Antibody:	anti-p21 (sc-6246)
Detection system:	Biotinylated secondary antibody/[Strept]avidin coupled to horseradish peroxidase

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial groove ectoderm	Present	Regionally restricted	2A	Along branchial clefts, groups of expressing cells are arranged in a roughly alternating pattern with Mki67-expressing proliferating cells

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial groove ectoderm	Present	Regionally restricted	2C	Along branchial clefts, groups of expressing cells are arranged in a roughly alternating pattern with Mki67-expressing proliferating cells

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial arch mesenchyme	Present	Single cells	2E	In the mesenchymal core of branchial arches, single expressing cells of unknown identity are seen.

Structure	Level	Pattern	Image	Note
TS17: geniculate placode	Present	Regionally restricted	3C	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 1.
TS17: 1st branchial pouch endoderm	Present	Regionally restricted	3C	Senescent cells located predominantly in rostral walls of pharyngeal pouches.

Structure	Level	Pattern	Image	Note
TS15: geniculate placode	Present	Regionally restricted	3D	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 1. Authors report almost simultaneous onset of senescence and apoptosis around E9.5.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	3E	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 2.
TS17: 2nd branchial pouch endoderm	Present	Regionally restricted	3E	Senescent cells located predominantly in rostral walls of pharyngeal pouches.

Structure	Level	Pattern	Image	Note
TS15: petrosal placode	Present	Regionally restricted	3F	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 2. Authors report clear lead in senescence only in epibranchial placode 1.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	3G	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 2. Authors report clear lead in senescence only in epibranchial placode 1.

Structure	Level	Pattern	Image	Note
TS15: nodose placode	Present	Regionally restricted	3H	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 3. Authors report almost simultaneous onset of senescence and apoptosis around E9.5.

Structure	Level	Pattern	Image	Note
TS17: nodose placode	Present	Regionally restricted	3I	Expression in senescent cells in in dorsal and ventral parts of epibranchial placode 3. Authors report almost simultaneous onset of senescence and apoptosis around E9.5.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	6E p21	Senescent cells mainly concentrated at periphery. Groups of senescent cells in weakly invaginating epibranchial placode 2 predominantly where density of proliferating cells is particularly low.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	6F p21	Senescent cells mainly concentrated at periphery. Groups of senescent cells in weakly invaginating epibranchial placode 2 predominantly where density of proliferating cells is particularly low.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	6G p21	Senescent cells mainly concentrated at periphery. Groups of senescent cells in weakly invaginating epibranchial placode 2 predominantly where density of proliferating cells is particularly low.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	6H p21	Senescent cells mainly concentrated at periphery. Groups of senescent cells in weakly invaginating epibranchial placode 2 predominantly where density of proliferating cells is particularly low.

Structure	Level	Pattern	Image	Note
TS17: petrosal placode	Present	Regionally restricted	10G	Expression at transition from placode tissue to surface ectoderm. Expression virtually absent among densely clustered Neurog2-expressing premigratory neuroblasts.

Structure	Level	Pattern	Image	Note
TS15: 2nd branchial pouch endoderm	Present	Regionally restricted	12A , 12A'	Between E9.5 and E10.5, stark contrast between steadily increasing number of expressing endodermal cells in rostral walls, and virtually complete absence of expression in caudal walls of pharyngeal pouch 2.

Structure	Level	Pattern	Image	Note
TS16: 2nd branchial pouch endoderm	Present	Regionally restricted	12B	Between E9.5 and E10.5, stark contrast between steadily increasing number of expressing endodermal cells in rostral walls, and virtually complete absence of expression in caudal walls of pharyngeal pouch 2.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial pouch endoderm	Present	Regionally restricted	12C' , 12C	Between E9.5 and E10.5, stark contrast between steadily increasing number of expressing endodermal cells in rostral walls, and virtually complete absence of expression in caudal walls of pharyngeal pouch 2.

Structure	Level	Pattern	Image	Note
TS15: 3rd branchial pouch endoderm	Present	Regionally restricted	12D	Expressing cells in pharyngeal pouch 3 initially appear dorsally and lateral also ventrally.

Structure	Level	Pattern	Image	Note
TS17: 3rd branchial pouch endoderm	Present	Regionally restricted	12E	pExpressing cells in pharyngeal pouch 3 initially appear dorsally and lateral also ventrally.

Structure	Level	Pattern	Image	Note
TS17: 3rd branchial pouch endoderm	Present	Regionally restricted	12F	From E10.5 onwards, expression in senescent cells in rostral, caudal, dorsal and ventral walls of pharyngeal pouch 3.

Structure	Level	Pattern	Image	Note
TS18: 3rd branchial pouch endoderm	Present	Regionally restricted	12G	From E10.5 onwards, expression in senescent cells in rostral, caudal, dorsal and ventral walls of pharyngeal pouch 3.

Structure	Level	Pattern	Image	Note
TS17: 1st branchial groove ectoderm	Present	Regionally restricted	15A	Expression in branchial surface ectoderm as well as pharyngeal endoderm.
TS17: 1st branchial pouch endoderm	Present	Regionally restricted	15A	Expression in branchial surface ectoderm as well as pharyngeal endoderm.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial groove ectoderm	Present	Regionally restricted	15C	Expression in branchial surface ectoderm as well as pharyngeal endoderm.
TS17: 2nd branchial pouch endoderm	Present	Regionally restricted	15C	Expression in branchial surface ectoderm as well as pharyngeal endoderm.

Structure	Level	Pattern	Image	Note
TS18: 1st branchial groove ectoderm	Present	Regionally restricted	15E	Expression in branchial surface ectoderm as well as pharyngeal endoderm.
TS18: 1st branchial pouch endoderm	Present	Regionally restricted	15E	Expression in branchial surface ectoderm as well as pharyngeal endoderm.

Structure	Level	Pattern	Image	Note
TS18: 2nd branchial pouch endoderm	Present	Regionally restricted	15G	Expression in pharyngeal endoderm.

Structure	Level	Pattern	Image	Note
TS14: 2nd branchial pouch endoderm	Absent		16A p21	Rostral walls of pharyngeal pouches typically lack expression.

Structure	Level	Pattern	Image	Note
TS15: 2nd branchial pouch endoderm	Present	Regionally restricted	16B p21	Rostral focus of expressing endodermal cells is established on E9.5. Salt-and-pepper pattern with first rostral expression within Mki67-expressing clusters.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial pouch endoderm	Strong	Clusters	16C p21	Rostral focus of expressing endodermal cells increases in size and intensity over time. Clusters of strongly expressing endoderm cells, clearly distinguised from clusters of Mki67-expressing cells.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial pouch endoderm	Strong	Clusters	16D p21	Rostral focus of expressing endodermal cells increases in size and intensity over time. Clusters of strongly expressing endoderm cells, clearly distinguised from clusters of Mki67-expressing cells.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial pouch endoderm	Strong	Clusters	16E p21	Rostral focus of expressing endodermal cells increases in size and intensity over time. Clusters of strongly expressing endoderm cells, clearly distinguised from clusters of Mki67-expressing cells.

Structure	Level	Pattern	Image	Note
TS17: 2nd branchial pouch endoderm	Strong	Clusters	16F p21	Rostral focus of expressing endodermal cells increases in size and intensity over time. Clusters of strongly expressing endoderm cells, clearly distinguised from clusters of Mki67-expressing cells.