Learn Portuguese (Portugal): Já que o laboratório está fechado, não trabalho hoje. - Since the laboratory is closed, I do not work today.

Já que (since/given that) is perfect for putting the cause before the result. In Portuguese, we generally avoid starting a sentence with porque. If you wanted to use porque, you would flip the sentence structure: Não trabalho hoje porque o laboratório está fechado.

Could I swap já que for visto que or dado que in this sentence?

Absolutely. Já que, visto que, and dado que are all interchangeable here. They all mean "since" or "seeing as" and work exactly the same way, though dado que sounds slightly more formal.

Does já que require the subjunctive mood?

No, causal expressions like já que, visto que, and dado que state concrete facts or known reasons, so they take the normal indicative mood. That is why we use está instead of the subjunctive esteja.

Why do we use está (from estar) instead of é (from ser) with fechado?