pri-miRNA is processed in a two-step reaction

The first step is catalyzed by Drosha, an RNase III superfamily member endonuclease, in the nucleus. Drosha reduces the pri-RNA to about a 70-bp, hairpin-shaped precursor fragment, pre-miRNA

TLS Online TPP Program

#Id: 2377

#Unit 5. Developmental Biology

Two distinct populations of neoblasts exist:

1. Sigma neoblast population 

2. Zeta neoblast population 

TLS Online TPP Program

#Id: 3799

#Unit 5. Developmental Biology

Dictyostelia (social amoebas)

TLS Online TPP Program

#Id: 3800

#Unit 5. Developmental Biology

Dictyostelium can utilize one of three survival strategies when food starvation-

Microcyst formation, favoured in dark & wet conditions, or ammonia levels are high.

Zygote formation, favoured in dark & wet conditions, & is triggered by ethylene produced by the cells. 

Cell aggregation & differentiation

TLS Online TPP Program

#Id: 3801

#Unit 5. Developmental Biology

Cell Aggregation & Differentiation is common to all Dictyostelids.

It consists of an interconnected programme of cell movement and cell differentiation.

TLS Online TPP Program

#Id: 3802

#Unit 5. Developmental Biology

During growth, unicellular D. discoideum monitor their cell density relative to that of their bacterial food source by secreting a glycoprotein called prestarvation factor at a constant rate.

TLS Online TPP Program

#Id: 3803

#Unit 5. Developmental Biology

When the ratio of PSF relative to that of bacteria exceeds a certain threshold, cells stop proliferating and initiate the expression of genes that are required for their aggregation.