Probe:	Flk-1 cDNA3
Probe preparation:	Antisense labelled with digoxigenin RNA
Visualized with:	Alkaline phosphatase

Structure	Level	Pattern	Image	Note
TS9: conceptus	Absent

Structure	Level	Pattern	Image	Note
TS10: embryo mesoderm	Present	Spotted	2A	Expression was detected in a wedge of proximal-lateral embryonic mesoderm that extended from the anteriormost part of the embryo back to the posterior primitive streak.
TS10: extraembryonic mesoderm	Present	Spotted	2A
TS10: allantois	Weak		2A
TS10: ectoplacental cone	Absent		2A
TS10: embryo ectoderm	Absent		2A
TS10: embryo endoderm	Absent		2A

Structure	Level	Pattern	Image	Note
TS11: embryo	Present		2B

Structure	Level	Pattern	Image	Note
TS11: allantois	Strong		2C
TS11: blood island	Strong		2C
TS11: heart	Strong		2C	Strong expression was seen within the endocardial tubes.
TS11: embryo mesoderm	Strong	Regionally restricted	2C	Expression was strong in a band of embryonic mesodermal cells lateral to the primitive streak.

Structure	Level	Pattern	Image	Note
TS10: conceptus	Present		2D right

Structure	Level	Pattern	Image	Note
TS11: heart	Present		2E	Labelled cells curve towards the midline to form the early endocardial tubes.

Structure	Level	Pattern	Image	Note
TS12: primitive heart tube endocardial tube	Absent			Transcripts were not readily detectable by whole-mount in situ hybridization in the endocardium at this stage.
TS12: dorsal aorta	Present	Regionally restricted		Labelled cells were observed in the forming dorsal aorta, dorsal and posterior to the endocardial tubes.

Structure	Level	Pattern	Image	Note
TS12: primitive heart tube	Weak		3A
TS12: yolk sac	Strong		3A
TS12: allantois	Very strong	Regionally restricted	3A	Highest levels of expression were found in the allantoic stalk.
TS12: vitelline vein	Present		3A

Structure	Level	Pattern	Image	Note
TS13: extraembryonic component	Very strong		3B	Throughout somitogenesis, the allantois and the allantoic stalk expressed the highest levels of flk-1.
TS13: head mesenchyme	Present		3B
TS13: left vitelline vein extraembryonic part	Present		3B
TS13: right vitelline vein extraembryonic part	Present		3B
TS13: heart	Present		3B	flk-1 was detected in the endocardium.
TS13: dorsal aorta	Present		3B	Expression was present throughout the length of the dorsal aorta.

Structure	Level	Pattern	Image	Note
TS14: extraembryonic component	Very strong		3C	Throughout somitogenesis, the allantois and the allantoic stalk expressed the highest levels of flk-1.
TS14: dorsal aorta	Present	Regionally restricted	3C	Labelled cells were clustered in clumps adjacent to the anteriormost somites.
TS14: branchial arch	Present	Spotted	3C
TS14: head mesenchyme	Present	Spotted	3C
TS14: ear	Present		3C	Transcripts could be detected surrounding the otic vesicle.
TS14: heart	Strong	Regionally restricted	3C	flk-1 continued to be expressed in the endocardium.

Structure	Level	Pattern	Image	Note
TS15: extraembryonic component	Very strong		3D	Throughout somitogenesis, the allantois and the allantoic stalk expressed the highest levels of flk-1.
TS15: left vitelline vein embryonic part	Present		3D
TS15: right vitelline vein embryonic part	Present		3D
TS15: vitelline artery	Present		3D
TS15: embryo	Present	Regionally restricted	3D	Expression occurred in the vicinity of the future forelimb bud.
TS15: cardiovascular system	Present	Regionally restricted	3D	Long vessels within the head, within the branchial arches, the intersegmental vessels, and the posterior cardinal veins were all clearly labelled.