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Kohler, U.

Publications and source records attributed to Kohler, U..

2 recordsLinked to original sources
bioRxiv2026

Experimental characterization of chicken OSX/SP7 and embryonic expression analysis reveal skeletal and neural expression domains

The specificity protein 7 (SP7), also known as Osterix (OSX), is a zinc-finger transcription factor essential for osteoblast differentiation and skeletal development. Hereafter, the protein is referred to as OSX/SP7 throughout the manuscript. Although OSX/SP7 has been extensively studied in mammals and teleost fish, its developmental expression pattern in chicken (Gallus gallus) has not been described. Using an experimentally isolated chicken OSX/SP7 sequence, we examined OSX/SP7 mRNA expression during embryogenesis by in situ hybridization. As expected, OSX/SP7 expression was detected in developing skeletal elements undergoing ossification. Unexpectedly, transcripts were also observed in the neuroepithelium, retina, central nervous system, embryonic muscles and integument. Notably, OSX/SP7 expression was present in the neural tube from Hamburger and Hamilton stage 9 and persisted in the developing central nervous system until at least HH40, suggesting that OSX/SP7 functions during avian development may extend beyond osteogenesis. In addition, we reconstructed the chicken OSX/SP7 coding sequence and inferred its associated untranslated regions. The reconstructed ORF was independently supported by maternal and paternal haplotype-resolved chicken genome assemblies and retained the characteristic domain architecture of vertebrate OSX/SP7 proteins despite substantial divergence outside the DNA-binding domain. Taken together, these findings broaden the developmental landscape of OSX/SP7 expression in birds and provide new molecular resources for future studies of OSX/SP7 regulation and function during vertebrate development.

developmental biology↗
bioRxiv2026

The role of the roof plate for mesencephalic trigeminal neuron

The mesencephalic trigeminal nucleus (MTN) contains the proprioceptive sensory neurons that innervate mechanoreceptors in the jaw closing muscles. In the chick embryo, MTN neurons are the first neurons generated in the mesencephalon. They arise bilaterally adjacent to the roof plate and then extend their axons ventrally before projecting caudally towards the rhombencephalon. MTN axons remain in a mid - dorsoventral position and pioneer the lateral longitudinal fasciculus. Notably, MTN axons never cross the roof plate, raising the question of which mechanisms underlie this restriction. Here, we investigated the effects of tissue transplants on the guidance of MTN axons. We found that both the diencephalon and the notochord exert repulsive effects on MTN axons, which could partially explain their early trajectory. We have also analysed the potential roles of the guidance cues BMP2/4, GDF7, SLIT and NETRIN in MTN axon navigation, both in vivo and in vitro. We found no evidence for a role of BMP2/4 or GDF7 in directing MTN axons. However, SLIT-ROBO signaling was found to play a significant role. SLIT proteins are repulsive guidance cues expressed by roof and floor plate. Loss or reduced expression of ROBO2 led to aberrant axon meandering within the dorsal midbrain. Most axons eventually reoriented posteriorly, and only a small fraction crossed the roof plate. Unexpectedly, in the absence of ROBO2, MTN somata migrated into the roof plate, resulting in the loss of a defined roof plate region. Taken together, these results suggest that SLIT2-ROBO2 signaling not only prevents MTN axons from crossing the roof plate but also maintains MTN cell bodies adjacent to the roof plate. With regards to MTN neuron guidance, we conclude that additional roof plate - derived factors are likely to co-operate with SLIT proteins to prevent crossing of the roof plate. Another possibility could be that SLIT might signal through additional receptors.

developmental biology↗