Antibody:	Anti-Sox9 (AB5535)
Detection system:	Secondary antibody coupled to Alexa Fluor 488

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		4A' , 4A
TS22: sternum	Present		4A' , 4A	At this anterior-most point, the presternum contained: paired dorsal elements that contact the clavicles; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		4N' , 4N	Similar as in the control.
TS22: sternum	Present		4N' , 4N	Similar as in the control.

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		4B' , 4B
TS22: sternum	Present		4B' , 4B	At this anterior-most point, the presternum contained: paired dorsal elements that contact the clavicles; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		4O , 4O'	Similar as in the control.
TS22: sternum	Present		4O , 4O'	Similar as in the control.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4C' , 4C	At the axial level of the intercostoclavicular, the ventral paired elements are larger and bar-shaped with increased expression.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4P' , 4P	Similar as in the control.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4D , 4D'	At the axial level of the intercostoclavicular, the ventral paired elements are larger and bar-shaped with increased expression.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4Q , 4Q'	Similar as in the control.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4E , 4E'	Lateral ends of the ventral bar-shaped elements curved dorsally and the medial portion formed a bulge. The paired dorsal elements remained rounded and composed of a less dense mesenchyme with lower expression compared to the ventral element.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4R , 4R'	Ventral paired elements were noticeably smaller than those of littermate controls.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4F' , 4F	Lateral ends of the ventral bar-shaped elements curved dorsally and the medial portion formed a bulge. The paired dorsal elements remained rounded and composed of a less dense mesenchyme with lower expression compared to the ventral element.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4S , 4S'	Ventral paired elements were noticeably smaller than those of littermate controls.

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4G , 4G'
TS22: sternum	Present		4G' , 4G	First contact of T1 with the sternum was seen.

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4T' , 4T
TS22: sternum	Present		4T , 4T'	Rib 1 appeared to make contact with the rounded, medial region.

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4H' , 4H
TS22: sternum	Present		4H' , 4H

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4U , 4U'	Rib 1 appeared to make contact with the rounded, medial region.
TS22: T1 rib cartilage condensation	Present		4U' , 4U

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4I' , 4I
TS22: sternum	Present		4I' , 4I

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4V' , 4V
TS22: sternum	Present		4V' , 4V	Mutant sternum remained misshapen.

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4J' , 4J
TS22: sternum	Present		4J' , 4J	The second attachment of T1 was seen, where the sternum shifted to a more rounded morphology and no longer contained laterally extended bars.

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		4W' , 4W
TS22: sternum	Present		4W' , 4W	Mutant sternum remained misshapen.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4K , 4K'	At the first intercostal region, the sternum was rounded dorsally and elongated in the dorso-ventral plane relative to more anterior regions.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4X' , 4X	Similar as in the control.

Structure	Level	Pattern	Image	Note
TS22: T2 rib cartilage condensation	Present		4L' , 4L
TS22: sternum	Present		4L' , 4L	Paired, fusing sternal bars were seen at the point of rib 2 attachment.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4Y' , 4Y	Similar as in the control.
TS22: T2 rib cartilage condensation	Present		4Y , 4Y'

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4M , 4M'	Paired, fusing sternal bars were seen at the point of rib 3 attachment.
TS22: T3 rib cartilage condensation	Present		4M , 4M'

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		4Z , 4Z'	Similar as in the control.
TS22: T3 rib cartilage condensation	Present		4Z , 4Z'

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		5A , 5A'

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		5B' , 5B
TS22: sternum	Present		5B' , 5B

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		5C' , 5C

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		5D' , 5D

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		5E , 5E'

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		5F , 5F'

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		5G , 5G'
TS22: sternum	Present		5G , 5G'

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		5H , 5H'
TS22: sternum	Present		5H , 5H'

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		5I' , 5I
TS22: sternum	Present		5I' , 5I

Structure	Level	Pattern	Image	Note
TS22: T1 rib cartilage condensation	Present		5J , 5J'
TS22: sternum	Present		5J , 5J'

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		5K , 5K'

Structure	Level	Pattern	Image	Note
TS22: T2 rib cartilage condensation	Present		5L , 5L'
TS22: sternum	Present		5L , 5L'

Structure	Level	Pattern	Image	Note
TS22: T3 rib cartilage condensation	Present		5M' , 5M
TS22: sternum	Present		5M' , 5M

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7A" , 7A	Expressed in the clavicles and presternum.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7B , 7B"	Expressed in the clavicles and presternum. Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7C" , 7C	Expressed in the clavicles and presternum. Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7D , 7D"	Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7E , 7E"	Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7F" , 7F	Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative. Rib 1 contacted the paired ventral elements that have not yet fused or fully condensed into the bar shape observed later.
TS20: T1 rib pre-cartilage condensation	Present		7F , 7F"	Meox1-Cre lineage/RFP-positive.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7G , 7G"	Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative. More posteriorly, the site of rib 1 attachment transitioned to the plow-shaped, dorso-ventrally elongated morphology characteristic of the sternal bars.
TS20: T1 rib pre-cartilage condensation	Present		7G , 7G"	Meox1-Cre lineage/RFP-positive.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	7H , 7H"	Presternum expression was seen in separate dorsal and ventral presternal elements, which were Meox1-Cre lineage/RFP-negative. Rib 2 similarly contacted the unfused sternal bars, and the bars were connected by a stream of Sox9-expressing cells.
TS20: T2 rib pre-cartilage condensation	Present		7H" , 7H	Meox1-Cre lineage/RFP-positive.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	8A , 8A"	Expressed in a broad lateral plate mesoderm-derived domain (Prrx1-Cre lineage/RFP+) around the midline, in the area that will form the clavicles and presternum. The positive mesenchyme cannot be resolved as separate dorsal and ventral domains, as it can at E12.5.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	8B , 8B"	Expressed in a broad lateral plate mesoderm-derived domain (Prrx1-Cre lineage/RFP+) around the midline, in the area that will form the clavicles and presternum. The positive mesenchyme cannot be resolved as separate dorsal and ventral domains, as it can at E12.5.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	8C , 8C"	Expressed in the presternum, with a stream of cells across the midline.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	8D" , 8D	Expressed in the presternum, with a stream of cells across the midline.

Structure	Level	Pattern	Image	Note
TS20: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	8E" , 8E	Expressed in the sternal bars appeared as a Sox9-positive triangle of cells in contact with the rib, with a stream of cells reaching across the midline.

Structure	Level	Pattern	Image	Note
TS22: clavicle cartilage condensation	Present		S2A' , S2A"' , S2A	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		S2C' , S2C , S2C"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in the dorsal and ventral elements of the presternum.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		S2E , S2E"' , S2E'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in the dorsal and ventral elements of the presternum.

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		S2G' , S2G , S2G"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in the dorsal and ventral elements of the presternum.
TS22: T1 rib cartilage condensation	Present		S2G' , S2G , S2G"'

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		S2I' , S2I , S2I"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in the dorsal and ventral elements of the presternum.
TS22: T1 rib cartilage condensation	Present		S2I"' , S2I' , S2I

Structure	Level	Pattern	Image	Note
TS22: sternum	Present		S2K' , S2K"' , S2K	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in the mesosternum.
TS22: T2 rib cartilage condensation	Present		S2K"' , S2K , S2K'

Structure	Level	Pattern	Image	Note
TS21: clavicle pre-cartilage condensation	Present		S4A' , S4A
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4A' , S4A	Expressed in the presternum, which contained: paired dorsal elements that contact the clavicles at a lower level; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4B , S4B'	Expressed in the presternum, which contained: paired dorsal elements that contact the clavicles at a lower level; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.
TS21: clavicle pre-cartilage condensation	Present		S4B , S4B'

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4C , S4C'	Expressed in the presternum, which contained: paired dorsal elements that contact the clavicles at a lower level; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.
TS21: trunk mesenchyme	Present	Regionally restricted	S4C , S4C'	Expressed in the ventral-most mesenchyme, which articulates with pectoral muscles.

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4D , S4D'	Expressed in the presternum, which contained: paired dorsal elements that contact the clavicles at a lower level; separate paired elements that lie ventral to the clavicle, and a ventral-midline element where pectoral muscle attachment occurs.

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4E , S4E'	Expressed in the presternum. The ventral paired elements were larger and bar-shaped with increased expression and incomplete fusion.

Structure	Level	Pattern	Image	Note
TS21: T1 rib cartilage condensation	Present		S4F , S4F'
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4F , S4F'	Expressed in the presternum. Rib 1 appeared to make contact with the rounded, medial region. Sternal bar fusion was also incomplete.

Structure	Level	Pattern	Image	Note
TS21: T1 rib cartilage condensation	Present		S4G' , S4G
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4G , S4G'	Expressed in the presternum. Rib 1 appeared to make contact with the rounded, medial region. Sternal bar fusion was also incomplete, with a loose collection of Sox9-expressing cells extending between them.

Structure	Level	Pattern	Image	Note
TS21: T1 rib cartilage condensation	Present		S4H' , S4H
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4H , S4H'	Expressed in the presternum. Rib 1 appeared to make contact with the rounded, medial region. Sternal bar fusion was also incomplete, with a loose collection of Sox9-expressing cells extending between them.

Structure	Level	Pattern	Image	Note
TS21: T1 rib cartilage condensation	Present		S4I' , S4I
TS21: T2 rib cartilage condensation	Present		S4I' , S4I
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4I' , S4I	Expressed in the presternum. Paired, unfused sternal bars were seen at the point of rib attachment, connected by a stream of Sox9-positive cells.

Structure	Level	Pattern	Image	Note
TS21: T3 rib cartilage condensation	Present		S4J , S4J'
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4J , S4J'	Expressed in the presternum. Paired, unfused sternal bars were seen at the point of rib attachment, connected by a stream of Sox9-positive cells.

Structure	Level	Pattern	Image	Note
TS21: clavicle pre-cartilage condensation	Present		S4K , S4K' , S4K"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4K' , S4K"' , S4K	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in presternum.

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4M , S4M' , S4M"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in presternum.

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4O , S4O' , S4O"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in presternum.
TS21: T1 rib cartilage condensation	Present		S4O"' , S4O' , S4O	Not co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).

Structure	Level	Pattern	Image	Note
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4Q"' , S4Q' , S4Q	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in presternum.
TS21: T1 rib cartilage condensation	Present		S4Q"' , S4Q' , S4Q	Not co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).

Structure	Level	Pattern	Image	Note
TS21: T1 rib cartilage condensation	Present		S4S"' , S4S' , S4S	Not co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).
TS21: T2 rib cartilage condensation	Present		S4S"' , S4S' , S4S	Not co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage).
TS21: pectoral-thoracic pre-cartilage condensation	Present	Regionally restricted	S4S' , S4S , S4S"'	Co-expressed with Prrx1 lineage cells (lateral plate mesoderm lineage) in presternum.