Lens placode

{{Short description|Thickened portion of ectoderm which serves as the precursor to the lens}}

{{Infobox embryology

| Name = Lens placode

| Latin = placoda lentis

| Image = Gray864.png

| Caption = Transverse section of head of chick embryo of fifty-two hours’ incubation.

| Image2 =

| Caption2 =

| System =

| CarnegieStage =

| Days =

| Precursor = Surface ectoderm

| GivesRiseTo = Lens

}}

The lens placode is a thickened portion of ectoderm that serves as the precursor to the lens.

Invagination

Invagination is the process of folding in cells. The lens placode invaginates to later develop the lens or lens pit. The development of the lens placode is typically seen between 44 and 50 hours; invagination occurs shortly after at around the 50–55-hour mark. (Mouse){{Cite journal|title=FGF-regulated BMP signaling is required for eyelid closure and to specify conjunctival epithelial cell fate| first1=Jie|last1=Huang| first2=Lisa K.|last2=Dattilo| first3=Ramya|last3=Rajagopal| first4=Ying|last4=Liu| first5=Vesa|last5=Kaartinen| first6=Yuji|last6=Mishina|author6-link=Yuji Mishina| first7=Chu-Xia|last7=Deng| first8=Lieve|last8=Umans| first9=An|last9=Zwijsen| first10=Anita B.|last10=Roberts| first11=David C.|last11=Beebe|date=May 15, 2009|journal=Development|volume=136|issue=10|pages=1741–1750|doi=10.1242/dev.034082|pmid=19369394|pmc=2673764}}

Both the formation of the lens placode, and the invagination of this to the lens pit are both morphogenetic events.{{Cite journal|title=Understanding the role of growth factors in embryonic development: insights from the lens|first1=F. J.|last1=Lovicu|first2=J. W.|last2=McAvoy|first3=R. U.|last3=de Iongh|date=April 27, 2011|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=366|issue=1568|pages=1204–1218|doi=10.1098/rstb.2010.0339|pmid=21402581|pmc=3061110}}

Cell shape, density, and surface area

Chick embryos studies show the lens placode contains a cuboidal to columnar cell shape and that it is not multilayered. Furthermore, the density of the cell appears to double in size once the placode has developed. And while the cell density increases, the surface area is not impacted.

Restricted expansion hypothesis

The restricted expansion hypothesis” states that the adhesion of the ectoderm cells to the matrix is a key factor in the lens placode formation. This adhesion is accompanied by cell proliferation, which also impacts crowding and cell elongation.

Transcription factors

Pax6 is a transcription factor that is essential to the development of the lens placode. More specifically, it is needed for the surface ectoderm to fully develop. Pax6 has been identified as a necessary transcription factor for the thickness of the lens placode.http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC42008&blobtype=pdf {{Bare URL inline|date=August 2024}}

SOX2 is a transcription factor that works alongside Pax6 to develop the lens placode. They maintain the same protein levels in the ectoderm. Therefore, SOX2 and Pou2f1 are involved in the development of the lens placode.https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3276313&blobtype=pdf {{Bare URL inline|date=August 2024}}

References

External links

{{EmbryologyUNC|eye|008}}
[https://web.archive.org/web/20071213145329/http://cwx.prenhall.com/bookbind/pubbooks/martini10/chapter18/custom3/deluxe-content.html Human Anatomy Chapter 18 – Embryology Atlas]
[https://web.archive.org/web/20070912010420/http://isc.temple.edu/neuroanatomy/lab/embryo_new/eye/2/ Neuroembryology: Development of the Eye: Lens Placode Appears (4 weeks)]

Category:Embryology of nervous system

Category:Eye