Temporal control of neuronal diversity: common regulatory principles in insects and vertebrates?

Abstract

It is well established in species as diverse as insects and mammals that different neuronal and glial subtypes are born at distinct times during central nervous system development. In Drosophila, there is now compelling evidence that individual multipotent neuroblasts express a sequence of progenitor transcription factors which, in turn, regulates the postmitotic transcription factors that specify neuronal/glial temporal identities. Here, we examine the hypothesis that the regulatory principles underlying this mode of temporal specification are shared between insects and mammals, even if some of the factors themselves are not. We also propose a general model for birth-order-dependent neural specification and suggest some experiments to test its validity.

Generation of Multiple Classes of V0 Neurons in Zebrafish Spinal Cord: Progenitor Heterogeneity and Temporal Control of Neuronal Diversity

“…This temporal order, however, is an end result of a mixture between the production of V0-eAs from distinct, nonproliferating progenitors (for V0-eAs) and temporal order of neurogenesis from common progenitors (for V0-eBs and V0-eDs). A temporal order of neurogenesis occurs in many region of the developing CNS including the cerebral cortex and the retina (Cepko et al, 1996;Molyneaux et al, 2007;Jacob et al, 2008). In these regions, recent studies have revealed the presence of heterogeneity among progenitor pool (Mizutani et al, 2007; A proposed model of V0 neuron differentiation.…”

“…What are the molecular mechanisms that account for this sequential genesis of different types of neurons? One potential mechanism is that the properties of progenitors intrinsically change over time, which probably depends on a change in gene expression within progenitors (Jacob et al, 2008). Temporal changes in gene expression within p0 progenitors for V0-eBs and V0-eDs may occur in zebrafish.…”

“…In addition to lineage analysis, we also investigate whether the time-dependent generation of different types of neurons is involved. This type of neurogenesis occurs in several areas of the developing CNS (Jacob et al, 2008), and thus, the temporal control of neuronal diversity might also be at work in developing spinal cord.…”

Ikaros promotes early-born neuronal fates in the cerebral cortex

“…Such a mode of action would be in contrast to other transcription factors that control neuronal identity in the cortex, including Satb2, Fezf2, Ctip2, Tbr1, and Sox5, which are expressed postmitotically in neurons of specific laminar fates (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Such postmitotic temporal factors are likely to act downstream of progenitor cell temporal factors and to function by directing correct differentiation programs of particular neuronal types (59). They may also fine-tune temporal fates by mutual repression of transcription factors in alternative layers (60).…”

Genetic mechanisms regulating proliferation and cell specification in the Drosophila embryonic CNS

“…These temporal changes lead to programmed changes in the daughter cell types produced within the same lineage at different time points [29,[62][63][64][65]. These temporal changes are controlled by a set of transcription factors expressed in a stereotyped sequence in embryonic NBs, referred to as the temporal cascade: Hunchback (Hb) Kruppel (Kr) Pdm1-2 Castor (Cas) Grainy head (Grh) [66,67].…”