Additional Supporting Information may be found in the online version of this article.

DVDY_22513_sm_suppfig1.tif2695KSupp. Fig. S1. Genotype results from wild type, single knockout, and double knockout mice. DNA isolated from wild type, β8−/−, 4.1B−/−, or β8−/−;4.1B−/− embryos or neonates was analyzed using synthetic primers and PCR to amplify specific regions of the 4.1B or β8 genes.
DVDY_22513_sm_suppfig2.tif4487KSupp. Fig. S2. Intracerebral hemorrhage develops in β8 integrin single knockout and double knockouts that survive beyond E11.5. A–D: Images of E12.5 wild type (A), single knockout (B, C), and double knockout embryos (D) showing intracerebral hemorrhage in β8−/− mice (B) and β8−/−;4.1B−/− mice (D), but not in wild type or 4.1B−/− embryos (A, C). E–H: Images of wild type (E), single knockout (F, G), and double knockout (H) brains from newborn (P0) pups. Note the intracerebral hemorrhage in β8 integrin single knockouts (arrows in F) and double knockouts (arrows in H).
DVDY_22513_sm_suppfig3.tif4009KSupp. Fig. S3. Post-natal survival comparisons for wild type, single knockout, and double knockout mice. Kaplan-Meier survival plot showing wild type (n=20), β8−/− (n=16), 4.1B−/− (n= 20), and β8−/−;4.1B−/− mice (n=18).
DVDY_22513_sm_suppfig4.tif2549KSupp. Fig. S4. β8 Integrin protein is not expressed in the yolk sac, but is expressed in the heart at E10.5. A: Detergent-soluble lysates prepared from E10.5 yolk sacs were immunoblotted with anti-αv, anti-β8, and anti-4.1B rabbit polyclonal antibodies, revealing lack of detectable β8 integrin protein expression in embryonic yolk sacs. B: Detergent-soluble protein lysates prepared from microdissected E10.5 hearts were immunoblotted with anti-αv, anti-β8, and anti-Band 4.1B antibodies, revealing expression of all three proteins.
DVDY_22513_sm_suppfig5.tif3285KSupp. Fig. S5. Reduced expression of desmin in double knockout embryos. A–D: Sagittal sections cut at the level of the aortocopulmonary septum from wild type (A), β8−/− (B), 4.1B−/− (C), or β8−/−;4.1B−/− (D) embryos (E10.5) immunostained with anti-Desmin and shown at 100×. Note the reduced expression of desmin protein in double knockout embryos (D).
DVDY_22513_sm_suppfig6.tif3893KSupp. Fig. S6. Abnormal patterns of neurofilament expression in double knockout embryos. A–D: Images of trunk regions from E10.5 wild type (A), β8−/− (B), 4.1B−/− (C), or β8−/−;4.1B−/− (D) embryos. Note the normal neural crest patterning in wild type and single knockouts (white arrows in A–C). In contrast, note the abnormal patterning of neurofilament-expressing cells in the double knockout embryo (white arrows in D).

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