FGFも神経誘導の能力があるという報告がありますが、BMPシグナルとの兼ね合いなどが今一つ不明瞭に感じていました。

下の論文の説明がしっくりきます。FGFの作用はBMPシグナリング経路へのクロストークの結果によるものではないかという解釈です。

FGF signaling has also been shown to inhibit BMP signaling in the early embryo by several mechanisms, thus potentially influencing the response of tissue to the activity of the BMP inhibitors produced by the organizer during neural induction. FGF signaling, for example, can promote phosphorylation of the linker domain and degradation of SMAD1, thereby reducing the efficacy of BMP signaling⁴³. FGF signaling can also inhibit BMP activity indirectly, by inducing the expression of a protein called Zeb2, a zinc-finger homeodomain protein also known as SIP1 (and Zfhx1b), which binds to and represses the transcriptional activity of the SMAD protein⁴⁴. For much of the neural plate, the role of FGF signaling is likely to be minor, since neural induction by the BMP inhibitors occurs readily in Xenopus in the absence of FGF signaling⁴⁵.

Neural induction and early patterning in vertebrates Mohammad Zeeshan Ozair 1, Chris Kintner 2, Ali H Brivanlou 1,*　Wiley Interdiscip Rev Dev Biol. 2012 Oct 15;2(4):479–498. doi: 10.1002/wdev.90 　https://pmc.ncbi.nlm.nih.gov/articles/PMC6945772/

まあ、神経誘導の研究者でＦＧＦの作用を見つけた人にしてみたら嬉しくない解釈でしょうが。