Talk:Kubke Lab:Research/CND/Records/MH008

Please discuss the accuracy of my annotations, cheers. --Reuben Cutfield 21:12, 8 February 2011 (EST)

Please provide references and the criteria you used to identify the structures --MF Kubke 22:32, 8 February 2011 (EST)

This is a photograph of a section from MH008. I was looking through several books in the library and then a few websites to help. Fact is I found nothing that specifically had what I was looking for. One website (click here) had cross sections but in a different plane and I had to interpret the sections using the plane our embryo was cut with. I also looked at photos of embryos I had taken such as the one in MH007 to imagine what structures would be included in each section and what the exact plane of our cutting was. Another website I found useful was this one(

(Note: Fixed the link)). Not sure what you are asking in terms of criteria. I was just comparing the morphology of different structures to those in diagrams whilst thinking about the angle we cut at. I think it will be easier to complete the labeling of all my section once I have confirmation that I am seeing what I think I am seeing and have a few structures labeled in concrete. Thanks.--Reuben Cutfield 01:59, 9 February 2011 (EST)

Both links you provide link to the same webpage. What I mean by criterion is on what basis are you deciding what each structure you identify. When you say that you compare the morphology, you need to be more specific. For example, why are you deciding that what you have labelled as the optic cup is the optic cup? What other structure could it be, how would you differentiate between those, is the morphology you see consistent with what you would expect for the age of the embryo you are looking at, etc.

Explanations for annotations:

The eye originates in the wall of the diencephalon (Carlson, 1999). I think I have labeled the optic cup incorrectly. Accoridng to Carlson, 1999 the optic vesicles become the optic cup following induction of the lens. In this section I think I can only see the pigment and sensory layers of the optic vesicle. There is a SEM photogprah on pg 264 and a diagram on pg 263 in Carlson, 1999 which shows the distinctive continuous double layered morphology of the developing optic vesicle.

(Note: how do you know that what you are seeing is the sensory and pigment layers? What histological criteria are you using? If I were to tell you that that was the auditory vesicle, what arguments would you use against that?--MF Kubke 18:30, 10 February 2011 (EST))

• The auditory vesicles are located on the dorsal side of the embryo lateral to the myelencephalon. The structures in question are located on the ventral side of the embryo.
• The auditory vesicles are located lateral to and nearby the notochord. These structures are on the opposite side of the embryo to the notochord.
• The auditory vesicles are single layered whilst the optic cups are double layered. The structures labeled as optic cups are clearly double layered.

• The optic cup has two layers which are continuous with each other. The outer layer of the cup (medialmost layer) is thinner and is the pigment layer. The innermost layer becomes thicker than the outer layer at the point of contact between the two layers. The inner layer remains about three times thicker than the outer layer and is the sensory layer. (Carlson, 1999 pg 263 fig. 12.1). The sensory layers has a striated pattern of fibres which is reflected in the staining where you can see parallel lines in the tissue radiating outwards from the cup. The inner layer is more congruently stained.

The diencephalon is recognizable by the prominent lateral optic vesicles extending from its walls (Carlson, 1999). So a cross section through the diencephalon should show symmetrical optic vesicles on either side.

(Note: I dont see what you call the optic vesicles as being attached to the diencephalon on this image --MF Kubke 18:30, 10 February 2011 (EST))

• The optic cups are not attached to the diencephalon in all sections through the optic cups. The optic stalk is thinner than the optic cups and so there will be sections where they appear as separate structures.

The structure labeled as the optic cup cannot be the optic cup since the primary optic vesicle forms as an outgrowth of the diencephalon (Carlson, 1999). This structure is not continuous with the large cavity in the section (labeled as diencephalon), there is no optic stalk-like structure connecting the cavity to the strucute that can be seen.Also there does not appear to be a structure forming through invagination of the head ectoderm within the 'optic cup' i.e. the structure does not appear to contain the lens. The section does not include the lens however the lens is smaller than the cup and so in some sections you will see only the cup and not the lens as well.

• After looking at the sections caudal and rostral to this one you can see a circular single-walled structure appear in the centre of the double layered 'optic cup' (suspected as the lens).
• One of my drawings includes a stalk-like structure attached between the 'optic cup' and the 'diencephalon' but I will need to relook at the slides to see if I can more definitively locate the stalk.

Due to the cephalic and cervical flexures the developing brain doubles back on itself and in certain cross sections you wll be able to see the brain appear twice in the section.

The dorsal side of the mylencephalon is thin compared to the walls of the diencephalon, telencephalon, metencephalon and mesencephalon. Within the structure labeled as myelencephalon you can see the dorsal wall is thinned. See here for diagram.

I looked at our atlas and according to Hamburger and Hamilton (1951) a stage 19 chick embryo has 37-40 somites. Looking at the O'RAHILLY (1963) paper describing the human embryo's optic vesicle I made the following inferences from human embryos at the 30+ somites and 5-7mm 'stages':

• The otic cup has developed into the otic vesicle.
• The remains of the otic stalk have most likely wont be seen in sections.
• It has become enclosed by its basement membrane if the stalk is not present.
• The otic vesicle has a single membrane coverings as opposed to the optic vesicle which has the lens and surrounding membrane.
• The vesicle appears circular in sections (From Plate 2).
• The optic vesicle appears in sections as a cavity with few nuclei and cell remnants visible, fewer than the optic vesicle.

The otic vesicle can be found in sections at the level of the mylencephalon (http://www.uoguelph.ca/zoology/devobio/72hrchck/72ck1.htm)

References:

Bruce Carlson (1999). Human Embryology and Developmental Biology, 2nd Edition, Mosby Inc, Missouri.
http://www.lawrence.edu/dept/biology/embryoatlas/
http://www.uoguelph.ca/zoology/devobio/72hrchck/72ck1.htm
http://www.developmentalbiology.net/node/58/
RONAN O'RAHILLY, The Early Development of the Otic Vesicle in Staged Human Embryos, J. Embryol. exp. Morph., Vol. 11, Part 4, pp. 741-755, December 1963, From the Department of Anatomy, St. Louis University School of Medicine, and the Department of Embryology, Carnegie Institution of Washington, Printed in Great Britain