Tanycytes: A rich morphological history to underpin future molecular and physiological investigations

Abstract

Tanycytes are located at the base of the brain and retain characteristics from their developmental origins, such as radial glial cells, throughout their life span. With transport mechanisms and modulation of tight junction proteins, tanycytes form a bridge connecting the cerebrospinal fluid with the external limiting basement membrane. They also retain the powers of self‐renewal and can differentiate to generate neurones and glia. Similar to radial glia, they are a heterogeneous family with distinct phenotypes. Although the four subtypes so far distinguished display distinct characteristics, further research is likely to reveal new subtypes. In this review, we have re‐visited the work of the pioneers in the field, revealing forgotten work that is waiting to inspire new research with today's cutting‐edge technologies. We have conducted a systematic ultrastructural study of α‐tanycytes that resulted in a wealth of new information, generating numerous questions for future study. We also consider median eminence pituicytes, a closely‐related cell type to tanycytes, and attempt to relate pituicyte fine morphology to molecular and functional mechanism. Our rationale was that future research should be guided by a better understanding of the early pioneering work in the field, which may currently be overlooked when interpreting newer data or designing new investigations.

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

“…The induction of Dio2 by TSH depends on the cAMP pathway; Dio2 is a CRE‐dependent gene . Considering that tanycytes are a hub for a host of signals, it is plausible that other GPCR‐dependent signalling pathways, coupled to either Gαs or Gαi, also impinge on Dio2 expression. Furthermore, Dio2 expression is enhanced in both hypothyroid rats and ewes, which indicates that T3 normally exerts a brake on Dio2 expression in tanycytes.…”

Targeting the Choroid Plexuses for Protein Drug Delivery

“…Tanycytes are minimally ciliated ependymal cells with apical microvilli on their ventricular-facing membrane in addition to basal elongated processes. These projections penetrate the parenchyma and can contact blood vessels and neurons [ 4 , 10 , 25 ]. Tanycytes are classified into several different types based on a variety of factors that includes their location and morphology.…”

“…They can possess tight junctions, but not always as was shown for tanycytes occupying the arcuate nucleus [ 26 , 27 , 28 , 29 , 30 ]. Tanycytes perform a variety of captivating and integral functions such as their role in neuroendocrine and metabolic regulation [ 25 , 31 , 32 , 33 , 34 ].…”

Targeting Tanycytes: Balance between Efficiency and Specificity

“…Since their characterization by Horstmann [1], tanycytes are now considered as key cells in the regulation of numerous physiological functions, ranging from reproduction to energy balance [2][3][4]. Elongated unipolar ependymoglial cells lining the bottom and the lateral wall of the third ventricle, they send a long radial process to connect blood-brain barrier capillaries in the mediobasal hy-pothalamus and the fenestrated capillaries of the hypothalamo-hypophysial portal system in the median eminence [5][6][7]. While still controversial, tanycytes would also contact other neural cells -including neurons -located in the arcuate nucleus, the ventromedial nucleus, and the dorsomedial nucleus [8,9].…”