Rat Timeline

From Embryology

Introduction

Adult Rat

Rats (taxon- rattus) are readily available as inbred, outbred and mutant strains. They have been generally beaten as a model by their mice brethren, as the molecular tools that became available (stem cells, knockout genes, etc).


Rat embryos do have the advantage of being much larger than mouse embryos and easy to breed. Another advantage of rats is in vision development studies, as that retinal development continues postnatally (most vertebrate neurological systems are difficult to access during periods of development). Rat development is also generally 1 day behind that of mouse. (The table below gives details relating to the staging of rat development).


Rat Links: Introduction | Stages | Rat Timeline | Albino Rat Development (1915) | Category:Rat

Day 1

  • Standard Witschi Stage 1, day 1 , Size (mm) 0.07
  • Features: Cleavage and Blastula, 1 cell (in oviduct)

Day 2

  • Standard Witschi Stage 2, day 2 , Size (mm) 0.08 x 0.06
  • Features: Cleavage and Blastula, 2 cells (in oviduct)

Day 3

  • Standard Witschi Stage 3, day 3 , Size (mm) 0.08 x 0.05
  • Features: Cleavage and Blastula, 4 cells (in oviduct)


  • Standard Witschi Stage 4, day 3.5
  • Features: Cleavage and Blastula, 8-12 cells (in oviduct)


  • Standard Witschi Stage 5, day 3.25 , Size (mm) 0.08 x 0.04
  • Features: Cleavage and Blastula, Morula (in uterus)

Day 4

  • Standard Witschi Stage 6, day 4 , Size (mm) (0.08 x 0.03)
  • Features: Cleavage and Blastula, Early blastocyst (in uterus)

Day 5

  • Standard Witschi Stage 7, days 5 , Size (mm) (0.12 x 0.05)
  • Features: Cleavage and Blastula, Free blastocyst (in uterus)

Day 6

  • Standard Witschi Stage 8, days 6 , Size (mm) (0.28 x 0.07)
  • Features: Implanting blastocyst, with trophoblastic cone and inner cell mass; outgrowth of endoderm (hypoblast)
  • Standard Witschi Stage 9, days 6.75
  • Features: Diplotrophoblast; inner cell mass (pendant), covered with endoderm

Day 7

  • Standard Witschi Stage 10, days 7.25 , Size (mm) (0.3 x 0.1)
  • Features: Near complete implantation; pendant begins differentiation into embryonic and extra-embryonic parts
  • Standard Witschi Stage 11, days 7.75 , Size (mm) (0.5 x 0.1)
  • Features: Completion of implantation; primary amniotic cyst; ectoplacental cone

Day 8

  • Standard Witschi Stage 12, days 8.5 , Size (mm) (1.04 x 0.26)
  • Features: Connecting ectochorionic and amniotic cavities; rudiments of amniotic folds; primitive streak; start of 3rd layer formation; blastemas of heart and pericardium

Day 9

  • Standard Witschi Stage 13, days 9 , Size (mm) 1.0
  • Features: Presomite neurula; fusion of chorio-amniotic folds, chorio-amniotic stalk; neural plate; embryo bent dorsally; bud of allantoic stalk
  • Standard Witschi Stage 14, days 9.5 , Size (mm) 1.5
  • Features: Somites 1-4 (occipital); pendant with 3 cavities: ectochorionic cyst, exocoelom, and amniotic cavity; ectochorionic cyst collapsing; allantoic stalk projects into exocoelom; embryo bent dorsally

Day 10

  • Standard Witschi Stage 15, days 10 , Size (mm) 2
  • Features: Somites 5-12 (cervical); 1st visceral arch; ectochorionic cyst fused with ectoplacenta and with allantoic stalk; regression of peripheral (distal) yolk sac and trophectoderm (diplotrophoblast); Reichert's membrane; gonia in endoderm; embryo bent dorsally


  • Standard Witschi Stage 16, days 10.5 , Size (mm) 2.4
  • Features: Somites 13-20 (upper thoracic); 2 visceral arches; disc and yolk sac placentas; appendicular folds; embryo reverses, curves ventrally

Day 11

  • Standard Witschi Stage 17, days 11 , Size (mm) 3.3
  • Features: Somites 21-25 (lower thoracic); yolk stalk closes at level of 15th somite; primary gonia in mesentery; primitive streak disappears; tail bud becomes organized; arm and leg buds recognizable

Tail Bud Embryo


  • Standard Witschi Stage 18, days 11.5 , Size (mm) 3.8
  • Features: Somites 26-28 (upper lumbar); 3 visceral arches; arm buds recognizable


  • Standard Witschi Stage 19, days 11.75 , Size (mm) 4.2
  • Features: Somites 29-31 (lower lumbar); visceral arches I-IV; cervical folds; appendicular folds and buds


  • Standard Witschi Stage 20, days 11.875 , Size (mm) 5
  • Features: Somites 32-33 (upper sacral)

Day 12

  • Standard Witschi Stage 21, days 12 , Size (mm) 5.1
  • Features: Somites 34-35 (lower sacral); deep cervical sinuses


  • Standard Witschi Stage 22, days 12.125 , Size (mm) 5.2
  • Features: Somite 36 (1st caudal); olfactory pits


  • Standard Witschi Stage 23, days 12.25 , Size (mm) 5.6
  • Features: Somites 37-38 (caudal); start of umbilical herniation


  • Standard Witschi Stage 24, days 12.375 , Size (mm) 6
  • Features: Somites 39-40 (caudal)


  • Standard Witschi Stage 25, days 12.5 , Size (mm) 6.2
  • Features: Somites 41-42 (caudal); occipital somites dispersing; 4 visceral arches; deep cervical sinuses; arm buds at somite levels 8-14, about as high as long; leg buds at somite levels 28-31, smaller; body forms a spiral of about 11/2 turns, the left face and trunk applied to yolk sac, the right side turned toward placenta; tail and allantoic stalk rise to the placenta


  • Standard Witschi Stage 26 , Size (mm) 12.75 , Size (mm) 7
  • Features: Somites 43-45 (caudal); mandibular, maxillary, and frontonasal processes; cervical sinuses closing; mammary welts; differentiaion of handplates; arm buds vascularized, brachial nerves entering; beginning of umbilical hernia


Diaphragm - pleuroperitoneal fold (PPF) first becomes apparent at E 12.5 (approximately 6 mm) and grows rapidly over the next 36 hours[1]

Day 13

  • Standard Witschi Stage 27, days 13 , Size (mm) 8
  • Features: Somites 46-48 (caudal); prominent facial processes and clefts; nose-snout projecting; cervical sinuses closed; primordia of mammary glands; round handplates and footplates; larger umbilical hernia


  • Standard Witschi Stage 28, days 13.5 , Size (mm) 8.5
  • Features: Somites 49-51 (caudal); 1st visceral cleft transforms into external ear duct; precartilaginous condensations in handplates

Day 14

  • Standard Witschi Stage 29, days 14 , Size (mm) 9.5
  • Features: Somites 52-55 (caudal); auricular hillocks on visceral arches I and II


  • Standard Witschi Stage 30, days 14.5 , Size (mm) 10.5
  • Features: Somites 56-60 (caudal); body uncoils; mandibular precartilage; nearly round opening of external ear duct; pleuroperitoneal canal has become very narrow

Day 15

  • Standard Witschi Stage 31, days 15 , Size (mm) 12
  • Features: Somites 61-63 (caudal); facial clefts closed; pleuroperitoneal canal closed; complete diaphragm


  • Standard Witschi Stage 32, days 15.5 , Size (mm) 14.2
  • Features: Somite 64 (caudal); pinna turns forward; maximal size of umbilical hernia

Day 16

  • Standard Witschi Stage 33, days 16 , Size (mm) 15.5
  • Features: Somite 65 (usually this is last caudal); snout lifts off chest; last stage of metamorphosis

Day 17-18

  • Standard Witschi Stage 34, days 17-18 , Size (mm) 16-20
  • Features: 1st fetal stage: rapid growth of eyelids (eyes entirely covered at end of 18th day); palate complete; pinna covers ear duct; umbilical hernia withdraws


Day 19-22

  • Standard Witschi Stage 35, antenatal, days 19-22 , Size (mm) 20-40
  • Features: 2nd fetal stage: sealed eyelids; fetal membranes and placentas reach peak of development; tail grows to 10mm;
  • Neural System Development Pathways to the supraoptic nucleus from the brainstem and the main olfactory bulb - on the expected day of parturition, but before birth, projections from the organum vasculosum of the lamina terminalis to the supraoptic nucleus became significantly activated.[2]

Birth occurs (22nd day in rat, 19th day in mouse)

Postnatal

  • Standard Witschi Stage 35, postpartum
  • 1-16 post-partum , Size (mm) 40-1001
  • Features: After birth, fetus becomes a breathing and suckling nestling2; during 1st 16 days (22 to 38 days total age), eyelids remain sealed and external ear ducts plugged with periderm


  • Standard Witschi Stage 36, post-natal

17+ post-partum , Size (mm) 100+1

  • Features: Periderm seals of ears and eyelids vanish; active feeding begins within next 3 days and weaning after 1 week (total weaning age, 45-48 days for rats and mice)

Species Stages Comparison

The table below gives an approximate comparison of human, mouse and rat embryos based upon Carnegie staging.

Species Stage
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Human [3] Days 20 22 24 28 30 33 36 40 42 44 48 52 54 55 58
Mouse [4] Days 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16
Rat [5] Days 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5

References

  1. Robin D Clugston, Wei Zhang, John J Greer Early development of the primordial mammalian diaphragm and cellular mechanisms of nitrofen-induced congenital diaphragmatic hernia. Birth Defects Res. Part A Clin. Mol. Teratol.: 2010, 88(1);15-24 PubMed 19711422
  2. S L Meddle, G Leng, J R Selvarajah, R J Bicknell, J A Russell Direct pathways to the supraoptic nucleus from the brainstem and the main olfactory bulb are activated at parturition in the rat. Neuroscience: 2000, 101(4);1013-21 PubMed 11113350
  3. R O'Rahilly Early human development and the chief sources of information on staged human embryos. Eur. J. Obstet. Gynecol. Reprod. Biol.: 1979, 9(4);273-80 PubMed 400868
  4. The House Mouse: Atlas of Mouse Development by Theiler Springer-Verlag, NY (1972, 1989). | online book
  5. Witschi, E. (1962) Development: Rat. In: Growth Including Reproduction and Morphological Development. Altman, P. L. , and D. S. Dittmer, ed. Fed. Am. Soc. Exp. Biol., Washington DC, pp. 304-314.

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Cite this page: Hill, M.A. 2017 Embryology Rat Timeline. Retrieved November 23, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Rat_Timeline

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G