TS 1(0-2.5)

TS 2(1-2.5)

TS 3(1-3.5)

TS 4(2-4)

TS 5(3-5.5)

TS 6(4-5.5)

TS 7(4.5-6)

TS 8(5-6.5)

TS 9(6.25-7.25)

11

21

32

43

54

64.5

75

86

96.5

107

117.5

128

138.5

149

159.5

1610

1710.5

1811

1911.5

2012

2113

2214

2315

2416

2517

2618

2719

Theiler Stagedpc

One-cell egg Dividing egg2-4 cells

Morula4-16 cells

Blastocyst, inner cell mass apparent16-40 cells

Blastocyst (zona-free)

Attachment of blastocyst, primary endoderm covers blastocoelic surface of inner cell mass

Implantation and formation of egg cylinder. Ectoplacental coneappears, enlarged epiblast, primary endoderm lines mural trophectoderm

Differentiation of egg cylinder. Implantation sites 2x3mm.Ectoplacental cone region invaded by maternal blood, Reichertís membrane and proamniotic cavity form

First sign of radial asymmetry. a Pre-streak (PS), advanced endometrial reaction, ectoplacental coneinvaded by blood, extraembryonic ectoderm, embryonic axis visible. b Early streak (ES), gastrulation starts, first evidence of mesoderm.

Figures represent development of F1 hybrid (C57BL X CBA) mice. Descriptions of embryos at TS9 – 11 based on Downs & Davies, 1993, and apply to outbred mice of the PO strain. Numbers in parentheses under Theiler stages represent approximate dpc range. Relative sizes of illustrations not to scale. The cartoons are intended as a illustrative guide only.

a

b

Theiler Staging Criteria for Mouse Embryo DevelopmentFor full descriptions of Theiler staging and mouse anatomy visit http://genex.hgu.mrc.ac.uk/Atlas/intro.html

TS 10(6.5-7.75)

TS 11(7.25-8)

TS 12(7.5-8.75)

TS 13(8-9.25)

TS 14(8.5-9.75)

TS 15(9-10.25)

TS 16(9.5-10.75)

TS 17(10-11.25)

TS 18(10.5-11.25)

11

21

32

43

54

64.5

75

86

96.5

107

117.5

128

138.5

149

159.5

1610

1710.5

1811

1911.5

2012

2113

2214

2315

2416

2517

2618

2719

Theiler Stagedpc

a Mid streak (MS), amniotic fold starts to form.b Late streak, no bud (LSOB), exocoelom.c Late streak, early bud (LSEB), allantoic bud first appears, node, amnion closing

a Neural plate (NP), head process developing, amnion completeb Late neural plate (LNP), elongated allantoic budc Early head fold (EHF)d Late head fold (LHF), foregut invagination

First appearance of somites.1-4 somites, allantois extends, 1st branchial arch, heart starts to form, foregut pocket visible, preotic sulcus (at 2-3 somite stage).5-7 somites, allantois contacts chorion at the end of TS12Absent 2nd arch, >7 somites

Turning of the embryo, 1st branchial arch has maxillary and mandibular components, 2nd arch present8-12 somites.Absent 3rd branchial arch

Formation & closure of ant. neuropore, otic pit indented but not closed, 3rd branchial arch visible13-20 somites.Absent forelimb bud

Formation of post. neuropore, forelimb bud, forebrain vesicle subdivides21-29 somites.Absent hindlimb bud, Rathke's pouch

Posterior neuropore closes, Formation of hindlimb & tail buds, lens plate, Rathke's pouch; the indented nasal processes start to form30-34 somites.Absent thin & long tail

Deep lens indentation, adv. devel. of brain tube, tail elongates and thins, umbilical hernia starts to form35-39 somites.Absent nasal pits

Closure of lens vesicle, nasal pits, cervical somites no longer visible40-44 somites.Absent auditory hillocks, anterior footplate

a

b

a

b

c c

d

Theiler Staging Criteria for Mouse Embryo DevelopmentFor full descriptions of Theiler staging and mouse anatomy visit http://genex.hgu.mrc.ac.uk/Atlas/intro.html

TS 19(11-12.25)

TS 20(11.5-13)

TS 21(12.5-14)

TS 22(13.5-15)

TS 23 TS 24 TS 25 TS 26 TS 27

11

21

32

43

54

64.5

75

86

96.5

107

117.5

128

138.5

149

159.5

1610

1710.5

1811

1911.5

2012

2113

2214

2315

2416

2517

2618

2719

Theiler Stagedpc

Lens vesicle completely separated from the surface epithelium. Anterior, but no posterior, footplate. Auditory hillocks first visible45-47 somites.Absent retinal pigmentation and sign of fingers

Earliest sign of fingers (splayed-out), posterior footplate apparent, retina pigmentation apparent, tongue well-defined, brain vesicles clear48-51 somites.Absent 5 rows of whiskers, indented anterior footplate

Anterior footplate indented, elbow and wrist identifiable, 5 rows of whiskers, umbilical hernia now clearly apparent52-55 somites.Absent hair follicles, fingers separate distally

Fingers separate distally, only indentations between digits of the posterior footplate, long bones of limbs present, hair follicles in pectoral, pelvic and trunk region56-~60 somites.Absent open eyelids, hair follicles in cephalic region

Fingers & toes separate, hair follicles also in cephalic region but not at periphery of vibrissae, eyelids open. Absent nail primordia, fingers 2-5 parallel

Repositioning of umbilical hernia, eyelids closing, fingers 2-5 are parallel, nail primordia visible on toes.Absent wrinkled skin, fingers & toes joined together

Skin is wrinkled, eyelids are closed,umbilical hernia is gone. Absent ear extending over auditory meatus, long whiskers

Long whiskers, eyes barely visible through closed eyelids, ear covers auditory meatus

Newborn mouse

Theiler Staging Criteria for Mouse Embryo DevelopmentFor full descriptions of Theiler staging and mouse anatomy visit http://genex.hgu.mrc.ac.uk/Atlas/intro.html