Table 1 Morphological features of BAT, WAT and BeAT

Cell shape

Variable, but classically spherical

Polygonal

Resembles WAT

Cell size

Variable, but large (25-200 μm)

Comparatively small (15-60 μm)

Variable

Nucleus

Peripheral, flattened

Central, round or oval in shape

To be determined

Cytoplasm

Thin, peripheral rim

Large volume evenly distributed throughout cell

To be determined

Lipid content

Single large droplet occupying up to 90% of cell volume

Multiple small lipid droplets

To be determined

Mitochondria

Few

Abundant

Intermediate

Endoplasmic reticulum (ER)

Little, but recognizable as rough and smooth ER

Present, but poorly developed

To be determined

Tissue organization

Small lobules of densely packed cells

Lobular, gland-like

To be determined

Cell content

Multiple other cell types present

Few other cell types present

Few other cell types present

Vascularity

Adequate

Highly vascularised

To be determined

Gene expression

PPAR-gamma, aP2, Adiponectin, adipsin, perilipin

UCP-1, PGC-1alpha, β-3 adreno receptor (ARB3), PRDM16, de-iodinase type II (D2)

Low UCP1, but activated by cAMP stimulation

Cell markers

CD34, ABCG2, ALDH

EVA1, EBF3, FBXO31

CD137, TMEM26, TBX1