Question

Classic experimental work led to the idea that underlying mesodermal tissue induces the formation of the neural ectoderm.

i. What experiments demonstrated that this type of induction occurs?

ii. What is our current understanding of the basis of this inductive process?

iii. More generally, what insights has this understanding, as well as our understanding of how stem-cell niches are regulated, provided about how multiple paracrine signals are used to influence developmental processes?

Answer 1

I) THIS CAN BE DEMONSTRATION BY A CLASSICAL EXPERIMENT WHERE MESODERM PIECES FROM DIFFERENT POSITION ALONG A/P axis was taken from newt neurula and placed in the blastocoel of early newt embryo , It lead to formation of neural structures at the site of transplantation .

the classical experiment of MANGOLD was to show induction was transplantation of DLP of pigmented embruo to non pigmented embryo to ventral side.formation of 2 body axis on the emxryo occurs.

II) Current understanding of the mechanism/basis of inductive process has introduced few new concepts such as competence, reciprcal and sequential induction events,

Ones the lens has formed it will induce other tissues like optic vesicle(sequential), lens is also inducing the ectoderm above it to become cornea(reciprocal)

iii)stem cell niche is the surrounding microencironment where the stem cell resides . stem cell fate in the niche is decided by the secreted factor or factor produced by the cells in the niche(paracrine).. During development various factor affect the stem cell differentiation and the niche provides spatial and temporal cues that are required to bring about the development. STEM CELL NICHE HAS BEEN CHARACTERISED IN MANY TISSUES

1.BONE MARROW( HSC NICHE)

2.DIGESTIVE(IEC NICHE)

3.RESPIRATORY

Studies done in Drosophila indicates that the supporting cells present adjacent to the stem cells secrete factor required for maintaining identity of stem cells and self renewal.

JAK -STAT AND TGF-BETA signaling has been used in regulation of stem cell behaviour by supporting cells, whereas in mammals Wnt signalling has been demonstrated to play role in specification of stem cell renewal in HSCs(HEMATOPOIETIC STEM CELLS)

ENDOTHELIAL PROGENITOR CELLS(EPCs)-