Cilia, ciliopathies and hedgehog-related forebrain developmental disorders

Neurobiol Dis. 2021 Mar:150:105236. doi: 10.1016/j.nbd.2020.105236. Epub 2020 Dec 28.


Development of the forebrain critically depends on the Sonic Hedgehog (Shh) signaling pathway, as illustrated in humans by the frequent perturbation of this pathway in holoprosencephaly, a condition defined as a defect in the formation of midline structures of the forebrain and face. The Shh pathway requires functional primary cilia, microtubule-based organelles present on virtually every cell and acting as cellular antennae to receive and transduce diverse chemical, mechanical or light signals. The dysfunction of cilia in humans leads to inherited diseases called ciliopathies, which often affect many organs and show diverse manifestations including forebrain malformations for the most severe forms. The purpose of this review is to provide the reader with a framework to understand the developmental origin of the forebrain defects observed in severe ciliopathies with respect to perturbations of the Shh pathway. We propose that many of these defects can be interpreted as an imbalance in the ratio of activator to repressor forms of the Gli transcription factors, which are effectors of the Shh pathway. We also discuss the complexity of ciliopathies and their relationships with forebrain disorders such as holoprosencephaly or malformations of cortical development, and emphasize the need for a closer examination of forebrain defects in ciliopathies, not only through the lens of animal models but also taking advantage of the increasing potential of the research on human tissues and organoids.

Keywords: Brain development; Cerebral cortex; Ciliopathy; Forebrain; Gli transcription factor; Holoprosencephaly; Microcephaly; Primary cilia; RPGRIP1L; Sonic hedgehog.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Abnormalities, Multiple / embryology
  • Abnormalities, Multiple / genetics
  • Brain / abnormalities*
  • Brain / embryology
  • Cerebellum / abnormalities
  • Cerebellum / embryology
  • Cilia / genetics*
  • Ciliary Motility Disorders / embryology
  • Ciliary Motility Disorders / genetics
  • Ciliopathies / embryology*
  • Ciliopathies / genetics
  • Craniofacial Abnormalities / embryology*
  • Craniofacial Abnormalities / genetics
  • Developmental Disabilities / genetics
  • Encephalocele / embryology
  • Encephalocele / genetics
  • Eye Abnormalities / embryology
  • Eye Abnormalities / genetics
  • Gene Expression Regulation, Developmental
  • Hedgehog Proteins / physiology*
  • Holoprosencephaly / embryology
  • Holoprosencephaly / genetics
  • Humans
  • Kidney Diseases, Cystic / embryology
  • Kidney Diseases, Cystic / genetics
  • Polycystic Kidney Diseases / embryology
  • Polycystic Kidney Diseases / genetics
  • Prosencephalon / embryology*
  • Retina / abnormalities
  • Retina / embryology
  • Retinitis Pigmentosa / embryology
  • Retinitis Pigmentosa / genetics
  • Signal Transduction
  • Zinc Finger Protein GLI1 / genetics
  • Zinc Finger Protein Gli2 / genetics
  • Zinc Finger Protein Gli3 / genetics


  • Hedgehog Proteins
  • Zinc Finger Protein GLI1
  • Zinc Finger Protein Gli2
  • Zinc Finger Protein Gli3

Supplementary concepts

  • Agenesis of Cerebellar Vermis
  • Forebrain Defects
  • Meckel syndrome type 1