Expression of BMP and Pax Proteins in the Central Nervous System of Human and Rat Embryos at Early Stages of Development

The roles of BMP and Pax in the embryonic development have been extensively studied in recent years and the formation of the neural tube is usually described as a self-evident process, but formation of nervous system in human embryos has actually not been examined in detail. In the present study 40 human embryos at Carnegie stages (CS) 10-20 were obtained, and the expression of BMP-2, BMP-4, Pax2, Pax6 and Pax7 proteins were examined in the developing brain. 22 rat embryos of CS 14, 18 and 20 were employed to compare the BMP-2, BMP-4 and Pax2 expression in the developing spinal cord of human and rat embryos throughout early stages of the nervous system development. To detect expression of proteins the method of immunohistochemistry was used. BMP-2 and BMP-4 are essential signalling molecules for the formation of the neural tube in human embryos as their expression was seen throughout all studied developmental stages 10-20. The expression of both proteins, BMP-2 and BMP-4, had a tendency to decline in the later stages of the development. In the developing CNS of rat embryos BMP-2 and BMP-4 have a similar spatial and temporal expression pattern compared to the corresponding stages of the human embryos. However, slight differences were noted as in the spinal cord of rat embryos BMP-2 and BMP-4 expression was weaker compared to human embryos. In the human embryos Pax2, Pax6 and Pax7 were identified as signalling molecules that are involved in the formation of the early spinal cord and brain. The expression of Pax2, Pax6 and Pax7 had a tendency to increase in the later stages of the development both in the spinal cord and the brain. Significantly weaker expression of the Pax proteins was observed at CS 10. The similar temporal expression pattern of Pax2 to human embryos was seen in the forming spinal cord of rat embryos, as the Pax2 expression was found to increase at the later stages of the development. Differently from human embryos, no clear regional differences in Pax2 expression in the developing spinal cord of the rat embryos were not seen. It can be said that in the human and rat embryos BMP-2, BMP-4, Pax2, Pax6 and Pax7 proteins are associated with the establishment of neuroepithelial cells within the developing neural tube and with the migration and the differentiation of specific neural cell populations. In particular, the studied signalling molecules play an essentially important role in the determining of the dorsal-ventral and rostral-caudal axis of the developing brain.

BMP ja Pax valgud on ühed olulisemad signaalmolekulid imetajate neuraaltoru moodustumisel ja edasises kesknärvisüsteemi arengus. BMP ja Pax valkude osalusest inimembrüo närvisüsteemi varajases arengus on siiani ilmunud üksikud teadusartiklid. Käesoleva töö eesmärgiks oli uurida BMP-2, BMP-4, Pax2, Pax6 ja Pax7 ekspressiooni inimembrüo arenevas pea- ja seljaajus. Lisaks inimembrüotele analüüsiti BMP-2, BMP-4 ja Pax2 avaldumist rottide embrüote seljaajus. Uuringuteks kogutud embrüod jäid Carnegie arenguetappidesse 10–20, roti embrüod vastavalt 14, 18 ja 20 arenguetappi. BMP ja Pax valkude ekspressiooni hindamiseks kasutati immunohistokeemilist meetodit. BMP ja Pax signaalmolekulide ekspressioon avaldus kõigis uuritud etappides 10–20. Nii BMP-2 kui ka BMP-4 avaldumisel ilmnes hilisemates arenguetappides ekspressiooni nõrgenemise tendents. BMP-2 ja BMP-4 on olulised kasvufaktorid inimembrüo seljaaju dorsoventraalse telje väljakujunemisel, eriti etappides 16–18, kus antud töö tulemused näitasid BMP-de tugevamat ekspressiooni areneva seljaaju dorsaalosas võrreldes ventraalosaga. Roti arenevas seljaajus ilmnes võrreldes inimembrüote vastavate arenguetappidega ajalise ja ruumilise BMP-2 ja BMP-4 ekspressiooni sarnasus. Nii Pax2, Pax6 kui Pax7 avaldumise hindamisel selgus ekspressiooni tugevnemine hilisematel arenguetappidel. Pax valkude ekspressioon etappidel 10–14 näitab antud signaalmolekulide vajalikkust seljaaju dorsoventraalse telje ja ajuvatsakeste moodustumisel. Hilisemates etappides 16–20 on Pax2, Pax6 ja Pax7 kaasatud ees-, kesk- ja tagaaju mitmete erinevate piirkondade arengusse. Roti ja inimembrüo arenevas seljaajus avaldus sarnane Pax2 ajaline ekspressioon – Pax2 signaal tugevnes hilisematel arenguetappidel. Erinevalt inimembrüotest, ei ilmnenud rottide embrüotel arenevas seljaajus Pax2 avaldumises selgeid regionaalseid erinevusi dorsaalse ja ventraalse poole vahel. Kokkuvõtlikult võib öelda, et BMP-2, BMP-4, Pax2, Pax6 ja Pax7 on olulisel määral seotud neuroepiteeli rakkude formeerumise, migreerumise ja diferentseerumisega erinevateks närvirakkude populatsioonideks. Uuritud singnaalmolekulid on inimese ja roti embrüote varajases kesknärvisüsteemi arengus määrava tähtsusega dorsoventraalse ja kraniokaudaalse telje väljakujunemisel.