Staging Definitions

The Edinburgh Mouse Atlas:
Staging Criteria

Mouse embryos can be staged according to a variety of criteria, the most general of which are those described by Theiler in "The House Mouse: Atlas of Mouse Development" (Springer-Verlag, New York, 1989). Theiler's criteria are too broad to distinguish many of the important phases of early development and must therefore be supplemented by others, for example, cell number, somite number or those charcteristics used by Downs and Davies (1993) Development, 118, 1255. We have therefore combined these different criteria in the table¹ below which defines a new set of stages based on the numbered Theiler series, but with intermediate divisions indicated by non-integer stage numbers. Embryos of the same gestational age may differ in their stage of development. We have therefore included in the table an indication of the expected range of gestational ages (days of gestation, dpc) over which each developmental stage may be found. Different mouse strains develop at different rates and, in some cases show differences in the relative rates of development of different organs. Strictly, the stages recognised by Downs and Davies apply to outbred mice of the PO strain. The data in the remainder of the table below refer to embryos of crosses between F1 hybrid (C57BL X CBA) mice.

Each Theiler stage is linked (click on the number) to its corresponding diagram, with more details of the defining features for that stage. A brief text or pictorial index to the diagrams is also provided.

Theiler Stage	dpc (range)²	Somite No.³	Cell number	(C57BLxCBA)F1 mice⁴	PO mice⁵
1	0-0.9 (0 -2.5)		1	One-cell egg
2	1 (1 -2.5)		2-4	Dividing egg
3	2 (1-3.5)		4-16	Morula
4	3 (2-4)		16-40	Blastocyst, Inner cell mass apparent
5	4 (3-5.5)			Blastocyst (zona-free)
6	4.5 (4-5.5)			Attachment of blastocyst, primary endoderm covers blastocoelic surface of inner cell mass
7	5 (4.5-6)			Implantation and formation of egg cylinder Ectoplacental cone appears, enlarged epiblast, primary endoderm lines mural trophectoderm
8	6 (5-6.5)			Differentiation of egg cylinder. Implantation sites 2x3mm. Ectoplacental cone region invaded by maternal blood, Reichertís membrane and proamniotic cavity form
9	6.5 (6.25-7.25 )			Pre-streak (PS), advanced endometrial reaction, ectoplacental cone invaded by blood, extraembryonic ectoderm, embryonic axis visible,	PS
9a				Early streak (ES), gastrulation starts, first evidence of mesoderm	ES
10	7 (6.5-7.75)			Mid streak (MS), amniotic fold starts to form	MS
10a				Late streak, no bud (LSOB), exocoelom	LS
10b				Late streak, early bud (LSEB), allantoic bud first appears, node, amnion closing
11	7.5 (7.25-8)			Neural plate (NP), head process developing, amnion complete	OB
11a				Late neural plate (LNP), elongated allantoic bud	EB/ LB
11b				Early head fold (EHF)	EHF
11c				Late head fold (LHF), foregut invagination	LHF
12	8 (7.5-8.75 )	1-4		1-4 somites, allantois extends, 1st branchial arch, heart starts to form, foregut pocket visible, preotic sulcus (at 2-3 somite stage)
12a		5-7		5-7 somites, allantois contacts chorion at the end of TS12 Absent 2nd arch, >7 somites
13	8.5 (8-9.25)	8-12		Turning of the embryo, 1st branchial arch has maxillary and mandibular components, 2nd arch present Absent 3rd branchial arch
14	9 (8.5-9.75)	13-20		Formation & closure of ant. neuropore, otic pit indented but not closed, 3rd branchial arch visible Absent forelimb bud
15	9.5 (9-10.25)	21-29		Formation of post. neuropore, forelimb bud, forebrain vesicle subdivides Absent hindlimb bud, Rathke's pouch
16	10 (9.5-10.75)	30-34		Posterior neuropore closes, Formation of hindlimb & tail buds, lens plate, Rathke's pouch; the indented nasal processes start to form Absent thin & long tail
17	10.5 (10-11.25)	35-39		Deep lens indentation, adv. devel. of brain tube, tail elongates and thins, umbilical hernia starts to form Absent nasal pits
18	11 (10.5-11.25)	40-44		Closure of lens vesicle, nasal pits, cervical somites no longer visible Absent auditory hillocks, anterior footplate
19	11.5 (11-12.25)	45-47		Lens vesicle completely separated from the surface epithelium. Anterior, but no posterior, footplate. Auditory hillocks first visible Absent retinal pigmentation and sign of fingers
20	12 (11.5-13)	48-51		Earliest sign of fingers (splayed-out), posterior footplate apparent, retina pigmentation apparent, tongue well-defined, brain vesicles clear Absent 5 rows of whiskers, indented anterior footplate
21	13 (12.5-14)	52-55		Anterior footplate indented, elbow and wrist identifiable, 5 rows of whiskers, umbilical hernia now clearly apparent Absent hair follicles, fingers separate distally
22	14 (13.5-15)	56-~ 60		Fingers separate distally, only indentations between digits of the posterior footplate, long bones of limbs present, hair follicles in pectoral, pelvic and trunk regions Absent open eyelids, hair follicles in cephalic region
23	15			Fingers & Toes separate, hair follicles also in cephalic region but not at periphery of vibrissae, eyelids open Absent nail primordia, fingers 2-5 parallel
24	16			Reposition of umbilical hernia, eyelids closing, fingers 2-5 are parallel, nail primordia visible on toes Absent wrinkled skin, fingers & toes joined together
25	17			Skin is wrinkled, eyelids are closed,umbilical hernia is gone Absent ear extending over auditory meatus, long whiskers
26	18			Long whiskers, eyes barely visible through closed eyelids, ear covers auditory meatus
27	19			Newborn Mouse
28				Postnatal development

Bard, J.B.L., Kaufman, M.H., Dubreuil, C., Brune. R.M., Burger, A., Baldock, R.A., Davidson, D.R. (1998). An internet-accessible database of mouse developmental anatomy based on a systematic nomenclature. Mechanisms of Development, in press.
Days post conception, with the morning after the vaginal plug is found being designated 0.5 dpc (or E0.5). For detailed discussion see Kaufman (1994). The Atlas of Mouse Development (2nd printing), pp. 515-525. London: Academic Press.
The figure given refers to the number of the most caudal somite. No account is taken of somites partitioning into dermomyotomes and sclerotomes, nor of their subsequent differentiation.
Adapted from Theiler (1989) [The House Mouse: Atlas of Embryonic Development. New York: Springer-Verlag] and Kaufman (1994); detailed staging for Theiler stages 9-12 courtesy of K. Lawson [personal communication].
From Downes, K.M. and Davies, T. (1993). Staging of gastrulating mouse embryos by morphological landmarks in the dissecting microscope. Development, 118, 1255 - 1266.

Comments

General comment on timing (dpc): In judging the lower and upper ranges of dpc equivalent to a particular Theiler stage, we have generally followed Theiler's book and, in most cases, have given a wider range than Theiler, because the numbers of embryos he cites are small. We have given a larger range at the maximum than the minimum because, in general, embryos are more likely to be retarded by their environment or genetic constitution than made to proceed more quickly through development. In most cases, however, the resulting dpc range is an estimate that is consistent with the results of Theiler, but not based on additional evidence.

Comment on somite numbers: The range of somite numbers for each stage is given only as a guide to what might be expected of typical embryos. As can be seen from Theiler (1989)⁴ the true range can be much wider. Therefore, for all stages after TS12, the somite number should not be taken as a reliable global indicator of the overall embryo stage.

Richard Baldock, Jonathan Bard, Duncan Davidson and Kirstie Lawson, 7th May 1998

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Document last modified:Friday, 25-Oct-2002 14:11:27 BST