Figure 2.
SREBP (SBP-1) promotes AC invasion and invasive protrusion formation. (A) Top: Merged DIC and fluorescence images (maximum intensity z-projections) of the AC (cyan, mCherry::PLCδPH) and the underlying BM (single central confocal slice, magenta, LAM-1::GFP) at the P6.p 4-cell stage in a control (empty RNAi vector treated) and an AC-specific sbp-1 RNAi treated animal. Bottom: Fluorescence images showing BM breach (brackets) in a control animal and lack of breach after sbp-1 RNAi (arrows). (B) Left: Maximum intensity z-projected fluorescence images showing the AC (cyan, mCherry::PLCδPH) protrusion (arrowheads) in a control and an AC-specific sbp-1 RNAi treated animal (BM, orange dashed lines) with a small and delayed (see Materials and methods) breach observed corresponding to the reduced protrusion after loss of sbp-1 (middle, bracket, observed in n = 8/8 sbp-1 RNAi time-lapses). Isosurfaces of the AC invasive protrusion (below, arrowheads) at the time of maximum protrusion volume (see Video 1). Right: Boxplot shows the maximum invasive protrusion volume in control and sbp-1 RNAi treated animals (n = 7 control and 8 sbp-1 RNAi animals, *** P ≤ 0.001, Mann–Whitney U test). For this and all subsequent boxplots, box edges indicate the 25th and 75th percentiles, whiskers the maximum and minimum values, and the line within the box the median value. (C) A schematic diagram illustrating SBP-1 proteolytic activation and entry into the nucleus where the SBP-1 bHLH domain binds sterol regulatory elements (SREs) to transcribe target genes. (D) Boxplot of mNG::SBP-1 mean fluorescence intensity in the AC nucleus from the L2/L3 molt stage to the P6.p 4-cell stage (n = 6 L2/L3 molt, nine 1-cell, six 2-cell, seven 2–4-cell, and six 4-cell stage animals, ** P ≤ 0.01, *** P ≤ 0.001, ns [not statistically significant], P > 0.05, Brown-Forsythe and Welch ANOVA tests followed by Dunnett’s T3 multiple comparisons test). (E) Top: Sum intensity z-projected fluorescence images of mNG::SBP-1 in the AC nucleus (white dashed circle) from the L2/L3 molt (time of AC specification) to the P6.p 4-cell stage. Bottom: Central plane DIC images showing dashed circles outlining the nucleus where SBP-1 fluorescence was measured. All data are from two or more replicates. Scale bars, 5 µm.

SREBP (SBP-1) promotes AC invasion and invasive protrusion formation. (A) Top: Merged DIC and fluorescence images (maximum intensity z-projections) of the AC (cyan, mCherry::PLCδPH) and the underlying BM (single central confocal slice, magenta, LAM-1::GFP) at the P6.p 4-cell stage in a control (empty RNAi vector treated) and an AC-specific sbp-1 RNAi treated animal. Bottom: Fluorescence images showing BM breach (brackets) in a control animal and lack of breach after sbp-1 RNAi (arrows). (B) Left: Maximum intensity z-projected fluorescence images showing the AC (cyan, mCherry::PLCδPH) protrusion (arrowheads) in a control and an AC-specific sbp-1 RNAi treated animal (BM, orange dashed lines) with a small and delayed (see Materials and methods) breach observed corresponding to the reduced protrusion after loss of sbp-1 (middle, bracket, observed in n = 8/8 sbp-1 RNAi time-lapses). Isosurfaces of the AC invasive protrusion (below, arrowheads) at the time of maximum protrusion volume (see Video 1). Right: Boxplot shows the maximum invasive protrusion volume in control and sbp-1 RNAi treated animals (n = 7 control and 8 sbp-1 RNAi animals, *** P ≤ 0.001, Mann–Whitney U test). For this and all subsequent boxplots, box edges indicate the 25th and 75th percentiles, whiskers the maximum and minimum values, and the line within the box the median value. (C) A schematic diagram illustrating SBP-1 proteolytic activation and entry into the nucleus where the SBP-1 bHLH domain binds sterol regulatory elements (SREs) to transcribe target genes. (D) Boxplot of mNG::SBP-1 mean fluorescence intensity in the AC nucleus from the L2/L3 molt stage to the P6.p 4-cell stage (n = 6 L2/L3 molt, nine 1-cell, six 2-cell, seven 2–4-cell, and six 4-cell stage animals, ** P ≤ 0.01, *** P ≤ 0.001, ns [not statistically significant], P > 0.05, Brown-Forsythe and Welch ANOVA tests followed by Dunnett’s T3 multiple comparisons test). (E) Top: Sum intensity z-projected fluorescence images of mNG::SBP-1 in the AC nucleus (white dashed circle) from the L2/L3 molt (time of AC specification) to the P6.p 4-cell stage. Bottom: Central plane DIC images showing dashed circles outlining the nucleus where SBP-1 fluorescence was measured. All data are from two or more replicates. Scale bars, 5 µm.

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