德國(guó)和奧地利一個(gè)聯(lián)合研究小組發(fā)現(xiàn)，在甲狀腺激素的調(diào)控下,，成年老鼠的視網(wǎng)膜錐細(xì)胞中能產(chǎn)生不同的視覺(jué)色素,。他們認(rèn)為，這一機(jī)制可能存在于人類等所有哺乳動(dòng)物中,，因此成人甲狀腺激素缺乏也會(huì)影響他們的色彩識(shí)別能力,。
視網(wǎng)膜錐體細(xì)胞熒光顯微照片
成年健康大鼠(頂部)和甲狀腺激素不足的大鼠(底部)
在視網(wǎng)膜中，視錐細(xì)胞負(fù)責(zé)識(shí)別顏色,。大部分哺乳動(dòng)物有兩種光譜的視錐細(xì)胞類型,，都包含了兩種視覺(jué)色素（視蛋白）,，一種對(duì)短波光（紫外/藍(lán)視蛋白）敏感，另一種對(duì)中長(zhǎng)波光（綠視蛋白）敏感,。視錐細(xì)胞會(huì)表達(dá)一種甲狀腺激素受體,，通過(guò)激素來(lái)抑制紫外/藍(lán)視蛋白的合成，而激活綠視蛋白的合成,。此前的研究認(rèn)為,，甲狀腺激素控制視蛋白合成只是發(fā)育中的自然現(xiàn)象，隨著機(jī)體發(fā)育,，成熟視錐細(xì)胞中會(huì)建立起一套確定的“視蛋白程序”,，不需要進(jìn)一步調(diào)控。
但最近,，德國(guó)馬普研究院法蘭克福腦研究所與法蘭克福大學(xué)以及奧地利維也納的幾家大學(xué)聯(lián)合,，研究了在小鼠出生后早期發(fā)育期間甲狀腺激素水平對(duì)視錐細(xì)胞的影響。結(jié)果發(fā)現(xiàn),，激素的影響會(huì)持續(xù)很長(zhǎng)時(shí)間,，在小鼠出生幾周以后，激素影響仍然存在,。
據(jù)研究小組分析,，成熟小鼠甲狀腺功能衰退幾周后，它的視錐細(xì)胞就會(huì)受到影響,，所有視錐細(xì)胞轉(zhuǎn)化為合成紫外/藍(lán)視蛋白,，綠視蛋白合成減少。經(jīng)治療激素水平恢復(fù)正常以后,，視錐細(xì)胞也會(huì)還原成以前的樣子,，繼續(xù)按“規(guī)定”工作：一種合成綠視蛋白，另一種合成紫外/藍(lán)視蛋白,。兩種視錐細(xì)胞在整個(gè)生命期間都受甲狀腺激素的調(diào)控并且過(guò)程可逆,。
馬普研究院研究所的馬丁·格魯斯曼說(shuō)，如果該機(jī)制在人類視錐細(xì)胞中也如此,，新發(fā)現(xiàn)在臨床上具有重要意義,。由飲食或甲狀腺切除造成的成人甲狀腺激素缺乏，將會(huì)影響他們的視蛋白合成與色彩識(shí)別能力,。（生物谷Bioon.com）
生物谷推薦英文摘要：
Journal of Neuroscience, 31(13): 4844-4851 (March 30, 2011) DOI: 10.1523/JNEUROSCI.6181-10.2011
Thyroid hormone controls cone opsin expression in the retina of adult rodents
Anika Glaschke, Jessica Weiland, Domenico Del Turco, Marianne Steiner, Leo Peichl, Martin Glösmann
Mammalian retinas display an astonishing diversity in the spatial arrangement of their spectral cone photoreceptors, probably in adaptation to different visual environments. Opsin expression patterns like the dorsoventral gradients of short-wave-sensitive (S) and middle- to long-wave-sensitive (M) cone opsin found in many species are established early in development and thought to be stable thereafter throughout life. In mouse early development, thyroid hormone (TH), through its receptor TRβ2, is an important regulator of cone spectral identity. However, the role of TH in the maintenance of the mature cone photoreceptor pattern is unclear. We here show that TH also controls adult cone opsin expression. Methimazole-induced suppression of serum TH in adult mice and rats yielded no changes in cone numbers but reversibly altered cone patterns by activating the expression of S-cone opsin and repressing the expression of M-cone opsin. Furthermore, treatment of athyroid Pax8?/? mice with TH restored a wild-type pattern of cone opsin expression that reverted back to the mutant S-opsin-dominated pattern after termination of treatment. No evidence for cone death or the generation of new cones from retinal progenitors was found in retinas that shifted opsin expression patterns. Together, this suggests that opsin expression in terminally differentiated mammalian cones remains subject to control by TH, a finding that is in contradiction to previous work and challenges the current view that opsin identity in mature mammalian cones is fixed by permanent gene silencing
