Question

A) Perichondria B) Melanocytes C) RhoA D) Rac E) Runx2 73. Formed by neural crest cells 74. Promotes actin polymerization. 75. Promotes formation of osteoblasts 76. Gives rise to osteoblasts 77. Expressed at leading edge of migrating neural crest cells

Answer 1

A. Perichondria : gives rise to osteoblasts

Perichondrial cells (osx/lacZ+) are ostrix expressing precursors of osteoblasts, stromal cells and osteocytes.

B. Melanocytes : formed by neural crest cells

Melanocytes are present in epidermis, hair follicles, iris, cochlea and mesencephalon. Melanocytes are derived from neural crest cells and form Melanin pigment in melanosomes.

C. Rho A : promotes actin polymerization

Rho A(RAS homologoue family A) is a GTPase associated primarily with regulation of cytoskeleton and is responsible for maintaining cell shape and cell polarity and also assists movement of cell. Rho promotes actin polymerization by activating formins thus converting actin filaments into actin polymers.

D. Rac : expressed at leading edge of neural crest cells

Rho is responsible for maintaining neural crest cells in their epithelial form, by facilitating the persistence of N cadherinnd stress fibres, but during movement of neural crest cells, Rac is expressed at the edge of lamellipodia of migrating neural crest cells (mesenchymal form) and Rho disappears.

E. Runx 2: Promotes formation of osteoblasts

Runx2 is a transcription factor having Runt DNA binding domain, it acts as a structural framework for binding of regulatory factors involved in regulation of expression of skeletal genes.

Runx2 is highly expressed by pre osteoblasts and promotes formation of osteoblasts.