Thiamine deficiency impairs common eider (Somateria mollissima) reproduction in the field.

The Baltic Sea population of the common eider (Somateria mollissima) has declined dramatically during the last two decades. Recently, widespread episodic thiamine (vitamin B1) deficiency has been demonstrated in feral birds and suggested to contribute significantly to declining populations. Here we show that the decline of the common eider population in the Baltic Sea is paralleled by high mortality of the pulli a few days after hatch, owing to thiamine deficiency and probably also thereby associated abnormal behaviour resulting in high gull predation. An experiment with artificially incubated common eider eggs collected in the field revealed that thiamine treatment of pulli had a therapeutic effect on the thiamine status of the brain and prevented death. The mortality was 53% in untreated specimens, whereas it was only 7% in thiamine treated specimens. Inability to dive was also linked to brain damage typical for thiamine deficiency. Our results demonstrate how thiamine deficiency causes a range of symptoms in the common eider pulli, as well as massive die-offs a few days after hatch, which probably are the major explanation of the recent dramatic population declines.

Saturation of the endoplasmic reticulum retention machinery reveals anterograde bulk flow

We have studied the possible mechanisms of endoplasmic reticulum (ER) export and retention by using natural residents of the plant ER. Under normal physiological conditions, calreticulin and the lumenal binding protein (BiP) are efficiently retained in the ER. When the ER retention signal is removed, truncated calreticulin is much more rapidly secreted than truncated BiP. Calreticulin carries two glycans of the typical ER high-mannose form. Both glycans are competent for Golgi-based modifications, as determined from treatment with brefeldin A or based on the deletion of the ER retention motif. In contrast to BiP, calreticulin accumulation is strongly dependent on its retention signal, thereby allowing us to test whether saturation of the retention mechanism is possible. Overexpression of calreticulin led to 100-fold higher levels in dilated globular ER cisternae as well as dilated nuclear envelopes and partial secretion of both BiP and calreticulin. This result shows that both molecules are competent for ER export and supports the concept that proteins are secreted by default. This result also supports previous data suggesting that truncated BiP devoid of its retention motif can be retained in the ER by association with calreticulin. Moreover, even under these saturating conditions, cellular calreticulin did not carry significant amounts of complex glycans, in contrast to secreted calreticulin. This result shows that calreticulin is rapidly secreted once complex glycans have been synthesized in the medial/trans Golgi apparatus and that the modified protein does not appear to recycle back to the ER.