in the body up to 6 hpi. Bands that were located at a level consistent with the DG standard were detected in yolk sac samples at 1, 3, and 6 hpi (red arrowheads) but were never observed in the body up to 6 hpi.

See also Figure S3.

The Effects of PPARγ Inhibition on the Lipid Profile and Gene Expression of Zebrafish Embryos

(A and B) ORO staining showed decreased lipid present in embryos treated with 5 µM BADGE from 26-52 hpf (B) compared with controls (A).

(C-J) Treatment with 5 µM BADGE from 50-72 hpf decreased the expression of c/ebpα (C and D, arrowheads) and lpl (E and F, arrowheads), did not affect the expression of pparγ (G and H, arrowheads) and increased the expression of fabp11a (I and J, arrowheads).

(K) Lipid amounts are depicted for lipid categories that were significantly changed by exposure to 5 µM BADGE from 26-52 hpf. Lipid species concentrations are shown in pmol/15 embryos (K). The amount of each individual lipid at a single time point in 5 µM BADGE-treated embryos was set relative to the level of that lipid species in control embryos. * p < 0.05.

(L) A log2 ratio was then calculated for the signals of each lipid species. Red indicates an increase compared to the mean, green indicates a decrease and black shows no change. Gray is displayed when there is no lipid present.

See also Figure S4.

The YSL separates the yolk and embryo during development and control in situ staining with the sense c/ebpα and pparγ probes (linked to Figure 1)

Left: The YSL is a multinucleated layer that forms within a few hours after fertilization that separates the yolk from the blastoderm of the embryo. Nutritional content from the yolk must pass through the YSL prior to delivery to cells. Abbreviations: EVL, enveloping layer; DEL, deep layer; YSL, yolk syncytial layer. Right: Lipid is transported from the yolk to the body at various sites during embryogenesis. Lipid must pass through the YSL (blue) to enter the body and this occurs from the early hours post fertilization through to complete yolk absorption at 5 dpf. At 24 hpf, circulation has begun and lipid can be transported by the caudal vein (green), which is in contact with the YSL, to the rest of the body. By 48 hpf, the pharynx (orange) expresses lipid metabolic genes, contains neutral lipids and is in contact with the yolk, indicating it may be involved in the lipid mobilization. At 4 dpf, lipids are present in the lumen of the gut (red), which may be processed and transported from that site. At 5 dpf, the yolk is substantially used up and feeding commences, allowing for nutritional intake to be processed in the gut. (A-C) sense c/ebpα probes showing no staining at 48, 72 and 120 hpf. (D-F) sense pparγ probes showing no staining at 48, 72 and 120 hpf. G: gut; Y: yolk sac.