Kawakami Group / Laboratory of Molecular and Developmental Biology

Retina-derived signals control pace of neurogenesis in visual brain areas but not circuit assembly

Sherman, S., Arnold-Ammer, I., Schneider, M.W., Kawakami, K., and Baier, H.

Nature Communications (2023) 14, 6020 DOI:10.1038/s41467-023-40749-1

Brain development is orchestrated by both innate and experience-dependent mechanisms, but their relative contributions are difficult to disentangle. Here we asked if and how central visual areas are altered in a vertebrate brain depleted of any and all signals from retinal ganglion cells throughout development. We transcriptionally profiled neurons in pretectum, thalamus and other retinorecipient areas of larval zebrafish and searched for changes in lakritz mutants that lack all retinal connections. Although individual genes are dysregulated, the complete set of 77 neuronal types develops in apparently normal proportions, at normal locations, and along normal differentiation trajectories. Strikingly, the cell-cycle exits of proliferating progenitors in these areas are delayed, and a greater fraction of early postmitotic precursors remain uncommitted or are diverted to a pre-glial fate. Optogenetic stimulation targeting groups of neurons normally involved in processing visual information evokes behaviors indistinguishable from wildtype. In conclusion, we show that signals emitted by retinal axons influence the pace of neuro- genesis in visual brain areas, but do not detectably affect the specification or wiring of downstream neurons.

This study was conducted as collaboration with Baier lab at Max Planck Institute.

Figure: (A)Transgenic zebrafish (HGn12C) expressing GFP in neurons of retinorecipient areas.
(B)The lakritz mutation was introduced into HGn12C (center), and transcriptional profiling analysis of GFP-positive neurons was conducted.

Sakai Group / Model Fish Genetics Laboratory

In vitro storage of functional sperm at room temperature in zebrafish and medaka

Takemoto K, Nishimura T, Kawasaki T, Imai Y, Levy K, Hart N, Olaya I, Burgess SM, Elkouby YM, Tanaka M, Sakai N,

Zebrafish (2023) 20, 229-235 DOI:10.1089/zeb.2023.0054
A PDF of this paper can be downloaded from here.

The longevity of sperm in teleost such as zebrafish and medaka is short when isolated even in saline-balanced solution at a physiological temperature. However, we thought that under suitable conditions sperm could be survived for a longer period of time, and we investigated these conditions. Here, we show that the sperm of zebrafish can survive and maintain fertility in L-15-based storage medium supplemented with 50 Units/ml penicillin, 50 µg/ml streptomycin, 0.5% (w/v) bovine serum albumin, 3% foetal bovine serum, 25 mM glucose, 0.1 mM lactic acid, 10 mM Hepes (pH 7.9), and 22% water for 28 days at room temperature. The fertilized embryos developed to normal fertile adults. This storage medium with increasing lactic acid two-fold was effective in medaka sperm stored for 7 days at room temperature. These results suggest that sperm from external fertilizer zebrafish and medaka has the ability to survive for at least 4 weeks and 1 week, respectively, in the body fluid-like medium at a physiological temperature. This sperm storage method allows researchers to ship sperm by low-cost methods and to investigate key factors for motility and fertile ability in those sperm.

Figure: Zebrafish cover featuring zebrafish and medaka sperm

Kawakami Group/Laboratory of Molecular and Developmental Biology

Determinants of motor neuron functional subtypes important for locomotor speed

Kristen P. D’Elia, Hanna Hameedy, Dena Goldblatt, Paul Frazel, Mercer Kriese, Yunlu Zhu, Kyla R. Hamling, Koichi Kawakami, Shane A. Liddelow, David Schoppik, and Jeremy S. Dasen

Cell Reports (2023) 42, 113049. DOI:10.1016/j.celrep.2023.113049

Locomotion requires precise control of the strength and speed of muscle contraction and is achieved by recruiting functionally distinct subtypes of motor neurons (MNs). MNs are essential to movement and differentially susceptible in disease, but little is known about how MNs acquire functional subtype-specific features during development. Using single-cell RNA profiling in embryonic and larval zebrafish, we identify novel and conserved molecular signatures for MN functional subtypes and identify genes expressed in both early post- mitotic and mature MNs. Assessing MN development in genetic mutants, we define a molecular program essential for MN functional subtype specification. Two evolutionarily conserved transcription factors, Prdm16 and Mecom, are both functional subtype-specific determinants integral for fast MN development. Loss of prdm16 or mecom causes fast MNs to develop transcriptional profiles and innervation similar to slow MNs. These results reveal the molecular diversity of vertebrate axial MNs and demonstrate that functional subtypes are specified through intrinsic transcriptional codes.

This study was conducted as collaboration with Schoppik lab at New York University.

Figure1: Zebrafish motor neuron diversity is regulated by the transcription factors prdm16 and mecom. The absence of these transcription factors results in fast motor neurons exhibiting characteristics of slow motor neurons.

Figure2: Overlap of prdm16 and mecom expression in motor neurons using transgenic fish.

A vertebrate-wide catalogue of T1R receptors reveals diversity in taste perception

Hidenori Nishihara, Yasuka Toda, Tae Kuramoto, Kota Kamohara, Azusa Goto, Kyoko Hoshino, Shinji Okada, Shigehiro Kuraku, Masataka Okabe, Yoshiro Ishimaru

Nature Ecology & Evolution 2023 Dec 13 DOI:10.1038/s41559-023-02258-8

Press release (In Japanese only)

EurekAlert! link about this artcle

• Unraveling the evolutionary origins of umami and sweet taste preferences

The perception of taste is one of the most important senses and helps us identify beneficial foods and avoid harmful substances. For instance, our fondness for sweet and savory foods results from our need to consume carbohydrates and proteins. Given their importance as an evolutionary trait, researchers around the world are investigating how taste receptors originated and evolved over a period of time. Obtaining these insights into the feeding behavior of organisms can help them paint a picture of the history of life on Earth.　read more>

Figure: A new study led by researchers from Kindai University identified five new groups of umami and sweet taste receptors within the TAS1R family (TAS1R 4, 5, 6, 7, and 8) and also diversity in TAS1R2 and TAS1R3 genes.