Axonal Projection Patterns of the Dorsal Interneuron Populations in the Embryonic Hindbrain

Dana Hirsch; Ayelet Kohl; Yuan Wang; Dalit Sela-Donenfeld

doi:10.3389/fnana.2021.793161

Axonal Projection Patterns of the Dorsal Interneuron Populations in the Embryonic Hindbrain

Front Neuroanat. 2021 Dec 24:15:793161. doi: 10.3389/fnana.2021.793161. eCollection 2021.

Authors

Dana Hirsch^{1

2}, Ayelet Kohl¹, Yuan Wang³, Dalit Sela-Donenfeld¹

Affiliations

¹ Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
² Department of Veterinary Resources, Weizmann Institute of Science, Rehovot, Israel.
³ Department of Biomedical Sciences, Program in Neuroscience, College of Medicine, Florida State University, Tallahassee, FL, United States.

Abstract

Unraveling the inner workings of neural circuits entails understanding the cellular origin and axonal pathfinding of various neuronal groups during development. In the embryonic hindbrain, different subtypes of dorsal interneurons (dINs) evolve along the dorsal-ventral (DV) axis of rhombomeres and are imperative for the assembly of central brainstem circuits. dINs are divided into two classes, class A and class B, each containing four neuronal subgroups (dA1-4 and dB1-4) that are born in well-defined DV positions. While all interneurons belonging to class A express the transcription factor Olig3 and become excitatory, all class B interneurons express the transcription factor Lbx1 but are diverse in their excitatory or inhibitory fate. Moreover, within every class, each interneuron subtype displays its own specification genes and axonal projection patterns which are required to govern the stage-by-stage assembly of their connectivity toward their target sites. Remarkably, despite the similar genetic landmark of each dINs subgroup along the anterior-posterior (AP) axis of the hindbrain, genetic fate maps of some dA/dB neuronal subtypes uncovered their contribution to different nuclei centers in relation to their rhombomeric origin. Thus, DV and AP positional information has to be orchestrated in each dA/dB subpopulation to form distinct neuronal circuits in the hindbrain. Over the span of several decades, different axonal routes have been well-documented to dynamically emerge and grow throughout the hindbrain DV and AP positions. Yet, the genetic link between these distinct axonal bundles and their neuronal origin is not fully clear. In this study, we reviewed the available data regarding the association between the specification of early-born dorsal interneuron subpopulations in the hindbrain and their axonal circuitry development and fate, as well as the present existing knowledge on molecular effectors underlying the process of axonal growth.

Keywords: axonal growth; dorsal interneurons; hindbrain; rhombic lip; rhombomere.

Publication types

Review